| TODA HIROYUKI | Last modified date：2024.04.18 |
Professor /
Strength of Materials /
Department of Mechanical Engineering /
Faculty of Engineering
Papers
| 1. | A. Ahmed, K. Uttarasak, T. Tsuchiya, S. Lee, K. Nishimura, N. Nunomura, K. Shimizu, K. Hirayama, H. Toda, M. Yamaguchi, T. Tsuru, S. Ikeno, K. Matsuda, Morphology evolution of β-phase in Al-Mg-Si alloys during aging treatment, Journal of Alloys and Compounds, 10.1016/j.jallcom.2024.174234, 988, 174234, 2024.06, This study aims to clarify the growth process of the β-phase in Al-Mg-Si alloys from the point of view of morphological evolution. The orientation relationship, shape, growth process, misfit value, and interfacial condition between the β-phase and Al matrix were investigated using high-resolution transmission electron microscopy (HR-TEM), focused ion beam (FIB), and optical microscope (OM). In a previous study, the growth process and shape of the β-phase were determined using scanning electron microscopy (SEM). It was proposed that the truncated octahedron (8{111}, 6{100} facets) transforms into a hexahedron (6{100} facets). This study proposes that two new three-dimensional shapes of the β-phase exist between the truncated octahedron and hexahedron, and we identified the {111}β facets at the edges of the β-phase. We proposed the morphology evolution during the growth process of Mg2Si crystals and calculated the misfit to understand that the unstable {111}β facet has a higher misfit value compared to the {001}β and {011}β facets. Our observations provide insight into how they influence the behavior of Mg2Si crystals, which is crucial for predicting the microstructural evolution of Al-Mg-Si alloys and for designing materials with desired properties.. |
| 2. | K. Shimizu, K. Nishimura, K. Matsuda, S. Akamaru, N. Nunomura, T. Namiki, T. Tsuchiya, S. Lee, W. Higemoto, T. Tsuru, H. Toda, Combining muon spin relaxation and DFT simulations of hydrogen trapping in Al6Mn, Scripta Materialia, 10.1016/j.scriptamat.2024.116051, 245, 116051, 2024.05, Hydrogen at the mass ppm level causes hydrogen embrittlement in metallic materials, but experimentally elucidating the hydrogen trapping sites is extremely difficult. We exploit the fact that positive muons can act as light isotopes of hydrogen to study the trapping state of hydrogen in matter. Zero-field muon spin relaxation experiments and density functional theory (DFT) calculations of the hydrogen trapping energy are carried out for Al6Mn. The DFT calculations reveal four possible trapping sites for hydrogen in Al6Mn, at which the hydrogen trapping energies are 0.168 (site 1), 0.312 (site 2), 0.364 (site 3), and 0.495 (site 4) in units of eV/atom. The variations in the deduced dipole field width (Δ) with temperature indicate noticeable changes at 94, 193, and 236 K. Considering the site densities, the observed Δ change temperatures are interpreted as muon trapping at sites 1, 3, and 4.. |
| 3. | H. Fujihara, H. Toda, K. Ebihara, M. Kobayashi, T. Mayama, K. Hirayama, K. Shimizu, A. Takeuchi, M. Uesugi, Assessment of hydrogen embrittlement behavior in Al-Zn-Mg alloy through multi-modal 3D image-based simulation, International Journal of Plasticity, 10.1016/j.ijplas.2024.103897, 174, 103897, 2024.03, Hydrogen can strongly embrittle aluminum alloys by accumulating at precipitate interface and triggering transgranular cracking, due to stress-driven hydrogen diffusion towards crack tip and grain boundaries. However, although mechanical features near crack tip and grain boundaries, and hydrogen diffusion/trapping processes have been extensively studied separately, very few quantitative information regarding the local interactions between hydrogen distribution and stress fields with full spatial complexity has been revealed. The present study attempts to fill this gap, by using a multi-modal three-dimensional image-based simulation that combines a crystal plasticity finite element method with hydrogen diffusion analysis, to fully capture the actual stress distribution and its effect on hydrogen distribution, and more importantly on cracking probability, near a real propagating hydrogen-induced crack. Stress-diffusion-trapping coupled simulations indicate the intergranular crack transitioned to a quasi-cleavage crack in the region where the interfacial cohesive energy of semi-coherent interface of the MgZn2 precipitate was reduced by hydrogen accumulation near the crack tip. The multi-modal three-dimensional image-based simulation used in the present study successfully bridged nanoscopic debonding and macroscopic hydrogen embrittlement fracture behavior.. |
| 4. | H. Toda, K. Hirayama, S. Yamaguchi, H. Fujihara, R. Higa, K. Shimizu, A.Takeuchi , M. Uesugi, Dominant factors controlling the initiation of hydrogen embrittlement in Al-Zn-Mg alloy, Materials Transactions, 10.2320/matertrans.MT-M2023116, 64, 12, 2729-2738, 2023.12, Surrogate-based microstructural optimization was applied to model the relationship between local crystallographic microstructure and intergranular hydrogen embrittlement in an Al–Zn–Mg alloy, and a support vector machine with an infill sampling criterion was used to realise high-accuracy optimisation with a limited data set. This methodology integrates thoroughgoing microstructural quantification, two coarsening processes, and surrogate modelling. An objective function was defined together with 66 design parameters that quantitatively express size, shape, orientation and damage during specimen machining for surface grain boundaries and grains. The number of design parameters was then reduced from 66 to 3 during the two-step coarsening process. It has been clarified that intergranular crack initiation can be described using the simple size of grains and grain boundaries together with grain boundary orientation with respect to the loading direction. It can be inferred that these design parameters are of crucial importance in crack initiation through elevation in stress normal to grain boundaries. Correlation between the selected design parameters and crack initiation was somewhat weak compared to past applications of a similar technique to particle damage. The reason for this is discussed. The present approach offers a cost-efficient solution for the prevention of hydrogen embrittlement through 3D design of crystallographic microstructure that cannot be obtained using conventional strategies for developing materials..  |
| 5. | J. Tang, Y. Wang, H. Fujihara, K. Shimizu, K. Hirayama, K. Ebihara, A. Takeuchi, M.Uesugi, H. Toda, Stress corrosion cracking induced by the combination of external and internal hydrogen in Al-Zn-Mg-Cu alloy, Scripta Materialia, 10.1016/j.scriptamat.2023.115804, Vol.239, 115804, 2024.01, Stress corrosion cracking (SCC) behaviors induced by the combination of external and internal hydrogen (H) in an Al-Zn-Mg-Cu alloy were systematically investigated via in-situ 3D characterization techniques. SCC of the AlZn-Mg-Cu alloy could initiate and propagate in the potential crack region where the H concentration exceeded a critical value, in which the nanoscopic H-induced decohesion of η-MgZn2 precipitates resulted in macroscopic cracking. External H that penetrated the alloy from the environment played a crucial role during the SCC of the Al-Zn-Mg-Cu alloy by generating gradient-distributed H-affected zones near the crack tips, which made Al alloys in water environment more sensitive to SCC. Additionally, the pre-existing internal H was driven toward the crack tips during plastic deformation. It was involved in the SCC and made contributions to both the cracks initiation and propagation.. |
| 6. | H. Fujihara, K. Shimizu, H. Toda, A. Takeuchi, M. Uesugi, Suppression of hydrogen embrittlement due to local partitioning of hydrogen to dispersed intermetallic compound particles in Al-Zn-Mg-Cu alloys, Materials Transactions, 10.2320/matertrans.MT-L2022007, 63, 10, 1406-1415, 2022.10, Recent studies have revealed that hydrogen embrittlement in Al-Zn-Mg alloys appears to be dominated by hydrogen partitioning to MgZn2 precipitates. A method has recently been proposed for reducing the hydrogen concentration at MgZn2 precipitates by adding specific intermetallic compound particles that have high hydrogen trap energy. In the present study, the effectiveness of Al7Cu2Fe particles on suppression of hydrogen embrittlement in Al-Zn-Mg-Cu alloys was evaluated using X-ray microtomography. Quasi-cleavage cracks were found to be initiated in regions where local volume fractions of the Al7Cu2Fe particles were relatively low. Hydrogen partitioning to the MgZn2 precipitate interface was suppressed, even in high hydrogen concentration material, by adding Al7Cu2Fe particles. However, the fractional area of the quasi-cleavage fracture in the material with high hydrogen concentration was higher due to insufficient hydrogen diffusion inside the Al7Cu2Fe particles and at the interface between the aluminum matrix and the particles. It appears that finely distributed small Al7Cu2Fe particles might effectively suppress hydrogen embrittlement.. |
| 7. | V. Tubei, H. Toda, W. Ketanond, H. Fujihara, O. Takakuwa, A. Takeuchi, M. Uesugi, Direct observation of three-dimensional short fatigue crack closure behavior in Ti-6Al-4V alloy using ultra-high-resolution X-ray microtomography, International Journal of Fatigue, 10.1016/j.ijfatigue.2022.107428, 168, 107428, 2023.03, Local 3D short fatigue crack closure behavior was investigated in Ti-6Al-4V alloy using ultra-high-resolution X-ray microtomography (XMT). The results show that the inhomogeneous distribution of plasticity-induced and roughness-induced crack closure is caused by the variation of crack path morphologies. These crack path morphologies exhibited heterogeneous plastic deformation at the crack-tips due to the anisotropic nature of α grains and varying extents of crack tilting and twisting caused by the interaction of the crack front with α/α boundary or α/α + β interface. It was revealed via surrogate-based statistical analysis that the Schmid factor has the strongest effect on crack growth rate.. |
| 8. | K. Hirayama, H. Toda, T. Suzuki, M. Uesugi, A. Takeuchi, W. Ludwig, Crystallographic analysis of hydrogen embrittlement behavior in aluminum alloy using diffraction contrast tomography, Materials Transactions, 10.2320/matertrans.MT-L2021020, 3, 4, 586-591, 2022.04, Crystallographic assessment of the hydrogen embrittlement behavior of AlZnMg alloy was performed by means of a technique combining fracture trajectory analysis and synchrotron X-ray diffraction contrast tomography. The 3D microstructure reconstructed using diffraction contrast tomography contained 119 grains. Fracture surfaces revealing intergranular fracture, ductile fracture, and quasi-cleavage fracture were observed in the alloy. While the intergranular crack initiated at a grain boundary with high grain boundary energy and a high angle between the grain boundary plane and loading direction, the crack propagation itself was not observed to be sensitive to these two parameters. The quasi-cleavage fracture surfaces were not characterized by any specific crystal orientation because of variation in the free surface segregation energy of hydrogen uniforms without depending on surface orientation.. |
| 9. | K. Shimizu, H. Toda, H. Fujihara, M. Yamaguchi, M. Uesugi, A. Takeuchi, M. Nishijima, Y. Kamada, Hydrogen embrittlement and its prevention in 7XXX aluminum alloys with high Zn concentrations, Corrosion, 10.5006/4300, 79, 8, 818-830, 2023.08. |
| 10. | 平山恭介, 戸田裕之, 蘇航, 岡村海, 鈴木芳生, 竹内晃久, 上椙真之, 清水一行, 高分解能・高エネルギーＸ線位相コントラスト法と構造材料への応用, SPring-8/SACLA利用研究成果集, 10.18957/rr.10.1.51, 10, 1, 51-59, 2022.02. |
| 11. | H. Toda, H. Li, R. Batres, K. Hirayama, H. Fujihara, Surrogate-based optimization of microstructural features of structural materials, Acta Materialia, 10.2139/ssrn.4349925, 257, 119188, 2023.09, This paper proposes a methodology for surrogate-based microstructural optimization of structural metals that integrates a limited number of 3D image-based numerical simulations with microstructural quantification and coarsening and optimisation processes. The support vector machine that was used had an infill sampling criterion to reduce the number of numerical trials, and the proposed methodology was found to be effective for wrought 2024 aluminium alloy with irregularly shaped particles. Appropriate objective functions were defined to assess particle damage. The number of design parameters, which quantitatively express the size, shape, and spatial distribution of particles, was initially 41, but they were reduced to four during a two-step coarsening process. The surrogate model provided highly accurate predictions, and the size, shape, and spatial distribution values of the optimal and weakest particles were successfully identified. It was shown that the optimal particle was small, spherical, sparsely dispersed, and perpendicular to the loading direction. However, it was also found that the smallest and most independent particle with a spherical shape was not necessarily strong, which implies the effects of particle clustering. It was also concluded that the dependency of in-situ particle strength on size was of crucial importance for weaker particles. The shape and spatial distribution of stronger particles were, however, more crucial for suppressing their internal stress than was their size. The results show that the proposed methodology offers a cost-efficient solution for microstructural designs involving 3D high-fidelity simulations that cannot be obtained with the existing approaches for developing materials.. |
| 12. | T. Tsuchiya, K. Uttarasak, S. Lee, A. Ahmed, S. Mikmekova, K. Nishimura, N. Nunomura, K. Shimizu, K. Hirayama, H. Toda, M Yamaguchi, T. Tsuru, J. Nakamura, S. Ikeno, K. Matsuda, Existence of hexagonal tabular β-phase in Al–Mg–Si alloys containing noble metal elements, Materials Today Communications, 10.1016/j.mtcomm.2023.106198, 35, 106198, 2023.01, The hexagonal tabular ß-Mg2Si phase (hex-ß) co-existed with conventional truncated octagonal shaped ß-Mg2Si (con-ß) in Al-1.0 mass% Mg2Si alloy containing a small amount of noble metal elements (NMEs; Cu, Pt, Ag, Pd or Au) at the over-aged condition of 673 K. As this hex-ß laid on the {111} plane of the Al matrix, and its six edges were parallel to ß, its orientation relationship with the Al-matrix is as follows:{111Al //{111}ß and Al //β was the same as our previous report of (hex-ß) in an ingot of Al-1.0 mass%Mg2Si- 0.5 mass% Cu alloy just homogenized at 723 K for 4 days, without cold-rolling, solution heat treatment, and aging. There is no significant difference in the lattice parameter of ß-Mg2Si by added NMEs. The formation of hex-ß was suggested to be related to defects in the Al-matrix, for example, by segregation of NMEs at the interface, altering the stacking fault energy, or introducing partial dislocations.. |
| 13. | H.Toda, K. Hirayama, K. Okamura, T. Suzuki, A. Takeuchi, M. Uesugi, H. Fujihara, Multimodal assessment of mechanically induced transformation in metastable multi‐phase steel using X‐ray nano‐tomography and pencil‐beam diffraction tomography, Acta Materialia, 10.1016/j.actamat.2022.117956, 234, 117956, 2022.08, A combination of X-ray nano-tomography and pencil-beam diffraction tomography was utilized for multimodal assessment of the mechanically induced transformation of individual retained austenite grains during tensile deformation in a 0.1C-5Mn-1Si multi-phase steel. In the present study, a newly developed high energy (20 - 30 keV) and high resolution (spatial resolution of 0.16 µm in this study) X-ray nano-tomography technique was applied for the first time to the in-situ observation of a steel under external loading. The gradual transformation, plastic deformation, and rotation behaviour of the individual austenite grains were clearly observed in 3D. It was revealed that the early stage of the transformation was dominated by the stress-assisted transformation that can be associated with measured mechanical driving force, whilst the overall transformation was dominated by the strain-induced transformation that is interrelated with measured dislocation multiplication. The transformation behaviour of individual grains was classified according to their initial crystallographic orientation and size. Noteworthy was the high stability of coarse austenite grains (i.e., 2.5 μm or larger in diameter), contrary to past reports in the literature. Characteristic rotation behaviour and wide data dispersion were also observed in the case of the individual austenite grains. It was conclusively demonstrated that such characteristic behaviour partly originated from interactions with surrounding soft and hard phases. The origins of these characteristics are discussed by combining the image-based and diffraction-based information.. |
| 14. | Y. Wang, B. Sharma, Y. Xu, K. Shimizu, H. Fujihara, K. Hirayama, A. Takeuchi, M. Uesugi, G. Cheng, H. Toda, Switching nanoprecipitates to resist hydrogen embrittlement in high-strength aluminum alloys, Nature Communications, 10.1038/s41467-022-34628-4, 13, 1, 6860, 2022.11, Hydrogen drastically embrittles high-strength aluminum alloys, which impedes efforts to develop ultrastrong components in the aerospace and transportation industries. Understanding and utilizing the interaction of hydrogen with core strengthening elements in aluminum alloys, particularly nanoprecipitates, are critical to break this bottleneck. Herein, we show that hydrogen embrittlement of aluminum alloys can be largely suppressed by switching nanoprecipitates from the η phase to the T phase without changing the overall chemical composition. The T phase strongly traps hydrogen and resists hydrogen-assisted crack growth, with a more than 60% reduction in the areal fractions of cracks. The T phase-induced reduction in the concentration of hydrogen at defects and interfaces, which facilitates crack growth, primarily contributes to the suppressed hydrogen embrittlement. Transforming precipitates into strong hydrogen traps is proven to be a potential mitigation strategy for hydrogen embrittlement in aluminum alloys.. |
| 15. | Y. Wang, H. Toda, Y. Xu, K. Shimizu, K. Hirayama, H. Fujihara, A. Takeuchi, M. Uesugi, In-situ 3D observation of hydrogen-assisted particle damage behavior in 7075 Al alloy by synchrotron X-ray tomography, Acta Materialia, 10.1016/j.actamat.2022.117658, 227, 117658, 2022.02, Al-Zn-Mg合金でZn量を１０％まで増やした新奇高強度合金を作製し、その水素脆化挙動をシンクロトロン放射光を用いた超高分解能3D連続観察で明らかにした。この合金の水素脆化挙動を解明すると共に、その防止策も提案した。. |
| 16. | Y. Xu, H. Toda, K. Shimizu, Y. Wang, B. Gault, W. Li, K. Hirayama, H. Fujihara, X. Jin, A. Takeuchi, M. Uesugi, Suppressed hydrogen embrittlement of high-strength Al alloys by Mn-rich intermetallic compound particles, Acta Materialia, 10.1016/j.actamat.2022.118110, 236, 118110, 2022.09, The pursuit of strong and ductile Al alloys with superior resistance to hydrogen embrittlement (HE) is practically significant across the aerospace and transportation industries among others. Unfortunately, effective ways to progress on the strength-HE trade-off for Al-alloys remain elusive. A strategy of suppressing HE by introducing intermetallic compound (IMC) particles to achieve hydrogen redistribution in various trapping sites was proposed. Here, we systematically induce the precipitation of a constant volume fraction of intermetallic compound (IMC) particles by adding one of 14 elements in a ternary Al-Zn-Mg high-strength alloy. We show a strong correlation between hydrogen trapping energies of the IMC obtained from ab initio calculations with the resistance to HE. Mn-rich Al11Mn3Zn2 particles exhibit the highest hydrogen trapping energy (0.859 eV/atom), leading to a decrease by approximately 5 orders of magnitude in the hydrogen occupancy in η2 (MgZn2) phase interfaces and grain boundaries, where HE cracks initiate. The Mn-addition did not deteriorate the ductility and most Al11Mn3Zn2 particles remained intact during plastic deformation which was revealed by in-situ 3D X-ray tomography. Hydrogen-induced strain localization at η2 phase interfaces and grain boundaries were inhibited due to strong hydrogen trapping capacity of Al11Mn3Zn2, hence preventing HE cracks initiation. Our approach effectively suppresses hydrogen-induced cracks without sacrificing the ductility, and our strategy can help the design roadmap of HE-tolerant high-strength metallic alloys.. |
| 17. | K. Hirayama, H. Toda, D. Fu, R. Masunaga, H. Su, K. Shimizu, A. Takeuchi and M. Uesugi, Damage micromechanisms of stress corrosion cracking in Al-Mg alloy with high magnesium content, Corrosion Science, 10.1016/j.corsci.2021.109343, 184, 109343, 2021.05, Al-Mg合金でMg量を１０％まで増やした新奇高強度合金を作製し、その応力腐食割れ挙動をシンクロトロン放射光を用いた超高分解能3D連続観察で明らかにした。この合金の応力腐食割れ挙動を解明すると共に、その防止策も提案した。. |
| 18. | M. Yamaguchi, T. Tsuru, K. Ebihara, M. Itakura, K. Matsuda, K.Shimizu, H. Toda, Hydrogen trapping in Mg₂Si and Al₇FeCu₂ intermetallic compounds in aluminum alloy : First-principles calculations, Materials Transactions, 10.2320/matertrans.MT-M2020201, 61, 10, 1907-1911, 2020.10, From first-principles calculations, we estimated the trapping energy of hydrogen atom at the interstitial site of perfect crystals of Mg2Si and Al7FeCu2 intermetallic compounds in the aluminum matrix. We found that Al7FeCu2 trapped hydrogen atoms strongly, whereas Mg2Si did not. The highest trapping energy in Al7FeCu2 is 0.56 eV/atom. We also found that the density of hydrogen trapping can be increased up to about 13 atoms/nm3 while keeping high trapping energy of about 0.40 eV/atom. We inferred that the Al7FeCu2 phase might remove hydrogen from the aluminum matrix, hence, preventing hydrogen embrittlement of aluminum alloy. . |
| 19. | C. Gupta, H. Toda, C. Schlacher, P. Mayr, C. Sommitsch, K. Uesugi, Y. Suzuki, A. Takeuchi, M. Kobayashi, Study of creep damage in a 10.86％ Cr heat resistant steel using synchrotron X-ray microtomography, Advanced Materials Research, Century of stainless steels, 10.4028/www.scientific.net/AMR.794.476, 794, 476-483, 2020.07. |
| 20. | T. Tsuru, K. Shimizu, M. Yamaguchi, M. Itakura, K. Ebihara, A. Bendo, K. Matsuda, H. Toda, Hydrogen-accelerated spontaneous microcracking in high-strength aluminium alloys, Scientific Reports, 10.1038/s41598-020-58834-6, 10, 1, 1998-1998, 2020.04. |
| 21. | Kazuyuki Shimizu, Hiroyuki Toda, Chihiro Kadogawa, Hiro Fujihara, Akihisa Takeuchi, Influence of nanovoids in the hydrogen embrittlement fracture of Al-Zn-Mg-Cu alloys, Materialia, 10.1016/j.mtla.2020.100667, 11, 100667-100667, 2020.06, Al–Zn–Mg alloys are representative high-strength aluminum alloys, but hydrogen embrittlement hinders further strengthening. The role of nanovoids in the hydrogen embrittlement of a hydrogen-charged Al–Zn–Mg–Cu alloy is examined using high-resolution imaging-type synchrotron X-ray tomography. Although nanovoids are initiated during deformation, their growth and coalescence behaviors are limited. Hydrogen partitioning analysis indicates that this is because most of the formed vacancies are not stabilized because of the low hydrogen occupancy. Furthermore, 3D/4D clustering analyses of nanovoids reveal that they do not aggregate on a specific plane to initiate a crack, and that linkage between nanovoids is less likely to occur.. |
| 22. | Analysis of Hydrogen Content in Pure Palladium via Neutron Radiography and Tomography. |
| 23. | M. S. Bhuiyan, H. Toda, K. Uesugi, A. Takeuchi, Y. Watanabe, Damage micromechanisms in high Mn and Zn content 7XXX aluminum alloys, Materials Science and Engineering: A, 10.1016/j.msea.2020.139423, 793, 139423-139423, 139423, 2020.08, The nucleation, growth, and coalescence of microvoids are examined in high Zn and Mn content 7XXX aluminum alloys using high-resolution synchrotron X-ray microtomography. The results have clearly shown that the addition of Mn content (0.6% mass) increases the ultimate tensile strength with limited ductility. The loading step in which each microvoid was nucleated together with its nucleation site is determined by tracking the microvoids in reverse chronological order from the final loading step towards the initial stress-free loading step. It was observed that microvoids were initiated due to particle cracking, and void nucleation occurs continuously with the applied strain. Furthermore, it was also observed that the particle underwent multiple fractures. It was concluded the ductile fracture was dominated by the nucleation and growth of microvoids due to particle fracture.. |
| 24. | Y. G. Tan, D.J. Bull, R. Jiang, A. Evangelou, S. Chaudhuri, S. Octaviani, F. Pierron, N. Gao, H. Toda, I. Sinclair and P.A.S. Reed, Data rich imaging approaches assessing fatigue crack initiation and early propagation in a DS superalloy at room temperature, Materials Science and Engineering A, 10.1016/j.msea.2020.140592, 805, 140592, 2021.02, Crack initiation and early propagation behavior of the directionally solidified (DS) superalloy CM247LC has been assessed by data rich imaging approaches. These include conventional characterization methods such as replica record analysis, 3D optical surface imaging, optical and scanning electron microscopy (SEM) as well as more recent techniques like digital image correlation (DIC) and synchrotron radiation computed tomography (SRCT). Three modes of secondary crack behaviors were found during evaluation of the fatigue process. The early stages of fatigue damage were controlled by microstructure-induced cracking, mainly consisting of carbide cracking. Fatigue damage was then promoted via slip band cracking and opening mode controlled carbide-cracking. The mechanisms of these different cracking behaviors are associated with the plastic zone of the main crack tip. Even though the early localized strain levels were of the same intensity within slip bands and at the intersection sites with carbides, carbide-induced cracking occurred prior to slip band cracking, characterized by SEM-DIC. This indicated that carbide-induced cracking was more likely to occur in the early stages of the fatigue process. Early crack growth behaviors were further investigated in situ at the microstructural scale via SRCT. The effect of carbides on crack initiation and propagation processes were evaluated in 3D. This revealed the phenomenon around pores, that cracks simultaneously grew on different slip planes in 3D, contrary to previous theories that such cracks tend to grow on a single favourable slip plane (in polycrystalline alloys). The SRCT result demonstrates the importance and necessity of 3D characterization of the crack propagation behavior at sub-surface, which is not fully analyzed by 2D characterization.. |
| 25. | H. Toda, F. Tomizato, R. Harasaki, D. Seo, M. Kobayashi, A. Takeuchi, K. Uesugi, 3D fracture behaviours in dual-phase stainless steel, ISIJ International, 10.2355/isijinternational.ISIJINT-2015-631, 56, 5, 883-892, 2016.05, Single-distance phase retrieval technique was applied to contrast-enhanced phase-sensitive imaging of dual-phase microstructures in ferrite/austenite dual-phase stainless steel. Contrast between the two phases was evaluated, together with noise and spatial resolution, under varying experimental and phase retrieval conditions. Serial sectioning technique was also employed, to validate the shape accuracy of related three-dimensional images. Although the density difference between the two phases was relatively small, the two phases were successfully segmented in the three-dimensional images. The imaging technique was also applied to observe microvoid nucleation and growth behaviour during tensile loading. The loading steps at which microvoids were nucleated were identified by tracking all the microvoids observed at the final loading step, in reverse chronological order, toward the initial unloaded state. Each absorptioncontrast image was then registered with a corresponding phase-contrast image, in order to classify all the targeted microvoids according to their nucleation site: ferrite, austenite or phase boundary. Premature damage initiation was observed at a relatively early stage at all the nucleation sites; however, subsequent growth was relatively moderate. On the other hand, microvoids initiated later, at fine particles located along the phase boundaries, exhibited enormous growth, thereby inducing the final rupture. It was concluded that the substantial driving force for the growth of microvoids located along morphologically characteristic austenitic particles was the predominant factor in the ductile fracture.. |
| 26. | Hiroyuki Toda, Takanobu Kamiko, Yasuto Tanabe, Masakazu Kobayashi, D. J. Leclere, Kentaro Uesugi, Akihisa Takeuchi, Kyosuke Hirayama, Diffraction-amalgamated grain boundary tracking for mapping 3D crystallographic orientation and strain fields during plastic deformation, ACTA MATERIALIA, 10.1016/j.actamat.2016.01.072, 107, -, 310-324, 2016.04, By amalgamating the X-ray diffraction technique with the grain boundary tracking technique, a novel method, diffraction-amalgamated grain boundary tracking (DAGT), has been developed. DAGT is a non-destructive in-situ analysis technique for characterising bulk materials, which can be applied up to near the point of fracture. It provides information about local crystal orientations and detailed grain morphologies in three dimensions, together with high-density strain mapping inside grains. As it obtains the grain morphologies by utilising X-ray imaging instead of X-ray diffraction, which latter is typically vulnerable to plastic deformation, DAGT is a fairly robust technique for analysing plastically deforming materials. Texture evolution and localised deformation behaviours have here been successfully characterised in Al-Cu alloys, during tensile deformation of 27% in applied strain. The characteristic rotation behaviours of grains were identified, and attributed to the effects of interaction with adjacent grains on the basis of the 3D local orientation and plastic strain distributions. It has also been revealed that 3D strain distribution in grains is highly heterogeneous, which is not explained by known mechanisms such as simple incompatibility with adjacent grains or strain percolation through soft grains. It has been clarified that groups consisting of a few adjacent grains may deform coordinately, especially in shear and lateral deformation, and the characteristic deformation pattern is thereby formed on a mesoscopic scale. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 27. | Hiroyuki Toda, Akihide Takijiri, Masafumi Azuma, Shohei Yabu, Kunio Hayashi, Dowon Seo, Masakazu Kobayashi, Kyosuke Hirayama, Akihisa Takeuchi, Kentaro Uesugi, Damage micromechanisms in dual-phase steel investigated with combined phase- and absorption-contrast tomography, ACTA MATERIALIA, 10.1016/j.actamat.2017.01.010, 126, 401-412, 2017.03, The single-distance phase retrieval technique was applied to contrast-enhanced imaging of the dual phase microstructure of a ferrite/martensite dual-phase with only 1.4% difference in density between the two phases. Each high-resolution absorption-contrast image was registered with a corresponding phase-contrast image, to analyse damage evolution behaviour. The loading step at which each microvoid was nucleated was identified by tracking the microvoid throughout tension, together with its nucleation site. Premature damage initiation was observed at a relatively early stage at various nucleation sites, such as the ferrite interior, martensitic interior and ferrite/martensite interfaces; however, the subsequent growth of such microvoids was relatively moderate. On the other hand, microvoids were also initiated later due to martensitic cracking after the maximum load was reached, and these microvoids subsequently exhibited rapid growth. The martensite cracking induced additional damage evolution mainly along nearby ferrite/martensite interfaces and intersections between the martensite and the ferrite grain boundary. It is notable that the microvoids originating from martensitic cracking exhibited characteristic shear-dominated growth under macroscopic tension, whereas those originating from the other nucleation sites exhibited traditional triaxiality-dominated growth. It was concluded that the ductile fracture was dominated by the substantial force driving the growth of microvoids located on morphologically characteristic martensitic particles. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd.. |
| 28. | H. Su, H. Toda, K. Shimizu, K. Uesugi, A. Takeuchi, Y. Watanabe, Assessment of hydrogen embrittlement via image-based techniques in Al-Zn-Mg-Cu aluminum alloys, Acta Materialia, 10.1016/j.actamat.2019.06.056, 176, 96-108, 2019.09. |
| 29. | A. Bendo, K. Matsuda, K. Nishimura, N. Nunomura, T. Tsuchiya, S. Lee, C. D. Marioara, T. Tsuru, M. Yamaguchi, K. Shimizu, H. Toda, The possible transition mechanism for the meta-stable phase in the 7xxx aluminium, Materials Science and Technology, 10.1080/02670836.2020.1821323, 36, 15, 1621-1627, 2020.09, Metastable phases in aluminium alloys are the primary nano-scale precipitates which have the biggest contribution to the increase in the tangible mechanical properties. The continuous increase in hardness in the 7xxx aluminium alloys is associated with the phase transformation from clusters or GP-zones to the metastable eta ' phase. The high-resolution electron imaging is used to observe the precipitates and reconstruct a kinetic model that might explain the transformation. This work is an attempt to gain insight into how the structural transformation may occur based on the shortest route of diffusion for the eventual structure to result in that of the eta ' phase.. |
| 30. | A. Takeuchi, K .Uesugi, M. Uesugi, H. Toda, K. Hirayama, K. Shimizu, K. Matsuo and T. Nakamura, High-energy X-ray nanotomography introducing an apodization Fresnel zone plate objective lens, Review of Scientific Instruments, 10.1063/5.0020293, 92, 23701, 2021.01, In this study, high-energy x-ray nanotomography (nano-computed tomography, nano-CT) based on full-field x-ray microscopy was developed. Fine two-dimensional and three-dimensional (3D) structures with linewidths of 75 nm-100 nm were successfully resolved in the x-ray energy range of 15 keV-37.7 keV. The effective field of view was ∼60 μm, and the typical measurement time for one tomographic scan was 30 min-60 min. The optical system was established at the 250-m-long beamline 20XU of SPring-8 to realize greater than 100× magnification images. An apodization Fresnel zone plate (A-FZP), specifically developed for high-energy x-ray imaging, was used as the objective lens. The design of the A-FZP for high-energy imaging is discussed, and its diffraction efficiency distribution is evaluated. The spatial resolutions of this system at energies of 15 keV, 20 keV, 30 keV, and 37.7 keV were examined using a test object, and the measured values are shown to be in good agreement with theoretical values. High-energy x-ray nano-CT in combination with x-ray micro-CT is applied for 3D multiscale imaging. The entire bodies of bulky samples, ∼1 mm in diameter, were measured with the micro-CT, and the nano-CT was used for nondestructive observation of regions of interest. Examples of multiscale CT measurements involving carbon steel, mouse bones, and a meteorite are discussed. . |
| 31. | H. Fujihara, H. Toda, M. Arita, K. Shimizu, A. Takeuchi, K. Uesugi, Assessment of hydrogen accumulation behavior in AlZnMg alloy under strain with Kelvin force microscopy, Materials Transactions, 10.2320/matertrans.l-m2020873, 62, 5, 636-641, 2021.05, Hydrogen embrittlement in aluminum alloys occurs due to local hydrogen accumulation during deformation. Investigating hydrogen diffusion with plastic deformation can help researchers further understand hydrogen embrittlement behavior in terms of its occurrence condition. We assessed hydrogen accumulation behavior in AlZnMg alloys under strain by combining tensile testing with Kelvin force microscopy. Additionally, the effects of microstructures on hydrogen accumulation were analyzed in detail. Hydrogen accumulated around specific grain boundaries, and it was likely that accumulated hydrogen was repartitioned to the generated vacancies, due to deformation, and the precipitate interfaces.. |
| 32. | CT Observation and Finite Element Analysis for Fatigue Crack Initiation in Cast Aluminum Alloy. |
| 33. | L. Blanchard, K. Sotoudeh, H. Toda, K. Hirayama, J. Laurencin, H. Dong, A quantified study of the resistance of duplex stainless steels to HISC: Part 1-significance of the three-dimensional phase distributions and morphological properties on hydrogen transport, Corrosion, 10.5006/3960, 78, 3, 249-257, 2022.03, This paper is associated with a larger program of research, studying the resistance to hydrogen-induced stress cracking (HISC) of a wrought and a hot isostatically pressed UNS S31803 duplex stainless steel (DSS), with respect to both the independent and interactive effects of the three key components of HISC: microstructure, stress/strain, and hydrogen. In the first part presented here, several material properties such as the three-dimensional microstructure, distribution, and morphology/geometry of the two phases, i.e., ferrite and austenite, and their significance on hydrogen transport have been determined quantitatively, using x-ray computed tomography microstructural data analysis and modeling. This provided a foundation for the study to compare resistance to HISC initiation and propagation of the two DSSs with differing microstructures, using hydrogen permeation measurements, environmental fracture toughness testing of single-edge notched bend test specimens, in Part 2 paper of this study (Blanchard, et al., Corrosion 78, 3 [2022]: p. 258-265).. |
| 34. | R. Oikawa, K. Shimizu, Y. Kamada, H. Toda, H. Fujihara, M. Uesugi, A. Takeuchi, Influence of hydrogen on the damage behavior of IMC particles in Al–Zn–Mg–Cu alloys, Materials Transactions, 10.2320/matertrans.MT-L2022020, 63, 12, 1607-1616, 2022.10, In recent years, it has been reported that intermetallic compound particles can suppress hydrogen embrittlement by hydrogen trapping. Some intermetallic particles in aluminum alloys, such as Al7Cu2Fe, have internal hydrogen trap sites; it is proposed that hydrogen embrittlement can be suppressed by preferential hydrogen partitioning in these sites. However, intermetallic compound particles act as fracture origin sites, and excessive addition degrades the mechanical properties of the material. In this study, we quantitatively evaluated the damage and decohesion behavior of intermetallic compound particles in high-hydrogen content 7XXX aluminum alloys by using in situ synchrotron radiation X-ray tomography. The results revealed that the hydrogen particles induced early high-strain localization, and the Al7Cu2Fe particles were damaged in that region due to its brittleness, resulting in early fracture. Hydrogen had no effects on the fracture and debonding behaviors of intermetallic compound particles, suggesting that the observed particle brittle fracture is dependent on their mechanical properties.. |
| 35. | T. Tsuru, K. Nishimura, K. Matsuda, N. Nunomura, T. Namiki, S. Lee, W. Higemoto, T. Matsuzaki, M. Yamaguchi, K. Ebihara, K. Shimizu, H. toda, Identification of hydrogen trapping in aluminum alloys via muon spin relaxation method and first-principles calculations, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 10.1007/s11661-023-07024-w, 2023.03, Although hydrogen embrittlement susceptibility of high-strength Al alloys is recognized as a critical issue in the practical use of Al alloys, identifying the hydrogen trapping or distribution has been challenging. In the present study, an effective approach based on experiment and simulation is proposed to explore the potential trap sites in Al alloys. At first, zero-field muon spin relaxation experiments were implemented in the temperature range from 5 K to 300 K. The plot of the temperature dependence of dipole field widths (∆) provides several characteristic peaks corresponding to the hydrogen trapping. Four dilute Al alloys (Al–Mg, Al–Cu, Al–Ti, and Al–V) were chosen to explore the possible trap sites. Atomic configurations of the muon trapping sites corresponding to the observed ∆ peaks are well assigned using the first-principles calculations for the binding energies of hydrogen around a solute and solute-vacancy pair. The extracted linear relationship between the muon ∆ peak temperature and the binding energy enables us to explore the potential alloying elements and their complex that have strong binding energies with hydrogen in Al alloys.. |
| 36. | 小林正和, 綿貫雅敏, 杉浦協司, 竹下裕市, 戸田裕之, Al-Mg-Si系鋳物における溶体化・時効処理に流動層炉を利用するための基礎的検討, 鋳造工学, 10.11279/jfes.86.209, 86, 3, 209-215, 2014.03. |
| 37. | Hiroyuki Toda, Takanobu Kamiko, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Masakazu Kobayashi, Assessment of Deformation Behavior of Polycrystalline Aluminum Using Diffraction-Amalgamated Grain-Boundary Tracking (DAGT) Technique, Materials Science Forum, Aluminum Alloys 2014 (ICAA14), 10.4028/www.scientific.net/MSF.794-796.57, 794-796, -, 57-62, 2014.06, A novel experimental method has been developed by amalgamating a pencil beam X-Ray diffraction (XRD) technique with the recently developed grain boundary tracking (GBT) technique. XRD and GBT are both non-destructive in-situ analysis techniques for characterizing bulk materials, which can be carried close to the point of fracture. DAGT provides information about individual grain orientations and 1-micron-level grain morphologies in 3-dimensions (3D) together with high-density local strain mapping. An Al-3 mass % Cu model alloy was used to investigate its deformation behavior under tension. The morphology of the grains was determined by the X-ray microtomography (XMT) imaging and the liquid metal wetting technique, after which GBT provided an accurate description of the position and morphology of all the grains in a region of interests. Diffraction spots in the XRD experiments were related to grains, making it possible to describe crystallographic orientation of all the grains. It has been revealed that deformation is localized at both microscopic and meso-scopic levels. Inhomogeneous deformation was observed in each individual grain. In addition, a group of a few grains coordinately interacts and specific grain boundaries thereby exhibit intense strain localization. Hydrostatic tension was also observed at quadruple junction points and its mechanism was analyzed.. |
| 38. | H. Su, H. Toda, K. Uesugi, A. Takeuchi, Y. Suzuki, Growth behavior of hydrogen micro pores in Al-Zn-Mg-Cu alloys during high temperature exposure, Proceedings of Materials Science & Technology 2015, -, -, 1589-1593, 2015.01. |
| 39. | Phase Contrast Imaging of Microsegregation of JIS ADCI2 Alloy and Damage Behavior. |
| 40. | A. Bendo, K. Matsuda, S. Lee, K. Nishimura, N. Nunomura, H. Toda, M. Yamaguchi, T. Tsuru, K. Hirayama, K. Shimizu, H. Gao, K. Ebihara, M. Itakura, T. Yoshida, S. Murakami, Atomic scale HAADF-STEM study of η′ and η1phases in peak-aged Al-Zn-Mg alloys, Journal of Materials Science, 10.1007/s10853-017-1873-0, 53, 6, 4598-4611, 2017.12. |
| 41. | T.Tsuru, M.Yamaguchi, K. Ebihara, M.Itakura, Y.Shiihara, K.Matsuda, H.Toda, First-principles study of hydrogen segregation at the MgZn2 precipitate in Al-Mg-Zn alloys, Computational Materials Science, 10.1016/j.commatsci.2018.03.009, 148, 301-306, 2018.06. |
| 42. | K. Nishimura, K. Matsuda, S. Lee, N. Nunomura, T. Shimano, A. Bendo, K. Watanabe, T. Tsuchiya, T. Namiki, H. Toda, M. Yamaguchi, Abnormally enhanced diamagnetism in Al-Zn-Mg alloys, Journal of Alloys and Compounds, 10.1016/j.jallcom.2018.10.037, 774, 405-409, 2019.02. |
| 43. | M.Yamaguchi, K.-I. Ebihara, M.Itakura, T.Tsuru, K.Matsuda, H.Toda, First-principles calculation of multiple hydrogen segregation along aluminum grain boundaries, Computational Materials Science, 10.1016/j.commatsci.2018.10.015, 156, 368-375, 2018.10. |
