Language：Others   Publishing type：Research paper (scientific journal)  

Hierarchical anisotropic nanostructured Mg-RE alloys, containing LPSO lamellae and dense nano-precipitates, exhibit superior mechanical properties. However, their reliability as structural materials for long-term service, especially in terms of fatigue, is still a matter of concern. Here, scattered oxide nodules are detected as a special kind of fatigue damage that assists crack initiation, rather than the typical slip-band structure. The LPSO lamellae and dense β′ nano-precipitates lead to the high localization of fatigue damage. The fatigue-induced oxide nodules form and grow within the soft α-Mg layer, but their growth is limited by the adjacent strong LPSO lamellae, resulting in microcrack nucleation. Finally, clusters of microcracks along the LPSO/oxide interface converge to form the trans-granular crack initiation.

DOI： 10.1016/j.ijfatigue.2023.107820

Web of Science

Scopus

researchmap

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Coupling effects of fretting wear and cyclic stress could result in significant fatigue strength degradation, thus potentially causing unanticipated catastrophic fractures. The underlying mechanism of microstructural evolutions caused by fretting wear is ambiguous, which obstructs the understanding of fretting fatigue issues, and is unable to guarantee the reliability of structures for long-term operation. Here, fretting wear studies were performed to understand the microstructural evolution and oxidation behavior of an α/β titanium alloy up to 108 cycles. Contact surface degradation is mainly caused by surface oxidation and the generation of wear debris during fretting wear within the slip zone. The grain size in the topmost nanostructured layer could be refined to ∼40 nm. The grain refinement process involves the initial grain rotation, the formation of low angle grain boundary (LAGB; 2°–5°), the in-situ increments of the misorientation angle, and the final subdivision, which have been unraveled to feature the evolution in dislocation morphologies from slip lines to tangles and arrays. The formation of hetero microstructures regarding the nonequilibrium high angle grain boundary (HAGB) and dislocation arrays gives rise to more oxygen diffusion pathways in the topmost nanostructured layer, thus resulting in the formation of cracking interface to separate the oxidation zone and the adjoining nanostructured domain driven by tribological fatigue stress. Eventually, it facilitates surface degradation and the formation of catastrophic fractures.

DOI： 10.1007/s40544-022-0729-z

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Heterogeneities of microstructure, tensile and fatigue behavior of FSWed titanium alloy joint were in-situ studied by utilizing replica, DIC and electron back-scattered diffraction methods. Banded TMAZ consisting of needle-like α precipitates and elongated αp within DRXed β grains bridges the HAZ and SZ. Fine β grains in SZ contribute to the highest tensile strength in the 3rd layer. Fatigue cracks prefer to nucleate from HAGBs and {1 1 2} 〈1 1 1〉 slip deformation of β structure in the 2nd layer of SZ below 210 MPa and 3rd layer of HAZ otherwise. Transgranular crack propagation along the {1 1 2} planes exhibits a higher crack growth rate in HAZ than SZ.

DOI： 10.1016/j.ijfatigue.2022.107426

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Bismuth titanate(BIT) ceramics have been widely studied for high temperature applications thanks to their high Curie temperature and large spontaneous polarization. The underlying domain structures play significant roles in regulating the macroscopic properties of ferroelectric materials, while there is only limited knowledge of the domain structures for BIT ceramics until now, substantially bad for the development of BIT-based new materials. In this study, the intriguing domain walls(DWs) in BIT ceramics were investigated in detail. The atomic-scale observation reveals that there primarily exist energetically favorable {110}-type 90° DWs in BIT ceramics. Combined with the theoretical analysis, these DWs are not only elaborated under multiple piezoelectric response modes, but also further corroborated by the quantitative reconstruction of spatial polarization distributions of twin-related ferroelectric variants. This work sheds insight into domain structure and piezoelectric response mechanism in BIT ceramics, and contributes to promoting their more applications in advanced electron devices.

DOI： 10.1016/j.scriptamat.2022.114793

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

In most cases, welding processes promote the application of structural materials at the expense of strength and ductility. Post-weld treatment is proposed to regain mechanical properties of weldment, which necessitates that microstructural and the associated mechanical behavior evolutions being clearly understood. In this study, post-weld heat treatment was conducted to enhance the mechanical properties of the electron beam welded Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy joint. Microstructural evolutions and monotonic mechanical properties were characterized to optimize the post-weld heat treatment parameters. It was found that direct aging at 630 °C for 2 h can upraise the strength and ductility of the joint by ∼31% and ∼511% respectively. Metastable needle-shaped martensite α′ within rapidly solidified fusion zone had been completely decomposed, and thin recrystallized α lamella precipitated in the prior β phase without forming consecutive coarse grain boundary α after above direct aging treatment. Such microstructural characteristics enable the direct-aged joint to exhibit a higher fatigue strength from high to very high cycle region than the as-welded joint. Moreover, the fatigue crack nucleation resistance was enhanced significantly through direct aged treatment.

DOI： 10.1016/j.msea.2021.142168

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

High cycle and very high cycle fatigue (VHCF) crack initiation mechanism of TC17 alloy joint with heterogeneous microstructures in FZ has been studied at the stress ratio of 0.1. Intrinsic deficiencies of slip deformation in β grains with few martensites and cracking coarse grain boundary between prior β grains with martensite colonies account for the high cycle fatigue (HCF) of joints. The average diameter of intergranular welding pores regarding VHCF crack nucleation is measured to be ∼36 μm. The driving force governing the crack nucleation from intrinsic deficiencies in HCF to porosity defects in VHCF is ∼1.66 MPa·m1/2.

DOI： 10.1016/j.ijfatigue.2021.106525

Web of Science

Scopus

researchmap

Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

CiNii Research

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/ffe.13520

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2021.106302

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.msea.2021.141850

Language：Others   Publishing type：Research paper (scientific journal)  

This paper investigated the effects of Gd and Y solutes on aging behaviour and corresponding mechanical properties of the extruded Mg–Gd(-Y)-Zn-Mn alloys at room and elevated temperatures. The results show that aging treatment provided significant improvement of ~100 MPa in strength by forming ellipsoidal β′ nanophases in the as-extruded alloys. Partially substituting Y for Gd in the as-extruded Mg-Gd-Zn-Mn alloys can delay age-hardening response, but improve the strength increment after aging treatment. As the Y/Gd atomic ratio changed from 0 to 1, the Mg-1.75Gd-0.75Y-0.5Zn–Mn(at.%) alloy with a Y/Gd atomic ratio of 0.4 obtained the higher peak-hardness and mechanical properties. Enhanced age-hardening response and better mechanical properties were detected after separate additions of Y and Gd. The extruded-T5 Mg-2.5Gd-0.75Y-0.5Zn-0.3Mn alloy exhibited superior ultimate tensile strengths of 520 MPa at room temperature, 344 MPa at 250 °C, and 225 MPa at 300 °C. Fracture behaviours reveal that a change in predominant deformation mechanism from one based on dislocations to one mediated by grain boundary (GB) processes was found as the tensile temperatures arise from 250 °C to 300 °C. The activation of GB sliding of the fine grains partially resulted in the decrease of tensile strength at 300 °C.

