Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
QIANG CHEN Last modified date:2019.06.29

Professor / Strength of Materials / Department of Mechanical Engineering / Faculty of Engineering


Papers
1. X. H. Shao, Q. Q. Jin, Y. T. Zhou, H. J. Yang, S. J. Zheng, B. Zhang, Qiang Chen, X. L. Ma, Segregation of solute atoms along deformation-induced boundaries in an Mg–Zn–Y alloy containing long period stacking ordered phase, Materialia, 10.1016/j.mtla.2019.100287, 6, 2019.06, 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 Mg 97 Zn 1 Y 2 (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..
2. Chao He, Yujuan Wu, Liming Peng, Ning Su, Qiang Chen, Shucheng Yuan, Yongjie Liu, Qingyuan Wang, Effect of microstructure on small fatigue crack initiation and early propagation behavior in Mg-10Gd-3Y-0.3Zr alloy, International Journal of Fatigue, 10.1016/j.ijfatigue.2018.10.002, 119, 311-319, 2019.02, Microstructural cyclic deformation mechanisms and their relation to small fatigue crack initiation and early propagation behavior were experimentally investigated in a rare earth-containing magnesium alloy (Mg-Gd-Y-Zr). The results indicate that basal slip is the dominant deformation mechanism, especially in coarse grains, and eventually leads to fatigue crack initiation. Early crack propagation behavior was strongly influenced by local microstructural heterogeneities in grain size and orientation. Three kinds of microstructures—favorably-oriented coarse grains, fine grain clusters and unfavorably-oriented coarse grains—are discussed in terms of their deformation mechanisms and resistance to crack propagation. These microstructural effects caused highly variable crack propagation rates within the first ∼200 μm of cracks..
3. Chao He, Xiaohong Shao, Shucheng Yuan, Liming Peng, Yujuan Wu, Qingyuan Wang, Qiang Chen, Small crack initiation and early propagation in an as-extruded Mg-10Gd-3Y-0.5Zr alloy in high cycle fatigue regime, Materials Science and Engineering A, 10.1016/j.msea.2018.10.015, 744, 716-723, 2019.01, High cycle fatigue testing was performed on an as-extruded Mg-10Gd-3Y-0.5Zr alloy to investigate its fatigue crack initiation and early propagation behaviors. Experimental results showed that only basal slip was activated at a low cyclic stress amplitude. Fatigue crack initiated from the slip bands along the basal plane, leading to the formation of cleavage-like facets on the fracture surface. The formation of facets around the crack initiation sites consumed a vast majority of the cyclic loadings in high cycle fatigue regime, and small fatigue crack propagation was significantly retarded by local microstructure heterogeneity of neighboring grains. This can be ascribed to the incompatible deformation at low cyclic stresses, resulting in the localization of slip bands within isolated grains..
4. X. H. Shao, Z. Z. Peng, Q. Q. Jin, Y. T. Zhou, B. Zhang, S. J. Zheng, Q. Chen, X. L. Ma, Unravelling the local ring-like atomic pattern of twin boundary in an Mg-Zn-Y alloy, Philosophical Magazine, 10.1080/14786435.2018.1539262, 99, 3, 306-317, 2018.01, Understanding the interactions between deformation twins and plate-like phases in magnesium alloys is one of the key issues to tailor the microstructure of magnesium alloys for better mechanical properties. The (Formula presented.) twin boundary with the local ring-like atomic pattern in magnesium alloy, accompanied by the interaction between deformation twin and solute atoms, has been investigated using aberration-corrected scanning transmission electron microscopy. We found that these boundaries featured local overlapping morphology near the intersection between deformation twins and stacking faults (SFs) enriched with solute atoms. The overlapping morphology is proposed to be induced by the asynchronous shuffling of the SFs and matrix during the twinning. The local ring-like atomic patterns shown here imply that the shearable specific SFs in magnesium alloys will increase twinning energy and resultantly hinder twinning propagation..