| 44. | M. Hassanipour, S. Watanabe, K. Hirayama, H. Toda, K. Uesugi, A. Takeuchi, Short crack growth behavior and its transitional interaction with 3D microstructure in Ti-6Al-4V, Materials Science and Engineering A, 10.1016/j.msea.2018.09.073, 738, 229-237, 2018.12. |
| 45. | Artenis Bendo, Kenji Matsuda, Seungwon Lee, Katsuhiko Nishimura, Hiroyuki Toda, Kazuyuki Shimizu, Tomohito Tsuru, Masatake Yamaguchi, Microstructure evolution in a hydrogen charged and aged Al–Zn–Mg alloy, Materialia, 10.1016/j.mtla.2018.09.035, 3, 50-56, 2018.11, Microstructure evolution of alloy with composition Al - 3.4 Zn - 1.9 Mg (at. %) was tracked using high resolution imaging and electron diffraction during ageing at 120 degrees C after being initially natural aged for 4 days. Hydrogen was charged in microstructure by cutting samples in Electrical Discharge Machine immediately after being quenched from solid solution temperature. Transmission Electron Microscope observations revealed a higher presence of high aspect ratio GPII-zones in microstructure of hydrogen charged and aged samples. Correlation was made with previously reported hydrogen effect into vacancy formation.. |
| 46. | S.Bhuiyan, H. Toda, K. Shimizu, H. Su, K. Uesugi, A. Takeuchi, Y. Watanabe, The Role of Hydrogen on the Local Fracture Toughness Properties of 7XXX Aluminum Alloys, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 10.1007/s11661-018-4880-0, 49, 11, 5368-5381, 2018.08. |
| 47. | Hongye Gao, Hang Su, Kazuyuki Shimizu, Chihiro Kadokawa, Hiroyuki Toda, Yasuko Terada, Kentaro Uesugi, Akihisa Takeuchi, Evolution Behavior of Hydrogen-Induced Nano Voids in Al–Zn–Mg–Cu Aluminum Alloys under Loading, MATERIALS TRANSACTIONS, 10.2320/matertrans.m2018156, 59, 9, 1532-1535, 2018.09, Synchrotron X-ray nanotomography, which offers a state-of-the-art resolution, has been applied for the 3D observations of hydrogen induced nano voids under different strain levels in Al-Zn-Mg-Cu aluminum alloys. A great number of nano voids are initiated uniformly across the whole specimen during a loading process. The average diameter and number density of initiated nano voids is 300nm and 5x10(15) m(-3), respectively. No evidence has been observed that the formation of nano voids results in the propagation of hydrogen induced quasi-cleavage cracks and premature fracture of Al-Zn-Mg-Cu aluminum alloys. Since nano void is one of the hydrogen trap sites in Al-Zn-Mg-Cu aluminum alloys, the majority of hydrogen can be repartitioned to nano voids during deformation due to their high density.. |
| 48. | Statistical evaluation of fracture of inclusions in cast aluminum alloy by massively-parallel voxel finite element analysis and geometrical measurements. |
| 49. | Size and distribution of micropores and voids in 5052 aluminum alloys during tensile deformation Micropore growth and void initiation and growth behaviors of 5052 aluminum alloys during tensile deformation were observed by means of X-ray computed tomography (CT) using the X-ray image beamline (BL20XU) of the Japanese synchrotron radiation facility (SPring-8). Tensile tests were carried out in ambient and wet conditions. In 5052 alloy tensile tested in wet condition, the drop of stress followed by the maximum stress was remarkable, and the fracture strain was reduced in comparison with those of 5052 alloy tested in ambient condition. The number of fine micropores and voids decreased in 5052 alloy when plastic deformation started and the decrease in the amount of fine micropores and voids in the wet condition was less than those in ambient condition. These might be caused by the acceleration of micropore growth and void initiation and growth during tensile testing in wet condition. . |
| 50. | Hydrogen desorption behavior in Al-8%Zn-1%Mg alloy © 2019 The Japan Institute of Light Metals The increase in Zn or Mg content results in an increase in Al-Zn-Mg alloys strength, however they become more susceptible to hydrogen embrittlement. To understand the hydrogen embrittlement behavior, it is necessary to study the hydrogen trapping behavior. In the present study, Al-8%Zn-1%Mg was made in order to have six trap sites (vacancies, dislocations, grain boundaries, particles, precipitates and micropores) and hydrogen trapping behavior in those trap sites was assessed by means of thermal desorption analysis (TDA). In addition, micropores were evaluated in detail using X-ray microtomography. Hydrogen desorption energies from grain boundaries and micropores were calculated using TDA curves. These values were 2 to 3 times larger than the ones reported in the literature due to a change in the trap sites during thermal desorption test. Increase in the number density of micropores was observed above 673 K during thermal desorption experiment. As the temperature increases, it has been reasonably inferred that some hydrogen desorbed from trap sites are released from the specimen and the rest of hydrogen is redistributed to form new micropores. It is revealed that low heating rate induces a change in trap sites and affect the measurement of hydrogen desorption energies.. |
| 51. | Influence of hydrogen on stress corrosion cracking behavior in Al-10Mg alloy © 2019 The Japan Institute of Light Metals It is known that the susceptibility to stress corrosion cracking of Al-Mg alloy increase with increasing Mg content, whereas the strength of Al-10Mg alloy reach to that of 2000 and 7000 series Al alloys. In-situ observation of the stress corrosion cracking of a hydrogen charged Al-10Mg alloy was conducted by using synchrotron X-ray mi-crotomography in SPring-8. The corrosion area and crack were observed in hydrogen charged material with water atmosphere. The corrosion and crack grow up with increasing applied strain. In addition, deformation localization and high hydrostatic strain that was caused by nucleation of nanovoids during deformation was also observed in crack tip. These observations indicated that the stress corrosion cracking of an Al-10Mg alloy occurs due to the influence of hydrogen.. |
| 52. | K. Shimizu, H. Toda, K. Uesugi, A. Takeuchi, Local Deformation and Fracture Behavior of High-Strength Aluminum Alloys Under Hydrogen Influence, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 10.1007/s11661-019-05304-y, 51A, 1-19, 2019.06. |
| 53. | A. Bendo, T. Maeda, K. Matsuda, A. Lervik, R. Holmestad, C. D. Marioara, K. Nishimura, N. Nunomura, H. Toda, M. Yamaguchi, K. Ikeda, T. Homma, Characterisation of structural similarities of precipitates in Mg-Zn and Al-Zn-Mg alloys systems, Philosophical Magazine, 10.1080/14786435.2019.1637032, 99, 21, 2619-2635, 2019.07. |
| 54. | M. Hassanipour, S. Watanabe, K. Hirayama, H. Toda, K. Uesugi, A. Takeuchi, Effects of 3D microstructural distribution on short crack growth behavior in two bimodal Ti-6Al-4V alloys, Materials Science and Engineering A, 10.1016/j.msea.2019.138264, 766, 138264, 138264, 2019.10. |
| 55. | M. Hassanipour, S. Watanabe, K. Hirayama, H. Li, H. Toda, K. Uesugi, A.Takeuchi, Assessment of predominant microstructural features controlling 3D short crack growth behavior via a surrogate approach in Ti-6Al-4V, Materials Science and Engineering: A, 10.1016/j.msea.2019.01.116, 751, 351-362, 2019.03. |
| 56. | K. Matsuda, T. Yasumoto, A. Bendo, T. Tsuchiya, S. Lee, K. Nishimura, N. Nunomura, C. D. Marioara, A. Levik, R. Holmestad, H. Toda, M. Yamaguchi, K. Ikeda, T. Homma, S.Ikeno, Effect of Copper Addition on Precipitation Behavior near Grain Boundary in AlZnMg Alloy, Materials Transactions, 10.2320/matertrans.L-M2019828, 60, 8, 1688-1696, 2019.06. |
| 57. | Quantitative evaluation of creep voids in Mod.9Cr-1Mo steel welded joints with X - Ray micro-tomography © 2019 The Society of Materials Science, Japan. High-chromium ferritic resisting steels have been commonly used for high temperature components of USC boilers. However, it is well known that in the welded joints TYPE IV damage occurs in the fine-grained HAZ during long-term use under elevated temperature, due to the multiaxial stress at the fine-grained HAZ region. TYPE IV damage develops by the creep void nucleation at grain boundaries, following the void growth and coalescence. In order to measure the amount of creep damage, the distribution of voids on two-dimensional cross section is normally observed. However, the damage evaluation has a limitation from the point of accuracy because the void grows three-dimensionally. Recently, X-ray CT has been applied to observe damage distribution in three dimensions, and it is known that X-ray μ-CT in SPring-8, which is synchrotron radiation facility, can detect a void of about 1 μm diameter. In this paper, the TYPE IV damage is observed with X-ray μ-CT. The amount of void nucleation and the size of voids in the fine-grained HAZ region with time are quantitatively evaluated. Comparison between the creep damage evaluations based on two dimensional cross section (average diameter, area fraction and number density) and three dimensional void observations is conducted. It appears that the evaluation based on the area fraction on cross section is closest to that in three dimensions and therefore the most suitable evaluation.. |
| 58. | Neutron Imaging Analysis of Hydrogen Content in Pure Palladium and Aluminum Alloys The visualization of hydrogen distribution in materials is important to understand hydrogen embrittlement behavior. Neutron imaging experiment was carried out in order to visualize the distribution of solute hydrogen in an Al-10.1％Zn-1.2％Mg alloy and a pure palladium after hydrogen charging. Changes in the contrast of neutron transmission images caused by hydrogen were clearly observed in a palladium. In the wavelength range of 2-3 Å and 5-13.5 Å, the mean neutron transmission around the center of a hydrogen-charged palladium were 0.692 and 0.511, respectively. The hydrogen content in a palladium was estimated to be 10.8 mol％ from the measured neutron transmission. In this study, it has been demonstrated that hydrogen content can be analyzed even in non-monochromatic neutron imaging by considering the wavelength dependence of neutron intensity, and the effects of incoherent scattering and of Bragg-edge on transmission. On the other hand, hydrogen could not be observed from the neutron transmission image in Al-Zn-Mg alloys. This was due to the low hydrogen content, which was mass ppm level even after hydrogen charging, and statistical precision was not sufficient to discuss the amount of hydrogen of the mass ppm order. . |
| 59. | K. Hirayama, H.Toda, M. Kobayashi, Mapping 3D crystallographic orientation and strain fields in deformed polycrystalline aluminium alloy by diffraction-amalgamated grain boundary tracking, SPring-8 / SACLA Research Frontiers 2016, 62, 63, 2017.08. |
| 60. | Damage Behavior of Al-7%Si Alloys with Refined Eutectic Silicon Particles due to Reduced Phosphor. |
| 61. | Precipitation structure and mechanical properties on peak-aged Al–Zn–Mg alloys including different with some Zn/Mg ratios. |
| 62. | D. Fu, H. Toda, H. Su, K. Hirayama, K. Uesugi, A. Takeuchi, 4D characterization of the stress corrosion cracking behavior in Al-10Mg aluminium alloy via synchrotron X-ray tomography, Proceedings of the International Offshore and Polar Engineering Conference (ISOPE 2019), 4, 4199-4203, ISOPE-I-19-591, 2019.06. |
| 63. | Leonardo Gutierrez, Han Li, Hiroyuki Toda, Masakazu Kobayashi, Osamu Kuwazuru, Rafael Batres, A Method for the Identification of Mechanical Properties Using Surrogate Models, International Journal of Computer Theory and Engineering, 10.7763/ijcte.2014.v6.868, 6, 3, 234-239, 2014.06. |
| 64. | Han Li, Leonardo Gutierrez, Masakazu Kobayashi, Osamu Kuwazuru, Hiroyuki Toda, Rafael Batres, A Numerical Evaluation of an Infill Sampling Criterion in Artificial Neural Network-Based Optimization, International Journal of Computer Theory and Engineering, 10.7763/ijcte.2014.v6.874, 6, 3, 272-277, 2014.06. |
| 65. | H. Toda, T. Kobayashi, Growth behavior of microstructurally-short cracks in the 6061 aluminum alloy reinforced with 22vol% SiC whisker, Proceedings of 10th International Conference on Strength of Materials, J. Inst. Met., 525-528, 1994.08. |
| 66. | H. Toda, T. Kobayashi, Simulation of fracture behavior on Al-SiCw composite, Proceedings of International Conference on Failure Analysis and Prevention, Failure Analysis and Prevention 1995,International Academic Publishers, 225-235, 1995.06. |
| 67. | H. Toda, A. Takahashi, T. Kobayashi, Effects of damaged coarse inclusion particles on mechanical properties of wrought aluminum alloys, ICAA-7, Charlottesville, Virginia, 331-337, 1261-1266, 2000.04. |
| 68. | H. Toda, T. Kobayashi, Al-X(X=Nb, Cr, Fe) ultra-high strength in-situ composite wire, ICAA-7, Charlottesville, Virginia, 331-337, 1133-1138, 2000.04. |
| 69. | H. Toda, T. Kobayashi, Toughness enhancement based on fracture mechanical simulation of Al-SiCw composite, 5th. International Conference on Aluminum Alloys, Their Physical and Mechanical Properties, Grenoble, Materials Science Forum, 242, 193-198, 1997.09. |
| 70. | T. Kobayashi, H. Toda, Improvement of mechanical properties of Al-SiCw composite by RRA treatment, 5th. International Conference on Aluminum Alloys, Their Physical and Mechanical Properties, Grenoble, Materials Science Forum, 217-222, 1127-1132, 1996.07. |
| 71. | H. Toda, Y. Shimasaki, I. Takada, S. Ishimori, T. Kobayashi, Designing principal to optimize strength of discontinuously-reinforced MMC, 8th. Pacific Conference on Automotive Engng., SAE Japan, Yokohama, 2, 265-270, 1995.11. |
| 72. | Kazuyuki Shimizu, Hiroyuki Toda, Hiro Fujihara, Kyosuke Hirayama, Kentaro Uesugi, Akihisa Takeuchi, Hydrogen partitioning behavior and related hydrogen embrittlement in Al-Zn-Mg alloys, Engineering Fracture Mechanics, 10.1016/j.engfracmech.2019.106503, 216, 106503-106503, 2019.07. |
| 73. | H. Toda, Time-resolved 3D measurements of mechanical behaviours in aluminium alloys, Boof of abstracts of Asian Forum on Light Metals 2012, 2012.11. |
| 74. | H Toda, T Gouda, T Kobayashi, Finite element analysis of observed high strengthening in composites with regularly segregated microstructures, MATERIALS SCIENCE AND TECHNOLOGY, 14, 9-10, 925-932, 1998.09, A distinct dual phase composite has been developed, comprising spherical reinforcement clusters and an unreinforced matrix, according to numerical simulation of crack initiation and propagation in discontinuously reinforced MMCs. The present work is aimed at interpretation of the high strengthening ratios which were actually measured ill such dual phase composites. Elastic-plastic finite element modelling is utilised to analyse rite strengthening ratio in a two-dimensional idealised microstructure with periodic clustering. As the degree of clustering increases, the strengthening ratio is predicted to increase. in composites with a networking cluster, much more strengthening is exhibited together with relatively uniform strain distribution. The primary mechanism leading to additional strengthening due to clustering derives from ail optimum ratio in deformation resistance between a matrix and a reinforcing phase. bl the proposed dual phase composites, each cluster can behave as a single reinforcement which can deform plastically and there is no distinct interface between the cluster and the softer phase. MST/4032.. |
| 75. | H Toda, T Kobayashi, A Takahashi, Mechanical analysis of toughness degradation due to premature fracture of course inclusions in wrought aluminium alloys, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 280, 1, 69-75, 2000.03. |
| 76. | L Wang, T Kobayashi, H Toda, M Hayakawa, Effect of loading velocity and testing temperature on the fracture toughness of a SiCw/6061Al alloy composite, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 280, 1, 214-219, 2000.03, The effects of loading velocity and testing temperature on the fracture toughness of a SiC whisker reinforced 6061 aluminum alloy composite were investigated. A precracked three-point bend specimen configuration was selected for fracture toughness measurement, with tests being conducted at loading velocities of 10(-2)-10 m s(-1), and from room temperature to 473 K. The results showed that the fracture toughness increases with increasing loading velocity, but, the difference with respect to room temperature is small, because the fracture toughness decreases slowly with the increase of testing temperature. The composite material failed mainly by whisker pull-out and whisker breaking. (C) 2000 Elsevier Science S.A. All rights reserved.. |
| 77. | LH Qian, ZG Wang, H Toda, T Kobayashi, High temperature low cycle fatigue and thermo-mechanical fatigue of a 6061Al reinforced with SiCW, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/S0921-5093(00)00892-3, 291, 1-2, 235-245, 2000.10. |
| 78. | LH Qian, ZG Wang, H Toda, T Kobayashi, Effect of reinforcement volume fraction on the thermo-mechanical fatigue behavior of SiCw/6061A1 composites, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/S0921-5093(03)00260-0, 357, 1-2, 240-247, 2003.09, Thermo-mechanical fatigue (TMF) tests were conducted on the 15 and 28 vol.% SiCW/6061Al composites under temperature cycling between 150 and 300 degreesC and mechanical strain ranges of 0.004-0.012. The effects of temperature-load phase and volume fraction of SiC whiskers on the TMF behavior were examined. The results showed that cyclic softening occurred in both composites during out-of-phase (OP) and in-phase (IP) TMF, In both composites, tensile mean stress was generated during OP-TMF, whereas compressive mean stress was generated during IP-TMF. The 15% SiCW composite demonstrated a longer life than the 28% SiCW composite in the case of OP-TMF, however, in the case of IP-TMF the fatigue life curves of the two composites passed across each other, i.e. at small strain range level the life of the 15% SiCW composite was longer than that of 28% SiCW composite, while at large strain range level, the life of the former composite became shorter than that of the latter composite. (C) 2003 Elsevier Science B.V. All rights reserved.. |
| 79. | Hiromi Miura, Taku Sakai, Hiroyuki Toda, Deformation and fracture of Cu-SiO2 bicrystals with [011] twist boundaries, Acta Materialia, 10.1016/s1359-6454(03)00212-x, 51, 16, 4707-4717, 2003.09. |
| 80. | H Toda, Sinclair, I, JY Buffiere, E Maire, KH Khor, P Gregson, T Kobayashi, A 3D measurement procedure for internal local crack driving forces via synchrotron X-ray microtomography, ACTA MATERIALIA, 10.1016/j.actamat.2003.11.014, 52, 5, 1305-1317, 2004.03, Synchrotron X-ray microtomography has been utilized for the in situ observation of fatigue crack opening/closure during load cycles. High-resolution phase contrast imaging technique has enabled the reconstruction of clear crack images together with the details of microstructural features. Physical displacements of micro-pores in a crack-tip stress field are used to obtain local mixed-mode crack driving forces along a crack front, and its feasibility is confirmed. Complicated crack closure behaviour are observed due to the combined effects of local modes II and III displacements. The technique used provides a highly effective way of assessing local crack driving forces together with supplementary ways of verifying and interpreting it by visualising and quantifying various forms of crack-tip shielding behaviour. The proposed technique is clearly advantageous compared to the limited procedures available in the current literature, where detailed internal information can only be achieved for limited types of material. (C) 2003 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 81. | KH Khor, JY Buffiere, W Ludwig, H Toda, HS Ubhi, PJ Gregson, Sinclair, I, In situ high resolution synchrotron x-ray tomography of fatigue crack closure micromechanisms, JOURNAL OF PHYSICS-CONDENSED MATTER, 10.1088/0953-8984/16/33/012, 16, 33, S3511-S3515, 2004.08, Fatigue crack closure has been identified as an important factor in determining crack growth rates. However, the methods of measurement of crack closure remain the subject of ongoing controversy. To date, computed finite element models, analytical models and widely established compliance-based experimental methods have offered limited micromechanical insight and/or direct information on the active crack tip region within bulk material. To understand the absolute contributions of crack closure mechanisms, such as plasticity-induced and roughness-induced closure, to fatigue properties, an internal, three-dimensional insight into crack behaviour during loading and unloading is clearly of value. In this work, synchrotron radiation x-ray microtomography is carried out at a high resolution of 0.7 mum to provide unique three-dimensional in situ observation of steady state plane strain fatigue crack growth in a 2024-type Al alloy (Al-Cu-Mg-Mn). Using such high resolution imaging (additionally exploiting the phase contrast effect in interface imaging), the details of fatigue cracks are readily observed, along with the occurrence of closure. A novel microstructural crack displacement gauging method is used to quantify the mixed mode character of crack opening displacement and the closure effect. A liquid gallium grain boundary wetting technique is used in conjunction with the microtomography to visualize the correlation between the three-dimensional structure of the grains and fatigue crack behaviour. Subsequently, electron backscattering diffraction assessment of the grain orientation on the samples provides a uniquely complete 3D description of crack-microstructure interactions.. |
| 82. | T. Ohgaki, H. Toda, I. Sinclair, J.-Y. Buffiere, W. Ludwig, T. Kobayashi, Quantitative assessment of liquid Ga penetration into aluminium alloy by high-resolution X-ray tomography, Materials Science & Engineering. A, 406, 1-2, 261-267, 2005.02. |
| 83. | YL Zhou, M Niinomi, T Akahori, H Fukui, H Toda, Corrosion resistance and biocompatibility of Ti-Ta alloys for biomedical applications, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2005.03.032, 398, 1-2, 28-36, 2005.05, Corrosion resistance, wear resistance and biocompatibility of the studied Ti-Ta alloys with Ta contents of 10, 30 and 70 mass% together with the currently used metallic biomaterials pure titanium (Ti) and Ti-6Al-4V extra low interstitial (ELI) alloy were investigated for biomedical applications. Corrosion resistance was measured by an anodic polarization test using an automatic potentiostat in 5% HCl solution at 310 K. Wear resistance was evaluated using a pin-on-disk type friction wear test system with a load of 4.9 N at 310 K in a simulated body fluid (Ringer's solution), and biocompatibility was judged by evaluating the cyto-toxicity through MTT assay. The passive behaviors are observed for all the studied Ti-Ta alloys, and the TiO2 passive films strengthened by the more stable Ta2O5 passive films result in improved corrosion resistance of the studied Ti-Ta alloys with increasing Ta content. All the studied Ti-Ta alloys are non-cytotoxic like pure Ti. The crystal structure shows little influence on the corrosion resistance and cyto-toxicity of the studied Ti-Ta alloys. The experimental results conform the expected excellent corrosion resistance and biocompatibility of the studied Ti-Ta alloys, which are better than or similar to those of pure Ti or Ti-6Al-4V ELI alloy used as standard biomaterials, suggesting their promising potential for biomedical applications. (c) 2005 Elsevier B.V. All rights reserved.. |
| 84. | T Akahori, M Niinomi, H Fukui, M Ogawa, H Toda, Improvement in fatigue characteristics of newly developed beta type titanium alloy for biomedical applications by thermo-mechanical treatments, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 10.1016/j.msec.2004.12.007, 25, 3, 248-254, 2005.05, Tensile and plain fatigue properties of P type titanium alloy, Ti-29Nb-13Ta-4.6Zr, which underwent various thermo-mechanical treatments, were investigated in order to judge its potential for biomedical applications. Microstructures of Ti-29Nb-13Ta-4.6Zr (TNTZ) aged directly at 723 K for 259.2 ks after cold rolling and TNTZ aged at 723 K for 259.2 ks after solution treatment are composed of precipitated alpha phase in beta phase. While, microstructures of TNTZ aged directly at 598 K and 673 K for 259.2 ks after cold rolling and aged at 598 K and 673 K for 259.2 ks after solution treatment are composed of precipitated omega phase, and precipitated alpha and omega phases in beta phase, respectively. Tensile strength of aged TNTZ after solution treatment and aged TNTZ after cold rolling decreases with increasing aging temperature although the elongation shows the reverse trend. TNTZ composed of omega phase or omega and alpha phases in beta phase shows the tensile strength of around 1000 MPa or more. Young's moduli of aged TNTZ after solution treatment and aged TNTZ after cold rolling decrease with increasing aging temperature. TNTZ conducted with solution treatment has the lowest Young's modulus of around 60 GPa. Fatigue strengths of aged TNTZ after solution treatment and aged TNTZ after cold rolling increase with increasing aging temperature. In particular, TNTZ aged directly at 723 K after cold rolling shows the greatest fatigue strength in both low cycle fatigue life and high cycle fatigue life regions, and the fatigue limit, which is around 770 MPa, is nearly equal to that of hot-rolled Ti-6Al-4V ELI conducted with aging, which is one of representative alpha + beta type titanium alloys for biomedical applications. (c) 2005 Elsevier B.V. All rights reserved.. |
| 85. | N Sakaguchi, M Niinomi, T Akahori, J Takeda, H Toda, Relationships between tensile deformation behavior and microstructure in Ti-Nb-Ta-Zr system alloys, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 10.1016/j.msec.2004.12.014, 25, 3, 363-369, 2005.05, Ti-Nb-Ta-Zr system alloys are receiving more attention for biomedical material component applications. However, the deformation behavior of the Ti-Nb-Ta-Zr system has not been evaluated to date. Therefore, the deformation behavior of Ti-Nb-Ta-Zr alloys with different Nb contents was investigated in this study. The behaviors of loading-unloading stress-strain curves of Ti-20Nb-10Ta-5Zr and Ti-25Nb-10Ta-5Zr air-cooled after final heating of the manufacturing process are similar to that obtained in metastable beta type titanium alloys that have the shape memory effect. Therefore, the shape memory effect was expected in Ti-20Nb-10Ta-5Zr and Ti-25Nb-10Ta-5Zr alloys. The elastic deformation of Ti-30Nb-10Ta-5Zr disobeyed Hooke's law. However, stress or strain-induced martensite (SIM) is not observed on the loading-unloading stress-strain curve. The deformation mechanism of Ti-25Nb-10Ta-5Zr changes with varying its microstructure. In Ti-25Nb-10Ta-5Zr air-cooled after final heating, the microstructure consisted of an omega phase in a beta phase. The stress for inducing martensite in a phase, am, was nearly equal to the yielding stress, sigma(y). Therefore, stress-induced martensitic transformation and movement of dislocations occurred together. In Ti-25Nb-10Ta-5Zr water-quenched after final heating of the manufacturing process, the microstructure consisted of a single phase, where am is lower than ay, Therefore, stress-induced martensitic transformation occurred before yielding. (c) 2005 Elsevier B.V. All rights reserved.. |
| 86. | N Sakaguchi, M Niinomi, T Akahori, J Takeda, H Toda, Effect of Ta content on mechanical properties of Ti-30Nb-XTa-5Zr, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 10.1016/j.msec.2005.04.003, 25, 3, 370-376, 2005.05, In this study, we investigated the effect of Ta content on the mechanical properties of Ti-30Nb-XTa-5Zr fabricated by a powder metallurgy method, for biomedical applications. The Ta content ranged from 0% to 20 mass%. The microstructures of Ti-30Nb-XTa-5Zr that contain less than 5 mass% Ta comprise beta phase and an omega phase. The tensile properties of Ti-30Nb-XTa-5Zr change with a change in their deformation mechanisms. The deformation mechanisms of Ti-30Nb-XTa-5Zr, which contains less than 10 mass% Ta, is the stress-induced martensite (SIM) transformation, while that of Ti-30Nb-XTa-5Zr, which contains over 20 mass% Ta, is the slip mechanism. The minimum elastic modulus is obtained in Ti-30Nb-10Ta-5Zr, which comprises a single phase. (c) 2005 Elsevier B.V. All rights reserved.. |
| 87. | M Niinomi, T Akahori, T Takeuchi, S Katsura, H Fukui, H Toda, Mechanical properties and cyto-toxicity of new beta type titanium alloy with low melting points for dental applications, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 10.1016/j.msec.2005.01.024, 25, 3, 417-425, 2005.05, Beta stabilized new alloys such as Ti-29Nb-13Zr-2Cr, Ti-29Nb-15Zr-1.5Fe, Ti-29Nb-10Zr-0.5Si, Ti-29Nb-10Zr-0.5Cr-0.5Fe and Ti-29Nb-18Zr-2Cr-0.5Si have been developed for dental applications. These alloys were designed based on master alloy Ti-29Nb-13Ta-4.6Zr (TNTZ) for biomedical applications. In this research, high melting temperature element Ta was replaced with beta stabilizing elements such as Cr, Fe and Si to lower the melting temperature of the alloy. Their melting points, mechanical properties, surface reaction layers and cyto-toxicity were investigated in this study. Melting points of designed alloys fall by about 50 K to 370 K as compared with that of TNTZ, and Ti-29Nb-13Zr-2Cr has the lowest melting point of around 2050 K. Vickers hardness of the surface of each designed alloy cast into modified magnesia based investment material is in the range of 400 Hv to 500 Hv, which is lower than that of TNTZ (around 560 Hv). Balances of strength and ductility of cast Ti-29Nb-13Zr-2Cr, Ti-29Nb-15Zr-1.5Fe and Ti-29Nb-10Zr-0.5Cr-0.5Fe are nearly equal to that of cast TNTZ. Cell viability of each cast designed alloy is excellent. (c) 2005 Elsevier B.V. All rights reserved.. |
| 88. | B. Gunawarman, M. Niinomi, T. Akahori, T. Souma, M. Ikeda, H. Toda, Mechanical properties and microstructures of low cost β titanium alloys for healthcare applications, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 10.1016/j.msec.2004.12.015, 25, 3, 304-311, 2005.05. |
| 89. | B Gunawarman, M Niinomi, T Akahori, J Takeda, H Toda, Mechanical properties of Ti-4.5Al-3V-2Mo-2Fe and possibility for healthcare applications, MATERIALS SCIENCE & ENGINEERING C-BIOMIMETIC AND SUPRAMOLECULAR SYSTEMS, 10.1016/j.msec.2004.12.012, 25, 3, 296-303, 2005.05, The mechanical properties of Ti-4.5Al-3V-2Mo-2Fe, a relatively low cost titanium alloy originally designed for structural applications (especially for aerospace applications), were investigated. The alloy was subjected to heat treatments with various solution treatment temperatures (annealing temperature) and cooling rates. The mechanical properties of the heat-treated alloys were then used in order to judge the prospects of practical usage of the alloy for healthcare equipment such as wheelchairs. The mechanical properties of Ti-4.5Al-3V-2W-Ne are highly affected by either solution treatment or cooling rate, and they change as a result of the change in the microstructure. The alloy single annealed at temperature in the alpha + beta field has very high fatigue ratio (0.80 - 0.85) and high specific strength (210-260 MPa/g cm(-3)) with a modest fracture toughness (J(IC)=25-35 kN/m). This balance of fatigue ratio and specific strength is better than that of the existing wheelchair materials. Thus, from the point of view of mechanical properties, Ti-4.5Al-3V-2W-2Fe has high potential to be used for healthcare applications. (c) 2005 Elsevier B.V. All rights reserved.. |
| 90. | Hiroyuki Toda, Masayuki Takata, Tomomi Ohgaki, Masakazu Kobayashi, Toshiro Kobayashi, Kentaro Uesugi, Koichi Makii, Yasuhiro Aruga, 3-D image-based mechanical simulation of aluminium foams: Effects of internal microstructure, ADVANCED ENGINEERING MATERIALS (EUROMAT 2005), 10.1002/adem.200600035, 8, 6, 459-467, 2006.06. |
| 91. | Tomomi Ohgaki, Hiroyuki Toda, Masakazu Kobayashi, Kentaro Uesugi, Toshiro Kobayashi, Mitsuo Niinomi, Toshikazu Akahori, Koichi Makii, Yasuhiro Aruga, In-situ high-resolution x-ray CT observation of compressive and damage behaviour of aluminium foams by local tomography technique, ADVANCED ENGINEERING MATERIALS, 10.1002/adem.200600039, 8, 6, 473-475, 2006.06. |
| 92. | H. Toda, K. Uesugi, A. Takeuchi, K. Minami, M. Kobayashi, T. Kobayashi, Three-dimensional observation of nanoscopic precipitates in an aluminum alloy by microtomography with Fresnel zone plate optics, APPLIED PHYSICS LETTERS, 10.1063/1.2359288, 89, 14, 143112-143112, 2006.10, Microtomography combined with hard x-ray imaging microscopy has been employed to observe nanoscopic features in a material, which has, to date, only been done by the transmission electron microscopy (TEM). Here, the authors show a characteristic microstructure in an aluminum alloy, such as a slant gap between growing precipitates that impinge on each other due to the presence of a solute-depleted zone. Such observation is not possible by conventional projection microtomography even using the highest resolution available. It would appear that the present technique has a unique potential to observe nanoscopic features inside materials that are several orders of magnitude thicker than TEM specimens. (c) 2006 American Institute of Physics.. |
| 93. | T. Ohgaki, H. Toda, M. Kobayashi, K. Uesugi, M. Niinomi, T. Akahori, T. Kobayash, K. Makii, Y. Aruga, In situ observations of compressive behaviour of aluminium foams by local tomography using high-resolution X-rays, PHILOSOPHICAL MAGAZINE, 10.1080/14786430600724454, 86, 28, 4417-4438, 2006.10, We have investigated the compressive behaviour of closed-cell aluminium foams using a high-resolution X-ray CT. The microstructures of cell walls or Plateau borders in the foams were visualized in 3D using the local tomography technique which is a high-resolution CT method to reconstruct a region of interest within a large sample. The shapes and the 3D distribution of micropores, particles, and regions of solute segregation in the foams are evaluated, comparing the cell walls with the Plateau borders. Under compressive loads, the damage behaviour of such microstructures has been observed using an in situ test rig. It is found that the microcracks were mainly initiated from the cell walls and the micropores with large diameters were also damaged. The crack initiation sites are classified from the results. In addition, a method for non-destructive characterization of elastic and plastic deformation in the foams, which is called a 3D microstructure gauge (MG) method, is presented. Thousands of micropores as markers on each load were automatically matched by the information of those volumes and surface areas. The local strain mapping by the MG indicates that the edges of the micropores with large diameters have large strain under compression and this is consistent with the crack analyses.. |
| 94. | M. Kobayashi, H. Toda, K. Uesugi, T. Ohgaki, T. Kobayashi, Y. Takayama, B. -G. Ahn, Preferential penetration path of gallium into grain boundary in practical aluminium alloy, PHILOSOPHICAL MAGAZINE, 10.1080/14786430600710933, 86, 28, 4351-4366, 2006.10, The preferential penetration of a liquid metal along grain boundaries (GBs) in polycrystalline metals is a well-known phenomenon. Gallium-decorated GB networks in rolled aluminium alloys have been visualized three-dimensionally using the high-resolution synchrotron radiation computer tomography (SRCT). The distribution of gallium concentration along GBs was measured using X-ray absorption. Statistical correction for blurring was performed to raise accuracy of the measurement, and then compared with orientation mapping by the SEM/EBSP method on the surface of a tomographic specimen. The pancake-like grain microstructure formed by a rolling process causes the anisotropy of penetration direction. Although the gallium penetrated into high-angle GBs, all of the high-angle GBs are not necessarily decorated by the gallium. The reason for this may be explained by considering geometrically possible penetration paths that seem to be dependent on local grain arrangement and GB structure through each path. The dependence of the gallium concentration on the rotation axis of misorientation has been found along the high-angle GBs. Especially, GBs with a specific misorientation ( as a misorientation axis) showed high gallium concentration.. |
| 95. | L. Qian, H. Toda, S. Nishido, T. Kobayashi, Experimental and numerical investigations of the effects of the spatial distribution of α phase on fracture behavior in hypoeutectic Al-Si alloys, Acta Mater., 10.1016/j.actamat.2006.06.036, 54, 18, 4881-4893, 2006.10. |
| 96. | Hiroyuki Toda, Michihiro Toyoda, Toshiro Kobayashi, Toshikazu Akahori, Mitsuo Niinomi, Feasibility study on smart coating for failure prevention under thermo-mechanical fatigue loading, JOURNAL OF INTELLIGENT MATERIAL SYSTEMS AND STRUCTURES, 10.1177/1045389X06065235, 17, 12, 1099-1103, 2006.12, In this article, a new concept of smart coating is presented, which enables failure prevention under thermo-mechanical fatigue loading by a simple coating without using any external devices. The feasibility of arresting fatigue crack propagation under thermo-mechanical loading is experimentally demonstrated for an Al-Si practical casting alloy by applying a simple and inexpensive coating prior to usage. An Sn alloy has been chosen as a coating material as a result of extensive screening tests. Valuable mechanistic insight has been gained from numerical simulation indicating that the crack driving force can be reduced by the crack closure mechanism induced by the impregnation of coating material.. |
| 97. | M. Toyoda, H. Toda, H. Ikuno, T. Kobayashi, M. Kobayashi, K. Matsuda, Preferential orientation of precipitates during thermomechanical cyclic loading in an aluminum alloy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2006.11.005, 56, 5, 377-380, 2007.03, The microstructural change during a compression-tension thermomechanical cyclic loading of an Al-Si-Cu-Mg alloy casting is investigated. Although the thermomechanical fatigue loading was applied after the alloy was tempered to the T6 peak aging condition, preferential orientation of precipitates is observed together with anisotropy in deformation behavior. The precipitates are observed to align perpendicular to a compressive stress during heating. The effects of preferential orientation are also discussed on the basis of a model analysis. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 98. | H. Zhang, H. Toda, H. Hara, M. Kobayashi, T. Kobayashi, D. Sugiyama, N. Kuroda, K. Uesugi, Three-dimensional visualization of the interaction between fatigue crack and micropores in an aluminum alloy using synchrotron X-ray microtomography, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 10.1007/s11661-007-9214-6, 38A, 8, 1774-1785, 2007.08, The effect of the flow-forming process on the fatigue behavior of an Al-Si-Mg alloy was investigated using synchrotron X-ray microtomography. The fatigue life of the flow-formed-T6 specimen was found to be longer than that of the as-cast-T6 in all the selected stress amplitudes. The X-ray-scanned radiographs of a flow-formed-T6 specimen were reconstructed to allow three-dimensional (3-D) visualization of distribution of micropores and pore-crack interactions. Observations were performed on different tomographic slices to investigate the interaction between the micropores and the crack. Micropores have been associated with deflections of the crack path. Mode I and Mode 11 stress-intensity factors (SIFs) were calculated at each position along the fatigue-crack path using a micromechanics model. The SIF increased rapidly when the fatigue crack came close to a micropore. It was found that the average value of SIFs along entire crack paths was slightly higher than the remotely applied stress intensity, although the level of antishielding was pronounced in some local regions. Crystallographic texture is proposed to be the important factor for the observed higher fatigue resistance in flow-formed-T6 material.. |
| 99. | Masaaki Nakai, Mitsuo Niinomi, Toshikazu Akahori, Naofumi Ohtsu, Hideki Nishimura, Hiroyuki Toda, Hisao Fukui, Michiharu Ogawa, Surface hardening of biomedical Ti-29Nb-13Ta-4.6Zr and Ti-6Al-4V ELI by gas nitriding, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2007.08.065, 486, 1-2, 193-201, 2008.06, The microstructure and hardness near the surface of a biomedical titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), subjected to gas nitriding at 1023-1223 K was investigated in comparison with the conventional biomedical Ti-6Al-4V ELI (Ti64). After gas nitriding, the microstructure near the specimen surface was observed by optical microscopy, X-ray diffraction (XRD), Auger electron spectroscopy (AES), and X-ray photoelectron spectroscopy (XPS). In both alloys, two types of titanium nitrides (TiN and Ti(2)N) are formed and the a phase is precipitated by gas nitriding. Furthermore, the oxygen impurity in the gas nitriding atmosphere reacts with the titanium nitrides; thus, TiO(2) is formed at the outermost titanium nitride layer. The surface hardening was also evaluated by Vickers hardness measurement. The Vickers hardness near the surface of TNTZ and Ti64 increases significantly by gas nitriding. (c) 2007 Published by Elsevier B.V.. |
| 100. | Masakazu Kobayashi, Hiroyuki Toda, Yuji Kawai, Tomomi Ohgaki, Kentaro Uesugi, David S. Wilkinson, Toshiro Kobayashi, Yoshimitsu Aoki, Mitsuru Nakazawa, High-density three-dimensional mapping of internal strain by tracking microstructural features, ACTA MATERIALIA, 10.1016/j.actamat.2007.12.058, 56, 10, 2167-2181, 2008.06, The three-dimensional (3-D) strain map is useful to elucidate the relationships between microstructures and locally caused deformation and fracture. However, a robust tracking method, which enables error-free tracking in synchrotron radiation computed tomography (SR-CT) images with >10 000 microstructural features, is not currently available. In this study, a model sample was subjected to a tensile test and scanned by the SR-CT technique in order to develop a new tracking method. The developed tracking methods indicated a high tracking ratio and tracking success ratio of nearly 100% in a wide strain range, which included the assumed strain in a practical experiment. It was confirmed that tracking errors produce an incorrect strain distribution in 3-D strain mapping. This study verified the validity of the developed tracking method. The application of this method to high-resolution SR-CT images will make measurement and visualization of the strain distribution possible in three dimensions in bulk materials. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 101. | L. Qian, H. Toda, K. Uesugi, T. Ohgaki, M. Kobayashi, T. Kobayashi, Three-dimensional visualization of ductile fracture in an Al-Si alloy by high-resolution synchrotron X-ray microtomography, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2006.10.201, 483-484, 293-296, 2008.06. |