DOI： 10.1016/j.msea.2021.141019

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.matchar.2020.110756

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2020.105868

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2020.105720

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jmatprotec.2020.116666

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.matlet.2020.127853

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.matchar.2020.110396

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2020.105580

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s42243-019-00347-2

Language：English   Publishing type：Research paper (scientific journal)  

We explored the very high cycle fatigue (VHCF) behavior of solution treated Mg–10Gd–3Y–1Zn–0.5Zr (wt. %, GWZ1031K-T4) alloy containing long-period stacking ordered (LPSO) structures. The fatigue strength of GWZ1031K-T4 alloy at 109 cycles is about 115.0 MPa, and the corresponding fatigue ratio is approximately 0.44. Crack initiation that causes fatal failure was found to occur primarily from the specimen surface in the high cycle fatigue regime and the subsurface in the very high cycle fatigue regime, accompanied by crystallographic facet formation irrespective of a lifetime. Our results reveal that the basal slip activated in the matrix grain substantially alleviated strain localization during VHCF testing. The unique microstructure, featuring block-shaped LPSO structures scattered at the grain boundary, a large amount of thin LPSO phase and stacking faults enriched with solute atoms (SFs) homogenously distributing in the alloy matrix, and supersaturated Gd and Y atoms in the nano-scale Mg layers in the grain, is proposed to account for the enhanced fatigue failure resistance of GWZ1031K-T4 alloy.

DOI： 10.1016/j.mtla.2020.100672

Language：English   Publishing type：Research paper (scientific journal)  

The precipitates inside deformation twins may block the dislocation motion and consequently affect the mechanical property of materials. Herein, at the atomic level, we directly visualize that the basal dislocation slips shear the twinned stacking faults (TSFs) within the deformation twins in an Mg–Zn–Y alloy containing long-period stacking ordered (LPSO) structures. The TSFs, enriched with solute atoms, could be considered as precipitates inside deformation twins. They are sheared by a single step or multiple shearing steps on the basal plane. The microstructural fingerprints, i.e., the width of basal shearing steps, enable a quantitative assessment of the local and total plastic shear strain due to the basal dislocation within the deformation twins. The TSFs can block dislocation slip, while the dislocation shearing induces large lattice distortion and even solute atoms redistribution at local intersection. The TSFs-dislocation interaction is expected to lower the basal dislocation motion and resultantly modulate the mechanical properties of magnesium alloys. These results may offer a novel strategy for strengthening and toughening magnesium alloys via tailoring the shearable precipitates.

DOI： 10.1016/j.msea.2020.139109

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jallcom.2019.151937

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2019.105210

Language：English   Publishing type：Research paper (scientific journal)  

The interfacial segregation plays an important role in affecting the mechanical performance of various materials. Here we study the segregation behaviors along deformation-induced interfaces in the matrix of an Mg97Zn1Y2 (at%) alloy compressed at 473 K using atomic-scale high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging techniques. The kink boundary, twinning-like boundary, and tilt boundary within the matrix grain are detected to be segregated with both solute Zn and Y atoms. The segregation along kink boundary and twinning-like boundary is closely linked to the associated partial dislocations, and these boundaries also could be regarded as the nucleation sites for the formation of long period stacking ordered (LPSO) structures of nanometer scale and stacking faults (SFs) during deformation. For the various tilt boundary, the segregation could be explained based on either the O-lattice theory or partial dislocations. The experimental results may shed some new light on tailoring microstructures for improving mechanical properties and thermal stability of magnesium alloys.

DOI： 10.1016/j.mtla.2019.100287

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2018.10.002

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/14786435.2018.1539262

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.msea.2018.10.015

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1080/02670836.2017.1407556

Language：Japanese  

<p>There are many studies reported that a fatigue crack propagated in a tensile mode macroscopically and the fracture surface was mainly occupied by striations in many metals. Whereas, a unique fracture in which a crack propagated in a macroscopic shear direction accompanied by ductile facets was observed in some aluminum alloys under specific conditions. In the present study, fatigue tests of age-hardened Al alloys of extruded 2017-T4 and 7075-T6 were conducted in relative humidity environments of 25% and 85% under rotating bending and ultrasonic loading conditions to clarify the crystallographic feature of a shear mode crack and propose its growth mechanism. Many facets showing a feature of shear mode crack propagation with an equivalent size to the grain size were observed at the fracture surface under both conditions of rotating bending in high humidity and ultrasonic loading irrespective of humidity. In addition, it was confirmed that the angle between the loading axis and the growth direction of the shear mode crack composed a constant value, ~35°, relating to the marked texture in the propagation process of the macroscopic shear mode crack. However, a crack growth rate was lower in the ultrasonic loading than in the rotating bending in high humidity. Based on their differences in occurrence conditions of the shear mode crack, two mechanisms for this unique propagation were proposed as follows; that is, one was a shear mode crack occurred by the promotion of the slip deformation to one direction due to hydrogen generated by reaction of Al alloy with water vapor in high humidity, and the other was a crack by the suppression of the deformation to one direction due to re-welding of crack faces under ultrasonic loading.</p>

DOI： 10.1299/transjsme.17-00273

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1155/2017/7189369

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Effect of humidity on the growth mechanism of a fatigue crack in an age-hardened Al alloy was investigated in relative humidity environments of 25% and 85% at loading frequencies of 50Hz and 6Hz. Macroscopic growth mode of a crack in low humidity was a tensile one irrespective of loading frequency. By contrast, the mode in high humidity was changed from the shear one to the tensile one with increase in fatigue life at 50 Hz, while it was the tensile mode only in the wide range of fatigue life at 6 Hz. In low humidity, the crack propagated by forming striations which are general in fatigue of many metals. On the other hand, in high humidity, most of fracture surface was occupied by many slip planes in the shear mode crack and by granular facets in addition to striations in the tensile mode one. The crack growth rate in high humidity was higher in the shear mode crack than in the tensile mode one. The differences in growth mechanism and growth rate of a crack were explained by the content of diffused hydrogen generated by reaction of water vapor and aluminum in addition to the microstructure with sub-grain and texture and the cyclic softening behavior of the alloy.