| 102. | A. Weck, D. S. Wilkinson, E. Maire, H. Toda, Visualization by X-ray tomography of void growth and coalescence leading to fracture in model materials, ACTA MATERIALIA, 10.1016/j.actamat.2008.02.027, 56, 12, 2919-2928, 2008.07, The literature contains many models for the process of void nucleation, growth and coalescence leading to ductile fracture. However, these models lack in-depth experimental validation, in part because void coalescence is difficult to capture experimentally. In this paper, an embedded array of holes is obtained by diffusion bonding a sheet filled with laser-drilled holes between two intact sheets. The experiments have been performed with both pure copper and Glideop. Using X-ray computed tomography, we show that void growth and coalescence (or linkage) are well captured in both materials. The Brown and Embury model for void coalescence underestimates coalescence strains due to constraining effects. However, both the Rice and Tracey model for void growth and the Thomason model for void coalescence give good predictions for copper samples when stress triaxiality is considered. The Thomason model, however, fails to predict coalescence for the Glidcop samples; this is primarily due to secondary void nucleation. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 103. | H. Toda, S. Yamamoto, M. Kobayashi, K. Uesugi, H. Zhang, Direct measurement procedure for three-dimensional local crack driving force using synchrotron X-ray microtomography, ACTA MATERIALIA, 10.1016/j.actamat.2008.08.022, 56, 20, 6027-6039, 2008.12, X-ray microtomography has been utilized for the observation of ductile fractures in ail aluminum alloy with in Al/Al-Si dual phase Structure. A procedure for analyzing a series of tomographic images is proposed for extracting the variation in the local crack-tip opening displacement (CTOD), and its feasibility is confirmed. Complicated crack growth behavior and the formation Of uncracked ligaments ahead of a crack tip are observed in the alloy owing to the marked difference in local fracture toughness between the two phases. The proposed technique has provided a quantitative interpretation for such phenomena. It is clarified that a conventional measurement significantly overestimates the CTOD level. The transition behavior in CTOD has been revealed over a certain distance across an interface between the two phases, suggesting the existence of scaling effects that influence the microstructure/fracture relationship. Overall the current method could offer a highly effective way of assessing three-dimensional local fracture behavior. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 104. | H. Toda, T. Fukunaga, A. Kobayashi, Improvement of thermomechanical fatigue life in an age-hardened aluminum alloy, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2008.11.005, 60, 6, 385-387, 2009.03, Preliminary thermomechanical treatments (PTMTs) for age-hardening aluminuml alloys have been proposed to improve thermomechanical fatigue (TMF) resistance. Preferential orientation of precipitates perpendicular to the loading direction, achieved in advance by applying an out-of-phase PTMT with small temperature and strain ranges, call effectively prolong in-phase TMF life. This has been shown to correlate with the degree of preferential orientation due mechanical anisotropy introduced during PTMTs. (c) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 105. | H. Toda, T. Hidaka, M. Kobayashi, K. Uesugi, A. Takeuchi, K. Horikawa, Growth behavior of hydrogen micropores in aluminum alloys during high-temperature exposure, ACTA MATERIALIA, 10.1016/j.actamat.2009.01.026, 57, 7, 2277-2290, 2009.04, X-ray microtomography was used to observe hydrogen micropores and thier growth behavior at high temperatures in several aluminium alloys. High-density micropores were observed in high-purity Al-Mg alloys, but their density and volume fraction were much lower in pure aluminum. Our results have revealed that the growth behaviour of micropores is dominated by Ostwald ripening. About 53% of hydrogen is trapped in micropores in Al-Mg alloy with low hydrogen content, making micropores the predominant hydrogen trap site. Although total hydrogen content is similar to that in the alloy, the ratio of hydrogen trapped in micropores is below 7% in pure aluminium. This difference is attributable to the lack of hydrogen precipitation sites in pure aluminium. Although the overall amounts of hydrogen at dislocations and grain boundaries are small in all the materials, the occupancies for these trap sites were concluded to be very high. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rigths reserved.. |
| 106. | H. Zhang, H. Toda, P. C. Qu, Y. Sakaguchi, M. Kobayashi, K. Uesugi, Y. Suzuki, Three-dimensional fatigue crack growth behavior in an aluminum alloy investigated with in situ high-resolution synchrotron X-ray microtomography, ACTA MATERIALIA, 10.1016/j.actamat.2009.03.036, 57, 11, 3287-3300, 2009.06, The fatigue crack propagation process in an Al-Mg-Si alloy was investigated using in situ high-resolution synchrotron radiation Xray microtomography. Tomography datasets were obtained at periodic intervals throughout the 120,000 fatigue cycles. Three-dimensional rendering of the through-thickness crack shape indicates that in a number of regions the adjacent sides of two branched cracks tend to overlap with fatigue cycling and form a crack overlapping region. Measured crack growth rates in each tomographic slice show that crack growth retardation generally occurs in these crack overlapping regions. The through-thickness variation in crack tip opening displacement was also measured and was used to account for the observed crack propagation behavior. Crack morphologies were observed at different load levels in a fatigue cycle. The crack closure level varied for two selected regions comprising different overlapping cracks. The correlation of the crack growth rate with both crack opening and Closure levels was discussed and interpreted. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 107. | H. Toda, K. Minami, K. Koyama, K. Ichitani, M. Kobayashi, K. Uesugi, Y. Suzuki, Healing behavior of preexisting hydrogen micropores in aluminum alloys during plastic deformation, ACTA MATERIALIA, 10.1016/j.actamat.2009.06.012, 57, 15, 4391-4403, 2009.09, Synchrotron X-ray microtomography was used to observe the shrinkage and annihilation behaviors of hydrogen micropores in three dimensions during hot and cold plastic deformation of an Al-Mg alloy. Whether complete healing of micropores is achieved after plastic deformation was examined by exposing the material to a high temperature after plastic deformation. Although micropores generally show a pattern of shrinking and closing, closer inspection of a single specimen revealed a variety of geometrically variable behaviors. It is noteworthy that some of the micropores are reinitiated in positions identical to those before their annihilation, even after an 8-22% macroscopic strain has been further applied after annihilation. We attribute local variations such as these to significant local strain variation, which we measured in a series of tomographic volumes by tracking the microstructural features. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 108. | Hiroyuki Toda, Hideyuki Oogo, Kentaro Uesugi, Masakazu Kobayashi, Roles of Pre-Existing Hydrogen Micropores on Ductile Fracture, MATERIALS TRANSACTIONS, 10.2320/matertrans.M2009123, 50, 9, 2285-2290, 2009.09, Synchrotron X-ray microtomography was used to observe hydrogen micropores. Competitive growth between pre-existing high-density micropores and voids originating from damage during loading was observed in an aluminum alloy during a tensile test. Extensive and premature growth of pre-existing hydrogen micropores has been observed during tension. while the ordinary damage initiation increased rapidly more later. According to the estimation on the areal fraction of dimple patterns originating from the pre-existing hydrogen micropores, it has been concluded that the hydrogen micropores more or less make contributions to ordinary ductile fracture. [doi:10.2320/matertrans.M2009123]. |
| 109. | Hiroyuki Toda, Takanori Nishimura, Kentaro Uesugi, Yoshio Suzuki, Masakazu Kobayashi, Influence of high-temperature solution treatments on mechanical properties of an Al-Si-Cu aluminum alloy, ACTA MATERIALIA, 10.1016/j.actamat.2009.11.044, 58, 6, 2014-2025, 2010.04, It has been demonstrated that the strength of an Al-Si-Cu alloy is maximized by high-temperature solution treatment at 807 K, which is approximately 16 K higher than the ternary eutectic temperature. The dual-energy K-edge subtraction imaging technique has been employed to obtain the spatial distribution of copper and its change during its solution treatment in three dimensions quantitatively, providing interpretations of the improved mechanical properties in terms of age-hardenability and its spatial variation. It has been also confirmed that the occurrence of incipient local melting and the accompanying growth of micro pores adjacent to the melt regions lead to fractures caused by these defects. However, it can be inferred that the positive effects can outweigh the negative effects even above the eutectic temperature, thereby realizing the maximum strength at such relative high temperature levels. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 110. | Hiroyuki Toda, Tomoyasu Yamaguchi, Mitsuru Nakazawa, Yoshimitsu Aoki, Kentaro Uesugi, Yoshio Suzuki, Masakazu Kobayashi, Four-Dimensional Annihilation Behaviors of Micro Pores during Surface Cold Working, MATERIALS TRANSACTIONS, 10.2320/matertrans.M2010069, 51, 7, 1288-1295, 2010.07, The annihilation behavior of micro pores in an aluminum alloy casting during surface cold working was continuously observed using the synchrotron radiation microtomography. To analyze micro pore annihilation behavior, the displacement of artificially dispersed particles was measured and thereby local strain distributions were mapped in high-density. A peening treatment annihilated most of the micro pores with a diameter of over 10 mu m in the upper part of the specimen that could initiate fatigue cracks. The annihilation behavior of the micro pores could be understood as a function of effective strain locally accumulated around them, and not as a function of local hydrostatic strain. The effective strain varied significantly, with some large pores remaining where local effective plastic strain was relatively low. The complete annihilation of large pores in the surface layer suggests that the application of sufficiently long surface cold working is effective in improving the high-cycle fatigue properties. [doi: 10.2320/matertrans.M2010069]. |
| 111. | M. Kobayashi, Y. Dorce, H. Toda, H. Horikawa, Effect of local volume fraction of microporosity on tensile properties in Al-Si-Mg cast alloy, MATERIALS SCIENCE AND TECHNOLOGY, 10.1179/174328409X441283, 26, 8, 962-967, 2010.08, Porosity in Al-Si-Mg cast alloys utilised in automotive parts affects directly products quality, i.e. mechanical properties. In this study, the effect of micropores on mechanical properties has been investigated by X-ray tomography from the viewpoint of clustering micropores. The local volume fraction (LVF) of porosity was introduced to analyse the effect of clustering micropores. The statistical Weibull method was also used in order to explain strength of the alloy tested. The fracture strain decreased drastically from 17 to 3% on an inverse parabolic relationship with increasing porosity. In the case of the specimens that contain the largest pore higher than 100 mm, the ultimate tensile strength decreases monotonically. It is found that the fracture surface passes through high LVF regions. The fracture strain obviously depends on the ratio of LVF higher than 10%. It is confirmed that the LVF, which represents unevenly distribution of micropores cluster, is one of important dominant factor for managing the mechanical properties in the Al-Si-Mg cast alloy.. |
| 112. | Hiroyuki Toda, Kazuyuki Shimizu, Kentaro Uesugi, Yoshio Suzuki, Masakazu Kobayashi, Application of Dual-Energy K-Edge Subtraction Imaging to Assessment of Heat Treatments in Al-Cu Alloys, MATERIALS TRANSACTIONS, 10.2320/matertrans.L-M2010819, 51, 11, 2045-2048, 2010.11, Dual-energy K-edge subtraction imaging technique has been employed to analyze the spatial distribution of copper and its change in three-dimensions quantitatively during a solution treatment. In order to realize it, some preliminary investigations on the verification and assurance of accuracy and repeatability have been performed. Inhomogeneous Cu concentration distribution is revealed even after the solution treatment for a sufficiently long period of time at a high temperature in an Al-Cu alloy. The present technique has a unique potential to realize four-dimensional chemical-concentration mapping. [doi:10.2320/matertrans.L-M2010819]. |
| 113. | H. Toda, E. Maire, S. Yamauchi, H. Tsuruta, T. Hiramatsu, M. Kobayashi, In situ observation of ductile fracture using X-ray tomography technique, ACTA MATERIALIA, 10.1016/j.actamat.2010.11.065, 59, 5, 1995-2008, 2011.03, Fast microtomography combined with local crack driving force analysis has been employed to analyze crack-tip stress/strain singularities in an aluminum alloy. The application of fast microtomography has made it possible to observe real crack initiation and propagation behaviors without intermediate unloading. The details of a crack and its local propagation behaviors are readily observed with this technique along with evidence of microstructure/crack interactions. After a preliminary investigation of the achieved spatial resolution, we show that conventional stationary and growing crack singularities can be quantitatively validated by deriving the local crack opening displacement. This is to our knowledge the first three-dimensional validation of conventional fracture mechanics during a real time continuous experiment that has been mainly developed via surface observations so far. We also reveal that there is a spatial transition from a stationary crack singularity to a growing crack singularity in addition to the well-known temporal transition that occurs with the onset of crack propagation. Local crack propagation behaviors are also discussed on the basis of this validation. To separate the effects of complex crack geometry from those of microstructure, we also perform an image-based numerical simulation. (c) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 114. | Hiroyuki Toda, Shotaro Masuda, Rafael Batres, Masakazu Kobayashi, Shunzo Aoyama, Masato Onodera, Ryosuke Furusawa, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Statistical assessment of fatigue crack initiation from sub-surface hydrogen micropores in high-quality die-cast aluminum, ACTA MATERIALIA, 10.1016/j.actamat.2011.04.049, 59, 12, 4990-4998, 2011.07, It has recently been discovered that micropores on the order of a few microns agglomerate in a high density in the sub-surface layer of aluminum alloys that have been produced in a high-quality die-casting process. It is known that fatigue behavior is dominated by the existence of the micropores. In the present study, geometrical parameters defining the relationship between fatigue crack initiation and micropores have been investigated using high-resolution X-ray microtomography, combined with two kinds of statistical analysis. It has been revealed that consideration of micropore pairs is necessary, and a number of parameters for paired micropores that may be strongly associated with fatigue crack initiation have been extracted and statistically evaluated. It is concluded that the mean diameter between paired micropores, and the mean distance to the casting surface, are predominant in fatigue crack initiation. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 115. | M. Kobayashi, H. Toda, A. Takeuchi, K. Uesugi, Y. Suzuki, Three-dimensional evaluation of the compression and recovery behavior in a flexible graphite sheet by synchrotron radiation microtomography, MATERIALS CHARACTERIZATION, 10.1016/j.matchar.2012.04.008, 69, 52-62, 2012.07, The compression and unloading behavior of flexible graphite sheets was investigated using synchrotron radiation microtomography with 1 gm voxel size. The recovery ratio of the flexible graphite sheet was measured accurately by in-situ observation. The three-dimensional strain distribution in the interior of the specimen was obtained using the microstructural tracking method. The inner strain distribution with micrometer scale indicated inhomogeneous deformation. The microstructural tracking analysis revealed that deformation units exist in the flexible graphite sheet. The units seem to deform, affecting the neighboring units with each other. The units had a similar size and shape with compacted exfoliated graphite worms that constitute the flexible graphite sheet. Microscopic deformations during compression and unloading are surely affected by the microstructure of the sheet. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.. |
| 116. | Hiroyuki Toda, Darren LeClere, Takanobu Kamiko, Yoshio Suzuki, Akihisa Takeuchi, Kentaro Uesugi, Masakazu Kobayashi, Development of diffraction-amalgamated grain-boundary tracking technique and its application to polycrystalline metals, Proc. SPIE 8506, Developments in X-Ray Tomography VIII, 10.1117/12.930608, 8506, 85060B, 1-8, 2012.10. |
| 117. | D. Seo, F. Tomizato, H. Toda, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Spatial resolution of synchrotron x-ray microtomography in high energy range: Effect of x-ray energy and sample-to-detector distance, Applied Physics Letters, 10.1063/1.4773239, 101, 26, 261901-261901, 2012.12, Spatial resolution of three-dimensional images obtained by synchrotron X-ray microtomography technique is evaluated using cyclic bar patterns machined on a steel wire. Influences of X-ray energy and the sample-to-detector distance on spatial resolution were investigated. High X-ray energies of 33-78 keV are applied due to the high X-ray absorption of transition metals. Best spatial resolution of about 1.2 μm pitch was observed at the sample-to-detector distance range of 20-110 mm and at the energy range of 68-78 keV. Several factors such as X-ray scattering and diffraction phenomena affecting the degradation of spatial resolution are also discussed. © 2012 American Institute of Physics.. |
| 118. | Qiang Zhang, Hiroyuki Toda, Masakazu Kobayashi, Kentaro Uesugi, Yoshio Suzuki, Characterization of Cell Wall Microstructure and Damage Behavior of Alloyed Aluminum Foam via Synchrotron-Based Microtomography, ADVANCED ENGINEERING MATERIALS, 10.1002/adem.201200142, 15, 3, 149-152, 2013.03, The internal microstructure of the high strength AlZnMg foam was characterized via the synchrotron-based X-ray microtomography. Using three-dimensional (3D) quantitative image analysis of the tomographic dataset, the microstructural features, such as content, size distribution, shape, and spatial distribution of micropores inside the cell wall, were determined. Together with a dual energy imaging technique, the 3D distribution of Zn in the alloyed foam was assessed by the subtraction of two images acquired above and below the Zn K-absorption edge. The damage behavior of the alloyed foam was also clarified by this element sensitive imaging technique.. |
| 119. | C. Gupta, H. Toda, C. Schlacher, Y. Adachi, P. Mayr, C. Sommitsch, K. Uesugi, Y. Suzuki, A. Takeuchi, M. Kobayashi, Study of creep cavitation behavior in tempered martensitic steel using synchrotron micro-tomography and serial sectioning techniques, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2012.12.002, 564, -, 525-538, 2013.03, Two three-dimensional (3-D) techniques, namely X-ray microtomography and serial sectioning, have been applied for characterization of creep cavitation behavior in tempered martensitic steel. For this purpose samples have been extracted from a series of specimens that were subjected to creep tests over the stress range of 120-180 MPa at 600 degrees C. The presence of creep voids in the series of samples was unambiguously detected in a non-destructive manner using synchrotron X-ray microtomography with a resolution of 1 gm. The 3-D visualization of the datasets provided an assessment of the spatial distribution and morphology of the creep voids as a function of creep stress and high temperature exposure time. The quantitative analyses of the image datasets enabled the development of functional relationships between the macroscopic creep parameters (such as rupture ductility, applied stress, creep life) and cavitation characteristics (such as volume fraction, and number density). The quantitative analyses also provided an evaluation of manifestations of growth and coalescence processes in the respective datasets. A transition of cavitation behavior of the steel has been found to occur in the stress range of 120-150 MPa at 600 degrees C. The evolution in the pattern of cavitation and its relation to the prior-austenite boundary was explored by combining micro-tomography and serial sectioning techniques, which revealed a new possibility in the progress of cavitation in the long term creep exposed specimens of 9-12% Cr heat resistant steels. (C) 2012 Elsevier B.V. All rights reserved.. |
| 120. | Hiroyuki Toda, Zul Azri Bin Shamsudin, Kazuyuki Shimizu, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Mitsuru Nakazawa, Yoshimitsu Aoki, Masakazu Kobayashi, Cavitation during high-temperature deformation in Al-Mg alloys, ACTA MATERIALIA, 10.1016/j.actamat.2013.01.012, 61, 7, 2403-2413, 2013.04, It has recently been revealed that high-density pre-existing hydrogen micropores, formed during production processes, exhibit premature growth and coalescence under external loading at room temperature, thereby inducing ductile fracture. This process is incidentally supplemented by the well-established ductile fracture mechanism based on particle damage. It is reasonable to assume that the pre-existing hydrogen micropores may also contribute to damage evolution at high temperatures. In the present study, synchrotron X-ray microtomography was applied to the in situ observation of deformation and fracture in Al-Mg alloys at a high temperature. High-density hydrogen micropores were observed in the alloys. Flow localization controlled deformation through the mechanism of solute drag creep. A combined effect of grain boundary sliding and heterogeneous nucleation on particles was also confirmed to accelerate the growth of pre-existing hydrogen micropores and cavities. Although continuous nucleation occurred together with the growth of pre-existing hydrogen micropores, the effects of the pre-existing hydrogen micropores, especially those located on grain boundaries, were predominant in the overall damage evolution. It seemed likely that supersaturated hydrogen in the aluminum alloys might also make an appreciable contribution to cavitation during high-temperature loading. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 121. | C. Gupta, H. Toda, T. Fujioka, M. Kobayashi, K. Uesugi, A. Takeuchi, Y. Suzuki, Micro-pore development phenomenon in hydrogen pre-charged aluminum alloy studied using synchrotron X-ray micro-tomography, APPLIED PHYSICS LETTERS, 10.1063/1.4826274, 103, 17, 171902, 2013.10, The paper provides an insight into the development of the micro-pore damage phenomenon during the hydrogen ingress and egress in a high strength aluminum alloy. High resolution micro tomography scans on samples subjected to combinations of cathodic hydrogen charging and de-sorption heat treatment were carried out. The quantitative analysis, spatial mapping, and probabilistic evaluation of the 3D datasets revealed that the development of micro-pore damage during hydrogen ingress-egress had a non-trivial dependence on the particle size distribution. This provides a rationale to mitigate the deleterious effects of hydrogen in aluminum alloys by controlling particle size characteristics. (C) 2013 AIP Publishing LLC.. |
| 122. | Hiroyuki Toda, Hideyuki Oogo, Keitaro Horikawa, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Mitsuru Nakazawa, Yoshimitsu Aoki, Masakazu Kobayashi, The True Origin of Ductile Fracture in Aluminum Alloys, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 10.1007/s11661-013-2013-3, 45A, 2, 765-776, 2014.02, It has generally been assumed that metals usually fail as a result of microvoid nucleation induced by particle fracture. Here, we concentrate on high-density micropores filled with hydrogen in aluminum, existence of which has been largely overlooked until quite recently. These micropores exhibit premature growth under external loading, thereby inducing ductile fracture, whereas the particle fracture mechanism operates only incidentally. Conclusive evidence of a micropore mechanism is provided by the observation of an instantaneous release of gas at failure. We can therefore conclude that the growth of micropores dominates ductile fracture. Since the material we used has a standard pore density, we can assume that an identical fracture mechanism operates in other aluminum alloys. This finding suggests that intense heat treatment, which is generally believed to enhance the mechanical properties through homogenization, may have entirely the opposite effect. This revelation will have a major impact on the engineering design of metals. (C) The Minerals, Metals & Materials Society and ASM International 2013. |
| 123. | H. Toda, P. C. Qu, S. Ito, K. Shimizu, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Formation behaviour of blister in cast aluminium alloy, INTERNATIONAL JOURNAL OF CAST METALS RESEARCH, 10.1179/1743133614Y.0000000123, 27, 6, 369-377, 2014.12, The formation behaviour of a blister in a die cast aluminium alloy was observed by employing a combined methodology of in situ three-dimensional observation using X-ray microtomography and image based simulation. It has been revealed, via a reverse approach based on the simulation, that nitrogen and carbon dioxide gases fill the blister nucleus. Spontaneous growth of the blister nucleus occurs through creep deformation of the surrounding aluminium due to the blister nucleus' high internal gas pressure. This internal gas pressure also induces hydrogen precipitation in the form of micropores, which undergo steady growth in a spherical shell region around the blister nucleus. The selective growth of the micropores is attributable to the elevation of hydrostatic stress in directions parallel to the casting surface, thereby promoting the expansion of the blister, also parallel to the casting surface, through the absorption of surrounding micropores into the blister nucleus.. |
| 124. | H. Li, H. Toda, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Application of Diffraction‐Amalgamated Grain Boundary Tracking (DAGT) to Fatigue Crack Propagation Behavior in High Strength Aluminum Alloy, The 2nd International Congress on 3D Materials Science, -, -, 91-96, 2014.07. |
| 125. | Effect of Phosphorus Content on Mechanical Properties in Al-7%Si Alloy. |
| 126. | C. Schlacher, T. Pelzmann, C. Beal, C. Sommitsch, C. Gupta, H. Toda, P. Mayr, Investigation of creep damage in advanced martensitic chromium steel weldments using synchrotron X-ray micro-tomography and EBSD, MATERIALS SCIENCE AND TECHNOLOGY, 10.1179/1743284714Y.0000000621, 31, 5, 516-521, 2015.03, In recent years, a design concept for the stabilisation of the microstructure by addition of boron and nitrogen was developed. This so called martensitic boron-nitrogen strengthened steel (MARBN) combines boron strengthening by solid solution with precipitation strengthening by finely dispersed nitrides. Welded joints of MARBN steels showed no formation of a uniform fine grained region in the heat affected zone (HAZ) which is in general highly susceptible to Type IV cracking. In this work, the crossweld creep strength of a newly developed MARBN steel was analysed and the evolution of damage was investigated using synchrotron microtomography supported by electron microscopy. Three-dimensional (3D) reconstructions of the tested samples together with electron backscatter diffraction investigations revealed an intense void formation in a restricted area along small grains at prior austenite grain boundaries in the HAZ as the main reason for premature creep failures in the HAZ of welded joints.. |
| 127. | C. Gupta, H. Toda, P. Mayr, C. Sommitsch, Cavitation studies in materials: new insights from modern techniques in 2D/3D/4D characterisation, MATERIALS SCIENCE AND TECHNOLOGY, 10.1179/0267083614Z.000000000853, 31, 5, 513-515, 2015.03. |
| 128. | Hiroyuki Toda, Hideki Tsuruta, Keitaro Horikawa, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Masakazu Kobayashi, Effects of Stress Triaxiality on Damage Evolution from Pre-Existing Hydrogen Pores in Aluminum Alloy, MATERIALS TRANSACTIONS, 10.2320/matertrans.L-M2013841, 55, 2, 383-386, 2014.02, It has recently been reported that aluminum alloy ductile fracture is dominated by micropore growth, whereas the particle fracture mechanism operates incidentally. The effects of stress triaxiality in front of a notch or crack were here investigated by employing microtomography observations. A fractional dimple pattern area originating in micropores increased with the increase in stress triaxiality on fracture surfaces. This implies that the effects of micropores on mechanical properties are more pronounced in notched and cracked materials.. |
| 129. | M Kobayashi, H Miura, H Toda, Non-destructive and three-dimensional measurement of local strain development during tensile deformation in an aluminium alloy, IOP Conference Series: Materials Science and Engineering, 10.1088/1757-899x/89/1/012030, 89, 1, 012030-012030, 2015.08. |
| 130. | Akihide Hosokawa, Hiroyuki Toda, Rafael Batres, Han Li, Osamu Kuwazuru, Masakazu Kobayashi, Hidetaka Yakita, Ductile fracture via hydrogen pore mechanism in an aluminum alloy; quantitative microstructural analysis and image-based finite element analysis, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2016.06.037, 671, 96-106, 2016.08, Finite element analyses based on 3D images of the microstructure in an aluminum alloy observed by X-ray microtomography (so called image-based finite element analysis = IB-FEA) were performed to assess the influences of microstructures on ductile fracture behavior. The exact microstructural features of the aluminum alloy (i.e. hydrogen pores and particles) were perfectly reproduced in the FE models. The microstructural parameters (e.g. diameter, sphericity, volume of pores/particles) were quantified through a handmade software. IB-FEA provided indirect measure of ductility (or risk of ductile fracture), extracting the damage-/fracture-related values (e.g. z-axis normal stress, stress triaxiality and equivalent plastic strain) through simple elasto-plastic simulations. This made it possible to discuss the microstructure -ductility relationship. Dimensionality reduction of data was performed to filter out the microstructural parameters that do not contribute to ductility by quantitative analysis of the importance of the individual microstructural parameters. (C) 2016 Elsevier B.V. All rights reserved.. |
| 131. | Md. Shahnewaz Bhuiyan, Hiroyuki Toda, Zhang Peng, Su Hang, Keitaro Horikawa, Kentaro Uesugi, Akihisa Takeuchi, Nobuto Sakaguchi, Yoshio Watanabe, Combined microtomography, thermal desorption spectroscopy, X-ray diffraction study of hydrogen trapping behavior in 7XXX aluminum alloys, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2015.12.092, 655, -, 221-228, 2016.02, In the present study, combined thermal desorption spectroscopy (TDS), microtomography and X-ray diffraction study has been carried out to identify the hydrogen trap sites in 7XXX aluminum alloys. Through constant heating rate TDS experiments, three distinct trap states have been identified. It is revealed that micropores are the predominant hydrogen trap site in alloys with medium hydrogen content, whereas grain boundaries is the major hydrogen trap site in alloys with low and high hydrogen content. We have clarified that the rate of trap site occupancy in grain boundaries is high compared to dislocations and vacancies. Such high hydrogen coverage at grain boundaries indicates that the hydrogen-assisted fracture would be intergranular. (C) 2016 Elsevier B.V. All rights reserved.. |
| 132. | Md. Shahnewaz Bhuiyan, Yuki Tada, Hiroyuki Toda, Su Hang, Kentaro Uesugi, Akihisa Takeuchi, Nobuto Sakaguchi, Yoshio Watanabe, Influences of hydrogen on deformation and fracture behaviors of high Zn 7XXX aluminum alloys, INTERNATIONAL JOURNAL OF FRACTURE, 10.1007/s10704-016-0092-z, 200, 1-2, 13-29, 2016.07, Hydrogen degrades the mechanical properties of high strength 7XXX aluminum alloys in two ways: (i) degrades the mechanical properties by hydrogen embrittlement, and (ii) partitioned into micropores as molecular hydrogen and make contributions to ordinary ductile fracture. The multifaceted effects of hydrogen on the mechanical properties of high Zn content 7XXX aluminum alloys during deformation and fracture is studied by using synchrotron X-ray microtomography. Our results have revealed that the hydrogen susceptibility has increased with increasing the Zn amount. High concentration of hydrogen was induced by the EDM wire eroder. This high concentrated hydrogen induces quasi-cleavage fracture and restricts the growth of micropores during ductile deformation. The threshold concentration of hydrogen ahead of the crack tip for the nucleation of quasi-cleavage feature was estimated to be .. |
| 133. | Han Li, Leonardo Gutierrez, Hiroyuki Toda, Osamu Kuwazuru, Wenli Liu, Yoshihiko Hangai, Masakazu Kobayashi, Rafael Batres, Identification of material properties using nanoindentation and surrogate modeling, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, 10.1016/j.ijsolstr.2015.11.022, 81, -, 151-159, 2016.03, In theory, identification of material properties of microscopic materials, such as thin film or single crystal, could be carried out with physical experimentation followed by simulation and optimization to fit the simulation result to the experimental data. However, the optimization with a number of finite element simulations tends to be computationally expensive. This paper proposes an identification methodology based on nanoin-dentation that aims at achieving a small number of finite element simulations. The methodology is based on the construction of a surrogate model using artificial neural-networks. A sampling scheme is proposed to improve the quality of the surrogate model. In addition, the differential evolution algorithm is applied to identify the material parameters that match the surrogate model with the experimental data. The proposed methodology is demonstrated with the nanoindentation of an aluminum matrix in a die cast aluminum alloy. The result indicates that the methodology has good computational efficiency and accuracy. (C) 2015 Elsevier Ltd. All rights reserved.. |
| 134. | C. Gupta, H. Toda, T. Fujioka, M. Kobayashi, H. Hoshino, K. Uesugi, A. Takeuchi, Y. Suzuki, State of 3-D micro-damage in hydrogen redistributed regions of precharged high strength aluminium alloy, CORROSION SCIENCE, 10.1016/j.corsci.2016.04.050, 111, 26-38, 2016.10, A comparison of the state of 3-D micro-damage induced by hydrogen redistribution due to thermal treatment and deformation near an intergranular fracture surface is carried out in high strength aluminium alloy using synchrotron microtomography. The mapping of various types of micro-damage provides evidence that hydrogen redistribution occurs along with a change in content and shape of micro-pores. The presence of intergranular cracks and an extended agglomerated micro-pore damage state are found to be in close proximity to each other, suggesting a mechanistic relationship for both formation of the unique damage architecture and insidious manifestation of embrittlement in high strength aluminium alloys. (C) 2016 Elsevier Ltd. All rights reserved.. |
| 135. | Masaki Teranishi, Osamu Kuwazuru, Shota Gennai, Masakazu Kobayashi, Hiroyuki Toda, Three-dimensional stress and strain around real shape Si particles in cast aluminum alloy under cyclic loading, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2016.10.004, 678, 273-285, 2016.12, The crack initiation mechanism of cast Al-Si-Mg alloy under low-cycle fatigue was addressed by using the synchrotron X-ray computed tomography (CT) and the image-based finite element analysis. The fatigue test and its in situ CT observation were conducted to visualize the crack initiation behavior. In the low-cycle fatigue, the cracking generally started with the voiding by the fracture of silicon particles, and the coalescence of these voids formed the crack. To elucidate the mechanism of silicon particle fracture, the finite element elastic-plastic analyses were performed with regard to twelve silicon particles including the fractured and intact particles detected by the chronological CT observation. By using the image-based modeling technique, the interested particle was embedded in the finite element model along with the surrounding particles as they were in the specimen. The material properties of silicon phase and aluminum matrix were identified by the nanoindentation tests. Ten cycles of loading by the uniform stress which was equivalent to the load in the fatigue test was applied to the finite element model, and the stress, strain and their cyclic response around the silicon particles were simulated. The morphology analysis was also carried out for the interested particles, and the geometrical parameters affecting the particle fracture were examined. By comparing the results of fractured and intact particles, we found that there were some geometrical conditions for the fracture of silicon particles, and a certain magnitude of hydrostatic stress was required to break the particles.. |
| 136. | Hang Su, Takuro Yoshimura, Hiroyuki Toda, Md Shahnewaz Bhuiyan, Kentaro Uesugi, Akihisa Takeuchi, Nobuhito Sakaguchi, Yoshio Watanabe, Influences of Hydrogen Micropores and Intermetallic Particles on Fracture Behaviors of Al-Zn-Mg-Cu Aluminum Alloys, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 10.1007/s11661-016-3773-3, 47A, 12, 6077-6089, 2016.12, The combined effects of hydrogen micropores and intermetallic particles on the voids initiation and growth behavior of Al-Zn-Mg-Cu aluminum alloys during deformation and fracture are investigated with the help of the high-resolution X-ray tomography. It is interesting to note that the high-hydrogen concentration induced by an EDM cutting process results in the initiation of quasi-cleavage fracture near surface. With the increase of strain, the quasi-cleavage fracture is gradually replaced by dimple fracture. Voids initiation related to the dimple fracture is caused by both intermetallic particles fracture and interfacial debonding between particles and matrix. The nucleation of hydrogen micropores on intermetallic particles accelerates the voids initiation. The existence of triaxial stress ahead of the tip of a quasi-cleavage crack enhances growth rate for both hydrogen micropores and voids.. |
| 137. | Hang Su, Shahnewaz Bhuiyan, Hiroyuki Toda, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Watanabe, Influence of intermetallic particles on the initiation and growth behavior of hydrogen micropores during high-temperature exposure in Al-Zn-Mg-Cu aluminum alloys, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2017.03.020, 135, 19-23, 2017.07, X-ray tomography is employed to observe the effects of intermetallic compound particles on the nucleation and growth of hydrogen micropores at high temperatures in Al-Zn-Mg-Cu aluminum alloys. Hydrogen micropores are heterogeneously nucleated on particles during exposure at 748 K. Growth and coalescence of the hydrogen micropores are observed with increasing exposure time. Interactions between hydrogen micropores and particles have a significant influence on the growth and coalescence of hydrogen micro pores. The growth speed of hydrogen micropores, nucleated on spherical, small particles is faster than those on other nucleation sites. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 138. | Artenis Bendo, Kenji Matsuda, Adrian Lervik, Tomohito Tsuru, Katsuhiko Nishimura, Norio Nunomura, Randi Holmestad, Calin D. Marioara, Kazuyuki Shimizu, Hiroyuki Toda, Masatake Yamaguchi, An unreported precipitate orientation relationship in Al-Zn-Mg based alloys, Materials Characterization, 10.1016/j.matchar.2019.109958, 158, 109958-109958, 2019.12. |
| 139. | C. Gupta, H. Toda, T. Fujioka, M. Kobayashi, H. Hoshino, K. Uesugi, A. Takeuchi, Y. Suzuki, Quantitative tomography of hydrogen precharged and uncharged Al-Zn-Mg-Cu alloy after tensile fracture, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2016.06.011, 670, -, 300-313, 2016.07, Quantitative tomography is carried out on datasets derived from tensile fracture sample of electrochemically precharged Al-Zn-Mg-Cu alloy in the underaged condition and its uncharged counterpart. It is shown that precharging which induces a transition of tensile fracture mode from ductile to brittle, results in a significant increase in micro-damage content in the regions near the fracture surfaces. Using quantitative tomography analysis based on spatial mapping of morphologically segmented micro-damage content of the datasets it is found that the precharged sample contains an inhomogenous distribution of micro-pores near grain boundaries. It is also shown that the spatial architecture of micro pores in the dataset is not influenced by the plastic zone of the intergranular cracks lying along the grain boundaries. Contrastingly the micro-pores in the tomographic dataset of the uncharged sample are shown to be present near intermetallic particles. It is therefore rationalized that the spatial architecture of micro-pores in the datasets from uncharged sample originate from particle cracking during ductile fracture, and from the tendency for damage enhancement by the synergism of hydrogen exposure near grain boundaries and localization of deformation in the precharged sample dataset. (C) 2016 Elsevier B.V. All rights reserved.. |
| 140. | C. Gupta, H. Toda, P. Mayr, C. Sommitsch, 3D creep cavitation characteristics and residual life assessment in high temperature steels: a critical review, MATERIALS SCIENCE AND TECHNOLOGY, 10.1179/1743284714Y.0000000693, 31, 5, 603-626, 2015.03, The need for a new paradigm to estimate remaining creep life of service exposed steels is critically assessed. New approaches to residual life assessment are proposed, in the light of a decade's experience of the use of micro-tomography to characterise the three-dimensional (3D) nature of cavitation damage in structural materials. Imaging of conventional structural materials such as steels with high absorption to X-rays has been realised by synchrotron micro-tomography (SR-mu CT), providing new insights into phenomena such as creep failure. The unique feature of SR-mu CT studies is the direct imaging in 3D of cavities (hundreds of micrometres in size) present in the bulk, revealing the spatial characteristics and morphology of the creep voids. Quantitative analyses of the cavitation characteristics revealed by 3D datasets, when scaled with respect to time, stress and temperature, provide functional information suitable for developing constitutive equations for creep. The application of SR-mu CT, a non-destructive technique providing high fidelity data, significantly reduces the ambiguity in developing functional relationships to predict creep failure. The explicit use of such constitutive equations to estimate the residual life of components in creep, and the consequent assessment of structural integrity, would prove invaluable. Micro-tomography studies related to creep in materials are reviewed, with special emphasis on a 10.86% Cr heat resistant steel, to demonstrate the type of data available for life assessment and design against creep failure. A brief discussion of current methods to estimate residual life in the light of recent 3D micro-tomography data follows. Finally, the possibility of new approaches, using micro-tomography data in conjunction with destructive 3D approaches such as serial sectioning, to formulate advanced residual life estimates, is briefly considered.. |
| 141. | A. Hosokawa, T. Kurino, H. Toda, K. Uesugi, A. Takeuchi, Y. Suzuki, Image-based finite element analysis for reverse 4D materials engineering Ductile fracture originated from hydrogen pores, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.64.611, 64, 11, 611-612, 2014.01. |
| 142. | M. Kobayashi, H. Toda, K. Uesugi, A. Takeuchi, Y. Suzuki, Recent progress of X-ray tomography in material science field, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.64.510, 64, 11, 510-517, 2014.01. |
| 143. | H. Toda, R. Batres, O. Kuwazuru, M. Kobayashi, A. Hosokawa, Reverse 4D materials engineering Its framework and recent evolution, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.64.518, 64, 11, 518-524, 2014.01. |
| 144. | A. Kouno, M. Kobayashi, H. Toda, H. Miura, Simulation of deformation texture evolution in aluminum alloy based on local strain obtained by synchrotron 3D measurement, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.64.557, 64, 11, 557-563, 2014.01, The presence of heterogeneous deformation is a one of key issue in a prediction model of deformation texture development. Recently, not only local strain mapping but also crystallographic orientation mapping is possible to obtain within aluminum alloy by using synchrotron radiation. In this study, local strain mapping and orientation mapping were obtained by microtomography and three-dimensional X-ray diffraction using synchrotron radiation in Al - 4Pb alloy. Simulation of deformation texture evolution has been performed based on crystal plasticity model. The simulation started from actual microstructure and the obtained local strain was applied. The simulation produced similar microstructure to the actual one. Therefore, heterogeneous strain distribution is very important for the development of deformation texture.. |
| 145. | O. Kuwazuru, K. Matsumura, V. A. De Souza, M. Kobayashi, H. Toda, Three-dimensional crack initiation behavior of cast aluminum alloy under low-cycle fatigue, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.64.570, 64, 11, 570-575, 2014.01, The crack initiation mechanism of cast aluminum alloy was addressed to quantitatively evaluate the fatigue strength. We employed the synchrotron radiation microtomography to visualize the three-dimensional damages around pores and silicon particles. Two types of specimens underwent a low-cycle fatigue test. The temperature of solution treatment was different, and it yielded a difference in the shape, size and distribution of silicon particles. After a certain cycles of fatigue, a catastrophic damage around many silicon particles occurred, and they connected to each other so as to form a crack especially within the high stressed region around a relatively large pore. The scanning electron microscopy after the test showed that the type of damage was the breakage of long-shaped silicon particles or the aluminum-silicon interface debonding of round silicon particles. The high temperature solution treatment facilitated the interface debonding by the enlargement of silicon particles.. |
| 146. | H. Toda, M. Kobayashi, T. Kubo, K. Moizumi, D. Sugiyama, Y. Yamamoto, T. Harada, K. Hayashi, Y. Hangai, Y. Murakami, 3D visualization of defects and microstructural features with laboratory-scale X-ray tomography apparatuses, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.63.343, 63, 10, 343-349, 2013.12, In the present study, various microstructural features, such as particles and pores, have been visualized in cast and wrought aluminum alloys by employing X-ray tomography apparatuses with a wide range of spatial resolution. Special care is dedicated to evaluate an identical sample for each entire series of imaging experiments. The X-ray tomography apparatuses used include the one performed at a synchrotron radiation facility, which has a spatial resolution level close to the theoretical limit of the projection-type imaging, in addition to two industrial apparatuses. It has been shown that even if industrial apparatuses, which inevitably possess limited spatial resolution levels, are used, the real size and fraction of microstructural features can be estimated by performing imaging experiments above a certain spatial resolution level. It would be, so far as the authors are aware, the first time to demonstrate the feasibility of laboratory-scale X-ray tomography imaging in microstructural observation in a systematic manner, especially focusing on spatial resolution and quantitative capability.. |
| 147. | M. Kobayashi, Y. Sugihara, H. Toda, K. Uesugi, Relationship between resolution and rotation stage in imaging X-ray CT, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.63.273, 63, 8, 273-278, 2013.11, In this study, evaluation of precision in rotation stage and investigation of effect of rotation stage blurring on resolution are performed in imaging X-ray tomography set-up, which allows nano-scale observation, for the purpose of improving resolution in X-ray tomography. In the result of precision evaluation of rotation stage in high-resolution imaging X-ray tomography, fluctuation, which was approximately 35 nm in maximum and approximately 13 nm in average, was found. This fluctuation was under 1 pixel. In the simulation that analyzed effect of fluctuation in rotation stage, it was found that long periodic fluctuation deteriorate reconstructed image terribly. But, impulse-like fluctuation does not almost affect reconstructed image quality. However, reconstructed image is deteriorated when the frequency of impulse-like fluctuation increase. If long periodic fluctuation, which was observed in the precision evaluation, is corrected, the resolution improvement was confirmed though the fluctuation was less than 1 pixel.. |
| 148. | M. Kobayashi, Y. Ohkawa, H. Toda, K. Uesugi, Y. Suzuki, A. Takeuchi, Development of 3d deformation analysis method in polycrystalline metal by combining synchrotron radiation tomography with X-Ray diffraction, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.J2013006, 77, 9, 375-384, 2013.09, The aim of this study was to establish a novel orientation analysis method that utilizes accurate grain position information, obtained by grain boundary tracking, to enable crystal-plasticity deformation analysis of polycrystalline metals. An experiment combining X-ray tomography and X-ray diffraction was performed, and the feasibility of the method was assessed by confirming the relation between diffraction spots and grains whose position was obtained by grain boundary tracking. Although some deviations were observed in diffraction spot intensity, owing to lack of beam stability and the extinction effect, several combinations of grain and spot features showed a high correlation. Furthermore, the diffraction spots originating from grains whose position was detected using grain boundary tracking showed higher correlation coefficients than those originating from grains whose position was detected using 3DXRD. In the case of the former grains, we could easily identify diffraction spots originating from specific grains by focusing on sets of grain and spot features having a high correlation. It was demonstrated that setting appropriate tolerance level enabled highly accurate orientation analysis, almost equivalent to that of 3DXRD.. |
| 149. | Hiroyuki Toda, Kodai Tsubone, Kazuyuki Shimizu, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Mitsuru Nakazawa, Yoshimitsu Aoki, Masakazu Kobayashi, Compression and recovery micro-mechanisms in flexible graphite, CARBON, 10.1016/j.carbon.2013.03.008, 59, -, 184-191, 2013.08, Utilization of synchrotron X-ray microtomography has enabled the virtual reconstruction of invisible microstructural units and their deformation during the compaction, compression and recovery of flexible graphite. Particles artificially affixed, in advance, to the surface of a given microstructural unit were connected by plane triangles to create a 3D mesh in the reconstruction. High density 3D mapping of strain and displacement has also been achieved, by tracing the physical displacement of the surface particles. Micro-mechanisms of compression and recovery behavior in flexible graphite have been examined involving the direct observations and measurements. The microstructural unit was found to be composed of thin expanded graphite discs with slightly misaligned basal planes of graphite. Highly localized deformation of a thin expanded graphite disc was observed during the compression and recovery processes, suggesting strong interaction with surrounding expanded graphite discs. The macroscopic compression behavior of flexible graphite is attributable to a combination of bending and thickness reduction/recovery of the discs. It has, however, been shown that only the thickness recovery of the individual discs, due to the presence of internal entrapped air, accounts for the macroscopic recovery behavior of flexible graphite. (C) 2013 Elsevier Ltd. All rights reserved.. |
| 150. | Hiroyuki Toda, Yoshikazu Ohkawa, Takanobu Kamiko, Takuma Naganuma, Kentaro Uesugi, Akihisa Takeuchi, Yoshio Suzuki, Masakazu Kobayashi, Grain boundary tracking: A four-dimensional visualization technique for determining grain boundary geometry via local strain mapping, ACTA MATERIALIA, 10.1016/j.actamat.2013.06.013, 61, 14, 5535-5548, 2013.08, A procedure for determining three-dimensional grain boundary geometry and its change under external loading is proposed for evaluating crystallographic deformation behaviours in polycrystalline materials, and the feasibility of this approach is confirmed for an aluminium alloy. X-ray microtomography has been combined with gallium-enhanced microscopy, in which grains are visualized in three dimensions by decorating grain boundaries with liquid gallium. Grain boundary particles are then extracted by comparing tomographic images with and without the gallium application. Three-dimensional reconstruction of grains is achieved using a connection scheme based on triplets of non-aligned points on grain boundaries. The deformation of the closed polygonal grains is visualized by combining the above technique with a microstructural tracking technique, in which the paths of particles are reconstructed by matching each pair of particles in consecutive images. This process also enables high-density four-dimensional strain mapping by tracking particles located in grains, providing direct interpretation of localized deformation caused by interaction between neighbouring grains. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 151. | M. Kobayashi, H. Hara, H. Toda, D. Sugiyama, N. Kuroda, Fatigue behaviour of hot worked cast aluminium alloys with different Si contents, International Journal of Cast Metals Research, 10.1179/1743133611Y.0000000012, 25, 1, 31-37, 2012.01, Cast aluminium alloy has sometimes been utilised for various products after applying plasticworking combining with heat treatment. The thermomechanical treatment will bring not onlypositive effects (workhardening and grain refinement) but also negative effects (damage onparticles and increase of porosity) on the mechanical properties in the cast aluminium alloy. In thisstudy, the relation between microstructures and fatigue properties has been investigated in hotforged and heat treated Al-Si-Mg casting alloys with different Si contents. An ex situ observationof fatigue crack propagation showed different crack behaviours depending on the microstructuresarising from the different Si contents. The crack in the & alpha phase propagated quickly incomparison with the crack located in the eutectic and grain boundaries in the Al-3& middot 1Si-0& middot 4Mgalloy. The crack propagation rate was not constant in the Al-7& middot 7Si-0& middot 4Mg alloy due to theagglomerated Si particles in the eutectic region. © 2012 W. S. Maney & Son Ltd.. |
| 152. | Mitsuru Nakazawa, Masakazu Kobayashi, Hiroyuki Toda, Yoshimitsu Aoki, Proposal of a method to analyze 3D deformation/fracture characteristics inside materials based on a stratified matching approach, MACHINE VISION AND APPLICATIONS, 10.1007/s00138-009-0242-7, 21, 5, 687-694, 2010.08, In the past, deformation/fracture (D/F) characteristics, defined as load-deformation relationships until the materials are fractured, have been analyzed and evaluated on the surface. The D/F characteristics are affected by more than 10,000 micro-scale internal structures like air bubbles (pores), dispersed particles and cracks in 1 mm(3); therefore, it is required to analyze nano-scale D/F characteristics inside materials. In this paper, we propose an analysis method by obtaining displacement vectors of dispersed particles from nano-order 3D-CT images. A problem of matching over 10,000 dispersed particles between deformation is solved by a stratified matching.. |
| 153. | P. Qu, H. Toda, H. Zhang, Y. Sakaguchi, L. Qian, M. Kobayashi, K. Uesugi, Local crack driving force analysis of a fatigue crack by a microstructural tracking method, SCRIPTA MATERIALIA, 10.1016/j.scriptamat.2009.05.004, 61, 5, 489-492, 2009.09, To study fatigue cracking behavior, an improved microstructural tracking method is used to calculate the local crack driving forces in a fatigue crack in an aluminum alloy by employing high-resolution in situ synchrotron X-ray micro tomography. Several valuable insights into actual three-dimensional fatigue cracking behavior of overlapping crack segments are obtained. A typical example is the complex deformation behavior in overlapping regions where pairs of crack segments partially overlap. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.. |
| 154. | T. Nishimura, H. Toda, M. Kobayashi, T. Kobayashi, K. Uesugi, Y. Suzuki, Change in microstructure of Al-Si-Cu casting alloys during high temperature solution treatment, INTERNATIONAL JOURNAL OF CAST METALS RESEARCH, 10.1179/136404608X361783, 21, 1-4, 114-118, 2008.08. |
| 155. | T. Ohgaki, H. Toda, I. Sinclair, J. Y. Buffiére, W. Ludwig, T. Kobayashi, M. Niinomi, T. Akahori, Erratum to "Quantitative assessment of liquid Ga penetration into an aluminium alloy by high-resolution X-ray tomorgarphy" [Mater. Sci. Eng. A, 427 (2006) 1-6] (DOI:10.1016/j.msea.2005.07.050), Materials Science and Engineering A, 10.1016/j.msea.2007.11.007, 486, 1-2, 699, 2008.07. |
| 156. | Lihe Qian, Hiroyuki Toda, Kentaro Uesugi, Masakazu Kobayashi, Toshiro Kobayashi, Direct observation and image-based simulation of three-dimensional tortuous crack evolution inside opaque materials, PHYSICAL REVIEW LETTERS, 10.1103/PhysRevLett.100.115505, 100, 11, 115505-115505, 2008.03, We present a combined novel methodology to study the three-dimensional complex geometry of a tortuous crack and identify the essential features of the crack and its propagation inside a heterogeneous material. We find that some severe damage events occur unexpectedly below a local mode-I crack within the sample; we realize that the severe plastic zone of the local mode-I crack is shifted down by another unseen crack segment hidden behind, which is responsible for the unusual damage phenomenon observed. We also find that the crack grows fast at some locations but slowly at some other locations along the crack front; we recognize that the crack-tip fields are reduced by neighboring hidden crack segments, which accounts for the retarded propagation of some part of the crack front. The feasibility and power of the proposed methodology highlights the potential of a new way to study fracture mechanisms in real materials.. |
| 157. | Lingqi Li, Hiroyuki Toda, Tomomi Ohgaki, Masakazu Kobayashi, Toshiro Kobayashi, Kentaro Uesugi, Yoshio Suzuki, Wavelet-based local region-of-interest reconstruction for synchrotron radiation x-ray microtomography, JOURNAL OF APPLIED PHYSICS, 10.1063/1.2818374, 102, 11, 114908, 2007.12, Synchrotron radiation x-ray microtomography is becoming a uniquely powerful method to nondestructively access three-dimensional internal microstructure in biological and engineering materials, with a resolution of 1 mu m or less. The tiny field of view of the detector, however, requires that the sample has to be strictly small, which would limit the practical applications of the method such as in situ experiments. In this paper, a wavelet-based local tomography algorithm is proposed to recover a small region of interest inside a large object only using the local projections, which is motivated by the localization property of wavelet transform. Local tomography experiment for an Al-Cu alloy is carried out at SPring-8, the third-generation synchrotron radiation facility in Japan. The proposed method readily enables the high-resolution observation for a large specimen, by which the applicability of the current microtomography would be promoted to a large extent. (C) 2007 American Institute of Physics.. |
| 158. | J. H. Kim, M. Niinomi, T. Akahori, H. Toda, Fatigue properties of bovine compact bones that have different microstructures, INTERNATIONAL JOURNAL OF FATIGUE, 10.1016/j.ijfatigue.2006.09.018, 29, 6, 1039-1050, 2007.06, Understanding the mechanism of fatigue crack propagation in bones is important because fatigue is probably the main cause of clinical stress fractures. Here, fatigue crack initiation and propagation behaviors of bovine humerus and femur regarding microstructures were investigated by the replica method. Fatigue tests were conducted to obtain SN curves of these compact bones. Both these bones are made up of haversian and plexiform, bones, classified by their microstructures. The crack propagation rate is faster when the microstructure is inclined to the bone axis than when parallel. The fatigue strength of plexiform bone is higher than that of haversian bone. (c) 2006 Elsevier Ltd. All rights reserved.. |
| 159. | T. Ohgaki, H. Toda, I. Sinclair, J.-Y. Buffiere, W. Ludwig, T. Kobayashi, M. Niinomi, T. Akahori, Quantitative assessment of liquid Ga penetration into an aluminium alloy by high-resolution X-ray tomography, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2005.07.050, 427, 1-2, 1-6, 2006.07, We have evaluated the liquid Ga penetration into an aluminium alloy by high-resolution X-ray tomography. The 3D visualization of a crack together with its surrounding grain structure was performed with the help of the Ga penetration technique. It is found that the advance directions of the crack-tip were strongly influenced by the grain microstructure and the branching of the crack is affected by grain distribution. In this study, the liquid Ga not only acts as a contrast agent for grain boundaries, but also expands the volume of the Al alloy due to Ga diffusion and associated processes. The 3D strain between the grains has been determined by microstructural gauging technique, which uses micropores as marker points. The 3D expansion of the sample volume, the volume reduction of micropores, and the brittle fracture were evidently observed. (c) 2005 Elsevier B.V. All rights reserved.. |
| 160. | Arnaud Weck, David S. Wilkinson, Hiroyuki Toda, Eric Maire, 2D and 3D visualization of ductile fracture, ADVANCED ENGINEERING MATERIALS, 10.1002/adem.200600034, 8, 6, 469-472, 2006.06. |
| 161. | JH Kim, M Niinomi, T Akahori, J Takeda, H Toda, Effect of microstructure on fatigue strength of bovine compact bones, JSME INTERNATIONAL JOURNAL SERIES A-SOLID MECHANICS AND MATERIAL ENGINEERING, 10.1299/jsmea.48.472, 48, 4, 472-480, 2005.10, Despite its clinical importance in developing artificial bone, limited information is available regarding the microstructure with respect to the fatigue characteristics of bones. In this study, the fatigue characteristics of the bovine humerus and femur were investigated with respect to microstructures. Fatigue tests were conducted on the bovine humerus and femur at a stress ratio of 0.1 and a frequency of 10 Hz. The fatigue strength of the plexiform bone is slightly greater than that of the haversian bone. This is because the volume fraction of voids in the haversian bone, which is the site of stress concentration, is higher than that of voids in the plexiform bone. Several microcracks are observed on the fatigue fracture surface of the haversian bone. The microcracks are short and their propagation directions are random. However, the number of the microcracks in the plexiform bone is very small. The microcracks are relatively long and their propagation directions are parallel to the longitudinal direction of the lamellar bone. Therefore, the crack requires relatively more energy to propagate across the lamella in the plexiform bone.. |
| 162. | H Toda, T Ohgaki, K Uesugi, M Kobayashi, N Kuroda, T Kobayashi, M Niinomi, T Akahori, K Makii, Y Aruga, Quantitative assessment of microstructure and its effects on compression behavior of aluminum foams via high-resolution synchrotron X-ray tomography, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 10.1007/s11661-006-1072-0, 37A, 4, 1211-1219, 2006.04, Synchrotron X-ray microtomography has been used for the three-dimensional characterization of microstructure in the cell walls of aluminum foams. A combination of high-resolution phase contrast imaging technique and several application techniques has enabled the quantitative image analyses of microstructures as well as the assessment of their effects on deformation behaviors. The application techniques include local area tomography, microstructural gauging and in-situ observation using a specially desioned material test rig. It has been clarified that ductile buckling of a cell wall occurs regardless of any of the microstructural factors in the case of a pure aluminum foam, while rather brittle fracture of a cell wall is induced by the existence of coarse micropores and their distribution independently of the intermetallic particles and the grain boundary in the case of aluminum foams alloyed with Zn and Mg. It has also been confirmed that coarse TiH2 particles, which are a residual foaming agent added to alloy melts, remain intact during the deformation. When cooling rate during foaming is high, however, lower energy absorption might be attributable to the significant amount of residual TiH2 particle and its inhomogeneous distribution. These tendencies are also confirmed by three-dimensional strain mapping by tracking internal microstructural features.. |
| 163. | LH Qian, S Nishido, H Toda, T Kobayashi, FEM modeling of crack propagation in a model multiphase alloy, JOURNAL OF MATERIALS SCIENCE & TECHNOLOGY, 22, 1, 59-65, 2006.01, In this paper, several widely applied fracture criteria were first numerically examined and the crack-tip-region J-integral criterion was confirmed to be more applicable to predict fracture angle in an elastic-plastic multiphase material. Then, the crack propagation in an idealized dendritic two-phase Al-7%Si alloy was modeled using an elastic-plastic finite element method. The variation of crack growth driving force with crack extension was also demonstrated. It is found that the crack path is significantly influenced by the presence of a-phase near the crack tip, and the crack growth driving force varies drastically from place to place. Lastly, the simulated fracture path in the two-phase model alloy was compared with the experimentally observed fracture path.. |
| 164. | L Qian, H Toda, K Uesugi, T Kobayashi, T Ohgaki, M Kobayashi, Application of synchrotron x-ray microtomography to investigate ductile fracture in Al alloys, APPLIED PHYSICS LETTERS, 10.1063/1.214208, 87, 24, 241907-241907, 2005.12, The in situ high-resolution synchrotron x-ray computed microtomography has been applied to visualize and quantify the ductile fracture process of a notched Al alloy specimen. The three-dimensional (3D) investigation reveals that voids are nucleated, grow and coalesce more easily near the notch front and in the central region of the sample. These voids are mainly associated with Si particles in the eutectic (EU) phase. The 3D packing architecture of particles in the EU region, and the 3D morphology of alpha phase are also visualized. The feasibility of this technique highlights the potential of its application in the field of micromechanics-based fracture. (c) 2005 American Institute of Physics.. |
| 165. | LH Qian, H Toda, S Nishido, T Akahori, M Niinomi, T Kobayashi, Numerical simulation of fracture of model Al-Si alloys, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 10.1007/s11661-005-0071-x, 36A, 11, 2979-2992, 2005.11, Hypoeutectic Al-Si alloys consist of primary alpha-Al and Al-Si eutectic phases and show typical elastic-plastic fracture. To understand their fracture behavior, fracture processes were simulated using an elastic-plastic finite-element method. The validity of the J-integral-based criterion was verified and applied to the simulations. A complicated model was used to simulate the fracture in an idealized dendritic microstructure, and four simplified models were intended to more clearly understand the interaction between a crack and individual alpha phases. Results show that the crack is attracted to the soft alpha phase when passing by the alpha phase, whereas it is repelled when the alpha phase is close in front of or behind the crack tip. The presence of alpha phase close in front of or behind the crack tip leads to an amplification of the driving force. However, the alpha phase beside the tip reduces the driving force. Furthermore, the fracture behavior is mainly affected by the adjacent alpha phase on one side around the crack tip, while the remote alpha phase on the opposite side has an offsetting effect. The local stress-strain fields were examined to analyze the simulated behavior. The simulated crack-growth path in the dendritic model was compared and verified with the experimentally observed path.. |
| 166. | H Toda, H Mizutani, T Kobayashi, T Akahori, N Niinomi, Image-based mechanical analysis of multifilamentary microstructure formation in Al-Fe heavily deformed in-situ composites, MATERIALS TRANSACTIONS, 10.2320/matertrans.46.2229, 46, 10, 2229-2236, 2005.10, It has been reported that nano-scale multifilamentary microstructure, which has been readily available in Al-Nb systems, was hardly realized in Al-Fe heavily-deformed composites systems. In the present study, state-of-the-art techniques are applied to gain basic insight into the necessary requirement for the texture development of the Al-Fe composites. Three-dimensional finite element meshes were generated to monitor local stress and strain distributions in real materials. The approach taken in this study may be characterized as ne,v type of the reverse engineering which is based on the visualization of microstructural features of materials. It has been clarified that local stress elevation occurs where the Fe phase is constricted or gnarled with flection when cutting chips are used as a matrix. Hydrostatic stress varies significantly in the Fe phase thereby promoting the plasticity of the Fe phase. Both sufficient strengthening of aluminum and irregular distribution of the embedded Fe phase are identified essential for multifilamentary microstructure formation.. |
| 167. | T Ohgaki, H Toda, Sinclair, I, JY Buffiere, W Ludwig, T Kobayashi, M Niinomi, T Akahori, Quantitative assessment of liquid Ga penetration into an aluminium alloy by high-resolution X-ray tomography, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/j.msea.2005.06.045, 427, 1-2, 1-6, 2006.07. |
| 168. | M Niinomi, J Takeda, T Akahori, H Fukui, M Touyama, H Toda, Effect of microstructure on tensile properties and static fracture toughness of dental gold alloy, MATERIALS TRANSACTIONS, 10.2320/matertrans.46.1540, 46, 7, 1540-1544, 2005.07, Tensile tests and static fracture toughness tests were conducted on dental type 4 gold alloys subjected to various heat treatments. The effects of microstructures on tensile characteristics and static fracture toughness are discussed. The tensile strength of dental type 4 gold alloy increases with the solutionizing temperature. Moreover, the tensile strength of dental type 4 gold alloy increases with aging time at a solutionizing temperature of 1023 K. On the other hand, dental type 4 gold alloy exhibits reduced elongation with an increase in the solutionizing temperature. Static fracture toughness of dental type 4 gold alloy increases with an increase in the solutionizing temperature. Static fracture toughness of dental type 4 gold alloy aged for 0.3 ks is the highest, and is the lowest when it is aged for 1.8 ks, with the solutionizing temperature at 1023 K.. |
| 169. | B. Gunawarman, M. Niinomi, T. Akahori, T. Souma, M. Ikeda, H. Toda, K. Terashima, Fatigue characteristics of low cost βtitanium alloys for healthcare and medical applications, Mater. Trans., 10.2320/matertrans.46.1570, 46, 7, 1570-1577, 2005.07. |
| 170. | T Akahori, M Niinomi, Y Koyanagi, T Kasuga, H Toda, H Fukui, M Ogawa, Mechanical properties of biocompatible beta-type titanium alloy coated with calcium phosphate invert glass-ceramic layer, MATERIALS TRANSACTIONS, 10.2320/matertrans.46.1564, 46, 7, 1564-1569, 2005.07, The presence of calcium phosphate invert glass-ceramic (designated as CPIG) layer on the surface of artificial implant products can improve the bonding between these products and bones. In this study, the morphology of the CPIG layer on the surface of a beta-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ), was investigated for biomaterial applications by a dip-coating treatment. Furthermore, the mechanical properties of TNTZ coated with the CPIG layer were also investigated. In the CPIG layer, a compositionally gradient zone with a thickness of approximately 2.0 mu m exists on the surface of the TNTZ. The titanium concentration in the zone increases with the decreasing distance from the CPIG surface toward the base materials. On the other hand, calcium and phosphorus concentrations in the zone increase with the distance from the TNTZ surface. The tensile bonding strength between TNTZ and the CPIG layer is 25 MPa and that between aged TNTZ and the CPIG layer is 18.6 MPa. For easily understanding the change in mechanical properties by a dip-coating treatment, the values of those on TNTZ and TNTZ coated with CPIG layer were shown as follows. The tensile strength increases remarkably by a dip-coating treatment as compared with that of assolutionized TNTZ while the elongation is a reverse trend. Young's modulus of TNTZ and aged TNTZ coated with the CPIG increases by 15 to 27 GPa after the dip-coating treatment as compared with that of as-solutionized TNTZ (approximately 60 GPa). The fatigue limit of TNTZ coated with the CPIG layer is nearly equal to that (approximately 300 MPa) of as-solutionized TNTZ. On the other hand, the fatigue limit of aged TNTZ coated with the CPIG layer is a 100 MPa higher than that of as-solutionized TNTZ.. |
| 171. | H Toda, J Katano, T Kobayashi, T Akahori, M Niinomi, Assessment of thermo-mechanical fatigue behaviors of cast Al-Si alloys by experiments and multi-step numerical simulation, MATERIALS TRANSACTIONS, 10.2320/matertrans.46.111, 46, 1, 111-117, 2005.01, Out-of-phase type thermo-mechanical fatigue tests have been performed for Al-Si cast alloys with the temperature range of 323-523 K and the applied mechanical strain range of 0.5-1.5%. Thermo-mechanical fatigue lives and stress-strain hysteresis loops are investigated by the experiments. In general, the thermo-mechanical fatigue is affected by various factors such as thermal expansion/contraction, elasto-plastic/ creep deformation, softening by overaging, dynamic recovery, damaging and cracking. Multi-step finite element simulation techniques have provided an effective way of assessing the local damaging behavior of silicon particles, along with extracting the contribution from creep. Although the size and shape of the silicon particles in the material with a higher solidification rate are similar to those of a slowly cooled material, it exhibits superior thermo-mechanical fatigue property together with a smaller secondary dendrite arm spacing (SDAS, hereinafter). Since the difference ill the stress-strain hysteresis loops between the two materials has vanished when the softening by overaging is almost finished, the observed difference in the thermo mechanical properties is attributed to age-hardenability rather than the SDAS. The effects of damaging at the silicon particles to this difference are also suggested. In fact, damaged silicon particles have been observed extensively from an early stage of the thermo-mechanical loading, then forming fatigue cracks by the linkage of the damages. It has been clarified by the simulation that interfacial debonding is likely to occur rather than particle cracking in the materials used. The simulation provides valuable insights into the understanding of the spatial distribution of damage in the eutectic region. The simulation has also enabled to assess the contribution of the creep deformation, indicating that medium to high cycle fatigues are significantly affected by it.. |
| 172. | L. Qian, H. Toda, S. Morita, T. Kobayashi, Z.G. Wang, In-situ observations of fracture processes in 0.6 μm and 9.5 μm SiCP/6061Al composites, Mater. Trans., 10.2320/matertrans.46.34, 46, 1, 34-41, 2005.01. |
| 173. | T. Imasuda, M. Takata, H. Toda, T. Kobayashi, L. Wang, Stress triaxiality effect on dynamic tensile properties in a 6061-t6 aluminum alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 54, 5, 175-181, 2004.05, In this study, the effect of high strain rate on the stress triaxiality is examined. The commercial 6061-T6 aluminum alloy which has wide applications as structural materials in the transport machine and construction industries is selected for this study. The response of the material to varying degrees of stress triaxiality under static and dynamic loading conditions is measured for circumfercntially round-notched tensile specimens. Tensile tests arc performed at RT with an Instron and servo hydraulic testing machines at three kinds of strain rates (ε=7.2X10-4, 1.0X102 and 1.0X10 3s-1). Fracture surface observations and finite element method simulations also reveal the effect of stress triaxiality on the mechanical response under dynamic loading condition. The plastic constraint factors of the round-notched specimen under dynamic loading condition arc lower than those under static loading condition. Stress triaxiality is decreased by the reflection of the stress wave near the notch root of the round-notched specimen under dynamic loading condition. The decrease of the stress triaxiality under the dynamic loading condition affects the relaxation of the plastic constraint in the round-notched specimens. The fracture surface of the round-notched specimen with the high stress triaxiality level shows the tensile fracture type under static loading condition. When the stress triaxiality decreases with increasing strain rate in the round-notched specimens, the fracture surface changes to the shear type. On the other hand, the temperature rise during impact tests hardly affects the relaxation of the plastic constraint in the round-notched specimens under high strain rates.. |
| 174. | LH Qian, T Kobayashi, H Toda, T Goda, ZG Wang, Fracture toughness of a 6061Al matrix composite reinforced with fine SiC particles, MATERIALS TRANSACTIONS, 10.2320/matertrans.43.2838, 43, 11, 2838-2842, 2002.11. |
| 175. | VA Mosneaga, T Mizutani, T Kobayashi, H Toda, Impact toughness of weldments in Al-Mg-Si alloys, MATERIALS TRANSACTIONS, 10.2320/matertrans.43.1381, 43, 6, 1381-1389, 2002.06, 6000 series Al-Mg-Si alloys are frequently used for welded structures. The present investigation is conducted to evaluate the level of mechanical properties, especially impact toughness of welded Al-Mg-Si alloys with different amounts of Mn addition and using two types of fillers Al-Si (A4043) and Al-Mg (A5356), respectively. Particular attention is paid to the effect of microstructure on toughness. As one of the most important characteristics of a structural material, toughness is evaluated by the instrumented Charpy impact test method. When Al-Mg filler is used and Mn is not added, recrystallization occurs in the heat affected zone (HAZ), however, recrystallization can be suppressed by a small amount of Mn addition. The structure having large coarsened recrystallized grains is more susceptible to liquation crack that is detrimental to the mechanical properties, especially toughness. The results obtained show that toughness of the welded metal can be improved 20-30% by adding Mn. Using A4043 filler, the level of absorbed energy decreases as the content of Mg increases, and low Mg and without Mn addition results in a good combination of the mechanical properties. However, using the A5356 filler, the level of absorbed energy increases as the content of Mg increases and decreases as the Si content increases. In this case, the highest value of absorbed energy was recorded for alloy 8 (0.7%Mn). When A5356 filler is used, the toughness is about 56% higher than using A4043 filler.. |
| 176. | Thermo-mechanical fatigue of SiC whisker reinforced 6061Al composites - II. Fatigue life and damage mechanism The In-phase (IP) and out-of-phase (OP) thermo-mechanical fatigue (TMF) life and damage mechanism were studied on 15%SiCW (volume fraction) and 28%SiCW/6061Al. The result indicates that in small strain range, the IP TMF life is longer than that of the OP-TMF; in large strain range it is close to (for 28%SiCW) or even shorter than the OP-TMF life (for 15%SiCW). A comparison of the fatigue lives between the two composites illustrates that in the case of the OP-TMF, 15%SiCW/6061Al shows longer life than 28% SiCW/6061Al, however, in the case of IP-TMF, there is a crossover between the fatigue life curves of the two composites, meaning that the life being longer or shorter depends on strain level. Their damage processes are all related to initiation, growth and coalescence of voids in the matrix around whiskers.. |
| 177. | LH Qian, T Kobayashi, H Toda, ZG Wang, Dynamic fracture toughness of 6061Al composites reinforced with SiC particulates, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 10.1016/S0921-5093(01)01267-9, 318, 1-2, 189-196, 2001.11, Dynamic fracture toughness experiments were conducted at room temperature on 6061Al alloy reinforced with 15 and 25% volume fractions of 9.5mum SiC particulates. The fracture properties were evaluated in terms of crack initiation toughness, crack propagation energy and total absorbed energy. The dynamic fracture of the unreinforced 6061Al alloy was also studied as a comparison. The results of dynamic tests for both composites and matrix alloy are compared with their respective quasi-static cases. It is found that addition of SiC particles can drastically decrease fracture toughness of 6061Al alloy at both quasi-static and dynamic loading rates. 15%SiCp composite shows a considerable increase in crack initiation toughness and a much greater increment of crack propagation energy in dynamic loading case compared with static loading case, whereas 25%SiCp composite exhibits a negligible increment of crack propagation energy and a reduced increase of crack initiation energy in dynamic case in contrast to 15%SiCp composite. Detailed SEM examination of the fracture surfaces and optical observation of microstructures beneath the fracture surfaces of both composites, combined with an in-situ SEM observation, were made to investigate the fracture processes of the composites. (C) 2001 Elsevier Science B.V. All rights reserved.. |
| 178. | VA Mosneaga, T Mizutani, T Kobayashi, H Toda, Experimental and analytical investigations of fracture toughness in weldments of 6082 Al alloy, MATERIALS TRANSACTIONS, 10.2320/matertrans.42.2386, 42, 11, 2386-2391, 2001.11, 6082 At alloys are commercial and medium strength alloys, widely used as materials for welded structures. The purpose of this study is to investigate the effects of Mn addition on toughness of welded Al-Mg-Si alloys. To evaluate microstructural effects quantitatively, in-situ SEM observations of crack initiation and propagation behaviors through weldment are carried out. For the consideration of in-situ observation of fracture toughness test, stress field at crack-tip is analyzed using elasto-plastic finite element method (Hereinafter, FEM.) assuming that a crack is near a boundary between a weld metal and heat affected zone (Hereinafter, HAZ.). When small amount of Mn is added, recrystallization is completely suppressed as compared to specimens to which no Mn is added, thereby fibrous grains are kept. On the other hand, recrystallization of HAZ causes drastic decrease in fracture toughness in the case of no Mn addition. With the extension of a main crack, many microcracks are formed at grain boundaries ahead of a crack-tip despite the fact that the stress is relatively low. Such microcracking is not attributed to so-called liquation cracks, but the degradation is caused by the formation of film like Al-Mg intermetallic compuonds at grain boundaries. The microcracks are aligned ahead of the crack-tip at an angle of 60 degrees from an initial notch direction, This is attributable to the experimentally-observed direction of the intermetallic compound film, which is also confirmed by the numerical analysis.. |
| 179. | Toshiro Kobayashi, Hiroyuki Toda, Al-X (X=Nb, Cr, Fe) Ultra-High Strength In-Situ Composite Wire, Materials Science Forum, Proc of 7th International Conference on Aluminum Alloys (ICAA-7), 10.4028/www.scientific.net/msf.331-337.1133, 331-337, 1133-1138, 2000.05. |
| 180. | H Fukumasu, T Kobayashi, H Toda, K Shibue, Dynamic fracture toughness of a Ti-45Al-1.6Mn alloy at high temperature, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 31, 12, 3053-3061, 2000.12. |
| 181. | P. Liu, Z. Wang, H. Toda, T. Kobayashi, Effect of frequency on cyclic creep behavior of SiCw/6061 composite at high temperatures, Cailiao Yanjiu Xuebao/Chinese Journal of Materials Research, 12, 2, 213-216, 1998.04, The effect of frequency on the cyclic creep behavior of SiCw/6061Al composite was studied. It was found that the composite showed cyclic creep acceleration (CCA) in the tested stress region at 196°C, while it showed cyclic creep retardation (CCR) at 350°C. Within the frequency range from 0 to 0.5 Hz, the cyclic creep stress exponent increased and the activation energy decreased at 196°C with increasing frequency, while both of them increased at 350°C. When the frequency increased to 1 Hz, the cyclic creep behavior of the composite did not follow the above trends at the two temperatures.. |
| 182. | P. Liu, Z. Wang, W. Wang, H. Toda, T. Kobayashi, Static creep and cyclic creep behaviour of SiCw/6061Al and SiCp/2024Al composites at elevated temperature, Jinshu Xuebao/Acta Metallurgica Sinica, 33, 11, 1231-1232, 1997.11, The high temperature creep and cyclic creep behaviours of SiCw/6061Al and SiCp/2024Al composites were studied at 298°C. It was found that SiCw/6061Al composite showed better creep resistance but lower creep threshold stress as compared to SiCp/2024Al composite. Both composites showed cyclic creep retardation (CCR) in the tested stress region, while the CCR for SiCp/2024Al composite was more pronounced. For the SiCw/6061Al composite, the minimum cyclic creep rate decreased first and then increased with increasing the unloading amount, while for the SiCp/2024Al, the minimum cyclic creep rate decreased monotonically with increasing unloading amount.. |
| 183. | PL Liu, ZG Wang, H Toda, T Kobayashi, Effect of cyclic stress on the high temperature creep behavior of SiCw/6061Al composite, SCRIPTA MATERIALIA, 10.1016/S1359-6462(96)00454-X, 36, 7, 807-812, 1997.04. |
| 184. | PL Liu, ZG Wang, H Toda, T Kobayashi, Effect of frequency on cyclic creep of SiCw/6061Al composite at high temperatures, JOURNAL OF MATERIALS SCIENCE LETTERS, 10.1023/A:1018532805098, 16, 19, 1603-1605, 1997.10. |