DOI： 10.1299/transjsme.14-00694

Language：Japanese   Publishing type：Research paper (scientific journal)  

The effect of aging condition on fatigue properties and the mechanism of decrease in fatigue strength in high humidity in 18&#37; Ni maraging steel of grade 350 were investigated under rotating bending in relative humidity of 25&#37; and 85&#37;. Aging conditions investigated were under-, peak- and over-aging ones at the conventional aging temperature of 753K. In addition, double-aging treatments which were under- peak- and over-aging treatments at 673K and under-aging one at 473K after the peak-aging at 753K were also examined. Both of static and fatigue strengths were increased by the double-aging without any decrease in ductility and fatigue fracture toughness. Fatigue strength was markedly decreased by high humidity in all of the steels, and the decrease in fatigue strength was mainly caused by the accelerations of crack initiation and its growth at the early stage of fatigue process. The decrease in fatigue strength in high humidity was also suppressed by the double aging. A few facets comparable to a grain size of a prior austenite were observed at the fracture origins in high humidity but transgranular cracks by slip deformation were in low humidity. However most of the fracture surfaces were covered with lath boundary cracking regardless of the humidity and aging conditions. River pattern was observed in the facets, suggesting that the acceleration of crack growth in high humidity was a behavior related to hydrogen generated in cathode reaction. Based on the results, new aging treatment for improvement of fatigue properties of maraging steel was proposed. © 2013 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.62.756

Language：Japanese  

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.4028/www.scientific.net/KEM.577-578.89

Language：Others   Publishing type：Research paper (other academic)  

Language：Others   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/ma5112280

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the effects of humidity change and loading frequency on growth behavior of a fatigue crack of an extruded bar of an age-hardened Al alloy 7075-T6, rotating bending fatigue tests were carried out in relative humidity of 25&#37; and 85&#37; at frequencies of 50Hz and 6Hz. At 50Hz, macroscopic appearances of fractures were a shear mode at high stress levels in high humidity, though those were a tensile mode in other conditions of humidity and stress levels. The crack growth rate was accelerated by high humidity. By changing humidity, both of the growth rate and the growth mode of a crack were immediately changed to those corresponding to the changed humidity. That is, the growth behavior and fatigue life under humidity change may be estimated by those in constant humidity. Fatigue life in high humidity at 6Hz was longer than that at 50Hz in spite of accelerations of both of the crack initiation and its growth rate in the early growth process in high humidity at both frequency, though there was no or little influence of frequency on fatigue life in low humidity. Moreover, the crack propagated in the tensile mode even at high stress levels where the shear mode crack propagated at 50Hz. These results were explained by the effect of hydrogen on the crack growth behavior. © 2012 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.61.712

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate effects of a texture and a slip characteristic on fatigue properties of Al alloys in high humidity, rotating bending fatigue tests were carried out using plain specimens of an extruded bar and a drawn one of age-hardened Al alloy 2017-T4 and an Al alloy annealed the extruded one in relative humidity of 25&#37; and 85&#37;. The extruded Al alloy and the annealed one had a marked texture of a (111) plane at the cross section of each bar, but a specified orientation was not observed in the drawn one. In addition, the aged-hardened Al alloys show a planar slip property and the annealed alloy shows a wavy one. In the all Al alloys, the obvious retardation of a small crack growth due to blocking effect of a grain boundary was observed in low humidity, though the retardation disappeared in high humidity. Moreover the acceleration of a crack growth was yielded due to the change in growth mechanism of a crack from a tensile mode in low humidity to a shear mode at high stress levels in high humidity in the extruded alloy, though the effect of humidity on the growth mechanism was very small in the drawn Al alloy and the annealed one. In the extruded Al alloy, the fracture surface yielded by the shear mode crack in high humidity was occupied by many slip planes and voids and was a (100) plane, though the fracture surface formed by the growth of the tensile mode crack in low humidity was covered with striations. In the drawn and annealed Al alloys, fracture surfaces were mainly occupied by striations irrespective of humidity and stress levels. © 2012 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.61.556

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1063/2.1203108

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s10853-011-5935-4

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the growth mechanism of a shear mode fatigue crack in an extruded bar of an age-hardened Al alloy 7075-T6, rotating bending fatigue tests were carried out using plain specimens of the alloy in environments of controlled relative humidity of 25&#37;, 50&#37;, 75&#37; and 85&#37;, distilled water and nitrogen gas. Fatigue strength was decreased by high humidity. The growth mechanism of a fatigue crack was different depending on environment and stress level. Although most of fractures occurred by the growth of a tensile mode crack, a crack propagated in a shear mode accompanying with slip planes and voids at high stress levels in high humidity and at all stress levels tested in nitrogen gas. The shear mode crack was related to the marked texture of the alloy. Growth rates of the shear mode crack were higher in high humidity than in nitrogen gas. Growth mechanisms of the shear mode crack were different between environments in nitrogen gas and in high humidity. That is, the reason for the growth of a shear mode crack in nitrogen gas was the suppression to growth of a tensile mode crack by reversible slip due to absence of oxide film. On the other hand, in high humidity, the growth of a shear mode crack was promoted by the formation and coalescence of voids, suggesting that the acceleration of the growth rate of a crack may be assisted by hydrogen accumulated around precipitated particles on glide planes. © 2011 The Society of Materials Science, Japan.

DOI： 10.2472/jsms.60.890

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.4028/www.scientific.net/KEM.488-489.45

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the availability of ultrasonic fatigue test for the evaluation of fatigue properties under conventional loading frequency, fatigue tests under ultrasonic frequency and rotating bending were carried out using plain specimens of an age-hardened and extruded Al alloy 7075-T6 in 7 kinds of environments of controlled humidity of 25, 50, 70 and 85%, distilled water oxygen gas and nitrogen gas. Although fatigue strength was decreased by high humidity, the decrease by high humidity was very small when the humidity was lower than about 60%～70% and fatigue strength was largely decreased above that humidity under both tests. However, the main reason for the decrease in fatigue strength by high humidity was different between rotating bending fatigue and ultrasonic fatigue. That is, the decrease in fatigue strength was mainly the acceleration of crack growth caused by brittle fracture under rotating bending and the transition to shear mode crack accompanied with glide plane decohesion and void formation under ultrasonic loading, respectively.

DOI： 10.1299/kikaia.76.1651

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s12541-010-0102-4

Language：Japanese  

DOI： 10.1299/kikaia.76.1651

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1142/S0217979210065179

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1142/S0217979210065751

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.76.1651

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijmachtools.2009.06.003

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/jmmp.2.1399

Language：Others   Publishing type：Research paper (other academic)  

Language：Japanese  

Ultrasonic fatigue tests of plain specimens with different grain sizes were carried out for Ni-base super alloy, Inconel 718, in ambient air in order to investigate the effect of grain size on fatigue properties. Fatigue strength was increased with decrease in grain size. The increase in fatigue strength by refining grain size was mainly caused by the suppression of crack initiation. That is, the effect of grain size on crack growth rate was hardly recognized, though crack morphology was rougher in the specimen of larger grain, meaning that the crack growth in the large-grained specimens was suppressed by roughness induced crack closure. On the other hand, however, more flat facets caused by twin boundary cracking were observed in the large-grained specimens, which inversely led to crack growth acceleration.