| 185. | H Toda, T Kobayashi, Simulation of crack propagating in discontinuously reinforced metal matrix composite, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 28, 10, 2149-2157, 1997.10, A fracture mechanics-based numerical simulation of a crack propagating under mode I loading through discontinuously reinforced metal matrix composites (MMCs) is presented. Microcrack initiation due to debonding and breakage of reinforcements, shielding and antishielding effects caused by both microcracks and the reinforcements, the effect of crack deflection, and growing crack singularity are considered in the calculation of local crack tip driving forces. Statistical variations of spatial distribution and strength of the reinforcements are also considered. The essential feature of the model is to predict crack initiation toughness and crack path morphologies using a mixed-mode crack propagation criterion. Application of the program to predict crack growth behavior in an SiC whisker/Al alloy composite is presented. Microcracking far ahead of the tip of a main crack, crack deflection toward the microcracks, and subsequent incorporation of the microcracks which most affect the main crack are well simulated. The predicted microcrack distribution and variation of mixed-mode crack tip driving forces with crack growth are also evaluated.. |
| 186. | L Wang, ZM Sun, T Kobayashi, H Toda, Cyclic deformation and low cycle fatigue behavior in a SiCw/6061Al composite at elevated temperature, MATERIALS TRANSACTIONS JIM, 10.2320/matertrans1989.37.1561, 37, 10, 1561-1567, 1996.10. |
| 187. | H Toda, T Kobayashi, Growth behavior of microstructurally short cracks in the 6061 aluminum alloy with and without 22 vol pct SiC whiskers, METALLURGICAL AND MATERIALS TRANSACTIONS A-PHYSICAL METALLURGY AND MATERIALS SCIENCE, 10.1007/BF02651950, 27, 7, 2013-2021, 1996.07, Short crack growth behavior of the 6051 Al alloy with and without SiC whiskers was investigated. Fluctuations in the growth rate of short cracks converge with growth of the cracks and become substantially constant between 25 and 40 mu m in the metal matrix composite (MMC) and 110 and 183 mu m in the unreinforced alloy. This is attributed to the release of the short cracks from the microstructural effects, i.e., the interaction with reinforcement structure in the MMC and grain boundaries in the unreinforced alloy. Furthermore, there exists slowing down of short crack advance in the MMC, and this was explained from rapid development of crack closure obtained in this study.. |
| 188. | Md. Shahnewaz Bhuiyan, Hiroyuki Toda, Zhang Peng, Su Hang, Keitaro Horikawa, Kentaro Uesugi, Akihisa Takeuchi, Nobuto Sakaguchi, Yoshio Watanabe, Corrigendum to "Combined microtomography, thermal desorption spectroscopy, X-ray diffraction study of hydrogen trapping behavior in 7XXX aluminum alloys" [Mater. Sci. Eng. A 655 (2016) 221-228] doi: 10.1016/j.msea.2015.12.092, Materials Science and Engineering A, 10.1016/j.msea.2016.05.010, 668, 271-272, 2016.06. |
| 189. | Biomineralization via microbiologically influenced corrosion induced by Pseudomonas aeruginosa biofilm. |
| 190. | Mitsuru Nakazawa, Yoshimitsu Aoki, Masakazu Kobayashi, Hiroyuki Toda, 3D image analysis for evaluating internal deformation/fracture characteristics of materials, 2008 19th International Conference on Pattern Recognition (ICPR 2008), 10.1109/icpr.2008.4761648, 1, 978-1-4244-2175-6, 2008.12. |
| 191. | D. Seo, H. Toda, M. Kobayashi, K. Uesugi, A. Takeuchi, Y. Suzuki, Three-dimensional investigation of void coalescence in free-cutting steel using X-ray tomography, ISIJ International, 10.2355/isijinternational.55.1483, 55, 7, 1483-1488, 2015.07. |
| 192. | D. Seo, H. Toda, M. Kobayashi, K. Uesugi, A. Takeuchi, Y. Suzuki, In situ observation of void nucleation and growth in a steel using X-ray tomography, ISIJ International, 10.2355/isijinternational.55.1474, 55, 7, 1474-1482, 2015.07. |
| 193. | H. Li, H. Toda, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Application of diffraction-amalgamated grain boundary tracking to fatigue crack propagation behavior in high strength aluminum alloy, Materials Transactions, 10.2320/matertrans.M2014340, 56, 3, 424-428, 2015.03. |
| 194. | H. Toda, F. Tomizato, F. Zeismann, Y. Motoyashiki-Besel, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, A. Bruckner-Foit, High-resolution Observation of Steel Using X-ray Tomography Technique, ISIJ International, 10.2355/isijinternational.52.516, 52, 3, 516-521, 2012.03. |
| 195. | D.Seo, H Toda and M. Kobayashi, Visualization of dual-phase structure in duplex stainless steel, Research Frontiers 2013, 2014.08, [URL]. |
| 196. | Y. Yamamoto, M. Asano, H. Yoshida, M. Kobayashi, H. Toda, Effect of micro-voids on crack initiation and propagation in bending deformation of Al-Mg-Si alloy sheet, Materials Science Forum, 10.4028/www.scientific.net/MSF.794-796.325, 794-796, 325-330, 2014.06. |
| 197. | N. Hayat, H. Toda, T. Kobayashi, N. Wade, Study of damage behaviour of cast aluminium alloys fabricated through rheocasting, Proceedings of 9th International Conference on Semi-solid Processing of Alloys and Composites, 245-250. |
| 198. | V.A. Mosneaga, T. Kobayashi, H. Toda, Fracture toughness of various zones in weldments of 6082 Al alloys, Proceedings of The 2nd International Conference on Light Materials for Transportation Systems , 653-658. |
| 199. | H. Toda, T. Kobayashi, T. Hashizume, Design and fabrication of shape memory alloy actuated titanium matrix composites, Proceedings of European Congress on Advanced Materials and Processes. Metal Matrix Composites and Metallic Foams, (EUROMAT), 221-226. |
| 200. | H. Toda, N. Inoue, T. Kobayashi, Effects of PFZ layers around reinforcements on deformation behaviors in age-hardenable aluminum matrix composites, Proceedings of International Symposium on Advanced Engineering Material '97, Toyohashi, JSPS 156th Advanced Engineering Committee, 577-582. |
| 201. | L. Wang, H. Toda, T. Kobayashi, Cyclic deformation and low cycle fatigue behaviors in a SiCw/6061 Al composite at different temperatures, Proceedings of International Symposium on Advanced Engineering Material '97, Toyohashi, JSPS 156th Advanced Engineering Committee, 553-558. |
| 202. | T. Kobayashi, H. Toda, Evaluation of fracture toughness and proposal of microstructurally-controlled composites by fracture-mechanical simulation, Proceedings of International Symposium on Processing and Fabrication of Advanced Materials Ⅳ, TMS, 69-78. |
| 203. | T. Kobayashi, H. Toda, M. Murakami, Crack initiation and growth characteristics in the dynamic and static fracture toughness tests of SiC whisker / Al. alloy composite, Proceedings of 10th International Conference on Strength of Materials, J. Inst. Met., 529-532. |
| 204. | L. Wang, Z.M. Sun, T. Kobayashi, H. Toda, Cyclic deformation and low cycle fatigue behavior in a 6061A1/22vol% SiC whisker composite, Materials Transactions JIM, 37, 4, 762-768, 1996.04. |
| 205. | H. Toda, T. Kobayashi, Growth behavior of microstructurally short cracks in the 6061 aluminum alloy with and without 22 vol pct SiC whiskers, Metallurgical and Materials Transactions. A, 27, 7, 2013-2021, 1996.07. |
| 206. | T. Kobayashi, H. Toda, Enhancement of mechanical properties by RRA treatment, Proceedings of 5th International Symposium on Processing and Fabrication of Advanced Materials, 255-264, 1996.10. |
| 207. | L. Wang, Z.M. Sun, H. Toda, T. Kobayashi, Cyclic deformation and low cycle fatigue behavior in a SiCw / 6061 Al composite at elevated temperature, Materials Transactions JIM, Vol.37, 1561-1567, 1996.10. |
| 208. | L. Wang, Z.M. Sun, T. Kobayashi, H. Toda, Cyclic deformation and low cycle fatigue behavior in a SiCw/6061Al composite at elevated temperature, Materials Transactions JIM, 37, 10, 1561-1567, 1996.10. |
| 209. | P.L. Liu, Z.G. Wang, H. Toda, T. Kobayashi, Effect of cyclic stress on the high temperature creep behavior of SiCw/6061Al composite, Scripta Metallurgica, 36, 7, 807-812, 1997.04. |
| 210. | H. Toda, T. Kobayashi, Simulation of crack propagating in discontinuously reinforced metal matrix composite, Metallurgical and Materials Transactions. A, 28, 10, 2149-2157, 1997.10. |
| 211. | P.L. Liu, Z.G. Wang, H. Toda, T. Kobayashi, Effect of frequency on cyclic creep of SiCw/6061Al composite at high temperatures, Journal of Materials Science Letters, 16, 19, 1603-1605, 1997.10. |
| 212. | T. Kobayashi, H. Toda, Modeling and simulation of fracture behavior of MMC, Proceedings of the EUROMEC 373 Colloquium, Modeling and control of adaptive mechanical structures, ADAMES, 89-94, 1998.03. |
| 213. | H. Toda, T. Kobayashi, T. Goda, Numerical analysis of crack initiation and propagation behavior in aluminum matrix composites , Proceedings of 6th International Conference on Aluminum Alloys, Their Physical and Mechanical Properties, 1873-1878, 1998.07. |
| 214. | S. Morita, T. Kobayashi, H. Toda, Strain rate dependence of impact tensile properties in 6061 aluminum alloy, Proceedings of 6th International Conference on Aluminum Alloys, Their Physical and Mechanical Properties, 1998.07. |
| 215. | Q. Yao, T. Kobayashi, H. Toda, S. Kitaoka, Fatigue behavior in Al-Si-Cu die cast alloys, Proceedings of 6th International Conference on Aluminum Alloys, Their Physical and Mechanical Properties, 1373-1378, 1998.07. |
| 216. | H. Kojima, T. Kobayashi, H. Toda, Q. Yao, Effects of microstructural variation on mechanical properties of hypereutectic Al-Si casting alloys, Proceedings of 6th International Conference on Aluminum Alloys, Their Physical and Mechanical Properties, 565-570, 1998.07. |
| 217. | A. Takahashi, T. Kobayashi, H. Toda, Impact tension properties in A2091 aluminum-lithium alloy, Proceedings of 6th International Conference on Aluminum Alloys, Their Physical and Mechanical Properties, 505-510, 1998.07. |
| 218. | P.L.Liu, Z.G.Wang, H. Toda, T. Kobayashi, The cyclic creep behavior of SiCw/6061 Al composite at high temperatures, Key Engineering Materials, 145-149, 1&2, 655-660, 1998.11. |
| 219. | H. Toda, T. Kobayashi, A. Takahashi, Micromechanisms of fracture in wrought aluminum alloy containing coarse inclusion particles, Aluminum Transactions, 1, 1, 109-116, 1999.01. |
| 220. | A. Takahashi, T. Kobayashi, H. Toda, Initiation stress of delamination cracking in A2091 Al-Li alloy, International Journal of Materials and Product Technology, 14, 2/3/4, 217-228, 1999.02. |
| 221. | L. Wang, T. Kobayashi, H. Toda, M. Hayakawa, Effects of loading velocity on fracture toughness of a SiCw/A6061 composite at elevated temperatures, Materials Transactions, JIM, 40, 10, 1056-1062, 1999.10. |
| 222. | F. Kamiya, T. Kobayashi, H. Toda, M. Takasu, N. Okamoto, Fracture behaviour of TiC particles dispersed Al2O3 ceramics, Proceedings of the 10th IKETANI conference, 365-366, 2000.01. |
| 223. | L. Qian, Z.G. Wang, H. Toda, T. Kobayashi, Q. Yao, Thermo-mechanical fatigue of a SiCw/6061A1 composite, Materials Transactions, JIM, 41, 6, 651-655, 2000.06. |
| 224. | H. Toda, T. Kobayashi, Al-X (X=Nb, Cr, Fe) ultra-high strength in-situ composite wire, Proceedings of ISAEM-2000, International Journal of Materials Product Technology, Special Issue, SPM1, 427-432, 2000.10. |
| 225. | T. Masuda, T. Kobayashi, H. Toda, S. Morita, Strain rate dependency of impact tensile properties in various commercial aluminum alloys, Proceedings of ISAEM-2000, International Journal of Materials Product Technology, Special Issue, SPM1, , 823-828, 2000.10. |
| 226. | T. Agag, T. Takeichi, H. Toda, T. Kobayashi, Epoxy-clay nanocomposites using polybenzoxazine as a curing agent, Proceedings of ISAEM-2000, International Journal of Materials Product Technology, Special Issue, SPM1, , 706-711, 2000.10. |
| 227. | M. Shibata, Y. Takemoto, T. Kobayashi, H. Toda, Expansion behavior of thermally cycled aluminium alloys reinforced with aluminium borate whiskers, Proceedings of ISAEM-2000, International Journal of Materials Product Technology, Special Issue, SPM1, , 275-280, 2000.10. |
| 228. | L. Qian, Z.G. Wang, H. Toda, T. Kobayashi, Isothermal fatigue and in-phase thermo-mechanical fatigue of a 6061Al/SiCw, Proceedings of ISAEM-2000, International Journal of Materials Product Technology, Special Issue, SPM1, , 799-804, 2000.10. |
| 229. | H. Fukumasu, T. Kobayashi, H. Toda, K. Shibue, Dynamic fracture toughness of a Ti-45Al-1.6Mn alloy at temperature, Metallurgical and Materials Transactions. A, 31, 12, 3053-3061, 2000.12. |
| 230. | V.A. Mosneaga, T. Kobayashi, H. Toda, Influence of ECAP and age hardening treatment in 6061 Al alloy, International Journal of Materials and Product Technology, 16, 8, 710-716, 2001.01. |
| 231. | T. Kobayashi, H. Toda, T. Hashizume, Design and evaluation of TiNi particle dispersed titanium matrix composite, Transactions of Materials Research Society of Japan, 26, 1, 247-250, 2001.01. |
| 232. | H. Toda, T. Hashizume, T. Kobayashi, Fabrication and evaluation of shape memory alloy particles dispersed Titanium composites, ICCM-13, Beijing, ID-1303, 1-10, 2001.06. |
| 233. | T. Masuda, T. Kobayashi, H. Toda, High strain rate deformation behavior of Al-Mg alloys, 1, 363-368, 2001.07. |
| 234. | H. Toda, T. Kobayashi, A. Takahashi, Effects of coarse intermetallic particles on fracture toughness of wrought aluminum alloys, THERMEC'2000, Las Vegas, USA(October 2001), 117/3, CDROM, Section A2, 2001.08. |
| 235. | T. Kobayashi, H. Toda, Shape memory alloy particles dispersed titanium composite, Proceedings of the International Symposium on Smart Materials and Structural Systems, JSME, 85-91, 2001.08. |
| 236. | H. Toda, T. Kobayashi, T. Noguchi, N. Wade, H.K. Ahn, C.H. Yu, Fatigue properties of Al-Si alloys fabricated through semi-solid process, EUROMAT 2001, FEMS, Rimini, Italy, CD-ROM., 2001.09. |
| 237. | V.A. Mosneaga, T. Mizutani, T. Kobayashi, H. Toda, Experimental and analytical investigations of fracture toughness in weldments of 6082 Al alloy, Materials Transactions, 42, 11, 2386-2391, 2001.11. |
| 238. | L. Qian, T. Kobayashi, H. Toda, Z.G. Wang, Dynamic fracture toughness of 6061Al composites reinforced with SiC particulates, Materials Science & Engineering. A, 318, 1-2, 189-196, 2001.11. |
| 239. | H. Toda, L. Wang, T. Kobayashi, Z.M. Sun, Fracture behavior of a SiCw/6061Al alloy composite under cyclic loading, Proceedings of Advances in Fracture Research, Elsevier, 2001.12. |
| 240. | T. Masuda, T. Kobayashi, H. Toda, High strain rate deformation behavior of Al-Mg alloys, Proceedings of Advances in Fracture Research, Elsevier, 2001.12. |
| 241. | T. Kobayashi, H. Toda, T. Masuda, Analysis of test data obtained from charpy V and impact tensile test, From Charpy to Present Impact Testing, Elsevier, 30, 173-180, 2002.01. |
| 242. | N. Hayat, H. Toda, T. Kobayashi, N. Wade, H.K. Ahn, C.H. Yu, H. Miura, Fatigue characteristics of AC4CH aluminium cast alloys fabricated by inclined cooling plate technique, International Journal of Cast Metals Research, 14, 5, 293-301, 2002.01. |
| 243. | N. Hayat, H. Toda, T. Kobayashi, N. Wade, Experimental investigations of fatigue characteristics of AC4CH cast aluminum alloys fabricated through rheocast and squeeze cast methods, Proceedings of ICAA-8, Materials Science Forum, 396-402, 1353-1358, 2002.01. |
| 244. | V.A. Mosneaga, T. Mizutani, T. Kobayashi, H. Toda, Impact toughness of weldments in Al-Mg-Si alloys, Materials Transactions, 43, 6, 1381-1389, 2002.06. |
| 245. | H. Toda, T. Kobayashi, In-situ strengths of various coarse intermetallic particles in wrought Aluminum alloys, ICAA-8, Cambridge, UK, 1097-1102, 2002.07. |
| 246. | L. Qian, T. Kobayashi, H. Toda, T. Goda, Z.G. Wang, Fracture toughness of a 6061Al matrix composite reinforced with fine SiC particles, Materials Transactions, 43, 11, 2838-2842, 2002.11. |
| 247. | Ｔ. Masuda, T. Kobayashi, L. Wang, H. Toda, Effects of strain rate on deformation behavior of A6061-T6 aluminum alloys, Materials Science Forum, 426-432, 285-290, 2003.01. |
| 248. | H. Toda, T. Kobayashi, Damage behaviours of various coarse Al-Fe-Si particles in model wrought alloys, Materials Science Forum, 426-432, 393-398, 2003.01. |
| 249. | K.H. Khor, M. Joyce, T. Connolley, H. Toda, I. Sinclair, E. Maire, J.-Y. Buffiere, Synchrotron microtomography of fatigue crack closure, 2002 ESRF Scientific Highlights, 79-80, 2003.01. |
| 250. | N. Hayat, T. Kobayashi, H. Toda, H. Kojima, Grain size refinement through gas bubble stirring in AC4CH cast aluminium alloy, International Journal of Cast Metals Research, 15, 5, 505-512, 2003.01. |
| 251. | H. Toda, I. Sinclair, J.-Y. Buffiere, E.Maire, T. Connolley, M. Joyce, K.H. Khor, P. Gregson, Assessment of fatigue crack closure phenomenon in damage tolerant aluminium alloy by in-situ high-resolution synchrotron X-ray microtomography, Philosophical Magazine A, 83, 21, 2429-2448, 2003.07. |
| 252. | H. Toda, T. Ohgaki, K. Uesugi, In-situ high resolution X-ray tomography of fracture micromechanisms in aluminium foams, Research Frontiers, 133-134, 2004.01. |
| 253. | S. Nishido, M. Kaneko, T. Kobayashi, H. Toda, Role of Si particle damage on fatigue characteristics of cast Al-Si alloys, International Journal of Cast Metals Research , 17, 6, 345-350, 2004.06. |
| 254. | H. Toda, T. Kobayashi, J. Sawamura, Up-grade recycling of metallic cutting chips by consolidation under severe plastic deformation, Proceedings of the 9th International Conference on Aluminium Alloys, Ed. By J.F.Nie, A.J.Morton and B.C.Muddle, Brisbane (August 2004). , 1328-1333, 2004.08. |
| 255. | S. Nishido, H. Toda, T. Kobayashi, J. Katano, Fracture analysis of a crack propagating in aluminium-7% silicon alloy casting, Proceedings of the 9th International Conference on Aluminium Alloys, Ed. By J.F.Nie, A.J.Morton and B.C.Muddle, Brisbane (August 2004). , 672-677, 2004.08. |
| 256. | M. Takata, T. Masuda, H. Toda, T. Kobayashi, Effect of notch on dynamic tensile properties in 6061 aluminum alloy, Proceedings of the 9th International Conference on Aluminium Alloys, Ed. By J.F.Nie, A.J.Morton and B.C.Muddle, Brisbane (August 2004). , 476-481, 2004.08. |
| 257. | T. Masuda, H. Toda, T. Kobayashi, Notch effects on impact tensile properties in A6061-T6 aluminum alloy, Materials Science Forum, 449, 137-140, 2004.11. |
| 258. | H. Toda, T. Kobayashi, Up-grade recycle by consolidating aluminium cutting chip under severe plastic deformation, Materials Science Forum, 449, 333-336, 2004.11. |
| 259. | J.J. Ahn, H. Toda, M. Niinomi, T. Kobayashi, K. Uesugi, T. Akahori, 3D strain mapping of small structures by synchrotron x-ray microtomography , JOM, 56, 11, 308, 2004.11. |
| 260. | H. Toda, T. Ohgaki, K. Uesugi, K. Makii, Y. Aruga, T. Akahori, M. Niinomi, T. Kobayashi, In-situ observation of fracture of aluminium foam using synchrotron X-ray microtomography, Key Engineering Materials, 297-300, 1189-1195, 2005.01. |
| 261. | H. Toda, J. Katano, T. Kobayashi, T. Akahori, M. Niinomi, Assessment of thermo-mechanical fatigue behaviors of cast Al-Si alloys by experiments and multi-step numerical simulation, Materials Transactions, 46, 1, 111-117, 2005.01. |
| 262. | T. Murakami, H. Toda, T. Kobayashi, Effects of temperature and loading rate on fracture toughness, Key Engineering Materials, 297-300, 2397-2405, 2005.01. |
| 263. | L. Qian, H. Toda, S. Morita, T. Kobayashi, Z.G. Wang, In-situ observations of fracture processes in 0.6 μm and 9.5 μm SiCP/6061Al composites, Materials Transactions, 46, 1, 34-41, 2005.01. |
| 264. | M. Niinomi, J. Takeda, T. Akahori, H. Fukui, M. Toyama, H. Toda, Effect of microstructure on tensile properties and static fracture toughness of dental gold alloy, Materials Transactions, 46, 4, 1540-1544, 2005.04. |
| 265. | H. Toda, N. Kuroda, M. Takata, K. Uesugi, T. Ohgaki, M. Kobayashi, K. Makii, Y. Aruga, T. Akahori, M. Niinomi, T. Kobayashi, 3D internal strain mapping by tracking microstructural features in tomographic volumes of structural materials, IPAP Conference Series 7, Proceedings of the 8th International Conference on X-ray Microscopy, Institute of Pure and Applied Physics, Japan, 240-242, 2005.07. |
| 266. | H. Toda, M. Toyoda, T. Kobayashi, T. Akahori, M. Niinomi, Feasibility study on smart coating for failure prevention under thermo-mechanical fatigue loading, Proceedings of the 6th International Conference on Intelligent Materials and Systems (ICIM’05) , 229-232, 2005.07. |
| 267. | T. Akahori, M. Niinomi, Y. Koyanagi, T. Kasuga, H. Toda, H. Fukui, M. Ogawa, Mechanical properties of biocompatible beta-type titanium alloy coated with calcium phosphate invert glass-ceramic layer, Materials Transactions, 46, 7, 1564-1569, 2005.07. |
| 268. | J. Ahn, H. Toda, M. Niinomi, T. Kobayashi, True-3D strain mapping for assessment of material deformation by synchrotron X-ray microtomography, Review of Progress in Quantitative NDE, American Institute of Physics, Melville, NY, 24, 1423-1430, 2005.07. |
| 269. | B. Gunawarman, M. Niinomi, T. Akahori, T. Souma, M. Ikeda, H. Toda, K. Terashima, Fatigue characteristics of low cost beta titanium alloys for healthcare and medical applications, Materials Transactions, 46, 7, 1570-1577, 2005.07. |
| 270. | H. Toda, T. Kobayashi, M. Niinomi, T. Akahori, T. Sakai, Improvement of mechanical properties by high temperature solution treatment in an aluminum casting alloy, Proceedings of the 23rd ASM Heat Treating Society Conference and Exposition, 364-369, 2005.09. |
| 271. | H. Toda, N. Kuroda, T. Ohgaki, M. Kobayashi, T. Akahori, M. Niinomi, T. Kobayashi, K. Uesugi, K. Makii, Y. Aruga, Image-based mechanical analysis of dynamic deformation and damage behaviors in an aluminium foam using synchrotron X-ray microtomography, Porous Metals and Metal Foaming Technology, Proceedings of the 5th International Conference on Porous Metals and Metal Foaming Technology., 409-414, 2005.09. |
| 272. | T. Ohgaki, H. Toda, M. Kobayashi, K. Uesugi, T. Kobayashi, M. Niinomi, T. Akahori, K. Makii, Y. Aruga, Assessment of fatigue behaviour of aluminium foams by synchrotron X-ray microtomography, Porous Metals and Metal Foaming Technology, Proceedings of the 5th International Conference on Porous Metals and Metal Foaming Technology., 565-570, 2005.09. |
| 273. | H. Toda, H. Mizutani, T. Akahori, M. Niinomi, T. Kobayashi, Image-based mechanical analysis of multifilamentary microstructure formation in Al-Fe heavily deformed in-situ composites, Materials Transactions, 46, 10, 2229-2236, 2005.10. |
| 274. | J.H. Kim, M. Niinomi, T. Akahori, J. Takeda, H. Toda, Effect of microstructure on fatigue strength of bovine compact bones, JSME International Journal Series A, Solid Mechanics and Material Engineering, 48, 4, 472-480, 2005.10. |
| 275. | T. Akahori, M. Niinomi, H. Toda, H. Fukui, H. Ogawa, Fatigue properties of beta-type titanium alloy for biomedical applications under various fatigue conditions, Medical Device Materials III - Proceedings of the Materials and Processes for Medical Devices Conference 2005, 154-162, 2005.11. |
| 276. | L. Qian, H. Toda, S. Nishido, T. Akahori, M. Niinomi, T. Kobayashi, Numerical simulation of fracture of model Al-Si alloys, Metallurgical and Materials Transactions. A, 36A, 11, 2979-2992, 2005.11. |
| 277. | L. Qian, H. Toda, K. Uesugi, T. Kobayashi, T. Ohgaki, M. Kobayashi, Application of synchrotron x-ray microtomography to investigate ductile fracture in Al alloys, Applied Physics Letters, 10.1063/1.214208, 87, 24, 241907, 2005.12. |
| 278. | L. Qian, S. Nishido, H. Toda, T. Kobayashi, FEM modeling of crack propagation in a model multiphase alloy, Journal of Materials Science and Technology, 22, 1, 59-65, 2006.01. |
| 279. | H. Toda, T. Ohgaki, K. Uesugi, M. Kobayashi, N. Kuroda, T. Kobayashi, M. Niinomi, T. Akahori, K. Makii, Y. Aruga, Quantitative assessment of microstructure and its effects on compression behavior of aluminum foams via high-resolution synchrotron X-ray tomography, Metallurgical and Materials Transactions. A, 37A, 4, 1211-1220, 2006.04. |
| 280. | H. Toda, K. Minami, M. Kobayashi, K. Uesugi, A. Takeuchi, T. Kobayashi, Observation of precipitates in aluminum alloys by sub-micrometer resolution tomography using Fresnel zone plate, Materials Science Forum, 519-521, 1361-1366, 2006.07. |
| 281. | T. Ohgaki, H. Toda, K. Uesugi, T. Kobayashi, K. Makii, T. Takagi, Y. Aruga, Application of local tomography technique to high-resolution synchrotron x-ray imaging, Materials Science Forum, 539-543, 287-292, 2006.07. |
| 282. | T. Kobayashi, H. Toda, Strength and fracture of aluminium alloys, Materials Science Forum, 539, 543, 127-134, 2006.07. |
| 283. | S. Yamamoto, H. Toda, L. Qian, T. Ohgaki, M. Kobayashi, T. Kobayashi, K. Uesugi, Assessment of damage and fracture behaviors in a cast aluminum alloy via in-situ synchrotron microtomography, Materials Science Forum, 519-521, 1005-1010, 2006.07. |
| 284. | M. Kobayashi, H. Toda, T. Ohgaki, K. Uesugi, D. S. Wilkinson, T. Kobayashi, Y. Kawai, Y. Aoki, 3-D high-density strain mapping procedure based on high-resolution CT, Materials Science Forum, 539-543, 2377-2382, 2006.07. |
| 285. | M. Kobayashi, Y. Takayama, H. Kato, H. Toda, In-situ SEM/EBSP analysis during annealing in a pure aluminum foil for capacitor, Materials Science Forum, 539-543, 362-367, 2006.07. |
| 286. | H. Toda, K. Minami, M. Kobayashi, K. Uesugi, A. Takeuchi, T. Kobayashi, 3-D microstructural observation by means of sub-micrometer-resolution imaging micro-tomography, Proceedings of the 16th International Microscopy Congress, Vol.3, 240-242, 2006.09. |
| 287. | A. Weck, D.S. Wilkinson, H. Toda, E. Maire, 2D and 3D visualization of ductile fracture, Advanced Engineering Materials, 8, 6, 469-472, 2006.09. |
| 288. | M. Nakazawa, Y. Aoki, M. Kobayashi, H. Toda, Y. Kawai, 3D image analysis for evaluating internal deformation / fracture characteristics of materials, Proceedings of the 32nd Annual Conference of the IEEE Industrial Electronics Society, 3525-3530, 2006.11. |
| 289. | M. Kobayashi, H. Toda, T. Ohgaki, K. Uesugi, D.S. Wilkinson, T. Kobayashi, Y. Aoki, Three-dimensional measurement of local strain distribution by tracking microstructural features in high-resolution SR-CT image, Key Engineering Materials, 345-346, 1153-1156, 2007.01. |
| 290. | L. Li, H. Toda, T. Ohgaki, M. Kobayashi, T. Kobayashi, K. Uesugi, Y. Suzuki, Wavelet-based local region-of-interest reconstruction for synchrotron radiation X-ray microtomography, Journal of Applied Physics, 102, 114908-1-9, 2007.01. |
| 291. | H. Toda, M. Kobayashi, K. Uesugi, D.S. Wilkinson, T. Kobayashi, 3-D strain mapping inside materials by microstructural tracking in tomographic volumes, Proceedings of MATERIALS CHARACTERISATION 2007 Computational Methods and Experiments in Materials Characterisation III, 177-186, 2007.06. |
| 292. | M. Niinomi, T. Akahori, T. Nozaki, M. Nakai, S. Horihata, T. Suzuki, K. Watanabe, K. Sone, H. Toda, Development of Titanium alloy for mouthpieceof brass instrument and its precision casting process, Ti-2007 Science and Technology, ed. By M. Niinomi, S. Akiyama, M. Ikeda, M. Hagiwara and K. Maruyama, the Japan Institute of Materials, 1571-1574, 2007.06. |
| 293. | M. Nakazawa, Y. Aoki, M. Kobayashi, H. Toda, Y. Kawai, 3D image analysis for evaluating internal deformation / fracture characteristics of materials, Proceedings of the First International Symposium on Information and Computer Elements, 76-81, 2007.09. |
| 294. | L. Li, H. Toda, T. Ohgaki, M. Kobayashi, T. Kobayashi, K. Uesugi, Y. Suzuki, Wavelet-based local tomography algorithm for high-resolution synchrotron radiation X-ray imaging, Proceedings of Materials Science and Technology 2007, 163-174, 2007.09. |
| 295. | M. Nakazawa, Y. Aoki, M. Kobayashi, H. Toda, Y. Kawai, 3D image analysis for evaluating internal deformation / fracture characteristics of materials, Proceedings of the International Symposium on Optomechatronic Technologies, Vol. 6718, 67180C-1-67180C-8, 2007.10. |
| 296. | T. Ohgaki, Y. Takami, H. Toda, T. Kobayashi, Y. Suzuki, K. Uesugi, K. Makii, T. Takagi, Y. Aruga, Three-dimensional Zinc mapping inside aluminum foams using synchroteon X-ray microtomography, Materials Science Forum, 561-565, 1677-1680, 2007.11. |
| 297. | M. Nakai, M. Niinomi, T. Akahori, N. Ohtsu, H. Nishimura, H. Toda, H. Fukui, M. Ogawa, Hard-ceramic layer formed on Ti-29Nb-13Ta-4.6Zr and Ti-6Al-4V ELI during Gas Nitriding, Materials Science Forum, 561-565, 1509-1512, 2007.11. |
| 298. | L. Qian, H. Toda, K. Uesugi, M. Kobayashi, T. Kobayashi, 3D image-based modeling of ductile fracture in an aluminum alloy using synchrotron X-ray CT images , Materials Science Forum, 561-565, 263-266, 2007.11. |
| 299. | T. Nishimura, H. Toda, M. Kobayashi, T. Kobayashi, K. Uesugi, Y. Suzuki, Change in microstructure of Al-Si-Cu casting alloys during high-temperature solution treatment, International Jounal of Cast Metals Research, 21, 1-4, 114-118, 2008.01. |
| 300. | M. Nakazawa, Y. Aoki, M. Kobayashi, H. Toda, Y. Kawai, 3D image analysis for evaluating internal deformation / fracture characteristics of materials, Proceedings of the International Workshop on Advanced Image Technology 2008 , B2-B4, 2008.01. |
| 301. | T. Nishimura, H. Toda, M. Kobayashi, T. Kobayashi, K. Uesugi, Y. Suzuki, Change in microstructure of Al-Si-Cu casting alloys during high-temperature solution treatment, International Jounal of Cast Metals Research, Vol.21, 118-114, 2008.04. |
| 302. | H. Toda, T. Hidaka, M. Kobayashi, T. Kobayashi, K. Uesugi, Y. Suzuki, Application of high resolution microtomography to cast aluminium alloys, Proceedings of The 10th Asian Foundry Congress, 121-127, 2008.05. |
| 303. | J.H. Kim, M. Niinomi, T. Akahori, H. Toda, Fatigue properties of bovine compact bones that have different microstructures , International Journal of Fatigue , 29, 6, 1039-1050, 2008.06. |
| 304. | M. Nakazawa, Y. Aoki, M. Kobayashi, H. Toda, 3D image analysis for evaluating internal deformation / fracture characteristics of materials, Proceedings of the Third Asia International Symposium on Mechatronics, 87-90, 2008.08. |
| 305. | H. Toda, Y. Takami, M. Kobayashi, T. Kobayashi, Y. Aruga, T. Takagi, Y. Suzuki, K. Uesugi, 3-D microstructural characterization of cell wall in a high strength aluminium foam, Proceedings of International Conference on Porous Metals and Metallic Foams 2007: Porous Metals and Metallic Foams, 445-448, 2008.09. |
| 306. | H. Toda, T. Hidaka, K. Minami, M. Kobayashi, K. Uesugi, Y. Suzuki, T. Kobayashi, 3-D tracking of hydrogen micro-pores during aluminium production process , Proceedings of the 11th International Conference on Aluminium Alloys, 575-581, 2008.09. |
| 307. | M. Kobayashi, H. Toda, Y. Ohkawa, K. Uesugi, T. Kobayashi, Three-dimensional analysis of grain deformation in Al-Cu alloy by means of high-resolution X-ray computed tomography, Proceedings of the 11th International Conference on Aluminium Alloys, 680-685, 2008.09. |
| 308. | K. Shimizu, H. Toda, M. Kobayashi, K. Uesugi, Y. Suzuki, T. Kobayashi, Synchrotron-based dual energy K-edge subtraction imaging for three-dimensional concentration mapping, Proceedings of the 11th International Conference on Aluminium Alloys, 868-873, 2008.09. |
| 309. | P. Qu, H. Toda, H. Zhang, L. Qian, M. Sakaguchi, M. Kobayashi, K. Uesugi, 3D image-based analyses of fatigue crack propagation in an Al-Mg-Si alloy, Proceedings of the Materials Science and Technology Conference and Exhibition, MS and T'08, 600-609, 2008.10. |
| 310. | H. Zhang, P. Qu, Y. Sakaguchi, H. Toda, M. Kobayashi, K. Uesugi, Y. Suzuki, Three-dimensional characterization of fatigue crack propagation behavior in an aluminum alloy using high resolution X-Ray microtomography, Proceedings of the Materials Science and Technology Conference and Exhibition, MS and T'08, 1107-1116, 2008.10. |
| 311. | L. Qian, H. Toda, K. Uesugi, M. Kobayashi, T. Kobayashi, Direct observation and image-based simulation of three-dimensional tortuous crack evolution inside opaque materials, Physical Review Letters, 100, 11, 115505, 2008.11. |
| 312. | M. Nakazawa, Y. Aoki, M. Kobayashi, H. Toda, 3D image analysis for evaluating internal deformation / fracture characteristics of materials, Proceedings of the nineteenth conference of the International Association for Pattern Recognition (IAPR). , 978-1-4244-2175-6, 2008.12. |
| 313. | P. Qu, H. Toda, H. Zhang, Y. Sakaguchi, L. Qian, M. Kobayashi, K. Uesugi, Local crack driving force analysis of a fatigue crack by a microstructural tracking method, Scripta Materialia, 60, 489-492, 2009.01. |
| 314. | H. Toda, K. Koyama, K. Ichitani, M. Kobayashi, 4-D observation of metal forming process, Proceedings of the 28th. Colloquium on Metal Forming, 239-247, 2009.02. |
| 315. | Q. Zhang, H. Toda, Y. Takami, Y. Suzuki, K. Uesugi, M. Kobayashi, Assessment of 3D inhomogeneous microstructure of highly alloyed aluminium foam via dual energy K-edge subtraction imaging, Philosophical Magazine, 10.1080/14786430903571438, 90, 14, 1853-1871, 2010.04. |
| 316. | K. Sakamoto, S. Ishimitsu, T. Oda, Y. Sugiyama, H. Toda, Analysis of the relationship between material structures and auditory impressions, ICIC Express Letters, 4, 3, 691-696, 2010.04. |
| 317. | M. Nakazawa, M. Kobayashi, H. Toda, Y. Aoki, Proposal of a method to analyze 3D deformation/fracture characteristics inside materials based on a stratified matching approach , Machine Vision and Applications , 21, 5, 687-694, 2010.05. |
| 318. | Q. Zhang, H. Toda, M. Kobayashi, Y. Suzuki, K. Uesugi, Three dimensional microstructure characterization of an Al-Zn-Mg alloy foam using synchrotron X-ray microtomography, Materials Science Forum, 654-656, 2358-2361, 2010.08. |
| 319. | P. Qu, H. Toda, H. Zhang, L. Qian, M. Sakaguchi, M.Kobayashi, K. Uesugi, 3D observation and image-based finite element analyses of fatigue crack propagation in an Al-Mg-Si alloy, Advanced Materials Research, 10.4028/www.scientific.net/AMR.89-91.449, 89-91, 449-454, 2010.08. |
| 320. | M. Kobayashi, H. Toda, K.Uesugi, A.Takeuchi, Y.Suzuki, 3D Characterisation of Grain Deformation under Synchrotron Radiation, Materials Science Forum, 10.4028/www.scientific.net/MSF.654-656.2303, 654-656, 2303-2306, 2010.08. |
| 321. | M. Kobayashi, H. Toda, K. Uesugi, Three-dimensional Visualization and Analysis of Grain Deformation by means of Synchrotron Radiation, Materials Science Forum, 10.4028/www.scientific.net/MSF.638-642.2523, 638-642, 2523-2528, 2010.08. |
| 322. | H. Zhang, P. C. Qu, Y. Sakaguchi, H. Toda, M. Kobayashi, K. Uesugi, Y. Suzuki, Three-dimensional characterization of fatigue crack propagation behavior in an aluminum alloy using high resolution X-ray microtomography, Materials Science Forum, 10.4028/www.scientific.net/MSF.638-642.378, 638-642, 378-383, 2010.08. |
| 323. | H. Toda, K. Uesugi, Y. Suzuki, M. Kobayashi, Hydrogen micro pores and their affects on mechanical properties, Proceedings of the 12th International Conference on Aluminium Alloys, 1353-1360, 2010.09. |
| 324. | S. Yamauchi, H. Toda, M. Kobayashi, T. Hiramatsu, E. Maire, Analysis of crack-tip stress field via observation of local crack extension by means of fast tomography technique, Proceedings of the 12th International Conference on Aluminium Alloys, 2369-2374, 2010.09. |
| 325. | P. Qu, H. Toda, H. Zhang, L. Qian, M. Kobayashi, K. Uesugi, Assessment of actual complicated fatigue crack propagation via 3D image-based numerical simulation, Proceedings of the 12th International Conference on Aluminium Alloys, 1342-1346, 2010.09. |
| 326. | M. Kobayashi, H. Toda, Y. Kawai, M. Nakazawa, Y. Aoki, K. Uesugi, Y. Suzuki, Development of three-dimensional plastic strain mapping technique for x-ray micro-tomography, Proceedings of the 12th International Conference on Aluminium Alloys, 1330-1335, 2010.09. |
| 327. | H. Tsuruta, H. Toda, P. Qu, M. Kobayashi, E. Maire, Image-based simulation of monotonic crack propagation through a 2024 aluminum alloy, Proceedings of the 12th International Conference on Aluminium Alloys, 2275-2280, 2010.09. |
| 328. | H. Toda, M. Kobayashi, K. Uesugi, Y. Suzuki, Hydrogen micro pores in cast aluminum alloys, Proceedings of 69th World Foundry Congress, 49-53, 2010.10. |
| 329. | Z. A. Shamsudin, H. Toda, M. Kobayashi, K. Koyama, K. Ichitani, K. Uesugi, Healing behavior of hydrogen micro pores during cold plastic deformation, Proceedings of Materials Scence & Technology, CD-ROM pp.1031-1036, 2010.10. |
| 330. | M. Kobayashi, H. Toda, Y. Kawai, M. Nakazawa, Y. Aoki, K. Uesugi, Y. Suzuki, Three-dimensional plastic strain mapping technique for X-ray micro-tomography, Proceedings of Materials Scence & Technology , CD-ROM pp.1037-1044, 2010.10. |
| 331. | Q. Zhang, H. Toda, Dual energy K- edge subtraction imaging of 3D inhomogeneous microstructure in highly alloyed aluminium foam, Research Frontiers 2010, 64-65, 2011.03. |
| 332. | H. Toda, A. Miyawaki, K. Uesugi, Y. Suzuki, M. Kobayashi, Localized deformation during fracture of high-strength aluminum alloy, Procedia Engineering, 10.1016/j.proeng.2011.04.427, 10, 2598-2603, 2011.06. |
| 333. | H. Toda, K. Uesugi, Y. Suzuki, M. Kobayashi, 3D/4D strain mapping using in-situ X-ray microtomography, Applied Mechanics and Materials, 10.4028/www.scientific.net/.249, 70, 249-254, 2011.09. |
| 334. | M. Kobayashi, H. Toda, A. Takeuchi, K. Uesugi, Y. Suzuki, Characterization of inhomogeneous deformation behaviors in a flexible graphite sheet by a synchrotron radiation microtomography, Proceedings of International Conference on Advanced Technology in Experimental Mechanics 2011 , CD-ROM pp.1-7, 2011.09. |
| 335. | C. Gupta, H. Toda, Y. Adachi, M. Kobayashi, C. Schlacher, P. Mayr, C. Sommitsch, H. Hoshino, S. Yamauchi, K. Uesugi, Y. Suzuki, A. Takeuchi, Analysis of creep cavitation in advanced 9-12%Cr steels using 3D characterisation techniques, Proceedings of 12th International Conference on Creep and Fracture of Engineering Materials and Structures, CD-ROM (4 pages), 2012.05. |
| 336. | H. Toda, H. Oogo, H. Tsuruta, K. Horikawa, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Origin of ductile fracture in aluminum alloys, 565-570, 2012.06. |
| 337. | D.J. LeClere, T. Kamiko, Y. Mizuseki, Y. Suzuki, A. Takeuchi, K. Uesugi, M. Kobayashi, H. Toda, Diffraction-Amalgamated Grain-boundary Tracking (DAGT) technique and its application to an aluminum alloy, Proceedings of 13th International Conference on Aluminum Alloys, 9-14, 2012.06. |
| 338. | C. Schlacher, C. Sommitsch, P. Mayr, C. Gupta, H. Toda, K. Uesugi, Y. Suzuki, Creep and damage investigation of improved 9% Cr steel welded joints, ASM Proceedings of the International Conference: Trends in Welding Research, 376-381, 2012.06. |
| 339. | H. Li, H. Toda, Y. Mizuseki, K.Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Assessment of fatigue crack propagation behavior in aluminum alloy by in-situ high-resolution synchrotron X-ray microtomography, Proceedings of the International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation, Joining and Welding Research Institute in Osaka Univ. , 239-240, 2012.11. |
| 340. | D. Seo, H. Toda, K. Kawakami, K. Uesugi, A. Takeuchi, Y. Susuki, M. Kobayashi, In-situ observation of void growth and coalescence in free-cutting steel using synchrotron X-ray microtomography, Proceedings of the International Symposium on Visualization in Joining & Welding Science through Advanced Measurements and Simulation, Joining and Welding Research Institute in Osaka Univ., 235-236, 2012.11. |
| 341. | A. Hosokawa, D.S. Wilkinson, L. Kang, M. Kobayashi, H. Toda, Void growth and coalescence in model materials investigated by high-resolution X-ray microtomography: Influence of work hardening behavior on ductility, International Journal of Fracture , 181, 1, 51-66, 2013.01. |
| 342. | C. Gupta, H. Toda, C. Schlacher, P. Mayr, C. Sommitsch, K. Uesugi, Y. Suzuki, A. Takeuchi, M. Kobayashi, Study of creep damage in a 10.86% Cr heat resistant steel using synchrotron X-ray microtomography, Advanced Materials Research, 794, 476-483, 2013.07. |
| 343. | H. Toda, Y. Ohkawa, T. Kamiko, T. Naganuma, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Grain boundary tracking technique: four-dimensional visualisation technique for determining grain boundary geometry with local strain mapping, Acta Materialia, 61, 14, 5535-5548, 2013.08, SPring-8を利用したX線CTを用いれば、結晶粒界にある粒子が鮮明に3D観察できることに着目した。このような粒子は、金属が変形し、破壊していく過程でも常に結晶粒界に位置する為、結晶粒界の粒子の情報を使えば、個々の結晶の形を4Dで求めることができると発想した。2011年度には、この手法を実用的な構造材料に適用できるレベルにまで高精度化することに成功した。この手法により、多結晶材料中のすべての結晶粒の形状の変化を時間を遡りながら4Dで観察することができるようになった。この成果は、金属材料工学では最も権威のある英文誌であるアクタ・マテリアリア誌に掲載が決定された。. |
| 344. | H. Toda, K. Tsubone, K. Shimizu, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Nakazawa, Y. Aokic, M. Kobayashi, Compression and recovery micro-mechanisms in flexible graphite, Carbon, 59, 184-191, 2013.08. |
| 345. | C. Schlacher, C. B?al, C. Sommitsch, H. Toda, P. Mayr, Study of creep damage in creep exposed martensitic high chromium steel weldments, Advances in Materials Technology for Fossil Power Plants - Proceedings from the 7th International Conference , 914-923, 2013.10. |
| 346. | H. Toda, T. Inamori, K. Horikawa, K. Uesugi, A.Takeuchi, Y. Suzuki, M. Kobayashi, Effects of hydrogen micro pores on mechanical properties in A2024 Aluminum alloys, Materials Transactions, 54, 12, 2195-2201, 2013.12. |
| 347. | M. Kobayashi, H. Toda, A. Takijiri, A. Takeuchi, Y. Suzuki, K. Uesugi, W-concentration 3D mapping in SKH51 steel by dual-energy K-absorption edge subtraction imaging, ISIJ International, 10.2355/isijinternational.54.141, 54, 1, 141-147, 2014.01, Three-dimensional W-concentration mapping is attempted in a high speed tool steel, SKH51 by applying K-absorption edge subtraction imaging utilizing high energy X-ray in synchrotron radiation facility. Effect of a sample-to-detector distance on spatial resolution had already been reported in high-energy X-ray microtomography. Therefore, effect of the sample-to-detector distance on W-concentration obtained by the Kabsorption edge subtraction imaging has been assessed in this study. A fine CT image was obtained in 65 mm sample-to-detector distance with the influence of both scattering and diffraction on spatial resolution. Although image quality depended on sample-to-detector distance, the distance did not affect Wconcentration measured by the absorption edge subtraction imaging so much, because the effect is limited on object interface. The average W-concentration in whole specimen was consistent with the chemical composition in the SKH51 steel. The maximum W-concentration also agreed with the SEM-EDS result. It was not easy to assess W-concentration on a carbide particle by means of segmentation based on a linear absorption coefficient. The average W-concentration at an aggregated particle, which looks a large coarse particle in CT image, corresponded to the average W-concentration that was estimated based on SEM-EDS. Therefore, it was concluded that W-concentration obtained by K-absorption edge subtraction imaging was accurate. Three-dimensional W-concentration mapping was available in steels by dual-energy K-absorption edge subtraction imaging utilizing high energy X-ray.. |
| 348. | K. Shimizu, H. Toda, K. Sasaki, K. Uesugi, A. Takeuchi, Optimization of hydrogen embrittlement in Al-Zn-Mg alloys, Proceedings of Materials Science & Technology 2015, 1583-1587, 2015.10. |
| 349. | M. Kobayashi, T. Matsuyama, A. Kouno, H. Toda, H. Miura, Construction of finite element meshes for polycrystal grains model from X-ray CT image, MATERIALS TRANSACTIONS, doi.org/10.2320/matertrans.M2016260, 57, 12, 2089-2096, 2016.12. |
| 350. | M. Kobayashi, T. Matsuyama, A. Kouno, H. Toda, H. Miura, Construction of finite element meshes for polycrystal grains model from X-ray CT image, Materials Transactions, 10.2320/matertrans.M2016260, 57, 12, 2089-2096, 2016.01, A method to build an image-based model from a high-resolution X-ray CT image has been proposed for crystal plasticity finite element (CPFE) analysis in this study. The grain microstructures of aluminum alloy were captured by X-ray CT in synchrotron radiation facility, SPring-8. An image-based model of crystallographic grains was reproduced by the proposed method, and the model was analyzed by CPFE. By this, it was represented that deformation analysis of a polycrystal microstructure considering actual grain shapes was available suggesting that the deformation mechanism would be made clear by the image-based CPFE with further work.. |