DOI： 10.1299/kikaia.74.1000

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the hardness dependence on the fatigue strengths for surface fracture and internal fracture, rotating bending fatigue tests were carried out for maraging steels using specimens with different hardness obtained by heat-treating at different under-aging conditions. Fatigue limit for surface fracture was evaluated in electro-polished specimens and the one for internal fracture was in shot-peened ones, where fatigue limits were defined as fatigue strengths at 107cycles for surface fracture and 108cycles for internal fracture, respectively. Fatigue limit for internal fracture increased with increase in hardness similar to the one for surface fracture. However, the proportional relationship between the fatigue limit and the hardness existed till higher hardness in the fatigue limit for internal fracture than in the one for surface fracture. This difference in the hardness dependence on fatigue limit was discussed from the viewpoint of the influence of humidity on the fatigue strength. © 2007 The Society of Materials Science.

DOI： 10.2472/jsms.56.1126

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.4028/www.scientific.net/kem.348-349.541

Language：English  

OS4-4-1 Influence of grain size on fatigue properties in carbon steel
In order to investigate the influence of grain size on the resistance to crack growth, fatigue properties of commercial fine-grained carbon steels with grain sizes of 6.5 and 20 μm were investigated based on the crack initiation and propagation behavior through the successive observation of surface state of smooth specimen under rotating bending. A crack initiated at the early stage of stress repetitions and most of fatigue life was occupied by the growth life of a crack smaller than 1～2 mm. The crack growth rate determined by the term σ_a^nl, uniquely in both steels, where σ_a and l are the stress amplitude and the crack length and n is constant. The fine grained- steel has an excellent resistance to crack growth in comparison with many annealed carbon steels.

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.4028/www.scientific.net/kem.353-358.227

Language：Others   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2005.09.017

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the growth mechanism of a fatigue crack of Ni-based super alloy at ultrasonic frequency, ultrasonic fatigue and rotting bending fatigue tests were carried out for Inconel 718 in ambient air and in N₂ gas using plain and notched specimens and the results in both tests were compared by focusing on the effects of strain rate and environment. In ambient air, fatigue strength was higher in ultrasonic fatigue than in rotating bending fatigue in plain specimen, while the results in notched specimen were the reverse. Many transgranular cracks and cleavage like cracks were observed on the fracture surface in ultrasonic fatigue in addition to striation and transgranular facets observed in rotating bending fatigue and there was no difference in the fracture mechanism between plain specimen and notched one. Moreover, these effects of frequency on the growth mechanism of a crack in ambient air were nearly the same in N₂ gas, though fatigue strength in N₂ gas was higher than that in air. The increase in fatigue strength in N₂ gas was mainly caused by the retardation of a crack initiation.

DOI： 10.1299/kikaia.72.1542

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2006.02.028

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the effect of frequency on the crack growth behavior, ultrasonic fatigue tests were carried out for an extruded age-hardened Al alloy, 7075-T 6, in ambient air and in N₂ gas, and the results were compared with those in rotating bending fatigue. Fatigue strength was higher in ultrasonic fatigue than in rotating bending one. This was caused by the retardation of a crack initiation and its early propagation. In ultrasonic fatigue, the growth direction of a crack changed macroscopically from a tensile mode to a shear one which the direction was about 35 degrees against to the specimen axis, and fracture mechanism also changed from striations to transgranular facets with voids microscopically. Crack growth rate at the transition of crack growth direction was about 3 × 10^-9 m/cycle. The relation between an applied stress σ_a and a crack depth at the transition of crack growth direction b_T was expressed by σⁿ_ab_T=constant. These results were explained from the time dependent environmental effect and texture of microstructure.

DOI： 10.1299/kikaia.72.1356

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Propagation behavior of an internal crack of a radical nitrided bearing steel

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.71.1362

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ijfatigue.2005.07.022

Language：English   Publishing type：Research paper (scientific journal)  

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.71.1226

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the fracture mechanism in fatigue of Ni-base superalloy at elevated temperatures, rotating bending fatigue tests were carried out for Inconel 718 at 500°C and 600°C up to 10⁸ cycles. At both temperatures, fracture occurred from a subsurface of the specimen in long life region, though the origin of fracture was the specimen surface in short life region. Consequently, S-N curves showed a two-step shape in elevated temperature tests. Although a surface crack was observed similar to the result at room temperature even in long life region at elevated temperatures, the surface crack stopped propagating. In this case, interganular cracks were observed at an origin of subsurface fracture. The subsurface damage was initiated at the early stage of fatigue life.

DOI： 10.1299/kikaia.71.1226

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the propagation behavior of an internal crack in surface treated steel, rotaing bending fatigue tests were carried out for a radical-nitrided bearing steel. The fracture occurred from a specimen surface under high stress levels, whereas a fish-eye fracture occurred under low stress levels. Consequently, S-N curve was duplex S-N one. A circular trace was observed inside the fish-eye when the fracture occurred under two-step variable stress amplitude test. It was suggested that the trace was formed by the change in stress amplitude. Moreover, from the change in the trace size depending on the stress level and the number of stress cycles, it was concluded that there is a fatigue limit for the internal fracture meaning the limit for crack propagation and most of fatigue life the internal fracture was occupied by the growth life of a small internal crack.

DOI： 10.1299/kikaia.71.1362

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the influence of loading frequency on the fatigue properties of Al alloy, ultrasonic fatigue tests were carried out for an age-hardened Al alloy, 6061-T6. The results were compared with those of rotating bending fatigue in view points of initiation and propagation behavior of a crack and fracture mechanism. Fatigue life was longer in ultrasonic fatigue than in rotating bending fatigue, which was mainly caused by the suppression of crack initiation. In ultrasonic fatigue, many fatigue voids and cleavage cracks were observed on the fracture surface in addition to the shear mode cracks, striations and dimples, which were typical fracture modes in rotating bending.

DOI： 10.1299/kikaia.70.1139

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.12989/sem.2004.18.3.277

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1023/B:JMSC.0000008091.55395.ee

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the influence of loading frequency on the fatigue strength and fracture mechanism of a high strength Al alloy, ultrasonic fatigue tests were carried out for an extruded Al alloy 7075-T 6 and the results were compared with those of rotating bending fatigue tests. Fatigue strength of ultrasonic was higher than that of rotating bending. The crack initiation and the crack growth rate in ultrasonic fatigue were delayed compared with those of rotating bending fatigue. In case of ultrasonic fatigue, the direction of crack growth changed from tensile mode to shear mode and many voids were observed on the fracture surface in shear mode growth, whereas the crack propagated in tensile mode and striations were observed in rotating bending fatigue.