| 351. | C. Gupta, H. Toda, P. Mayr, C. Sommitsch, Cavitation studies in materials New insights from modern techniques in 2D/3D/4D characterisation, Materials Science and Technology, 10.1179/0267083614Z.000000000853, 31, 5, 513-515, 2015.03. |
| 352. | H. Li, H. Toda, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Application of Diffraction-Amalgamated Grain Boundary Tracking to Fatigue crack propagation behavior in high strength aluminum alloy, Materials Transactions, 10.2320/matertrans.M2014340, 56, 3, 424-428, 2015.01, Fatigue crack propagation behavior in a 7075-type Al alloy (Al-5.6%Zn-2.5%Mg-1.6%Cu) was investigated by applying Diffraction-Amalgamated Grain Boundary Tracking (DAGT), which provides grain morphologies and crystallographic orientations in three dimensions (3D). 3D crack morphologies at different propagation stages in the bulk of the sample were successfully obtained using synchrotron radiation X-ray microtomography (SRCT) technique. The apparent crack growth rate, da/dN, which varies significantly along a crack front line, was calculated. There are rapid acceleration and deceleration regions of da/dN due to the interaction with grain boundary (GB) and crack closure segments. Typical crack morphology under the influence of Mode II (in-plane shear) and Mode III (out-of-plane shear), such as crack deflection and twist, is detected by the observation of 2D tomographic slice image. A detailed direct assessment of microstructure-crack interaction behaviors has been achieved by applying the DAGT technique.. |
| 353. | H. Toda, P. C. Qu, S. Ito, K. Shimizu, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Formation behaviour of blister in cast aluminium alloy, International Journal of Cast Metals Research, 10.1179/1743133614Y.0000000123, 27, 6, 369-377, 2014.12, The formation behaviour of a blister in a die cast aluminium alloy was observed by employing a combined methodology of in situ three-dimensional observation using X-ray microtomography and image based simulation. It has been revealed, via a reverse approach based on the simulation, that nitrogen and carbon dioxide gases fill the blister nucleus. Spontaneous growth of the blister nucleus occurs through creep deformation of the surrounding aluminium due to the blister nucleus’ high internal gas pressure. This internal gas pressure also induces hydrogen precipitation in the form of micropores, which undergo steady growth in a spherical shell region around the blister nucleus. The selective growth of the micropores is attributable to the elevation of hydrostatic stress in directions parallel to the casting surface, thereby promoting the expansion of the blister, also parallel to the casting surface, through the absorption of surrounding micropores into the blister nucleus.. |
| 354. | H. Toda, H. Oogo, K. Horikawa, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Nakazawa, Y. Aoki, M. Kobayashi, The true origin of ductile fracture in aluminum alloys, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 10.1007/s11661-013-2013-3, 45, 2, 765-776, 2014.02, It has generally been assumed that metals usually fail as a result of microvoid nucleation induced by particle fracture. Here, we concentrate on high-density micropores filled with hydrogen in aluminum, existence of which has been largely overlooked until quite recently. These micropores exhibit premature growth under external loading, thereby inducing ductile fracture, whereas the particle fracture mechanism operates only incidentally. Conclusive evidence of a micropore mechanism is provided by the observation of an instantaneous release of gas at failure. We can therefore conclude that the growth of micropores dominates ductile fracture. Since the material we used has a standard pore density, we can assume that an identical fracture mechanism operates in other aluminum alloys. This finding suggests that intense heat treatment, which is generally believed to enhance the mechanical properties through homogenization, may have entirely the opposite effect. This revelation will have a major impact on the engineering design of metals.. |
| 355. | Effect of Phosphorus Content on Mechanical Properties in Al-7%Si Alloy. |
| 356. | Fundamental Assessments of Application of Fluidized Bed Furnaces to Solution and Aging Treatments in Al-Mg-Si Castings. |
| 357. | K. Shimizu, Y. Sakaguchi, K. Sakai, H. Toda, K. Uesugi, A. Takeuchi, M. Kobayashi, 3D/4D fracture mechanics evaluation on shear band of aluminum alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.63.188, 63, 5, 188-195, 2013.07, The localizations of plastic deformation in shear band which initiated at the ahead of crack tip of 7075 aluminum alloys have been investigated via in-situ fracture tests using synchrotron X-ray tomography. Local crack driving forces and local strain distributions were measured from tomographic images. The distributions of crack-tip opening displacement along a crack front line were found to vary randomly across specimen thickness. This was attributed to the interaction of stress shielding/anti-shielding effects. The strain distributions around crack-tip were quite different from the understanding which was derived by the elastic-plastic fracture mechanics. With further loadings, the development of equivalent strains in shear bands increased leading to the localizations of plastic deformation. The widths of shear band were observed to decrease at the same time. The degree of localization was affected not only by well-known factors such as aging conditions but also polycrystalline texture and crystallographic orientation. Beyond more than ten times as large strain region which is defined by the fracture mechanics, particles were damaged with developing shear band. Thus, extensive damage within shear bands has been induced the complex behavior of crack propagation in practical materials.. |
| 358. | A. Hosokawa, D. S. Wilkinson, J. Kang, M. Kobayashi, H. Toda, Void growth and coalescence in model materials investigated by high-resolution X-ray microtomography Influence of work hardening behavior on ductility, International Journal of Fracture, 10.1007/s10704-013-9820-9, 181, 1, 51-66, 2013.05, The influences of work hardening behavior of materials on ductile fracture, and especially on void growth and coalescence, have been investigated in model materials by in-situ X-ray computed tomography (XCT) coupled with tensile deformation. The model materials contain an artificial void array embedded in a metal matrix. By producing such materials with different metal matrices (pure copper, brass, Glidcop = copper strengthened by Al2O3 nanoparticles), the influences of the work hardening behaviors on void growth and coalescence/linkage process are analyzed. This set of experiments were performed at Japanese synchrotron radiation facility SPring-8 BL20XU beamline, whereby the X-ray tomography setup with one of the highest spatial resolution in the world is available. This beamline however provides less brilliant X-rays compared to the ESRF ID15 beamline where the our previous experiments were performed Hosokava et al. (Acta Mater, 60:2829-2839, 2012), (Acta Mater, 61:1021-1036, 2013). To compensate for the X-ray absorption problems, the specimens to be tested have to be much smaller, making the experiments more difficult. Nevertheless, the growth and linkage behaviors of the artificial voids were successfully visualized, and the plastic strain whereby the linkage takes place (referred to as the linkage strain, hereafter) were quantitatively captured. The models for void coalescence developed by Thomason and by Pardoen and Hutchinson both predict coalescence rather well for both brass and Glidcop, even though the linkage events were found to be dominated by the meso/macro shear localization process.. |
| 359. | H. Toda, Takaaki Inamori, K. Horikawa, K. Uesugi, A. Takeuchi, Y. Suzuki, M. Kobayashi, Effects of hydrogen micro pores on mechanical properties in a2024 aluminum alloys, Materials Transactions, 10.2320/matertrans.L-M2013832, 54, 12, 2195-2201, 2013.01, It has been reported that most aluminum alloys contain high-density micro pores which make an appreciable contribution to damage evolution during ductile fracture. It is reasonable to assume that the mechanical properties of aluminum alloys are more or less improved by controlling micro pores in aluminum alloys. In the present study the volume fraction of micro pores is controlled by controlling hydrogen content over a wide range. Tensile tests are performed using smooth and notched specimens at room and elevated temperatures together with a fracture toughness test. It has been shown that both strength and ductility increase with decreasing micro pore volume fraction. The elimination of micro pores has pronounced effects especially on high-temperature ductility notched tensile strength and fracture toughness. It has been observed in the in-situ observation of a room temperature tensile test that pre-existing hydrogen micro pores exhibit premature growth immediately after the onset of plastic deformation whereas the well-known particle fracture mechanism operates only after the maximum load in the alloys with the least micro pores fraction. It can be inferred that in the notched and pre-cracked specimens the premature growth of micro pores are driven by triaxial stress state thereby inducing more degradation in mechanical properties.. |
| 360. | T. Sezume, H. Toda, M. Kobayashi, T. Fukunaga, Improvement of thermo-mechanical fatigue properties in age-hardened aluminum alloys by controlling preferred orientation of precipitates, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.61.402, 61, 8, 402-403, 2011.10. |
| 361. | M. Nakazawa, M. Kobayashi, H. Toda, Y. Aoki, High-precision analysis of internal deformation/fracture characteristics of a material by using submicron 3D CT images, IEEJ Transactions on Industry Applications, 10.1541/ieejias.131.548, 131, 4, 548-556+17, 2011.09, In material engineering, it is widely recognized that deformation and fracture (D/F) characteristics are important because the safety of developed materials can be determined on the basis of D/F characteristics. The D/F characteristic is defined as the load required to break the material and the strain caused by applying a particular load. To observe the effect of grain boundary slip at the micron level, we have proposed a method of obtaining displacement vectors of internal structures from submicron 3D CT images. In this paper, we introduce an improved method for accurately acquiring D/F characteristics. The results of a simulation and a real test confirm the effectiveness of the improved method.. |
| 362. | H. Oogo, H. Toda, K. Uesugi, Y. Suzuki, M. Kobayashi, Growth behavior of hydrogen micro pores during ductile fracture of a 5154 aluminum alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.60.409, 60, 8, 409-410, 2010.11. |
| 363. | K. Sakamoto, S. Ishimitsu, T. Oda, Y. Sugiyama, H. Toda, Analysis of the relationship between material structures and auditoryimpressions, ICIC Express Letters, 4, 3, 691-696, 2010.06, There have been no significant investigations into the effects ofinsulators on auditory impressions. Consequently, in our previous study wecarried, out research on economical and, ecological insulators with layers ofaluminum, waste material and, gray cast iron and established the effects oflayered construction on auditory impressions. In this study, we carried, outfurther research on other economical and, accessible materials that have bettercharacteristics than those previously investigated, and determined theirmaterial characteristics for auditory impressions. We determined the dampingcharacteristics of the insulators using the integrals of their power spectrumsin the vicinity of the power spectrum, peaks. Furthermore, we established, thatthe envelope curve for the impulse response of the insulators had differentmaterial characteristics and conveyed different auditory impressions. ICIC International. |
| 364. | H. Toda, M. Kobayashi, T. Niihara, T. Yamada, Y. Ooba, M. Kakizaki, Thermo-mechanical fatigue property of a surface-hardened AC4B cast aluminum alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.60.190, 60, 4, 190-191, 2010.04. |
| 365. | H. Toda, M. Motoe, K. Kadoumi, Y. Nakayama, M. Kobayashi, T. Kobayashi, Effects of up-quenching on age-hardening behaviors in Al-Mg-Si alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.59.569, 59, 10, 569-575, 2009.10, Inspired by a success in applying a fluidized bed furnace to high-temperature solution treatments, the present authors have attempted to modify the age-hardening characteristics of Al-Mg-Si alloys by utilizing its superior heating rate. Two-step ageing treatments have been applied to five kinds of alloys with different Mg 2Si and excess Si contents. Heating rates for the first and the second ageing treatments have been varied as well as ageing temperature for the first ageing treatment. It has been clarified that the rapid heating to the first ageing temperature enhances strength compared to the standard T6-temper for all the alloys tested, especially for a balanced alloy with a low Mg 2Si content. It has been confirmed that small precipitates are formed in high density in such cases. In most cases, the improvements in hardness have been observed by adding the ageing treatment at 353 or 373 K for only 0.8 ks before the ordinary ageing at 450 K. We attribute this to the suppression of unfavorable clusters which ordinarily form below those temperatures during heating.. |
| 366. | H. Toda, M. Kobayashi, Thermal fatique fracture of materials, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.59.312, 59, 6, 312-319, 2009.06. |
| 367. | M. Kobayashi, H. Toda, K. Minami, T. Mori, K. Uesugi, A. Takeuchi, Y. Suzuki, Three-dimensional observation of micro-pores in a 2024 aluminum alloy by synchrotron X-ray projection- And imaging-type microtomography techniques, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.59.30, 59, 1, 30-34, 2009.01, Synchrotron X-ray microtomography has been utilized for the ex-situ observation of micro-pore growth/annihilation behaviors of a 2024 aluminum alloy at a high temperature. High-resolution experimental configurations have enabled the 3D reconstruction of micro-pore and intermetallic compound particle images with isotropic voxels with 0.088-0.474 μm edges. The variations in micro-pore shape, size and spatial distribution at the high temperature are readily observed, with the tomographic volumes then being provided for the quantitative image analysis of such quantities. It has been clarified that micro-pores, that appear to be nucleated heterogeneously on particles, exhibit the Ostwald growth behavior during the high temperature exposure. Three-dimensional finite element meshes have been generated to monitor distributions of local stress and strain in real materials with such micro-pores. Since micro-pores tend to lie along (former) grain boundary, there seems to be some anisotropic effect on the strain redistribution due to the existence of micro-pores. Since local strain elevation is predicted by 50-200% in the vicinity of micro-pores aligned along grain boundary, it can be inferred that ductile fracture would be promoted considerable by the growth of pre-existing micro-pores.. |
| 368. | M. Nakazawa, Y. Aoki, H. Toda, M. Kobayashi, 3D image analysis for evaluating internal deformation/fracture characteristics of materials, Electronics and Communications in Japan, Part II: Electronics (English translation of Denshi Tsushin Gakkai Ronbunshi), 10.1002/ecj.1005, 91, 12, 16-23, 2008.12, In the past, all methods which understand deformation/fracture (D/F) characteristics have been limited on the surface indirectly. D/F characteristics are impacted by nano-scale structural features like air bubbles (pores); therefore, they need to be analyzed including inside. In this paper, we propose a system which automatically obtains the corresponding relations between pre- and post-D/F pores. Our system enabled analyzing three-dimensional, local, high-accuracy D/F characteristics.. |
| 369. | M. Kobayashi, K. Fujitaki, H. Toda, T. Yasui, M. Fukumoto, M. Tsubaki, Production of dissimilar metal composite by friction stir processing, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.58.524, 58, 10, 524-525, 2008.10. |
| 370. | H. Toda, T. Fukunaga, M. Kobayashi, K. Uesugi, T. Kobayashi, T. Yamada, Y. Ooba, M. Kakizaki, Thermo-mechanical fatigue property of a surface-hardened AC4CH cast aluminum alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.58.236, 58, 6, 236-241, 2008.06, The thermo-mechanical fatigue life and microstructural change under a compression-tension thermo-mechanical cyclic loading of a surface-hardened Al-Si-Mg alloy casting are investigated. A surface cold working technique using steel balls is utilized for the surface hardening. Out-of-phase type thermo-mechanical fatigue tests have been performed with the temperature range of 323-523K and the applied mechanical strain range of 0.75-2.0%. The surface-hardened material exhibits better thermo-mechanical fatigue property especially in a low cycle regime, together with higher generated stress, suggesting that it is even superior under stress-controlled loading. The differences in the stress-strain hysteresis loops and hardness variation near specimen surface between the materials with and without surface hardening have not vanished until final fracture. The observed difference in the thermo-mechanical property is attributed to some microstructural differences. The effects of damaging at the silicon particles to this difference are also investigated using the high-resolution microtomography technique. It has been clarified by microstructural observations that recovery and recrystallization are suppressed in the surface-hardened material. It can be inferred that such thermal stability is attributed to the multi-axial deformation by a combination of the surface hardening and the thermo-mechanical loading.. |
| 371. | T. Hidaka, H. Toda, M. Kobayashi, K. Uesugi, T. Kobayashi, Three-dimensional observation of ductile fracture process by deflection contrast imaging in cast Al-7%Si alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.58.58, 58, 2, 58-64, 2008.02, Synchrotron X-ray microtomography has been utilized for the in-situ observation of ductile fracture in cast Al-7%Si alloys exposed at a high temperature for 0-106 s. A high resolution experimental configuration and deflection contrast imaging technique have enabled the reconstruction of silicon particle images with an isotropic voxel with a 0.474 μm edge. The variations in particle shape, size and spatial distribution at the high temperature are readily observed, along with the existence and growth of high-density micro-pores. Three-dimensional image analysis is applied and its feasibility is confirmed. It is clarified that in the case of an as-cast material void nucleation and growth have been observed as has been reported for the general ductile fracture of metallic materials. When it is exposure at the high temperature for a long time, however, ductile fracture is found to be attributable mainly to the growth of pre-existing micro-pores and not the nucleation of new voids at silicon particles. Since such tendency has been also confirmed for other materials, more detailed analysis might be expected in a near future in order to understand actual ductile fracture process in practical materials.. |
| 372. | M. Kobayashi, H. Toda, T. Ohgaki, K. Uesugi, D. S. Wilkinson, T. Kobayashi, Y. Aoki, Three-dimensional measurement of local strain distribution by tracking microstructural features in high-resolution SR-CT image, Key Engineering Materials, 345-346 II, 1153-1156, 2007.05, The local elastic and plastic strain during deformation are very complicated and different form the macroscopic strain, because most materials have inhomogeneous microstructure. In this study, local strain distribution in three dimensions has been measured using the new developed method based on image analysis in high-resolution synchrotron radiation computed tomography (SR-CT). Model and practical specimens, which made of cupper alloy and aluminum alloy, respectively, were prepared for a development procedure and application of local strain measurements. Gauging intervals of microstructural features before and after deformation gave us information of inhomogeneous local strain distribution in three dimensions. High strain was observed in a necking region appeared after tensile deformation in the model sample. A combination of non-destructive measurements by SR-CT and three-dimensional analysis revealed inhomogeneous strain distributions in practical aluminum samples.. |
| 373. | M. Nakai, M. Niinomi, T. Akahori, N. Ohtsu, H. Nishimura, H. Toda, H. Fukui, M. Ogawa, Effects of alloying elements on hard ceramic layer formation on surfaces of biomedical Ti-29Nb-13Ta-4.6Zr and Ti-6Al-4V ELI during gas nitriding, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.71.415, 71, 4, 415-422, 2007.04, Formation of the reaction product layer on the surface of biomedical titanium alloys, Ti-29Nb-13Ta-4.6Zr (TNTZ) and Ti6A1-4V ELI (Ti64), during gas nitriding was investigated. These alloys were exposed to nitrogen atmosphere at 1023, 1073, 1123 and 1223 K. After the gas nitriding, a reaction product layer was observed on the surface of both alloys, and was analyzed using an X-ray diffraction (XRD), Auger electron spectroscopy (AES) and X-ray Photoelectron spectroscopy (XPS). The layer was comprised of two phases, which were outer oxide layer (mainly Ti02) and inner nitride layer (mainly TiN or Ti 2N). In these layers, the thickness of the oxide layer particularly depended on the kinds of alloys. According to the thermodynamics and point defect theory, the growth rate of oxide layer is expected to be increased by the presence of Al in TiO2. Namely, the dissolution of Al into TiO 2 may increase the number of oxygen vacancies, resulting in acceleration of oxygen diffusion inward. On the other hand, the elements that accelerate the growth of the oxide layer are not contained in TNTZ. Thus, the oxide layer formed on Ti64 was thicker than that of TNTZ. In a similar way, the elements that accelerate the growth of the nitride layer are not contained in both TNTZ and Ti64. Thus, the nitride layers with similar thicknesses may be formed on TNTZ and Ti64 during gas nitriding.. |
| 374. | H. Toda, T. Kobayashi, M. Kobayashi, J. Sawamura, M. Oyake, Microstructural evolution in heavily deformed in-situ composites produced from cutting-chip mixtures of dissimilar metals, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.71.368, 71, 3, 368-377, 2007.03, The present authors have proposed in-situ composites in which cold working was applied to the cutting chip mixture of dissimilar materials. The composites have exhibited superior strength together with ultra-fine grain structure. In this study, such composite materials are produced by combining 6061 aluminum alloy and IF steel chips. Microstructural evolution processes are visualized by means of the microtomography as well as the TEM observation. It has been clarified that ultra-fine grains with a large fraction of high angle boundaries are obtained due to the effects of severe plastic deformation during cutting. Grain size of the matrix aluminum alloy is reduced to about 220 nm by applying swaging strain of only 1.9. It should be noted that the significant strain hardening of the chips occurs during initial deformation stage where strain applied by swaging seems to be consumed mostly for consolidation. The chips gradually change their orientation in the material at this stage. It can be inferred that the rapid development of ultra-fine structure in the matrix is also attributed to gradual change in deformation axis thereby realizing effective multi-axial deformation. Overall, the utilization of chips is identified as a highly effective way of grain refining compared to the other uni- and multi-axial deformation processes.. |
| 375. | M. Kobayashi, H. Toda, Y. Kawai, T. Kobayashi, K. Uesugi, D. S. Wilkinson, E. Maire, Y. Aoki, Measurement of 3-D strain distribution by means of high-resolution X-ray CT image and tracking of microstructural features, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.71.181, 71, 2, 181-186, 2007.02, Measurement of interior strain distribution has been developed based on the synchrotron radiation computed tomography (SR-CT). In metal deformation, local strain distribution differs from macroscopic strain due to microstructural factors such as grains, grain boundaries, particles, pores, voids, and cracks. A model sample, which was made from a copper alloy strengthened with alumina, was prepared containing artificial pores. Tensile loading was applied to the sample step by step. High-resolution tomographic experiment was performed at the third-generation synchrotron radiation facility (SPring-8) in Japan. Gravity center position, volume and surface area in the pores, which were regarded as markers in a tracking procedure, were measured by 3-D digital image analysis in the SR-CT images. The markers before and after the deformation were provided for registration and macroscopic strain correction before the tracking procedure. The marker tracking was carried out by means of matching parameter that was described as functions of distance, volume and surface at markers. The ratio of success tracking was evaluated in order to clarify whether the tracking method developed in this study was reliable. The 3-D strain distribution was represented successfully by the tracking results. A combination of high-resolution SR-CT and tracking of microstructural features is effective to visualize interior strain distribution in materials in 3-D.. |
| 376. | M. Nakazawa, Y. Aoki, H. Toda, M. Kobayashi, 3D image analysis for evaluating internal deformation / Fracture characteristics of materials, IEEJ Transactions on Electronics, Information and Systems, 127, 6, 824-830+2, 2007.01, In the past, all methods which understand deformation / fracture (D/F) characteristics have been limited on the surface indirectly. D/F characteristics are impacted by nano-scale structural features like air bubbles (pores); therefore, they need to be analyzed including inside. In this paper, we propose a system which automatically obtains the corresponding relations between pre- and post-D/F pores. Our system enabled analyzing three dimensional, local, high-accuracy D/F characteristics.. |
| 377. | N. Sakaguchi, M. Niinomi, T. Akahori, H. Toda, Analysis of tensile deformation behaviors of Ti-XNb-10Ta-5Zr alloys for biomedical applications, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.70.572, 70, 7, 572-578, 2006.07, Ti-XNb-10Ta-5Zr alloys were fabricated based on Ti-30Nb-10Ta-5Zr alloy, which was the composition that simplified that of Ti-29Nb-13Ta-4.6Zr alloy for biomedical applications. The tensile deformation mechanisms of the Ti-25Nb-10Ta-5Zr, Ti-30Nb-10Ta-5Zr, and Ti-35Nb-10Ta-5Zr alloys were investigated using X-ray diffraction analysis under several loading conditions. Under loading conditions, the X-ray diffraction peaks of all specimens in this study shift to higher angles than those obtained under non-loading conditions. In the crystal orientation of Ti-30Nb-10Ta-5Zr alloy, in which the lattice strain has reached the maximum elastic lattice strain, plastic deformation (for example slip) is moved with elastic deformation. Therefore, the elastic modulus of this alloy appears to decrease in terms of strain over a proportional limit. Thus, the elastic deformation behavior of the Ti-30Nb-10Ta-5Zr alloy does not obey Hooke's law.. |
| 378. | T. Akahori, M. Niinomi, Y. Koyanagi, T. Kasuga, H. Toda, H. Fukui, M. Ogawa, Aging treatment and mechanical properties of Ti-29Nb-13Ta-4.6Zr alloy for biomaterial applications coated with bioactive calcium phosphate invert glass, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.70.314, 70, 4, 314-321, 2006.04, In recent years, the opportunity of the hard tissues such as bones, hip joints and tooth to be replaced by metallic biomaterials is increasing. In general, metallic biomaterials lack bioactivity, which is the ability to directly form a chemical bond with bones. Therefore, the bioactive surface modifications on surface of metallic biomaterials have been investigated and applied. Among them, the calcium phosphate invert glass coating method, which is dip-coating treatment (DCT), can be granted the bioactivity on the surface of β-type titanium alloy, Ti-29Nb-13Ta-4.6Zr (TNTZ) alloy, for biomaterial applications. In this study, aging characteristics and mechanical properties of TNTZ alloy surface-modified with DCT were investigated. There is an oxide layer and a case near boundary between calcium phosphate invert glass layer and TNTZ surface in TNTZ surface-modified with DCT (TNTZ DCT). A very fine ω phase precipitates in an equiaxed β phase with an average diameter of 20 μm at a distance of 200 μm from specimen surface. On the other hand, the microstructure of aged TNTZ DCT has an α phase. The tensile strength of TNTZ DCT is around 30% greater than that of as-solutionized TNTZ (TNTZ ST). On the other hand, the elongation is around 48% smaller than that of TNTZ ST. Tensile strength of aged TNTZ DCT is around 26% greater than that of TNTZ DCT. While the elongation of aged TNTZ DCT is around 52% smaller than that of TNTZ DCT. Fatigue limit of TNTZ DCT is nearly equal to that of TNTZ ST. Fatigue limit of aged TNTZ DCT is around 80 MPa greater than that of TNTZ ST. Fatigue limits of TNTZ DCT and aged TNTZ DCT, where their fatigue specimen surfaces are mirror-polished, rise as compared with those of TNTZ DCT and aged TNTZ DCT, where their fagigue specimen surfaces are shot-blasted.. |
| 379. | M. Niinomi, T. Akahori, H. Toda, D. Iizuka, H. Fukui, M. Ogawa, Bioactive surface modification of newly developed β-type titanium alloy for biomedical applications by electrochemical treatment, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.70.304, 70, 4, 304-313, 2006.04, In order to produce a novel bioactive beta-type titanium alloy -Ti-29Nb-13Ta-4.6Zr - and pure titanium for biomedical applications, an electrochemical treatment involving anodic oxidizing and cathodic polarization was applied to the alloy in calcium nitrate solution under various conditions. For creating a hydroxyapatite (HAP) coating on the alloy, the treated alloy and pure titanium were dipped into simulated body fluid (SBF) and then into 1.5SBF, wherein the concentration of constituents was 1.5 times that of SBF. The characterization and morphology of HAP formed on the alloy were examined in comparison with those of pure titanium. In Ti-29Nb-13Ta-4.6Zr, the formability of HAP in SBF after the electrochemical treatment is less than that in pure titanium. The thickness of a calcium hydroxide layer formed by the cathodic polarization can be controlled by the cathodic potential. In both pure titanium and Ti-29Nb-13Ta-4.6Zr, the formability of HAP increases up to a certain increase in the thickness of the oxide layer formed by the anodic oxidizing. Therefore, the formability of HAP decreases due to a reduction in the formability of the calcium hydroxide layer. The number of hydroxyl groups on the surface of Ti-29Nb-13Ta-4.6Zr is less than that in pure titanium after the anodic oxidizing. The tensile bonding strength of HAP in Ti-29Nb-13Ta-4.6Zr is similar to that in pure titanium.. |
| 380. | T. Akahori, M. Niinomi, A. Noda, H. Toda, H. Hukui, M. Ogawa, Effect of aging treatment on mechanical properties of Ti-29Nb-13Ta-4.6Zr alloy for biomedical applications, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.70.295, 70, 4, 295-303, 2006.04, The relationships between mechanical properties and microstructure of Ti-29Nb-13Ta-4.6Zr in under aged, peak aged and over aged conditions at various aging temperatures were investigated. The maximum Vickers hardness values of Ti-29Nb-13Ta-4.6Zr aged at 573 K, 673 K and 723 K are obtained at aging times of around 2419.2 ks, 3024 ks and 1209.6 ks, respectively. ω phase precipitates in β phase of Ti-29Nb-13Ta-4.6Zr at relatively low aging temperature, 573 K, while a phase precipitates in β phase of Ti-29Nb-13Ta-4.6Zr at relatively higher aging temperature, 723 K. At an aging temperature of 673 K that lies between aging temperatures of 573 K and 723 K, ω phase precipitates at the early stage of aging, but a phase precipitates at relatively longer aging time. The precipitation site of a phase changes from intragrain to grain boundary at around peak aging time when Ti-29Nb-13Ta-4.6Zr is aged at 673 K and 723 K. The tensile strength of Ti-29Nb-13Ta-4.6Zr aged at 573 K, 673 K and 723 K increases up to a peak aging time with increasing aging time, but under over aging conditions, the tensile strength decreases. While the elongation decreases with increasing aging time at every aging temperature. The fatigue strength of Ti-29Nb-13Ta-4.6Zr increases greater when α phase precipitates than when ω phase precipitates. The fatigue strength of Ti-29Nb-13Ta-4.6Zr decreases a little due to the coarsening of α phase precipitated in β grain.. |
| 381. | J. H. Kim, M. Niinomi, T. Akahori, H. Toda, Fatigue crack initiation and propagation behaviors of bovine compact bones, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.70.350, 70, 4, 350-358, 2006.04, An understanding of how fatigue cracks propagate in the bone is important because fatigue is thought to be the main cause of clinical stress fractures. In this study, fatigue crack initiation and propagation behaviors of bovine humerus and femur were investigated with respect to their microstructures. The initiation and propagation of fatigue cracks were observed in a specimen surface by using the replica method. Fatigue tests were also conducted on the bovine humeral and femoral compact bones in order to obtain S-N curves. Based on their microstructures, the bovine humeral and femoral compact bones are classified into the haversian and plexiform bones. In haversian bone, when the microstructure is inclined toward the bone axis, the fatigue crack initiates at the osteon-ossein interface and osteon lamellae interface. In case the microstructure is parallel to the bone axis, the fatigue cracks initiate at the haversian canals, Volkmann's canals, osteon-lamellae interface, and osteon-ossein interface. Among these, the fatigue crack that initiates at the Volkmann's canal may receive a relatively greater maximum shear stress; therefore, it has a tendency to be the main propagating fatigue crack that connects the fatigue cracks initiated at the other above mentioned sites. In the plexiform bone, when the microstructure is inclined toward the bone axis, fatigue crack initiates at the interface of the lamellae. When the microstructure is parallel to the bone axis, fatigue cracks initiate at the blood vessel and interface of the lamellae. The fatigue crack that initiates at the blood vessel may receive a relatively greater maximum shear stress; therefore, it has a tendency to be the main propagating fatigue crack that connects the fatigue crack initiated at the other site. In the haversian and plexiform bones, the crack propagation rate when the microstructure is inclined toward the bone axis is greater than that when the micro-structure is parallel to the bone axis.. |
| 382. | T. Mukaiyama, M. Niinomi, H. Toda, T. Akahori, T. Kobayashi, I. Yamamoto, Effect of loading rate on absorbed energy and fracture surface area in wrought aluminum alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.56.15, 56, 1, 15-20, 2006.01, The effect of loading rate on absorbed energy and fracture surface area of three types of wrought aluminum alloys, namely high toughness 5083-O and 6061-T651 alloys and low toughness 7075-T6 alloy are studied. A laser displacement measuring equipment and a scanning laser microscope are used in order to measure three-dimensional geometry of the fracture surface. Shear lip and plastic hinge can be observed in 5083-O and 6061-T651 aluminum alloys. According to a measuring region, the calibration factor K is notably different. Moreover, the calibrated fracture surface area of each fracture geometry changes considerably with increasing loading rate. On the other hand, in 7075-T6 aluminum alloy, macroscopic fracture geometries are not clearly defined, and almost no difference appears in the calibration factor K within the same fracture surface. Moreover, calibrated whole surface area increases linearly with increasing loading rate. In any aluminum alloys, the tends in the loading rate change of calibrated whole fracture surface area, A W, and the total absorbed energy, E t, with loading rate are similar each other. Therefore, the change of fracture surface area is one of the main factors that affect the change of absorbed energy.. |
| 383. | N. Sakaguchi, M. Niinomi, T. Akahori, H. Toda, Tensile deformation behavior of Ti-30Nb-10Ta-XZr alloys for biomedical applications, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.70.89, 70, 1, 89-95, 2006.01, Ti-30Nb-10Ta-XZr alloys were fabricated based on Ti-30Nb-10Ta-5Zr alloy, which was the composition simplified that of Ti-29Nb-13Ta-4.6Zr alloy for biomedical applications. The tensile deformation mechanisms of Ti-30Nb-10Ta-XZr alloys (X: 0, 3, 5, 7 and 10%) were then investigated. The plastic deformation mechanisms of Ti-30Nb-10Ta-XZr alloys during tensile loading change with changing Zr content. Microstructure of Ti-30Nb-10Ta alloy without Zr after tensile test shows a stress-induced transformation of β phase. In Ti-30Nb-10Ta alloy, the plastic deformation mechanism is mainly dominated by the stress-induced transformation of β phase. Microstructure of Ti-30Nb-10Ta-3Zr alloy after tensile test shows a stress-induced transformation of β phase and many dislocations in β phase. In Ti-30Nb-10Ta-3Zr alloy, the plastic deformation mechanism is mainly dominated by the stress-induced transformation of β phase and slip. Microstructures of Ti-30Nb-10Ta-XZr alloys (X: 5, 7 or 10%) after tensile test show many dislocations in β phase. In these alloys, the plastic deformation mechanisms are mainly dominated by slip. The elastic deformations of Ti-30Nb-10Ta-XZr alloys (X: 3, 5 or 7%) do not depend on Hooke's law. The maximum recovery strains of these alloys increase with increasing the total strain.. |
| 384. | Contact pressure and fretting fatigue characteristics of highly workable titanium alloy with equiaxed α and Widmanstätten α structure. |
| 385. | Microstructure and fretting fatigue characteristics of highly workable titanium alloy with equiaxed α and Widmanstärten α structure. |
| 386. | T. Akahori, M. Niinomi, M. Otani, H. Toda, H. Fukui, M. Ogawa, Notch fatigue properties of a Ti-29Nb-13Ta-4.6Zr alloy for biomedical applications, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.55.575, 55, 11, 575-581, 2005.11, The effects of microstructures on notch fatigue propertes of a Ti-29Nb-13Ta-4.6Zr alloy (TNTZ) subjected to various thermo-mechanical treatments were investigated in this study. The notch fatigue strengths of TNTZ subjected to aging at 673 K and 723 K after solution treatment or cold rolling at stress concentration factors of 1 (without the notch), 2 and 6 in both low and high cycle fatigue life regions are greater than those of as-cold rolled and as-solutionized TNTZ, and TNTZ subjected to aging at 598 K after solution treatment or cold rolling. A single fatigue crack initiates on a specimen surface and at the tip of the notch at stress concentration factors of 1 and 2. While, a few cracks initiate the tip of the notch having a stress concentration factor of 6. Notch sensitivity factor of TNTZ is almost equal to or smaller than those of other materials such as Ti-6Al-4V, CP-Ti, S35C, S45C and SUS304. It is considered that the notch sensitivity factor decreases with decreasing the width of lath like α phase and its volume fraction.. |
| 387. | T. Akahori, M. Niinomi, H. Toda, K. Yamauchi, H. Fukui, M. Ogawa, Mechanical properties and deformation behavior of β-type titanium alloy (TNTZ) drawn wires, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.69.530, 69, 7, 530-537, 2005.07, Tensile and fatigue properties are important mechanical properties in drawn wires for biomedical and dental applications because of the credibility against the monotonic loading fracture or fatigue failure. The mechanical properties and deformation behavior of drawn wires of Ti-29Nb-13Ta-4.6Zr with diameters of 1.0 mm and 0.3 mm (designated as TNTZ d1.0 and TNTZ d0.3) were investigated to know a potential for biomedical and dental applications in this paper. The microstructure of forged Ti-29Nb-13Ta-4.6Zr subjected to a solution treatment at 1063 K (TNTZ ST) comprises a single β phase with an average diameter of 25 μm. While that of TNTZ d1.0 comprises a needle-like single β phase elongated parallel to the drawing direction. Tensile strengths of TNTZ d1.0 and TNTZ d0.3 are approximately 740 MPa and 800 MPa, respectively. While both elongations are nearly equal to each other (approximately 5.0%). The elastic modulus of TNTZ d1.0 is approximately 50 GPa and that slightly smaller than approximately 55 GPa of TNTZ d0.3. The notch-fatigue limit of TNTZ d1.0 is 250 MPa. TNTZ ST exhibits the maximum elastic strain of approximately 1.4%. And the stress-strain curve shows a single gradient during elastic deformation region. The stress-strain curves of TNTZ d1.0 and TNTZ d0.3 in the elastic deformation region show two gradients, and the values of the maximum elastic strains in both wires are approximately 2.9% and 2.8%, respectively.. |
| 388. | T. Murakami, H. Toda, T. Akahori, M. Niinomi, T. Kobayashi, Assessment of fracture toughness by CT and round bar specimens in a HT780 steel, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane1955.91.4_415, 91, 4, 415-420, 2005.04, It is known that fracture toughness value of steels is affected by test temperature, specimen thickness and loading rate. In this research, it is attempted to investigate it by changing temperature and loading rate with the rate parameter then being applied. The fracture toughness value is also obtained by round bar specimen with a circular notch. This result has been compared with the results by the CT specimens, and the validity of the fracture toughness value that has been obtained from round bar specimen with a circular notch is examined. The sample material used is HT780 steel. The CT specimens were IT, 2T and 4T-CT defined in ASTM E399, test temperature is varied from 77K to room temperature. The loading rate is also varied for the 1T-CT and the round bar specimen with a circular notch from static to 1 m/s. The fracture toughness value decreases as the test temperature decreases. It decreases with loading rate and specimen thickness. The fracture toughness test result is arranged using the stress intensity factor rate to obtain the rate parameter. Moreover, the fracture toughness value which has been obtained from the round bar specimen with a circular notch is lower than those by 1T-CT specimen, closer to 2T-CT specimen. The test temperature and the loading rate dependency of the fracture toughness value can be arranged by the rate parameter that is the function of temperature and stress intensity factor rate. Availability of the round bar specimen with a circular notch test specimen is discussed to obtain valid fracture toughness values.. |
| 389. | Y. Irinouchi, H. Toda, T. Sakai, T. Kobayashi, L. Wang, Improvement of mechanical properties by high temperature solution treatment in an AC4CH aluminum cast alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.55.159, 55, 4, 159-163, 2005.04, The authors have realized that solution treatment may be possible at a higher temperature than that by the conventional atmosphere furnace if a fluidized bed furnace is utilized. In this study, solution treatment temperatures close to binary or ternary eutectic temperatures were used for a JIS AC4CH cast aluminum alloy. Mechanical properties were tested with internal microstructures such as micro-pores and intermetallic compound particles then being correlated using high resolution computed tomography. It is clarified that the solution treatment at the ternary eutectic temperature brings the improvement of strength by about 15.7% for a relatively short solution treatment time (typically about 1/10 of the conventional condition by an atmosphere furnace). On the other hand, the solution treatment at the binary eutectic temperature causes significant degradation by coalescence of micro-pores forming crack-like pores. These behaviors can be assessed by visualizing internal microstructures using the high resolution CT. Overall, the combination of the superior heating furnace with the state-of-the-art temperature control and sophisticated visualization technique may enable the improvement of mechanical properties in aluminum cast alloys.. |
| 390. | S. Nishido, L. Qian, H. Toda, T. Kobayashi, M. Niinomi, T. Akahori, Influences of spatial distribution of Si particles on crack propagation in model Al-Si cast alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.55.75, 55, 2, 75-81, 2005.02, In-situ SEM observation has been used to characterize crack propagation behaviors and microscopic damage evolution at Si particles in three model hypoeutectic Al-Si cast alloys with different eutectic microstructures. It was clarified that the extents of damage and crack propagation path are significantly affected by the microstructures. A crack propagates in an eutectic region in a gravity cast alloy with dendritic a phase. Meanwhile, in the case of a rheo-cast alloy, a crack often propagates into α phases. Generally, the observed tendencies appear to be dominated by the fundamental crack-tip shielding/anti-shielding behaviors. However, the actual crack paths can not be fully assessed only from the experimental efforts. The crack propagation simulations are therefore performed for this purpose. Similar complicated crack propagation paths are well reproduced in the simulations, thereby providing mechanistic insights for the crack deflection behaviors.. |
| 391. | T. Murakami, H. Toda, T. Kobayashi, Effects of temperature and loading rate on fracture toughness, Key Engineering Materials, 10.4028/0-87849-978-4.2397, 297-300 IV, 2397-2402, 2005.01, It is known that fracture toughness value is affected by test temperature, specimen thickness and loading rate. In the present study, specimen size and test temperature are varied widely with the obtained data then being analyzed using rate parameter. Additionally, the fracture toughness values are obtained using round bar-type specimen with a circular notch. This result is compared with the result of the CT specimens, and the advantage of using the round bar-type specimen with a circular notch to modify specimen size requirement is discussed. Sample material used is HT780 high tensile strength steel. The test specimens were 1T, 2T and 4T-CT that are described in ASTM E399. Notched round bar-type specimen with a diameter of 15mm and notch root radius of 0.25mm is also used. The test temperature is varied from a low temperature to room temperature, and loading rate is varied about the 1T-CT specimen and the notched round bar-type specimen between static and 1000mm/sec. The test temperature and the loading rate dependency of the fracture toughness values were arranged by the rate parameter. The fracture toughness value has decreased with the decrease in test temperature and with the increase in specimen thickness and loading rate. The fracture toughness value obtained from the notched round bar-type specimen indicated a value close to 2T-CT specimen. It is shown that valid fracture toughness value can be obtained with a small test specimen by the notched round bar-type specimen. The test temperature and the loading rate dependency of the fracture toughness values can be successfully arranged by the rate parameter that can express both temperature and strain rate dependencies. Feasibility of using round bar-type specimen to obtain valid fracture toughness values with less specimen mass was demonstrated.. |
| 392. | H. Toda, T. Ohgaki, K. Uesugi, K. Makii, Y. Aruga, T. Akahori, M. Niinomi, T. Kobayashi, In-situ observation of fracture of aluminium foam using synchrotron X-ray microtomography, Key Engineering Materials, 10.4028/0-87849-978-4.1189, 297-300 II, 1189-1195, 2005.01, Synchrotron X-ray microtomography has been utilized for the 3D characterisation of microstructure in the cell materials of aluminium foams. Tomographs, consisting of about 109 isotropic voxels with a maximum of l.0μm edge, were collected at the SPring-8 in Japan. A combination of high-resolution phase contrast imaging technique and several state-of-the-art application techniques has enabled the quantitative image analyses of micro-pore, intermetallic particles and grain boundary as well as the assessment of their effects on compressive deformation and fracture behaviours in two kinds of aluminium foams.. |
| 393. | T. Akahori, M. Niinomi, M. Harada, J. Takeda, H. Toda, S. Katsura, T. Takeuchi, H. Fukui, Mechanical properties and cyto-toxicity of newly designed β type Ti alloys for dental applications, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.69.96, 69, 1, 96-102, 2005.01, Ti-29Nb-13Zr-2Cr, Ti-29Nb-15Zr-1.5Fe, Ti-29Nb-10Zr-0.5Si, Ti-29Nb-10Zr-0.5Cr-0.5Fe and Ti-29Nb-18Zr-2Cr-0.5Si were newly designed for dental applications. These alloys were designed based on Ti-29Nb-13Ta-4.6Zr (TNTZ), replacing relatively high melting point element, Ta, with beta stabilizing elements such as Cr, Fe and Si, which would lower the melting point of the alloy. Their melting points, mechanical properties, and cytotoxicity were investigated in this study. The following results were obtained. Melting points of designed alloys decrease about 50 to 370 K as compared with that of TNTZ, and Ti-29Nb-13Zr-2Cr has the lowest melting point around 2050 K. Vickers hardness of the surface of each designed alloy cast into modified magnesia based investment material is in the range of 400HV to 500HV, which is lower than that of TNTZ (around 560HV). Balances of the strength and the ductility of Ti-29Nb-13Zr-2Cr, Ti-29Nb-15Zr-1.5Fe and Ti-29Nb-10Zr-0.5Cr-0.5Fe are nearly equal to those of TNTZ. Cell viability of each designed alloy is excellent.. |
| 394. | N. Sakaguchi, M. Niinomi, T. Akahori, J. Takeda, H. Toda, Effects of Ta and Zr contents on microstructure, tensile properties and elastic modulus of Ti-Nb-Ta-Zr system alloys, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet.68.1076, 68, 12, 1076-1082, 2004.12, Effect of Ta content on mechanical properties of Ti-30Nb-XTa-5Zr alloys and effect of Zr content on mechanical properties of Ti-30Nb-10Ta-XZr alloys were investigated. Ti-30Nb-10Ta-5Zr, which is the simplified compositional alloy of Ti-29Nb-13Ta-4.6Zr developed for biomedical applications, has been selected as the basic alloy composition. Tensile tests and elastic modulus measurements and microstructural observations were carried out on those alloys. Microstructures of Ti-30Nb-XTa-5Zr alloys containing Ta less than 10 mass% show the mixture of β and ω phases. Microstructures of Ti-30Nb-XTa-5Zr alloys containing 10 mass%Ta or greater than 10 mass%Ta show single β phase. The tensile strength and elongation of Ti-30Nb-XTa-5Zr alloy show a great change with changing Ta content. The threshold of Ta content for the changing exists between 5 mass% and 10 mass%Ta. The tensile properties of Ti-30Nb-10Ta-XZr alloys are affected by the change of deformation mechanism of β phase. The tensile strength of Ti-30Nb-10Ta-XZr alloys increases with increasing Zr content. The elongation of these alloys decreases with increasing Zr content. The tendency of tensile properties of Ti-30Nb-10Ta-XZr alloys is also caused by the change in deformation mechanism of β phase. From the point of view of stress-strain curves obtained by tensile tests and variation of elastic modulus with changing Zr content, Zr found to act as β stabilizer in Ti-Nb-Ta-Zr system alloy. Ti-30Nb-5Ta-5Zr, Ti-30Nb-10Ta and Ti-30Nb-10Ta-3Zr have relatively lower elastic moduli and greater elongation. Thus, these three Ti-Nb-Ta-Zr system alloys have potential to be used for biomedical applications.. |
| 395. | S. Nishido, M. Kaneso, T. Kobayashi, H. Toda, Role of Si particle damage on fatigue characteristics of cast Al-Si alloys, International Journal of Cast Metals Research, 10.1179/136404604225022702, 17, 6, 345-350, 2004.12, In the present study, initiation and evolution of damage at eutectic and primary Si particles during monotonic and cyclic loadings were investigated utilising in situ studies. Al-7%Si and Al-20%Si binary alloys were produced as model materials. Their damage behaviour was analysed in terms of composite theory. In the tensile tests, particles were found to crack perpendicular to a loading axis, being triggered by a far-field uniaxial stress. The damage is accumulated gradually with an increase in applied strain. The in situ strengths of the Si particles are 500-900 MPa for the small eutectic Si particles, whereas it is as low as 200 MPa for the coarse primary Si particles. During the cyclic loading, gradual accumulation of damage at the Si particles was observed with the increase in number of cycles. Propagating through such a weakened zone, a fatigue crack seems to receive some acceleration by the existence of the cracked particles ahead of it. The degree of acceleration was quantitatively evaluated by experiments.. |
| 396. | H. Toda, J. Sawamura, T. Kobayashi, Up-grade recycling of metallic cutting chips by employing heavily-deformed in-situ composite technique, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.54.418, 54, 10, 418-424, 2004.10, The present authors have realized that cutting chips may be identified utilizable for the strengthening of materials due to large plastic strain accumulated during cutting. The authors have proposed up-grade recycling techniques in which severe plastic deformation in room temperature air is utilized to cutting chip mixture of dissimilar materials, thereby consolidation and further accumulation of strain are simultaneously achieved. In this study, such composite materials are produced and evaluated with combinations of 6061 aluminum/IF steel and 6061 aluminum/pure copper. It is clarified that appropriate second phase cutting chip is a BCC metal. The ultimate tensile strength of the 6061 alloy is improved approximately up to 500 MPa (about 1.6 times that of the material before cutting) when the volume fraction of the IF steel is 20%. To predict the attainable maximum tensile strength by the current method, the Eshelby equivalent inclusion model is employed. The present method is identified to have a potential of realizing 713 MPa (about 2.3 times that of the material before cutting) in the case of the 6061 alloy/20%IF steel composite by eliminating production defects adjusting the matrix/second phase combination and conditions for cutting and plastic working.. |
| 397. | T. Masuda, T. Kobayashi, H. Toda, L. Wang, Dynamic Deformation Behavior and Microstructure Evolution of 5000 Series Aluminum Alloys, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.52.981, 52, 8, 981-987, 2003.08, The aim of the present study is to investigate strain rate dependency of Al-Mg alloys within a wide range of strain rates. Tensile tests of a wide range of strain rate are carried out using Instron universal, servo-hydraulic impact and split-Hopkinson bar testing machines. Also, strain rate sensitivity is evaluated by test of changing the strain rate. The SEM technique is used to analyze the fracture surface characteristics of deformed specimens. The negative strain rate dependency shows at strain rate region between 4.3 × 10-4 and 1.0 × 102s-1 for Al-Mg alloys. However, the extent of rate sensitivity over 1.0 × 102s -1, ultimate tensile strength increases with increasing strain rate. Although the shear dimple type fracture surface is mainly observed under static loading condition, normal type dimple fracture surface is found under high strain rate. The fracture behavior under the variation of strain rates is also discussed based on the results of the microstructure observation.. |
| 398. | H. Toda, I. Sinclair, J. Y. Buffi?re, E. Maire, T. Connolley, M. Joyce, K. H. Khor, P. Gregson, Assessment of the fatigue crack closure phenomenon in damage-tolerant aluminium alloy by in-situ high-resolution synchrotron X-ray microtomography, Philosophical Magazine, 10.1080/1478643031000115754, 83, 21, 2429-2448, 2003.07, Synchrotron X-ray microtomography has been utilized for the in-situ observation of steady-state plane-strain fatigue crack growth. A high-resolution experimental configuration and phase contrast imaging technique have enabled the reconstruction of crack images with an isotropic voxel with a 0.7 μm edge. The details of a crack are readily observed, together with evidence of the incidence and mechanical influence of closure. After preliminary investigations of the achievable accuracy and reproducibility, a variety of measurement methods are used to quantify crack-opening displacement (COD) and closure from the tomography data. Utilization of the physical displacements of microstructural features is proposed to obtain detailed COD data, and its feasibility is confirmed. Loss of fracture surface contact occurs gradually up to the maximum load. This is significantly different from tendencies reported where a single definable opening level is essentially assumed to exist. The closure behaviour is found to be attributable mainly to pronounced generation of mode III displacement which may be caused by local crack topology. Many small points of closure still remain near the crack tip, suggesting that the near-tip contact induces crack growth resistance. The effects of overloading are also discussed.. |
| 399. | H. Toda, T. Kobayashi, Assessments of damage and fracture behaviours of Al-Mg-Si alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.53.469, 53, 11, 469-475, 2003.01. |
| 400. | Y. Fujii, H. Toda, T. Kobayashi, Creation of aluminum alloy by severe plastic deformation of cutting chip and its mechanical properties, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.53.368, 53, 9, 368-372, 2003.01, Cutting chip is, generally, separated from cutting oil and then remelted for recycling solely as raw materials. In terms of microstructures, however, the cutting chip may be identified utilizable due to highly-accumulated strain during its formation. In this study, aluminum chips are consolidated by cold severe plastic deformation so that their highly deformed microstructure is utilized for the strengthening of an aluminum alloy. After a preliminary investigation in which a variety of cutting processes and conditions are examined to find the optimum one for the present purpose, the aluminum chips have been successfully consolidated by a combination of pressing and swaging. The consolidated chips exhibit superior strength together with finer microstructure to a wrought alloy when compared at a same applied strain. In addition, a couple of methods are demonstrated effective to eliminate the undesirable effects of oxide film on the surface of the chips, which inevitably causes debonding during loading.. |
| 401. | N. Hayat, T. Kobayashi, H. Toda, H. Kojima, Grain size refinement through gas bubble stirring in AC4CH cast aluminium alloy, International Journal of Cast Metals Research, 10.1080/13640461.2003.11819536, 15, 5, 505-512, 2003.01, A comparison has been made of the mechanical properties of gravity and squeeze cast aluminium alloys that have been grain refined using gas bubbling and those that have not. To find the optimum gas bubbling conditions, the alloy melt temperature, the gas flow rate and the gas bubbling times were varied over wide ranges. The microstructure of the gas bubbled gravity and squeeze cast materials is fine, equiaxed and non-dendritic with an average primary α size of 52 μm and 163 μm respectively. However, gas bubbling has no effect on the morphology of the eutectic Si. There seems to be no noticeable difference between the measured mechanical properties of the gravity and squeeze cast materials with or without the gas bubbling. The lack of improvement in the mechanical properties of the gravity cast alloy is due to casting defects and porosity, which offset the effects of the grain refinement. The crystal separation and showering mechanisms are operative for the formation of equiaxed grains.. |
| 402. | T. Kobayashi, H. Toda, T. Masuda, Analysis of test data obtained from Charpy V and impact tensile test, European Structural Integrity Society, 10.1016/S1566-1369(02)80018-8, 30, C, 173-180, 2002.12, The standard Charpy V-notch specimen has received a great deal of attention as small, inexpensive and convenient material test specimen which provides deep insights of inherent fracture toughness problems. In this study, Charpy impact tests are performed utilizing the Computer-Aided Instrumented Charpy impact test (CAI) method which has been developed by one of the present authors (TK) for nearly 40 years. The well-known Server's equation is used to estimate tensile properties directly from the Charpy tests. Agreement between the prediction and experiments are checked for major practical aluminum alloys heat-treated to respective standard heat treatment states. Discrepancy between them is almost negligible in the case of age-hardening alloys, while it amounts sometimes several ten % in the solution hardening alloys. Especially in the case of age-hardening alloys, which is considered important as primary structural materials, feasibility of utilizing the Charpy tests to obtain tensile properties over a wide strain range is clarified by being based on the thermally activate deformation process of the aluminum alloys.. |
| 403. | L. Qian, Z. Wang, T. Kobayashi, H. Toda, Dynamic tensile deformation of SiCp/6061Al composite. Part 1 Strain hardening characteristic, Cailiao Yanjiu Xuebao/Chinese Journal of Materials Research, 16, 3, 285-288, 2002.06, An investigation was made on the dynamic tensile deformation and strain hardening characteristic of a SiCP/6061Al composite and its matrix alloy using tensile split Hopkinson pressure bar apparatus. It is shown that under dynamic loading condition, as in the case of static loading, the strength of the SiCP/6061Al is higher and its elongation to fracture is lower than those of 6061Al alloy. At a low strain, the dynamic tensile strain hardening exponent of the studied composite is higher than that of its matrix alloy. However, the strain hardening exponent of the composite decreases rapidly with increasing strain, and becomes lower than that of its matrix alloy at a higher strain. The deformation and damage mechanisms are discussed in terms of dislocation.. |
| 404. | L. Qian, Z. Wang, T. Kobayashi, H. Toda, Dynamic tensile deformation of SiCP/6061Al composite. Part 2 Strain rate sensitivity, Cailiao Yanjiu Xuebao/Chinese Journal of Materials Research, 16, 3, 289-295, 2002.06, A dynamic tensile experiment for a SiCP/6061Al composite and its matrix alloy in an over-aged state was performed using split Hopkinson bar apparatus, and a study was made on the strain rate sensitivity of their tensile properties. Results show that SiCP/6061Al composite and its matrix alloy exhibit and obvious strain rate effect of strength and fracture stain, and the strain rate sensitivity of the SiCP/6061Al composite is higher than that of 6061Al alloy. The high strain rate sensitivity of the SiCP/6061Al composite is considered to be originated from the high dislocation accumulation rate during dynamic deformation and the constraint of SiC particles on the surrounding matrix, which dramatically enhances strain rate of the matrix.. |
| 405. | H. Toda, T. Kobayashi, Al-X (X= Nb, Cr, Fe) ultra-high strength in-situ composite wire, International Journal of Materials and Product Technology, SPEC. ISS. VOL.1, 427-432, 2001.12, Heavily deformed in-situ composite wires based on aluminum were produced through a powder metallurgy process to avoid interfacial reaction. Metal filaments get finer and closer together as the drawing strain increases. Mechanical properties such as tensile strength were evaluated with particular interests on relationships with microstructures. Tensile strength increases to 1063 MPa at a drawing strain of 14.6, which is the maximum drawing strain in this study. The dependence of ultimate tensile strengths of the composites on the mean filamentary spacing is investigated. There is a good correlation with the Hall-Petch type relationship. This result suggests that the filaments act as barriers against dislocation motion, and that shear modulus of the second phase barrier is a predominant parameter for the strengthening of the wires.. |
| 406. | T. Agag, T. Takeichi, H. Toda, T. Kobayashi, Epoxy-clay nanocomposites using polybenzoxazine as a curing agent, International Journal of Materials and Product Technology, SPEC ISS. VOL.2, 706-711, 2001.12, Novel nanocomposites have been prepared from the blending of epoxy resin, benzoxazine monomer and stearyl ammonium modified-montmorillonite. The featureless XRD pattern suggests the disordered dispersion of the clay nanolayers into the epoxy/polybenzoxazine copolymer. The Tgs of the hybrid materials were higher than that of the pristine resin. Consequently, the storage modulii of the hybrid materials were maintained up to a higher temperature than the pristine copolymer. The hardness of the nanocomposites increased with the inclusion of clay accompanied with a decrease in the toughness. TGA showed that the thermal stability of the nanocomposites increased over the pure copolymer.. |
| 407. | M. Shibata, Y. Takemoto, T. Kobayashi, H. Toda, Expansion behavior of thermally cycled aluminum alloy composites reinforced with aluminum borate whiskers, International Journal of Materials and Product Technology, SPEC. ISS. VOL.1, 275-280, 2001.12, A6061 aluminum alloy composites reinforced with aluminum borate whiskers were thermally cycled between 293K and Tmax=573K, 673K and 773K. Composites thermally cycled above Tmax=673K initially expanded with increasing the number of thermal cycles, and finally contracted. Isothermally heated composites contracted proportionally to the heating time. Thermal stress and strain generated in the composites on cooling from 773K to 293K were analyzed using finite element methods (FEM). Expansion in thermally cycled composites was explained from the results of FEM. It is assumed that contraction in the composites occurred as a result of the resolution of whiskers during thermal cycling.. |
| 408. | V. A. Mosneaga, T. Kobayashi, H. Toda, Influence of ECAP and age hardening treatment in 6061 Al alloy, International Journal of Materials and Product Technology, 10.1504/IJMPT.2001.001290, 16, 8, 710-716, 2001.12, In the present work, ECA pressing is used to deform a commercial 6061 Al (T6 condition) alloy to very large strains. An ultrafine grained structure has been formed by the fragmentation of the original grains, after one pass and after four passes the structure becomes more uniform. The results show the presence of precipitates from the Al-Mg-Si system. Peak ageing values increase with the number of passes because the density of precipitates increases with the number of passes through fine distribution of precipitates, and the precipitates become smaller with grain refinement. The aim of the present paper is to demonstrate the efficiency of this technique to form ultrafine grained structure and the influence of ECAP on peak ageing structure.. |
| 409. | H. Toda, T. Ueda, T. Kobayashi, T. Gouda, Interfacial debonding criteria under combined stress in composites, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.50.1375, 50, 12, 1375-1381, 2001.12, A novel test procedure is suggested for the exploration of interfacial bonding strength under combined stress states using a test piece in which a single sphere is embedded in its center to avoid a generation of stress singularity at the edge of bonded interface between two materials. The combined stresses are applied due to combinations of tension, torsion and bending loads for a tensile specimen, and by shifting the position of a sphere from a center for a three point bending specimen. Quantitative analyses of AE signals combined with finite element calculations in which thermal residual stresses are taken into account, lead to local interfacial debonding criteria under combined stresses. According to the criteria obtained, shear stress necessary for debonding increases linearly with an increase in compressive normal stress at interface. That is the Mohr-Coulomb criterion is predominant while quadratic and elliptical interaction criteria such as the Hoffman's rule are not applicable. This is attributed to the difference in the test procedures. In the conventional procedures using laminated cylinder specimens, the generation of stress singularity at the free edge of bonded interface between two materials reduces apparent shear stress necessary for debonding, whilst in the present procedure, the actual shear stress is exactly evaluated.. |
| 410. | L. Qian, Z. G. Wang, H. Toda, T. Kobayashi, Isothermal fatigue and in-phase thermo-mechanical fatigue of a 6061Al/SiCw, International Journal of Materials and Product Technology, SPEC ISS. VOL.2, 799-804, 2001.12, The isothermal low cycle fatigue (IF) at 300°C and in-phase thermo-mechanical fatigue (IP-TMF) with temperature cycling between 150-300°C of a 6061 Al alloy reinforced with 28 vol % SICw were studied. Experimental results indicate that IP-TMF shows continuous cyclic softening until failure, while IF loading initially shows several cycles of cyclic hardening followed by cyclic softening till final fracture. A comparison of IF and IP-TMF lives has been made and various damage mechanisms operative under different strain ranges and loading conditions have been explained. SEM micrographs show that the damage processes under both IF and IP-TMF conditions consist of initiation, growth and coalescence of voids in the matrix around whiskers.. |
| 411. | T. Masuda, T. Kobayashi, H. Toda, S. Morita, Strain rate dependency of impact tensile properties in various commercial aluminum alloys, International Journal of Materials and Product Technology, SPEC ISS. VOL.2, 823-828, 2001.12, At present, there is no standard impact tensile and compression test method. In the present study, impact tensile tests for high strain rate range are carried out using the split-Hopkinson bar technique and the servo-hydraulic impact testing machine on ten kinds of commercial aluminum alloys. Stress-strain curves are measured for strain rate between 10 -4 and 10 4 s -1 and strain rate dependency of tensile properties is investigated. All the aluminum alloys show an increase in 0.2% proof stress, ultimate tensile strength, elongation and reduction in area by increasing the strain rate. Stress-strain curves are of similar shape below strain rate of 10 3 s -1 and a significant change in shape is observed with strain rate larger than 10 3 s -1 .. |
| 412. | L. Qian, Z.G. Wang, H. Toda and T. Kobayashi, Thermo-mechanical fatigue of SIC whisker reinforced 6061a1 composites, Jinshu Xuebao/Acta Metallurgica Sinica, 37, 11, 1201-1202, 2001.12, In-phase and out-of-phase thermo-mechanical fatigue (TMF) experiments were conducted on 6061 aluminum alloy reinforced with 15% and 28% (volume fraction) whiskers . The mechanical behavior and deformation mechanism of both TMF were investigated and discussed. The results show that the two kinds of TMF cycling exhibited continuous cyclic softening, out-of-phase TMF loading gave rise to tensile mean stress, whereas in-phase TMF cycling led to compressive mean stress. It is also demonstrated that at an equivalent strain range, the 28% SiCw/6061Al showed higher stress range than the 15% SiCw/6061Al.. |
| 413. | L. Qian, Z. Wang, H. Toda, T. Kobayashi, Thermo-mechanical fatigue of SiC whisker reinforced 6061Al composites II. Fatigue life and damage mechanism, Jinshu Xuebao/Acta Metallurgica Sinica, 37, 11, 1203-1207, 2001.11, The In-phase (IP) and out-of-phase (OP) thermo-mechanical fatigue (TMF) life and damage mechanism were studied on 15%SiCW(volume fraction) and 28%SiCW/6061Al. The result indicates that in small strain range, the IP TMF life is longer than that of the OP-TMF; in large strain range it is close to( for 28%SiCW) or even shorter than the OP-TMF life (for 15%SiCW). A comparison of the fatigue lives between the two composites illustrates that in the case of the OP-TMF, 15%SiCW/6061Al shows longer life than 28% SiCW/6061Al, however, in the case of IP-TMF, there is a crossover between the fatigue life curves of the two composites, meaning that the life being longer or shorter depends on strain level. Their damage processes are all related to initiation, growth and coalescence of voids in the matrix around whiskers.. |
| 414. | K. Osako, H. Toda, T. Kobayashi, Strain rate dependency of strength in TiB particle reinforced Ti matrix composite, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane1955.87.9_619, 87, 9, 619-622, 2001.09, In this study, TiB particle reinforced Ti matrix composite has been produced using a relatively new powder metallurgy process, the spark plasma sintering and its tensile properties have been investigated over a wide strain rate range. It has been clarified that tensile strength increases moderately with an increase in the strain rate below ε̇≒103 s-1, and subsequently increases rapidly above it. This tendency is interpreted in terms of the Eshelby equivalent inclusion method. The analytical results have suggested that the strain rate dependency of strength is simply attributable to that of unreinforced matrix and no extra effects due to the addition of TiB particles are observed. The analysis also reveals that the lower bound estimate of the strength of the TiB particle is several thousand MPa which exceeds that of SiC particle reported in earlier studies. It can be concluded that the TiB particle is excellent in its in-situ strength and interfacial compatibility with the Ti matrix.. |
| 415. | H. Toda, A. Takahashi, T. Kobayashi, Experimental evaluation of effects of damage evolution at coarse secondary phase particles on mechanical properties of aluminum alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.51.361, 51, 7, 361-367, 2001.07, The present work is aimed at experimental evaluation of the effects of damage evolution at coarse intermetallic particles in Al-Li-Cu-Mg alloy, with particular attention on fracture toughness. To vary volume fraction of the particles, various thermo-mechanical treatments have been applied. Strength, ductility and fracture toughness decrease with the increase in volume fraction from 1.2 to 2.2%. Especially, σ0.2 and crack propagation resistance are significantly affected. In-situ SEM observation of the fracture toughness test has also been used to characterize damage evolution at the particles and crack propagation behavior. Some types of particles remain intact even adjacent to the fracture surface, while others are extensively fractured far ahead of a crack-tip. A combination of the crack-tip singularity and micromechanics is used to estimate in-situ strengths of the particles. It is concluded that the particle strengths have strong dependence on diameter, and that, due to the existence of the damaged particles, crack deflection and formation of secondary cracks occur in the case of high particle volume fraction. Fracture mechanical analysis reveals that reduction in the crack propagation resistance is attributed to the amplification of mode I crack driving force due to the existence of microcracks. Finally, measured fracture toughness is interpreted utilizing a computer simulation constructed in the previous study. Although individual microstructural factors have only modest effects, competitive and synergistic effects are attributable to the measured large drop in the fracture toughness.. |
| 416. | H. Toda, H. Kagajo, K. Hosoi, T. Kobayashi, Y. Ito, T. Higashihara, T. Gohda, Evaluation of mechanical properties of hollow particle reinforced composites and analyses aimed at their improvement, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.50.474, 50, 5, 474-481, 2001.05, Hollow particle filled epoxy composites are fabricated by an ordinary molding technique. Young's modulus, tensile strength, fracture toughness and dielectric constant are measured as a function of density of the composites (i.e. wall thickness of the hollow particles). Specific strength is almost flat irrespective of the density, while specific modulus and the dielectric constant increase, and the fracture toughness simultaneously decreases with the decrease in the density. Fracture path varies from fracture particles in the case of particles with thinner shell to interfacial debonding in the case of thicker shell in the fracture toughness tests, while particle fracture is predominant in the tensile tests. In-situ observation of the material tests and finite element analyses are utilized to interpret the deformation and fracture behaviors and also to estimate the in-situ strength of silica. It is clarified by the observation that particles larger than 30 μm in diameter are predominantly damaged and smaller particles less than 15 μm are never fractured. Premature fracture of such coarse particles in early stage of loading is attributable to the strength properties. The in-situ strength of silica increases with the decrease in the particle diameter. According to the result of the finite element analysis, stress concentrates near inner surface along an equator under uni-axial loading, and this tendency becomes remarkable with the decrease in the wall thickness. On the other hand, interfacial stress decreases rapidly with the decrease in the wall thickness. The stress concentration along the equator is relaxed under multi-axial loading which is possible in the fracture toughness tests. All of these results indicate that elimination of the coarse particles is essential to improve the tensile properties, and that interfacial modification is effective only for toughness enhancement. SiCp reinforced Al2O3 and SiCp reinforced aluminum composites are also analyzed numerically to evaluate the efficiency of introducing hollow particles into ceramics and polymer materials.. |
| 417. | M. Kawakami, K. Murayama, M. Shibata, T. Takenaka, H. Toda, Reactivity of coke with CO2 and evaluation of strength after reaction, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane1955.87.5_252, 87, 5, 252-258, 2001.05, For the investigation on coke degradation in the blast furnace, reactivity of coke with CO2, the morphological change after reaction and the change in its strength were examined. Five kinds of cokes were used. They were machined in the spherical form of 20 mm ø and reacted with pure CO2 at 1073 to 1673K. After the reaction, the specimen were visually observed and the porosity distribution was estimated. Further, they were pressed by universal test machine to estimate the strength after reaction. The reaction mode changed at 1373K. At lower temperature, the reaction proceeded homogeneously throughout the specimen, while restricted near the surface at higher temperature. The porosity was almost uniform at lower temperature, but increased near the surface at higher temperature. The tensile strength was estimated indirectly from the results of compression test. The tensile strength was 0.85 to 1.77 MPa before the reaction. It decreased to 0.51 MPa after 50% reaction at 1273K. At 1573K, however, the strength did not decrease so much for the blast furnace coke and highly reactive coke. The strength of formed coke increased after 25% reaction. These changes in strength at 1573K can be attributed to the reaction mode where the reaction did not proceed to the core of specimen, and the crystallization proceeded in the core at higher temperature. The fracture energy, which might show the strength of matrix, decreased by the reaction in all case.. |
| 418. | H. Toda, T. Mizutani, A. Takahashi, T. Kobayashi, V. A. Mosneaga, Fracture toughness of various zones in weldments of 6082 aluminum alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.51.163, 51, 3, 163-168, 2001.03, The effects of Mn addition on toughness of welded Al-Mg-Si alloys have been investigated. In-situ SEM observations of fracture toughness tests have also been used to characterize crack initiation and propagation behavior through the weldment. Recrystallization of HAZ is completely suppressed by adding Mn, while a sample without Mn exhibits recrystallized coarse grain structure. Recrystallization in HAZ can lead to drastic decrease of its fracture toughness comparing with the samples containing Mn. Many microcracks are distributed at grain boundaries within several mm ahead of a crack-tip where crack-tip stresses are relatively weak. Fracture-mechanical analysis reveals that the toughness degradation is attributed to such premature damage evolution before the onset of crack extension. However, the microcracking is not attributed to so-called liquation cracks, but degredation of the grain boundaries due to the formation of film-like Al-Mg intermetallic compounds. The microcracks ahead of the crack-tip aligned at an angle of approximately 60° from an initial notch direction. Tension obliquely applied to the HAZ next to welding pool appears to give rise to such inclination of the microcracks. It is suggested that the toughness degradation can be suppressed by utilizing such anisotropy even if the GB films are formed during welding.. |
| 419. | T. Hikosaka, T. Imai, T. Kobayashi, H. Toda, High strain rate superplasticity of the SiCp/7075 aluminum alloy composite made by a vortex method, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.51.169, 51, 3, 169-174, 2001.03, A SiCp/7075 aluminum alloy composite has been fabricated by a vortex method followed by squeeze casting, extrusion and rolling. The composites were hot rolled to the total rolling reduction of about 94% at temperatures between 573 K to 773 K and at a rolling strain per pass of 0.10. Superplastic characteristics such as microstructure and apparent activation energy were compared with these of the composites made by other processes in order to clarify the superplastic deformation mechanism. Fine grain size of about 1 μm was attained in the composite rolled at a temperature of 573 K and at the strain per pass of 0.1. In the case of rolling at 573 K, the composite obtained exhibited high strain rate superplasticity with a maximum elongation of about 230% at strain rate of 7 × 10-1 s-1 and at 798 K. Plots between ε̇1/n and σ showed linear relation when exponent of n=2 was assumed. Threshold stress obtained from the linear relations were largely dependent on the testing temperature. Apparent activation energy determined from relationship between strain rate and testing temperatures was 244 kJ/mol, which was smaller than that for the powder metallurgical and mechanically alloyed aluminum composites. It seems that there is no substantial difference of high strain rate superplastic mechanism between the composite fabricated by a vortex method and powder metallurgical aluminum alloy composites.. |
| 420. | T. Hikosaka, T. Imai, T. Kobayashi, H. Toda, Effect of the particle size and volume fraction on superplasticity of SiCp/6061 aluminum alloy composite, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.51.86, 51, 2, 86-92, 2001.02, Effects of particle size and volume fraction of SiC particle on superplastic characteristics of SiCp/6061 aluminum alloy composites made by a vortex method before squeeze casting, extrusion and hot rolling were investigated in order to make clear the superplastic deformation mechanism. Flow stress of the SiCp (0.6 μm)/6061 aluminum alloy composite decreased with increasing the volume fraction in the case of the volume fraction of 0.13 and 0.20, and the m value became 0.30∼0.46 in the initial strain rate region of more than 2.4 × 10-1 s-1, and the maximum total elongation more than 200% was obtained at 853 K. And also, SiCp (1.2 μm) /6061 aluminum alloy composite exhibited m value of 0.32 at an initial strain rate of 7 × 10-2 s-1 and maximum total elongation of about 170%. However, 5 and 10 μmSiCp/6061 aluminum alloy composites did not produce superplasticity. It is thought that in SiCp/6061 aluminum alloy composite made by a vortex method, Vf=0.20 is optimum volume fraction for maximum total elongation. The threshold stress of the composites decreased with increasing SiC volume fraction. The stress exponent (n) indicated 3 for the creep deformation in the case of SiCp (5 and 10 μm) /6061 aluminum alloy composites, n showed 2 for the superplastic deformation in the case of SiCp (0.6 and 1.2 μm) /6061 aluminum alloy composites. On and near the fracture surface of the composite after superplastic deformation, filaments and striation bands were formed at sliding grain boundaries and interfacial sliding were observed and it is thought that high strain rate superplasticity of the composite could occur by grain boundary sliding and liquid phase accommodation mechanisms.. |
| 421. | F. Kamiya, H. Toda, T. Kobayashi, M. Takasu, N. Okamoto, Analysis of fracture toughness and TiC/Al2O3 composites, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.65.4_323, 65, 4, 323-330, 2001.01, Al2O3/TiC composites having various fraction ratio between Al2O3 and TiC phases are prepared through the hot-press process. Static and dynamic fracture toughness values are measured experimentally. Crack deflection angle and areal fraction of each fracture path (intergranular and transgranular fractures both through the Al2O3 and TiC phases and Al2O3/TiC interface) are measured on lateral surface of specimens and fracture surfaces, respectively. Local fracture toughness in each fracture path is analyzed using the above data. Measured fracture toughness increases with the increase in the mass percent TiC phase. Local fracture toughness is higher for the passes through the TiC phase than those through the Al2O3 phase, whether it is transgranular or intergranular. The weakest path is the Al2O3/TiC interface in all of the samples. Microstructural configuration for improved fracture toughness in Al2O3/TiC composites is discussed in light of local fracture toughness at both grain interior and boundaries.. |
| 422. | S. Morita, H. Toda, A. Takahashi, A. Hoshiyama, T. Kobayashi, H. Nagashima, Effects of quenching rate on mechanical properties of 6061 aluminum alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.51.307, 51, 6, 307-312, 2001.01, The effects of quenching rate after a solution treatment on strength and fracture toughness of a 6061 aluminum alloy have been investigated, varying the width of PFZ layer and coarse secondary phase particles at grain boundaries by changing the quenching rate utilizing both water quenching and air-cooling. In-situ observation of the fracture toughness tests was also performed to investigate the effects of such microstructural parameters on crack initiation and propagation behaviors. By decreasing the quenching rate, the width of the PFZ layer increases from about 40 to 310 nm, and density and size of the coarse particles increase at the grain boundaries. Mechanical properties such as tensile strength, 0.2% proof stress, elongation, fracture toughness and crack propagation resistance are decreased simultaneously. Especially, the effects of quenching rate on the strength and the crack propagation resistance are remarkable. Such degradation of the mechanical properties is attributed to expansion of the PFZ layer with decreases in quenching rate. It causes localization of plastic deformation, and consequently, transition of fracture mechanisms from grain interior ductile fracture to grain boundary ductile fracture at the PFZ layers. In-situ SEM observation reveals that the effects of the coarse particles at grain boundaries are much less effective than those of the PFZ.. |