DOI： 10.1299/kikaia.69.1672

Language：Others   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S1359-6462(03)00365-8

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

In order to investigate the effect of load frequency on the fatigue strength and fracture mechanism of a nickel-base superalloy, Inconel 718, fatigue tests were carried out under an ultrasonic frequency (19.5kHz) in ambient air environment. The results were compared with those obtained under conventional rotatary bending fatigue at a frequency of 50 Hz. Fatigue strength increased at ultrasonic frequency, which is mainly caused by the suppression of crack initiation and its growth at the early stage. Under both ultrasonic and rotary bending fatigue tests, most of fatigue life consumed in the growth of a crack smaller than 1 mm. In the ultrasonic fatigue, intergranular and cleavage crack propagations were observed in addition to striation, which was a dominant fracture mechanism in the conventional fatigue.

DOI： 10.1299/kikaia.69.626

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0142-1123(02)00037-3

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

The fatigue properties of a nickel-base superalloy, Inconel 718, in long-life region up to 10⁸ cycles were investigated under rotating bending at room temperature and elevated temperature of 300°C, 500°C and 600°C. S-N curves at 500°C and 600°C showed the stepwise shapes, though those in cases of room temperature and 300°C were the conventional one-step ones. All the fractures originated from the specimen surface at room temperature and 300°C, while the internal fractures occurred in long-life region beyond 10⁷ cycles and the surface fractures at the stress levels over the horizontal line of S-N curves corresponding to the fatigue limit for the surface fracture at 500°C and 600°C. Intergranular crackings were observed at the origin of internal fracture.

DOI： 10.1299/kikaia.68.1192

Language：Others   Publishing type：Research paper (other academic)  

DOI： 10.1117/12.468825

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.67.314

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11661-000-0228-6

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1046/j.1460-2695.2000.00263.x

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaic.66.1700

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1007/s11661-000-0228-6

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0921-5093(99)00555-9

Language：Others   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/s0142-1123(99)00081-x

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1016/B978-008043011-9/50022-3

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1361/105994999770346981

Language：Japanese   Publishing type：Research paper (scientific journal)  

Initiation and growth behavior of a fatigue crack in inconel 718 at elevated temperatures

DOI： 10.1299/kikaia.65.1954

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0142-1123(99)00081-X

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.64.839

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.64.2869

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.63.1398

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.63.1844

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.63.2298

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/kikaia.62.960

Language：English   Publishing type：Research paper (scientific journal)  

Event date： 2011.9

Language：English  

Country：Croatia  

Event date： 2008.9

Language：English  

Country：Czech Republic  

Event date： 2007.8

Language：English  

Country：United States  

Event date： 2003.3

Language：English  

Country：Greece  

Event date： 2002.5

Language：English  

Country：Japan  

Event date： 2001.6

Language：English  

Country：Spain  

Event date： 2001.6

Language：English  

Country：United States  

Language：Others  

Country：Japan  

Language：English  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Because of its excellent mechanical properties at elevated temperature, a nickel-base superalloy has been widely used in the aerospace industry and nuclear power plants. In this study, rotating bending fatigue tests were carried out for Inconel 718 at room temperature and elevated temperatures of 300°C, 400°C and 500°C to investigate the notch sensitivity at the elevated temperatures. It was found that the fatigue limits of plain specimens were higher at the elevated temperatures than at room temperature, which might be due to the suppression of the crack initiation at the elevated temperatures, however, the resistance to crack growth became smaller at the elevated temperatures than at room temperature. Therefore, the fatigue strength of a notched specimen, in which a crack initiated easily owing to the stress concentration introduced, was lower at the elevated temperatures than at room temperature. Consequently, the fatigue strength reduction factor was larger at the elevated temperatures than at room temperature.

Language：Japanese  

Country：Japan  

Because of its excellent mechanical properties at elevated temperature, a nickel-base superalloy has been widely used in the aerospace industry and nuclear power plants. In this study, rotating bending fatigue tests were carried out for Inconel 718 at room temperature and elevated temperatures of 300 °C, 400 °C and 500 °C to investigate the notch sensitivity at the elevated temperatures. It was found that the fatigue limits of plain specimens were higher at the elevated temperatures than at room temperature, which might be due to the suppression of the crack initiation at the elevated temperatures, however, the resistance to crack growth became smaller at the elevated temperatures than at room temperature. Therefore, the fatigue strength of a notched specimen, in which a crack initiated easily owing to the stress concentration introduced, was lower at the elevated temperatures than at room temperature. Consequently, the fatigue strength reduction factor was larger at the elevated temperatures than at room temperature.

Language：Japanese  

Country：Japan  

Rotating bending fatigue tests were carried out for Inconel 718 at room temperature and elevated temperatures of 300℃, 500℃ and 600℃ to investigate the influence of temperature on the fatigue crack growth resistance. The crack growth rate can be expressed by the small crack growth law, dl/dN=C_1σ^n_al=C_2(σ_a/σ_B)^nl, at all the temperatures, where σ_B, σ_a and l are the tensile strength, the stress amplitude and the crack length, and C_1,C_2 and n are constants. Therefore, the resistance to crack growth was evaluated using the small crack growth law. The fatigue crack growth resistance decreased with the increase of temperature.

Language：Japanese  

Country：Japan  

Rotating bending fatigue tests were carried out for Inconel 718 at room temperature to investigate the growth characteristics of a small crack. It was found that : (1) The crack initiated at the grain boundary and then propagated as a transgranular crack. (2) When the stress level was higher than the fatigue limit, the fatigue life was mainly controlled by the growth life of a crack smaller than 1mm. (3) The fatigue limit was a limiting stress for the crack propagation. (4) At low stress levels (σ_a/σ_0.2<0.5, σ_a : stress amplitude, σ_0.2 : 0.2% proof stress), the crack growth rate was determined by the stress intensity factor range ΔK ; and at high stress levels (σ_a/σ_0.2>0.6), it was determined by the small crack growth law.

Language：Others  

Country：Japan  

Fatigue strength of specimens ground by a CBN wheel (In cases of carbon steels and a nickel-base super alloy)
Rotating bending fatigue tests were carried out on carbon steels and a nickel-based super alloy, Inconel 718, for investigation of the effect of CBN wheel grinding on the fatigue strength at room temperature and 500 °C. The results are discussed from several view points, including surface roughness, residual stress and work hardening or softening due to grinding. The fatigue strength increased upon CBN wheel grinding at room temperature, primarily because of generation of compressive residual stress due to the CBN wheel grinding. However, this marked increase in the fatigue strength due to CBN wheel grinding tended to disappear at elevated temperature.