| 423. | H. Toda, T. Kobayashi, A. Hoshiyama, A. Takahashi, In-situ SEM study on damage evolution at coarse secondary particles in 6061 aluminum alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.51.113, 51, 2, 113-118, 2001.01, In-situ SEM observations of fracture toughness tests have been used to characterize microscopic damage evolution at coarse particles around a main crack in a 6061 aluminum alloy. About 13% of the particles coarser than 1 μm in diameter is identified as Mg2Si and the remaining is α-AlFeSi. All of the coarse Mg2Si particles suffer from damage within several hundred micrometers from a crack-tip. Meanwhile, some of the α-AlFeSi particles remain intact. The coarser the particles, the more considerably they are damaged. Fracture of the particles is predominantly observed for the coarser particles, while the tendency of interfacial debonding increases with decreases in the particle size. In addition, in-situ fracture strength values of the two kinds of particles are estimated as a function of particle size. Stronger dependency of the strength on the size is shown in the α-AlFeSi particles than in the Mg2Si particles. It is concluded that the fracture toughness of the alloy is scarcely affected by the damage at the coarse particles. However, much more considerable effects on strength and ductility are predicted due to the very low strengths of the particles.. |
| 424. | H. Toda, T. Kobayashi, A. Takahashi, A. Hoshiyama, Numerical simulation of fracture induced by damage of intermetallic particles in wrought aluminum alloy, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.65.1_29, 65, 1, 29-37, 2001.01, Coarse inclusion materials have shown evidence of inclusion cracking ahead of a crack-tip by in-situ SEM observations, which degrades the fracture toughness. In-situ strengths of various inclusions have also been estimated in the preliminary analysis. The present work is aimed at numerical analyses of toughness degradation due to the existence of damaged inclusions with an A2091 alloy as its model material. Especially, microstructural control for toughness enhancement is discussed in the lights of the results. The investigation employs a combination of HRR singularity and an Eshelby model, which considers both elastic mismatches between a matrix and inclusions and back stresses due to rigidity of the inclusions, to conduct an estimation of internal stresses in the inclusions. The essential feature of the model is to predict crack initiation toughness and crack path morphologies using a mixed-mode fracture criterion. An appropriate criterion for the damage initiation, effects of a deflected crack-tip and shielding/antishielding effects due to the damaged inclusions are taken into consideration. The toughness is found to be degraded in the case of large matrix grains, high volume fraction of inclusions, and low fracture strength of the inclusions. When the spatial distribution of the inclusions is homogeneous, these effects are predicted less than 10%. However, the effect is remarkably pronounced when the inclusions are agglomerated. Some of these results are consistent with those by in-situ SEM observations reported elsewhere. The estimated lower boundary values of the fracture strengths are 2520 and 2440 MPa respectively for Al3Zr and Al3Ti particles. These values are of particular interests, because they are several times larger than the measured in-situ strengths of CuAl2 and Al2CuMg particles. Aligned weak inclusions on grain boundaries act to deflect the crack along the grain boundaries even when inferior crack propagation resistance within grain boundary PFZs is not considered.. |
| 425. | L. Qian, Z. G. Wang, H. Toda, T. Kobayashi, High temperature low cycle fatigue and thermo-mechanical fatigue of a 6061 A1 reinforced with SiCW, Materials Science and Engineering A, 10.1016/S0921-5093(00)00892-3, 291, 1-2, 235-245, 2000.10, The high temperature isothermal low cycle fatigue (IF) and thermo-mechanical fatigue (TMF) of a 6061 A1 alloy reinforced with 28 vol.% silicon carbide whiskers were studied. IF experiments were conducted at a temperature of 300°C, and two types of TMF tests, i.e. in-phase (IP) and out-of-phase (OP), were performed with temperature cycling between 150 and 300°C. All experiments were carried out under mechanical strain range control. Experimental results of mechanical behavior and mean stresses for TMF and IF loadings are provided. It can be seen that both IP and OP TMF show continuous cyclic softening until failure, while IF loading initially shows several cycles of cyclic hardening followed by cyclic softening until final fracture. A comparison of TMF and IF lives has been made and various damage mechanisms operative under different strain ranges and loading conditions have been explained. SEM micrographs show that damage processes under both IF and TMF conditions consist of initiation, growth and coalescence of voids in the matrix around whiskers. Due to the complexity of the relationship between IF and TMF damage, IF data cannot be used to evaluate TMF life. (C) 2000 Elsevier Science S.A. All rights reserved.. |
| 426. | A. Takahashi, T. Kobayashi, H. Toda, T. Mizutani, Effect of testing temperature from cryogenic to high temperatures on dynamic fracture properties in 5083 aluminum alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.50.386, 50, 8, 386-391, 2000.08, Effect of temperature on mechanical properties of an 5083 aluminum alloy has been investigated for various testing temperatures from 10 to 773 K. For that purpose, the static tensile, dynamic fracture toughness test and fractography are carried out, and stop block method is employed to characterize fracture behavior at cryogenic temperatures. Mechanical properties such as 0.2% proof stress and ultimate tensile strength increase with decreasing temperature. The high temperature embrittlement, which has been often reported for 5000 series alloys having high Mg content, was not observed in the present study. The dynamic fracture toughness value, Jd, and dynamic crack extension toughness, Tmat, at 20 K are approximately 57% and 74% lower than that at 150 K, respectively. Fracture toughness at cryogenic temperatures shows strong dependence on formation of delamination cracks. The delamination cracks are initiated at grain boundaries. According to a SEM-EDX analysis, Mg is detected adjacent to the delamination cracks. Therefore, it is concluded that the formation of delamination cracks are concerned with β(Al3Mg2) phase at the grain boundaries.. |
| 427. | L. Qian, Z.G. Wang, H. Toda, T. Kobayashi, Q. Yao, Thermo-mechanical fatigue of a SiCW/6061Al composite, Materials Transactions, JIM, 10.2320/matertrans1989.41.651, 41, 6, 651-655, 2000.06, In-phase (IP) and out-of-phase (OP) thermo-mechanical fatigue (TMF) experiments were undertaken on 6061 aluminum alloy reinforced with 15% volume fraction whiskers. Both TMF tests were conducted under mechanical strain range control with temperature cycling between 150 - 300°C. The mechanical behavior and fatigue resistance of both TMF fatigue was investigated and discussed. The result shows that the two kinds of TMF cycling exhibited continuous cyclic softening, out-of-phase TMF loading gave rise to tensile mean stress, whereas in-phase TMF cycling led to compressive mean stress. It is also illustrated that at small strain range, the in-phase TMF life was longer than that of the out-of-phase TMF; on the contrary, out-of-phase TMF showed longer life at large strain range. This is tentatively explained by the various damage mechanisms with the help of SEM, which were predominantly operative under different strain ranges and different phasing conditions.. |
| 428. | L. Wang, T. Kobayashi, H. Toda, M. Hayakawa, Effect of loading velocity and testing temperature on the fracture toughness of a SiCw/6061Al alloy composite, Materials Science and Engineering A, 10.1016/S0921-5093(99)00669-3, 280, 1, 214-219, 2000.03, The effects of loading velocity and testing temperature on the fracture toughness of a SiC whisker reinforced 6061 aluminum alloy composite were investigated. A precracked three-point bend specimen configuration was selected for fracture toughness measurement, with tests being conducted at loading velocities of 10-2-10 m s-1, and from room temperature to 473 K. The results showed that the fracture toughness increases with increasing loading velocity, but, the difference with respect to room temperature is small, because the fracture toughness decreases slowly with the increase of testing temperature. The composite material failed mainly by whisker pull-out and whisker breaking.. |
| 429. | H. Toda, T. Kobayashi, A. Takahashi, Mechanical analysis of toughness degradation due to premature fracture of course inclusions in wrought aluminium alloys, Materials Science and Engineering A, 10.1016/S0921-5093(99)00658-9, 280, 1, 69-75, 2000.03, The present work is aimed at numerical analyses of toughness degradation due to damage evolution at coarse inclusions, with particular interests on microstructural control for toughness enhancement by controlling the damage initiation. The investigation employs a combination of crack-tip singularity and Eshelby internal stress analysis within each inclusion. The essential feature of the model is to predict crack initiation toughness and crack path morphology using a mixed-mode fracture criterion. The procedure accounts a criterion for the damage evolution, effects of a deflected crack-tip, and shielding/antishielding effects due to the damaged inclusions. The toughness is found to be degraded by increasing the grain size of the matrix and the volume fraction of the inclusion, and also by decreasing the fracture strength of the inclusion and hence its coarsening. The effects are remarkably pronounced when the inclusions are agglomerated. Especially, weak inclusions agglomerated on grain boundary act to deflect the crack along the grain boundary even when inferior crack propagation resistance within grain boundary PFZ is not considered. The in-situ fracture strengths of several inclusions are also estimated in the lights of the numerical results.. |
| 430. | T. Kobayashi, M. Otani, S. Morita, H. Toda, Effects of striker shape and attached position of strain gage on measured load in Instrumented Charpy impact test, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane1955.86.9_595, 86, 9, 595-601, 2000.01, Instrumented Charpy impact test is widely used for the evaluation of toughness of many kinds of materials such as steel, aluminum alloys, polymers and ceramics with small scale specimens. In the test, therefore, it is important to record an accurate impact load. Generally, one can obtain measured load in the instrumented Charpy impact test by multiplying the output signal from strain gage attached to the instrumented striker by load-calibration factor assuming a liner relationship between the strain gage signal and applied load. Although JIS or ISO describes about the instrumented striker, amplifier, data processing parameter and etc., detailed method on load measurement is hardly described in any standard. In the present study, two types of striker were used. The strain gages were attached to 4 positions in each striker. Instrumented Charpy impact test was carried out using these strikers in order to investigate the effect of gage position on actual impact load. By the finite element analysis, the effect of the strain gage position on the measured load was also investigated. As the result, it became clear that the accurate impact load was not measured around the end of slit which was introduced to release the constraining effect of deformation of the gage position from surrounding hammer; the effect of the vibration of the hammer appeared strongly around this position. However, it was possible to prevent the effect of such vibration by attaching the gage away from such position.. |
| 431. | T. Kobayashi, T. Higashihara, H. Yamaya, K. Hosoi, H. Toda, Effect of CTBN addition on mechanical properties of epoxy resins filled with SiO2 particles, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.48.1386, 48, 12, 1386-1392, 1999.12, In the present study, fracture toughness at various strain rates was measured as well as fatigue crack propagation properties to investigate the effect of addition of calboxy terminated copolymers butadiene-acrylonotrile (CTBN) on mechanical properties of glass particles reinforced epoxies. Glass transition temperature decreased with increasing rubber content. Both tensile strength and yield stress decreased with increasing rubber content. Fracture toughness and fatigue crack propagation resistance were strength improved by adding CTBN. These improvements are due to an increase of intrinsic ductility brought by add CTBN. The dynamic fracture toughness showed the minimum value between the loading velocities of 4m/s and 10m/s. The loading velocity where the dynamic fracture toughness becomes increases with increasing the CTBN content. According to fracture surface observation it was fund test crack is attributed to interface decohesion between the epoxy matrix and the SiO2 particles. However, cracks grew through the matrix and CTBN when consolidated CTBN particles were large.. |
| 432. | A. Takahashi, T. Kobayashi, H. Toda, Initiation stress of delamination cracking in A2091 Al-Li alloy, International Journal of Materials and Product Technology, 14, 2-4, 217-228, 1999.12, The measurement of the velocities of ultrasonic waves has been used to detect the delamination cracking during tensile tests in an A2091 Al-Li alloy at both liquid helium and room temperatures. The measured tensile far-field stresses at the onset of the delamination cracking are 335 and 357 MPa, at cryogenic and room temperatures, respectively. The density of delamination cracks in the alloy is estimated from the reduction in the ultrasonic wave velocity and resultant decrease in modulus of elasticity. It is estimated that the interfacial bonding strengths normal to a grain boundary are 116 and 113 MPa, at cryogenic and room temperatures, respectively. Fracture mechanics analysis has been used to estimate the onset of delamination cracking in fracture toughness tests on the basis of the results of the tensile tests. The predicted levels of far field applied stresses are much lower than those for macroscopic crack initiation at both temperatures.. |
| 433. | L. Wang, T. Kobayashi, H. Toda, M. Hayakawa, Effects of loading velocity on fracture toughness of a SiCw/A6061 composite at elevated temperatures, Materials Transactions, JIM, 10.2320/matertrans1989.40.1056, 40, 10, 1056-1062, 1999.10, The influence of loading velocity on the fracture toughness of a SiC whisker reinforced 6061 aluminum alloy composite was investigated at elevated temperatures. A precracked three-point bend specimen configuration was selected for fracture toughness measurement, with tests being conducted at loading velocities of 10-2 to 10 m·s-1, and at temperatures up to 473 K. The results showed that the fracture toughness increases with increasing loading velocity, but the difference with respect to room temperature is small, because the fracture toughness decreases slowly with increasing testing temperature. The composite material failed mainly by whisker pull-out and whisker breaking.. |
| 434. | A. Takahashi, T. Kobayashi, H. Toda, Stress criterion of delamination cracking in 2091 aluminum alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.49.249, 49, 6, 249-252, 1999.06, The measurement of ultrasonic wave velocity has been used to detect the delamination cracking during tensile tests in an 2091 T-8 Al-Li alloy at both liquid helium and room temperature. The measured stresses for initiation of delamination cracking are 335 and 357 MPa, for the cryogenic and room temperatures, respectively. The density of delamination cracks in the alloy is estimated from the observed reduction in ultrasonic wave velocity and resultant decrease in modulus of elasticity. It is estimated that the interfacial debonding strengths normal to a grain boundary are 116 and 113 MPa, for the cryogenic and room temperature, respectively. Fracture mechanics analysis has been used to estimate the onset of delamination cracking in the case of a cracked tensile specimen. The predicted levels of far field applied stresses are much lower than that for macroscopic crack initiation at both cryogenic and room temperatures, respectively.. |
| 435. | A. Kawabe, A. Oshida, T. Kobayashi, H. Toda, Fabrication process of metal matrix composite with nano-size SiC particle produced by vortex method, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.49.149, 49, 4, 149-154, 1999.04, The fabrication of metal matrix composite (MMCp) by vortex process is the general method due to the advantage of its convenience. However in the case of fine particles the surface property of the particle appears dominantly, especially in nano-size particles the agglomeration occurs and the fabrication of MMCp is reduced to be difficult. It is analyzed that the strength of the MMCp is dominated by the ascent of the dislocation density. Further, as the dispersion strengthening mechanism can be anticipated, dispersions of more fine particles into the matrix are required. In this study, the influences on various primary factors for solving an agglomeration problem are examined using SiC particles of 0.3 μm (the minimum diameter in the market) into 6061 Al alloy by the vortex method. From this study, the following results are obtained. (1) It is found that MMCp with no agglomeration can be fabricated by conducting the following procedure; pre-treatment, disagglomeration of powder, Ca addition and stirring in the semi-solid range. (2) It is deduced that the main factors of forming the agglomeration in the matrix of MMCp are the yield of SiO2 on the surface of SiC and the reduction of the void ratio of SiC powder.. |
| 436. | Q. Yao, T. Kobayashi, H. Toda, S. Kitaoka, Effect of microstructure on fatigue crack propagation characteristic of Al-Si-Cu die casting alloys, Unknown Journal, 10.2464/jilm.49.443, 49, 9, 443-449, 1999.01, Fatigue crack propagation characteristics of a eutectic and two hypereutectic Al-Si-Cu die casting alloys were investigated, where the stress ratio was 0.1 and the load frequency was 50 Hz at an ambient temperature. Relationships between fatigue crack propagation characteristic and microstructure have been discussed. The fatigue crack propagation rate decreases with increasing Si content in a low stress intensity factor range, ΔK. In this range, the crack propagation rate is very slow because it is considered to increase effects of crack deflection and branching induced crack closures with increasing Si content. At a high ΔK, because the effects of crack closures are decreased, the higher the Si content, the higher the fatigue crack propagation rate becomes. In this study, the fatigue crack propagation rate for the Al-15%Si-T5 alloy becomes higher than the other two alloys. It is considered to decrease effects of crack deflection and branching induced crack closures with many intermetallic compounds in the Al-15%Si-T5 alloy. The fractographic study on fractured specimens after fatigue crack propagation tests reveals the fracture surfaces consisting of the cleavage fractures of Si and intermetallic compound particles, and the striation pattern in α-aluminum.. |
| 437. | T. Kobayashi, N. Inoue, A. Sakaguchi, H. Toda, Effect of specimen size on the load calibration in the instrumented impact test, Tetsu-To-Hagane/Journal of the Iron and Steel Institute of Japan, 10.2355/tetsutohagane1955.85.1_78, 85, 1, 78-83, 1999.01, Accurate measurement of load is essential in the instrumented impact test. Especially, significant variation in load has been reported in the instrumented Charpy impact test, for example when miniaturized specimens were tested. Load calibration values are evaluated by means of both finite element analyses and experiments. Decrease in specimen thickness results in slight decrease of calibration parameters. This is attributable to strain localization near the region in which strain gages are placed. The results strongly suggest that the system must be calibrated for each different size of specimens to know accurate toughness data.. |
| 438. | T. Hikosaka, T. Imai, T. Kobayashi, H. Toda, Effect of the hot roll working on the superplasticity of the SiCp/6061 aluminum alloy composite made by a Vortex method, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.49.600, 49, 12, 600-606, 1999.01, Effect of hot rolling and testing temperature on superplastic characteristics of a SiCp/6061 aluminum alloy composite made by a vortex method before squeeze casting and extrusion were investigated in order to make clear the superplastic deformation mechanism. Total rolling strain of about 94% was given to the composites in rolling temperatures from 843 K to 873 K and in the rolling strain per passes of 0.05 to 0.30. Fine grain size of about 1.6 μm was obtained in the composite rolled at temperature of 573 K and at the strain per pass of 0.10. The flow stress was not so effected by rolling strain per passes, and the composite exhibits m-value of 0.33 and the maximum total elongation of about 350% at the strain rate of 0.24 s-1 and at 853 K. Total elongation of more than 100% was obtained in the wide strain rate region from 0.003 to 1.30s-1 and in rolling temperatures of 573 K, 673 K, and 723 K. Relationship between ε1/2 and σ became linear when exponent of n = 2 was selected. Apparent activation energy determined from relationship between strain rate and effective stress (= flow stress minus threshold stress) was higher than that of lattice self diffusion of aluminum so that it is thought that high strain rate superplasticity of the composite could occur by grain boundary sliding, and grain boundary diffusion and liquid phase accommodation mechanisms. On the fracture surface of the composite after superplastic deformation, filaments and cavities in striation structures were observed and it became clear that on the microstructural level superplastic phenomena occur.. |
| 439. | A. Takahashi, T. Kobayashi, H. Toda, In-situ SEM study on effect of inclusion particles on fracture behavior in Al-Li system alloy, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.49.166, 49, 4, 166-171, 1999.01, In-situ SEM observations of specimen surfaces during a 3-point bend test have been made to characterize the microscopic damage initiation and the fracture behavior of an Al-Li system alloy. Damage initiation from inclusion particles larger than several micrometers is always attributed to their breakage. Neither interfacial debonding nor interfacial cavitation is observed for such coarse particles. Some kinds of such coarse inclusion particles are fractured several hundred micrometers ahead of a main crack tip. Simultaneous extension of microcracks and the main crack, and subsequent incorporation of the microcracks into the main crack are observed. In such a way, it is clarified that the fracture of the Al-Li alloy is significantly affected by the coarse inclusions. A combination of HRR singularity and Eshelby type internal stress analysis has been used to calculate the actual fracture strengths of various inclusion particles. Fracture strength of both CuAl2 and Al2CuMg particles is about 710 MPa for the diameter ranging 5 and 8 μm, and the fracture strength decreases with increasing particle size. Damage initiation in Al3Zr and Al3Ti particles has not been observed in this study. The lower bound values of the fracture strength of these two kinds of particles are estimated as 900 to approximately 1000 MPa by the same analysis.. |
| 440. | P. L. Liu, Z. G. Wang, H. Toda, T. Kobayashi, Cyclic creep behavior of SiCw/6061Al composites at high temperatures, Key Engineering Materials, 149 PART II, 655-660, 1998.12, The tensile creep and tensile-tensile cyclic creep behavior of 15 vol % and 28 vol % SiCw/6061 Al composites at different temperatures has been investigated and analyzed. The comparison between cyclic and static creep behavior indicates that the cyclic creep acceleration behavior is more likely to take place at lower temperatures. It is also found that the unloading amount affects the minimum creep rate significantly at the tested temperatures. The minimum cyclic creep rate decreases first and then increases with increasing the unloading amount. The unloading amount corresponding to the turning point of the minimum cyclic creep rates increases with increasing the temperature. Based on the concept of the back movement of dislocations during unloading portion, this result can be explained.. |
| 441. | H. Toda, T. Gouda, T. Kobayashi, Finite element analysis of observed high strengthening in composites with regularly segregated microstructures, Materials Science and Technology, 14, 9--10, 925-932, 1998.09, A distinct dual phase composite has been developed, comprising spherical reinforcement clusters and unreinforced matrix, according to numerical simulation of crack initiation and propagation in discontinuously reinforced MMCs. The present work is aimed at interpretation of the high strengthening ratios which were actually measured in such dual phase composes. Elastic-plastic finite element modelling is utilised to analyse the strengthening ratio in a two-dimensional idealised microstructure with periodic clustering. As the degree of clustering increases, the strengthening ratio is predicted to increase. In composites with a networking cluster, much more strengthening is exhibited together with relatively uniform strain distribution. The primary mechanism leading to additional strengthening due to clustering derives from an optimum ratio in deformation resistance between a matrix and a reinforcing phase. In the proposed dual phase composites, each cluster can behave as a singe reinforcement which can deform plastically and there is no distinct interface between the cluster and the softer phase.. |
| 442. | H. Toda, T. Kobayashi, Y. Tanaka, T. Gouda, Superior strengthening mechanisms in dual phase composites having reinforcement agglomeration, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.62.5_488, 62, 5, 488-496, 1998.01, The present authors have developed distinct two-phase composites comprising a spherically-clustered phase on the basis of a numerical crack propagation simulation. The composites showed much higher strength as well as the predicted higher crack propagation resistance than the conventional composite with uniform reinforcement distribution. The present work aims to clarify the superior strengthening mechanisms for the composites with the segregated microstructure. Two-dimensional idealized microstructures in which one phase is continuous and the other isolated are modeled for the case where the clustered phase is continuous and for the opposite case. To predict the effect of the segregated microstructures on the strengthening ratio of composites in comparison to unreinforced materials, elastic-plastic finite element method is applied. As the degree of clustering increases, the strengthening ratio of composites increases within the context of this study. The strengthening ratio of composites with a continuous cluster is superior to that of an opposite case. This result could be attributed to the local relaxation of additional internal stresses in the clusters due to the predominant plastic deformation of a softer phase around the clusters when they are isolated. The regular array of clusters always enhances composite strengthening when each cluster contains a sufficient number of reinforcements and its spatial distribution in the clusters is uniform. Primary mechanism, by which additional strengthening arises due to the clustering, is attributed to the large difference in deformation resistance between the metal and the ceramic reinforcement in MMCs. The present composite models are considered to have a structure that the reinforcement clusters reinforce the softer phase. When the overall volume fraction of reinforcements is held constant, the existence of the optimum ratio of elastic moduli or secant moduli between two phases is predicted for the strengthening ratio of composites. Since the optimum ratio is much lower than that of the case of metal/ceramic, i.e., ordinary MMCs, the introduction of a dual phase structure in which both phases can deform elastic-plastically produces high strengthening ratio of composites.. |
| 443. | T. Kobayashi, H. Toda, Toughness enhancement based on fracture mechanical simulation of Al-SiCw composite, Materials Science Forum, 242, 193-198, 1997.12, Fracture-mechanical simulation is constructed based on the information of the crack propagation mechanisms through discontinuously-reinforced MMCs that have been clarified by the in-situ fracture toughness tests. Shielding and anti-shielding effects caused by both microcracks and reinforcements, effect of crack deflection, and growing crack singularity are evaluated to calculate local crack-tip driving forces using adequate microcrack initiation criteria and mixed-mode crack propagation criterion. Consequently actual crack growth mechanisms are well simulated by the computation. Parametric studies are carried out to calculate effects of microstructures on crack initiation and growth characteristics in the SiC whisker-reinforced 6061 Al alloy composites. Based on the results of the simulation, the MMC with improved microstructures has been proposed. It has been actually fabricated by high pressure infiltration casting, and it is confirmed that the crack growth resistance of the MMC is significantly improved by controlling the microstructures without spoiling the other mechanical properties.. |
| 444. | Q. Yao, T. Kobayashi, H. Toda, H. Hori, Effect of microstructure on fracture toughness of cast and forged aluminum casting alloys, Keikinzoku/Journal of Japan Institute of Light Metals, 10.2464/jilm.47.613, 47, 11, 613-619, 1997.11, Tensile and fracture toughness properties of three typical aluminum casting alloys, A (0.7%Si)-T6, B (4%Si)-T6 and C (7%Si) -T6, were evaluated in both as-cast and as-forged conditions. Cast and forged alloys showed increased elongation and fracture toughness with increase in forging ratio, especially in A (0.7%Si)-T6 alloy. The tensile and yield strengths of cast and forged alloys of B (4%Si)-T6 and C (7%Si)-T6 increased with forging ratio, but decreased in 50% forging ratio. Mechanism of the increased fracture toughness are considered to be a decrease in the size of casting defects with forging ratio. On the other hand, it is also considered to change microstructures of α phase and eutectic Si particle. In the Al-Si-Mg alloys, Mg2Si is a major precipitate, however, it is considered that the excess Si also contributes to the increase of the strength.. |
| 445. | H. Toda, T. Kobayashi, N. Inoue, Numerical analysis of effects of inhomogeneous matrix microstructures on deformation characteristics in aluminum matrix composites, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.61.2_120, 61, 2, 120-127, 1997.01, Recently it has been reported that PFZ layers, ranging several ten and 100 nm in thickness, and coarse interfacial equilibrium precipitates were formed around reinforcements, and that solute atoms were simultaneously segregated toward the interface. In this study, SiC whisker-reinforced 6061 Aluminum alloys are adopted as model materials. Effects of such locally-inhomogeneous microstructures of a matrix on the deformation and fracture characteristics of the MMCs are analyzed by means of the elastic-plastic finite element analysis. Due to the ductile nature of the PFZ layers, the concentrated plastic flow within the PFZ layers increases the effective plastic strain in the whole matrix, thereby reducing the strength of the MMCs. On the other hand, the interfacial precipitates effectively retard the concentrated plastic flow within the PFZ layers and consequently suppress the reduction in strength due to the formation of the PFZ. However, the interfacial precipitates never exhibit such preferable influence when the matrix is homogeneous. Both the axial stress within the whiskers and the initiation rate of voids due to the strain concentration around edges of the whiskers increase with extension of the PFZ layers and the interfacial precipitates. The initiation rate of the void is remarkably affected by the morphology and density of the precipitates. Since both the shear stress at the precipitate-reinforcement interface and the internal stresses within the precipitates are considerably high, the properties of the precipitates except for Young's modulus are important. Interphase having intermediate Young's modulus remarkably improves the strength of the MMCs.. |
| 446. | T. Kobayashi, H. Toda, Improvement of mechanical properties by RRA treatment in AL-SiCw composite, Materials Science Forum, 217-222, PART 2, 1127-1132, 1996.12, Formation of PFZ layers around reinforcements and simultaneous precipitation of the equilibrium phase on the interface has been clarified. Also the segregation of the solute atoms in the vicinity of the reinforcements is analyzed in this study. Effects of the PFZ layer and the solute atom segregation in the vicinity of the reinforcement in the discontinuously-reinforced metal matrix composite on deformation behavior and strength are analyzed by means of non-linear finite element method. With a view of eliminating baneful effects exerted by the formation of the PFZ layer which are predicted by the FEM analysis, new heat treatment procedure which has been developed to control the matrix microstructure by a simple heat treatment process is introduced. Improvement of the mechanical properties in this microstructurally-controlled MMCs is also reported in this study.. |
| 447. | L. Wang, Z. Sun, T. Kobayashi, H. Toda, Z. G. Wang, Cyclic deformation and low cycle fatigue behavior in a 6061Al/22vol% SiC whisker composite, Materials Transactions, JIM, 10.2320/matertrans1989.37.762, 37, 4, 762-768, 1996.01, A 6061A1 matrix composite reinforced with 22vol% SiC whiskers and the unreinforced matrix alloy in different aged conditions were examined at the ambient temperature. Total strain controlled cyclic deformation under fully-reversed loading and low cycle fatigue properties were measured. The mechanical test results demonstrated that the composite materials in different aged conditions cyclically hardened at the applied strain amplitudes, typically at 0.4%, 0.6% and 0.8%. The underaged composite specimens showed the most pronounced cyclic hardening, while the overaged composite only hardened to a limited amount at the first a few cycles.?It has been found that the addition of SiC whiskers into the 6061A1 increased the cyclic stress to the largest extent in the underaged condition while to the smallest in the overaged. The low cycle fatigue resistance of the composite to cyclic straining was found to be inferior to that of the unreinforced matrix alloy. When the saturation cyclic stress amplitude is considered, however, the composite material showed superior fatigue strength to the matrix alloy in this low cycle fatigue region. The experimental phenomena are interpreted in terms of the result of the electron microscopy and the fractography of the fatigue failed samples.. |
| 448. | H. Toda, T. Kobayashi, Fracture and fatigue in aluminum alloy matrix composite material, Journal of Japan Institute of Light Metals, 10.2464/jilm.45.610, 45, 11, 610-621, 1995.01. |
| 449. | H. Toda, T. Kobayashi, Y. Wada, Fracture mechanical simulation of a crack propagating in discontinuously-reinforced metal matrix composites, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.59.1_94, 59, 1, 94-102, 1995.01, A simulation program based on the fracture mechanics was constructed to evaluate crack initiation and growth characteristics in discontinuously-reinforced MMCs. Spatial patterns of reinforcement are quantified by using one of the three statistical probability functions. Reinforcement strength is assumed to vary according to the three-parameter Weibull distribution function. The crack-tip stress field is computed by HRR singularity for both stationary cracks and growing cracks. It was identified by preliminary in-situ CODs measurement. The results of FEM analysis are used for computing the extent of stress concentration around the reinforcement in the HRR field, and adequate criteria for microcrack initiation are defined. Shielding effects and crack deflection are taken into consideration. Finally, the strain energy density factor is used as a criterion for crack initiation and growth. Microcrack formation ahead of a major crack-tip and crack deflection towards the microcracks, which has been often observed in-situ in the discontinuously-reinforced MMCs, are well simulated by the numerical calculation. Parametric studies were carried out to evaluate crack initiation and growth through an Al alloy composite reinforced with SiC whiskers.. |
| 450. | H. Toda, T. Kobayashi, M. Niinomi, Effects of aging treatments on fracture characteristics of 6061 aluminum alloy reinforced with SiC whisker, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.58.4_468, 58, 4, 468-475, 1994.01, The effect of matrix microstructure on fracture characteristics of 6061 aluminum alloy reinforced with SiC whisker was investigated. The underaged composite exhibits stable slow crack growth behaviour and possesses a high fracture toughness value of 20.0 MPa √m. On the other hand, with increasing aging time, the fracture characteristics changes drastically to low stress type brittle fracture without stable crack growth, and the fracture toughness is degraded to the minimum level of 13.6 MPa √m in the peakaged composite. Detailed SEM observations of the fracture surfaces and cross-section of a specimen show that the microscopic fracture mechanisms of the underaged composite has the tendency of void nucleation and growth at the sharp corners of whiskers, and it is considered due to severe stress concentration. Meanwhile whisker breakage is mainly observed in the peakaged and overaged composites, and it is considered to be attributed to immediate rapid and unstable fracture. From the microstructural observations carried out using TEM, narrow PFZ is observed around whiskers and it is accompanied by coarse precipitates on their surfaces in the peakaged composite. Further, the density and size of the precipitates, according to direct and high-magnification observations on the surfaces of whiskers, increase with increasing aging time. The change of the microscopic fracture mechanism with increasing aging time in the mechanical property tests is attributed to both lowering of whisker fracture strength due to existence of coarse precipitates on its surface and depression of hydrostatic stress around sharp edges of whiskers due to existence of ductile PFZ layers. Therefore the premature fracture of whisker is considered to occur at a lower load level than nucleation of voids at the corners of whiskers in the peakaged and overaged composites.. |
| 451. | H. Toda, T. Kobayashi, M. Niinomi, Microstructural control by retrogression and reaging treatment in SiC whisker reinforced aluminum alloy composite, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.58.9_1086, 58, 9, 1086-1094, 1994.01, STEM-EDX analysis has been carried out to study segregation in the SiCw/6061 Al composite, and Mg was found to be segregated at reinforcement-matrix interfaces. It is shown that the segregation of Mg to the interface is consistent with the hypothesis of non-equilibrium segregation based on the vacancy-drag mechanism. A method is described of thermally treating the MMC to improve and tailor its precipitation structure according to these informations. The method comprises subjecting the MMC for a short period of time above a solvus temperature of the GP (II) zone or β′ transition phase, and a subsequent aging treatment. Partial dissolution of the GP zone or the transition phase is caused by dependence of the solvus temperatures on the solute concentration, and produces a more homogeneous distribution of the precipitates after the re-aging treatment. The beneficial effects on the mechanical properties of the MMC became clear, and its mechanism has been investigated.. |
| 452. | H. Toda, T. Kobayashi, Microstructurally-short fatigue crack in SiC whisker reinforced 6061 aluminum alloy composite, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.58.3_337, 58, 3, 337-345, 1994.01, Short crack propagation behaviour of 6061 aluminum alloy with and without SiC whisker was investigated. Short fatigue cracks initiate and grow in a much lower ΔK range than the threshold stress intensity ranges, ΔKth, of long fatigue cracks in both materials. In addition, there exists a growth dip in the MMC, and it could be explained by measured abrupt awakening of crack closure which is mainly induced by asperity contact. Statistic scatter in the growth rates of microstructurally short crack is observed in both of the materials. The distribution of crack growth rates well follows a three parameter Weibull distribution function. The shape parameters of this distribution function which reflects the extent of scatter in the crack growth rates are initially small in both of the materials and they increase and close to the respective asymptotic lines with increasing crack length. The crack length range when the scatter converges is 110 to approximately 183 μm for the unreinforced alloy and 25 to approximately 40 μm for the composite. This is considered as upper bounds of microstructurally short cracks. The differences in crack length may be attributed to the respective crack growth mechanisms that crystallographic crack growths such as slip band cracking and intergranular cracking, which are generally observed in the unreinforced alloy, are suppressed in the MMC due to the existence of closely spaced reinforcement, and a microstucturally short crack mainly interacts with reinforcement itself and a packet of whiskers.. |
| 453. | T. Kobayashi, H. Iwanari, S. Hakamata, M. Niinomi, H. Toda, Fatigue crack propagation characteristics in SiCp/6061-T6 composite, Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, 10.2320/jinstmet1952.55.1_72, 55, 1, 72-78, 1991.01, The effect of volume fraction of SiC particles on the fatigue crack propagation characteristics of 6061 aluminum alloys reinforced with SiC particles (SiCp/6061-T6 composites) manufactured by powder metallurgy was investigated. In a higher stress intensity range, unstable fatigue crack propagation was found as the threshold stress intensity range ΔKth and ΔKeff.th increased with increasing content of SiC particles. ΔKeff.th is suggested to be solely a function of the mean SiC particle size and to be independent of the volume fraction. This implies that for near-threshold crack extension, the maximum plastic zone size at the crack tip must exceed the mean SiC particle size.. |
Unauthorized reprint of the contents of this database is prohibited.