Language：Others  

Country：Japan  

Fatigue crack growth resistance in nickel-base superalloy at elevated temperatures
Rotating bending fatigue tests were carried out for Inconel 718 at room temperature and elevated temperatures of 300 °C, 500 °C and 600 °C to investigate the influence of temperature on the fatigue crack growth resistance. The crack growth rate can be expressed by the small crack growth law, dl/dN = C1σanl = C2(σa/σB)nl, at all the temperatures, where σB, σaand l are the tensile strength, the stress amplitude and the crack length, and C1, C2and n are constants. Therefore, the resistance to crack growth was evaluated using the small crack growth law. The fatigue crack growth resistance decreased with the increase of temperature.

Language：Japanese  

Country：Japan  

Rotating bending fatigue tests were carried out for Inconel 718 at room temperature to investigate the growth characteristics of a small crack. It was found that: (1) The crack initiated at the grain boundary and then propagated as a transgranular crack. (2) When the stress level was higher than the fatigue limit, the fatigue life was mainly controlled by the growth life of a crack smaller than 1 mm. (3) The fatigue limit was a limiting stress for the crack propagation. (4) At low stress levels (σa/σ0.2<0.5, σa: stress amplitude, (σ0.2:0.2&#37; proof stress), the crack growth rate was determined by the stress intensity factor range ΔK; and at high stress levels (σa/σ0.2>0.6), it was determined by the small crack growth law.

Language：Japanese  

Country：Japan  

Rotating bending fatigue tests were carried out on carbon steels and a nickel-based super alloy, Inconel 718, for investigation of the effect of CBN wheel grinding on the fatigue strength at room temperature and 500°C. The results are discussed from several view points, including surface roughness, residual stress and work hardening or softening due to grinding. The fatigue strength increased upon CBN wheel grinding at room temperature, primarily because of generation of compressive residual stress due to the CBN wheel grinding. However, this marked increase in the fatigue strength due to CBN wheel grinding tended to disappear at elevated temperature.

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Rotating bending fatigue tests were carried out for nickel-base superalloy Inconel 718 in air at room temperature and the elevated temperatures of 300℃, 500℃ and 600℃ using the 60 degree V-grooved specimen in order to investigate the influence of temperature on the notch sensitivity of the alloy. The notch sensitivity was assessed in terms of the limiting stress for crack initiation σ_<w1> and that for crack growth σ_<w2>, based on the Linear Notch Mechanics (LNM). It was found that the fatigue limits σ_<w1>, σ_<w2> of notched specimen can be evaluated by LMN at each temperature. Although the notch sensitivity of Inconel 718 to the two fatigue limits is relatively low considering its high static strength at all the temperatures, especially to the fatigue limit for crack growth, it becomes more sensitive at the elevated temperatures than at room temperature. The results were discussed with the effect of temperature on the arresting behavior of fatigue crack growth.

Language：Japanese  

Country：Japan  

Rotating bending fatigue tests were carried out for Ni base super alloy Inconel 718 at room temperature and elevated temperatures of 300℃, 500℃ and 600℃ in order to investigate the effect of surface oxidation at the elevated temperatures on the fatigue crack initiation and its early growth process. The fatigue strength was higher at the elevated temperatures than at room temperature when stress levels were low. This phenomenon was caused from that the growth of a crack smaller than the size of a few grains was suppresed at the elevated temperatures, though the growth of a larger crack was accelerated. The main reason for the suppression of the early growth of a small crack was a formation of oxide films on the specimen surface at the elevated temperatures.

Language：Japanese  

Country：Japan  

Language：English  

Country：Japan  

Language：English  

Country：Japan  

Language：English  

Country：Japan  

Language：English  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Fatigue fracture is a serious problem in high-speed machines and lightened structures. Therefore, it is very important for fully automated machines to predict or estimate fatigue damage of the machines nondestructively. On the other hand, acoustic emission is the phenomenon that elastic waves caused by released elastic deformation energy propagate in materials, and initiation and propagation of cracks can be detected by using the acoustic emission.. Accordingly, fatigue damage of a specimen in plane bending fatigue test was tried to be estimated by using pattern of occurrence of AE per cycle of periodic change of stress. As a result, it was verified that proposal method can estimate fatigue damage, but with a little error.

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

The fatigue strength of a nikel-base superalloy, Inconel 718, was investigated at room temperature under an ultrasonic frequency (19.5kHz) loading in ambient air environment. The endurance (S-N) data show that fatigue strength was enhanced at ultrasonic frequency as compared with those at conventional frequencies. Small crack initiation and propagation behavior was observed during the fatigue progress at both ultrasonic fatigue and conventional rotary bending fatigue. The effect of frequency on the fatigue mechanism was examined from a microscope viewpoint.

Language：Japanese  

Country：Japan  

The fatigue properties of a nickel-base superalloy, Inconel 718, in long-life region up to 10⁸ cycles were investigated under rotating bending at room temperature and elevated temperature of 300°C, 500°C and 600°C. S-N curves at 500°C and 600°C showed the stepwise shapes, though those in cases of room temperature and 300°C were the conventional one-step ones. All the fractures originated from the specimen surface at room temperature and 300°C, while the internal fractures occurred in long-life region beyond 10⁷ cycles and the surface fractures at the stress levels over the horizontal line of S-N curves corresponding to the fatigue limit for the surface fracture at 500°C and 600°C. Intergranular crackings were observed at the origin of internal fracture.

Language：Others  

Country：Japan  

Language：English  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

In order to investigate the influence of loading frequency on the fatigue strength and fracture mechanism of a high strength Al alloy, ultrasonic fatigue tests were carried out for an extruded Al alloy 7075-T 6 and the results were compared with those of rotating bending fatigue tests. Fatigue strength of ultrasonic was higher than that of rotating bending. The crack initiation and the crack growth rate in ultrasonic fatigue were delayed compared with those of rotating bending fatigue. In case of ultrasonic fatigue, the direction of crack growth changed from tensile mode to shear mode and many voids were observed on the fracture surface in shear mode growth, whereas the crack propagated in tensile mode and striations were observed in rotating bending fatigue.

Language：Others  

Country：Japan  

Language：Others  

Country：Japan  

Language：Japanese  

Country：Japan  

In order to investigate the effect of load frequency on the fatigue strength and fracture mechanism of a nickel-base superalloy, Inconel 718, fatigue tests were carried out under an ultrasonic frequency (19.5kHz) in ambient air environment. The results were compared with those obtained under conventional rotatary bending fatigue at a frequency of 50 Hz. Fatigue strength increased at ultrasonic frequency, which is mainly caused by the suppression of crack initiation and its growth at the early stage. Under both ultrasonic and rotary bending fatigue tests, most of fatigue life consumed in the growth of a crack smaller than 1 mm. In the ultrasonic fatigue, intergranular and cleavage crack propagations were observed in addition to striation, which was a dominant fracture mechanism in the conventional fatigue.

Language：English  

Country：Japan  

Language：English  

Country：Japan  

Language：English  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

In order to investigate the influence of loading frequency on the fatigue properties of Al alloy, ultrasonic fatigue tests were carried out for an age-hardened Al alloy, 6061-T6. The results were compared with those of rotating bending fatigue in view points of initiation and propagation behavior of a crack and fracture mechanism. Fatigue life was longer in ultrasonic fatigue than in rotating bending fatigue, which was mainly caused by the suppression of crack initiation. In ultrasonic fatigue, many fatigue voids and cleavage cracks were observed on the fracture surface in addition to the shear mode cracks, striations and dimples, which were typical fracture modes in rotating bending.

Language：Others  

Country：Japan  

Language：English  

Country：Japan  

Language：English  

Country：Japan  

Language：Others  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

In order to investigate the effect of frequency on the crack growth behavior, ultrasonic fatigue tests were carried out for an extruded age-hardened Al alloy, 7075-T6, and the results were compared with those in rotating bending fatigue. Fatigue strength in ultrasonic was higher than that in rotating bending. Growth direction of a crack changed from tensile mode to shear one in ultrasonic. The relation between an applied stress σ_a and a crack length at transition of growth direction b_T was expressed as σ_a ^nb_T=C.

Language：Japanese  

Country：Japan  

In order to investigate the growth mechanism of a fatigue crack of Ni-based super alloy at ultrasonic frequency, ultrasonic fatigue and rotating bending fatigue tests were carried out for Inconel 718 in ambient air and in N_2 gas using plain and notched specimens and the results in both tests were compared by focusing on the effects of strain rate and environment. In ambient air, fatigue strength was higher in ultrasonic fatigue than in rotating bending fatigue in plain specimen, while the results in notched specimen were the reverse. Many transgranular cracks and cleavage like cracks were observed on the fracture surface in ultrasonic fatigue in addition to striation and transgranular facets observed in rotating bending fatigue and there was no difference in the fracture mechanism between plain specimen and notched one. Moreover, these effects of frequency on the growth mechanism of a crack in ambient air were nearly the same in N_2 gas, though fatigue strength in N_2 gas was higher than that in air. The increase in fatigue strength in N_2 gas was mainly caused by the retardation of a crack initiation.

Language：English  

Country：Japan  

Language：English  

Country：Japan  

Language：Others  

Country：Japan  

Language：Others  

Country：Japan  

Language：Japanese  

Country：Japan  

In order to investigate the effect of frequency on the crack growth behavior, ultrasonic fatigue tests were carried out for an extruded age-hardened Al alloy, 7075-T6, in ambient air and in N_2 gas, and the results were compared with those in rotating bending fatigue. Fatigue strength was higher in ultrasonic fatigue than in rotating bending one. This was caused by the retardation of a crack initiation and its early propagation. In ultrasonic fatigue, the growth direction of a crack changed macroscopically from a tensile mode to a shear one which the direction was about 35 degrees against to the specimen axis, and fracture mechanism also changed from striations to transgranular facets with voids microscopically. Crack growth rate at the transition of crack growth direction was about 3×10^<-9> m/cycle. The relation between an applied stress σ_a and a crack depth at the transition of crack growth direction b_T was expressed by σ^n_ab_T=constant. These results were explained from the time dependent environmental effect and texture of microstructure.

Language：Japanese  

Country：Japan  

In order to investigate the hardness dependence on the fatigue strengths for surface fracture and internal fracture, rotating bending fatigue tests were carried out for maraging steels using specimens with different hardness obtained by heat-treating at different under-aging conditions. Fatigue limit for surface fracture was evaluated in electro-polished specimens and the one for internal fracture was in shot-peened ones, where fatigue limits were defined as fatigue strengths at 107cycles for surface fracture and 108cycles for internal fracture, respectively. Fatigue limit for internal fracture increased with increase in hardness similar to the one for surface fracture. However, the proportional relationship between the fatigue limit and the hardness existed till higher hardness in the fatigue limit for internal fracture than in the one for surface fracture. This difference in the hardness dependence on fatigue limit was discussed from the viewpoint of the influence of humidity on the fatigue strength. © 2007 The Society of Materials Science.

Language：Japanese  

Country：Japan  

A novel strain controlled, free standing tensile fatigue system was developed by using the combined PZT and micromachining technologies in order to conduct in-situ observation and assessment of high cycle fatigue behavior in LP-CVD poly Silicon thin films within a scanning electron microscope (SEM).

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Ultrasonic fatigue tests of plain specimens with different grain sizes were carried out for Ni-base super alloy, Inconel 718, in ambient air in order to investigate the effect of grain size on fatigue properties. Fatigue strength was increased with decrease in grain size. The increase in fatigue strength by refining grain size was mainly caused by the suppression of crack initiation. That is, the effect of grain size on crack growth rate was hardly recognized, though crack morphology was rougher in the specimen of larger grain, meaning that the crack growth in the large-grained specimens was suppressed by roughness induced crack closure. On the other hand, however, more flat facets caused by twin boundary cracking were observed in the large-grained specimens, which inversely led to crack growth acceleration.

Language：Others  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

In order to investigate the availability of ultrasonic fatigue test for the evaluation of fatigue properties under conventional loading frequency, fatigue tests under ultrasonic frequency and rotating bending were carried out using plain specimens of an age-hardened and extruded Al alloy 7075-T6 in 7 kinds of environments of controlled humidity of 25, 50, 70 and 85%, distilled water oxygen gas and nitrogen gas. Although fatigue strength was decreased by high humidity, the decrease by high humidity was very small when the humidity was lower than about 60%～70% and fatigue strength was largely decreased above that humidity under both tests. However, the main reason for the decrease in fatigue strength by high humidity was different between rotating bending fatigue and ultrasonic fatigue. That is, the decrease in fatigue strength was mainly the acceleration of crack growth caused by brittle fracture under rotating bending and the transition to shear mode crack accompanied with glide plane decohesion and void formation under ultrasonic loading, respectively.

Language：Japanese  

Country：Japan  

Parylene C is an inert, hydrophobic, flexible and biocompatible polymer coating material, which has recently found broad MEMS and BioMEMS applications including microstructures, micro sensors and actuators. As a result, many researches have been conducted by focusing on the utilization of Parylene C thin films. Little attention, however, was paid to and rare was known about the mechanical properties of the thin films that may subject to severe tension, bending, twisting or the combination of these loading, especially in biomedical implants in which strength reliability must be secured during a reasonable lifetime. The objective of the present study, therefore, is to investigate the tensile properties of Parylene C thin films fabricated by micromachining process in the range of thickness from submicron to tens of microns. The effect of sample thickness is discussed.

Language：Japanese  

Country：Japan  

In order to investigate effects of a texture and a slip characteristic on fatigue properties of Al alloys in high humidity, rotating bending fatigue tests were carried out using plain specimens of an extruded bar and a drawn one of age-hardened Al alloy 2017-T4 and an Al alloy annealed the extruded one in relative humidity of 25% and 85%. The extruded Al alloy and the annealed one had a marked texture of a (111) plane at the cross section of each bar, but a specified orientation was not observed in the drawn one. In addition, the aged-hardened Al alloys show a planar slip property and the annealed alloy shows a wavy one. In the all Al alloys, the obvious retardation of a small crack growth due to blocking effect of a grain boundary was observed in low humidity, though the retardation disappeared in high humidity. Moreover the acceleration of a crack growth was yielded due to the change in growth mechanism of a crack from a tensile mode in low humidity to a shear mode at high stress levels in high humidity in the extruded alloy, though the effect of humidity on the growth mechanism was very small in the drawn Al alloy and the annealed one. In the extruded Al alloy, the fracture surface yielded by the shear mode crack in high humidity was occupied by many slip planes and voids and was a (100) plane, though the fracture surface formed by the growth of the tensile mode crack in low humidity was covered with striations. In the drawn and annealed Al alloys, fracture surfaces were mainly occupied by striations irrespective of humidity and stress levels. © 2012 The Society of Materials Science, Japan.

Language：Japanese  

Country：Japan  

In order to investigate the effects of humidity change and loading frequency on growth behavior of a fatigue crack of an extruded bar of an age-hardened Al alloy 7075-T6, rotating bending fatigue tests were carried out in relative humidity of 25% and 85% at frequencies of 50Hz and 6Hz. At 50Hz, macroscopic appearances of fractures were a shear mode at high stress levels in high humidity, though those were a tensile mode in other conditions of humidity and stress levels. The crack growth rate was accelerated by high humidity. By changing humidity, both of the growth rate and the growth mode of a crack were immediately changed to those corresponding to the changed humidity. That is, the growth behavior and fatigue life under humidity change may be estimated by those in constant humidity. Fatigue life in high humidity at 6Hz was longer than that at 50Hz in spite of accelerations of both of the crack initiation and its growth rate in the early growth process in high humidity at both frequency, though there was no or little influence of frequency on fatigue life in low humidity. Moreover, the crack propagated in the tensile mode even at high stress levels where the shear mode crack propagated at 50Hz. These results were explained by the effect of hydrogen on the crack growth behavior. © 2012 The Society of Materials Science, Japan.

Language：Japanese  

Country：Japan  

The effect of aging condition on fatigue properties and the mechanism of decrease in fatigue strength in high humidity in 18% Ni maraging steel of grade 350 were investigated under rotating bending in relative humidity of 25% and 85%. Aging conditions investigated were under-, peak- and over-aging ones at the conventional aging temperature of 753K. In addition, double-aging treatments which were under- peak- and over-aging treatments at 673K and under-aging one at 473K after the peak-aging at 753K were also examined. Both of static and fatigue strengths were increased by the double-aging without any decrease in ductility and fatigue fracture toughness. Fatigue strength was markedly decreased by high humidity in all of the steels, and the decrease in fatigue strength was mainly caused by the accelerations of crack initiation and its growth at the early stage of fatigue process. The decrease in fatigue strength in high humidity was also suppressed by the double aging. A few facets comparable to a grain size of a prior austenite were observed at the fracture origins in high humidity but transgranular cracks by slip deformation were in low humidity. However most of the fracture surfaces were covered with lath boundary cracking regardless of the humidity and aging conditions. River pattern was observed in the facets, suggesting that the acceleration of crack growth in high humidity was a behavior related to hydrogen generated in cathode reaction. Based on the results, new aging treatment for improvement of fatigue properties of maraging steel was proposed. © 2013 The Society of Materials Science, Japan.

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Effect of humidity on the growth properties of a fatigue crack in an age-hardened Al alloy was investigated in relative humidity of 25% and 85% at loading frequencies of 50 and 6Hz. Macroscopic growth mode of a crack was a tensile one in low humidity, while the mode changed from the shear one to the tensile one with increase in fatigue life in high humidity. The crack in low humidity propagated by forming striation. On the other hand, in high humidity, most of fracture surface was occupied by many slip planes in the shear mode crack, and many granular facets in addition to striations were observed in the tensile mode growth. The difference in growth mechanism was explained by microstructure and cyclic softening behavior of the alloy and hydrogen content.

Language：English  

Country：Japan  

Language：English  

Language：English  

DOI： 10.2495/SURF010201

Language：English  

DOI： 10.7449/2001/superalloys_2001_573_582

Language：Japanese  

Rotating bending fatigue tests were carried out to investigate the influence of radical nitriding on the surface integrity and the fatigue strength for a maraging steel. Fatigue strength increased by nitriding. Although the initiation site of fracture was the surface in the aged steel, it was the specimen surface at high stress levels and the interior at low stress levels in the nitrided steel. The main reason for the surface fracture was the surface embrittlement and the one for the interior fracture was the surfce hardening due to nitriding. As the results, S-N curves of the nitrided maraging steel showed a double staged curve.

DOI： 10.1299/kikaia.67.314

Language：English  

In-process measurement of tool flank wear is very important for judgment of tool life with the object of running fully automated machine tools economically. The purpose of this study is to propose a new method of detecting tool flank wear by using characteristic values of dynamic cutting process during steady-state cutting in turning operation. In this report, a simple calculation model of dynamic thrust force was proposed to derive equations of characteristic values from it, and effectiveness of the equations was experimentally verified under many cutting conditions and excitation conditions of a workpiece system. As a result of the calculations and the experiments, we reached conclusions that two characteristic values of dynamic cutting process, standard deviation of dynamic thrust force normalized by the standard deviation of workpiece vibration displacement and coefficient of correlation between dynamic thrust force and vibration displacement, have the following properties. (i)The characteristic values remained almost constant with variation of feed rate of a cutting tool and vibration amplitude of a workpiece. (ii)On condition that vibration frequency of a workpiece is constant, the characteristic values obtained under different cutting speeds can be standardized by normalizing the width of flank wear to the cutting speed. (iii)Tendency of calculated characteristic values with increase of vibration frequency was partly disagree with that of experimental values.

DOI： 10.1299/kikaic.66.1700

Language：Japanese  

Rotating bending fatigue tests were performed for Inconel 718 at room temperature and elevated temperatures of 300℃, 500℃ and 600℃ to investigate the influence of temperature on the fatigue crack initlation and its propagation. Although the propagation of a micro-crack smaller than about 20 μm is suppressed at elevated temperatures, that of the larger-crack is accelerated inversely. These results were discussed from the viewpoints of the softening of matrix and the oxidation of surface caused by the high temperature.

DOI： 10.1299/kikaia.65.1954