5. Chao He, Yongjie Liu, Jiukai Li, Kun Yang, Qingyuan Wang, Qiang Chen, Very-high-cycle fatigue crack initiation and propagation behaviours of magnesium alloy ZK60, Materials Science and Technology, 10.1080/02670836.2017.1407556, 34, 6, 639-647, 2017.11, The aim of this paper is to assess the very-high-cycle fatigue (VHCF) behaviour of a magnesium alloy (ZK60). Results indicate that the fatigue crack initiates from an area consisting of many distributed facets, while the region of early crack propagation is characterised by parallel traces, based on a fractographic analysis. The significant differences in morphology around the crack initiation area result from the interaction between the deformation twinning and the plastic zone at the crack tip. In addition, the fatigue crack propagation rate around the crack initiation site is also estimated based on a modified Murakami model. It is found that the formation stage for the fatigue crack is of great importance to the fatigue failure mechanism in the VHCF regime..
6. Chao He, Kazuhiro Kitamura, Kun Yang, Yong Jie Liu, Qing Yuan Wang, Qiang Chen, Very High Cycle Fatigue Crack Initiation Mechanism in Nugget Zone of AA 7075 Friction Stir Welded Joint, Advances in Materials Science and Engineering, 10.1155/2017/7189369, 2017, 2017.01, Very high cycle fatigue behavior of nugget zone in AA 7075 friction stir welded joint was experimentally investigated using ultrasonic fatigue testing system (20 kHz) to clarify the crack initiation mechanism. It was found that the fatigue strength of nugget zone decreased continuously even beyond 107 cycles with no traditional fatigue limits. Fatigue cracks initiated from the welding defects located at the bottom side of the friction stir weld. Moreover, a special semicircular zone could be characterized around the crack initiation site, of which the stress intensity factor approximately equaled the threshold of fatigue crack propagation rate. Finally, a simplified model was proposed to estimate the fatigue life by correlating the welding defect size and applied stress. The predicted results are in good agreement with the experimental results..
7. Norio Kawagoishi, Yuzo Nakamura, Kohji Kariya, Qiang Chen, Takanori Nagano, Yoshikazu Maeda, Aging condition for improvement of fatigue properties of maraging steel, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.62.756, 62, 12, 756-763, 2013.12, 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..
8. Xi Shu Wang, Min Zhang, Xi Ping Song, Su Jia, Qiang Chen, Norio Kawagoishi, Fatigue failure analyses on a Ti-45Al-8Nb-0.2W-0.2B-0.1Y alloy at different temperatures, Materials, 10.3390/ma5112280, 5, 11, 2280-2291, 2012.11, The fatigue micro crack initiation and propagation tests of a TiAl alloy with 8% Nb content were carried out by using scanning electron microscopy in situ technology at room temperature and at 750°C. These results indicated that the fatigue micro crack initiation was mainly caused by the stress concentration at room temperature, but at an elevated temperature (750°C) the multi-cracks were caused by the coupled factors of both lamellar microstructure and stress concentration. Therefore, fatigue micro crack initiation behavior is much more dependent on the lamellar structure at an elevated temperature. One of the reasons is that the elevated temperature degrades the interface strength between the lamellar of the TiAl alloy with 8% Nb content. Therefore, the small fatigue crack propagation behavior of the alloy exhibited a mixture damage model of interlamellar and translamellar at a micro scale. The crack growth path and fracture characteristics provided a proof of crack deflection, branching and/or bridging induced either by interlamellar or by translamellar failure mode..
9. Kohji Kariya, Hideki Maeda, Norio Kawagoishi, Qiang Chen, Yuzo Nakamura, Kazuhiro Morino, Effect of humidity on growth behavior of a fatigue crack of 7075-T6 extruded Al alloy, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.61.712, 61, 8, 712-718, 2012.08, 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..
10. Norio Kawagoishi, Akihiro Higashi, Qiang Chen, Yuzo Nakamura, Kazuhiro Morino, Effect of microstructure on fatigue properties of Al alloy 2017 in high humidity, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.61.556, 61, 6, 556-563, 2012.06, 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..
11. Nu Yan, Qingyuan Wang, Xishu Wang, Qiang Chen, N. Kawagoishi, Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading, Theoretical and Applied Mechanics Letters, 10.1063/2.1203108, 2, 3, 2012.01, Fatigue properties of age-hardened Al alloy 2017-T4 under ultrasonic loading frequency (20 kHz) were investigated and compared with the results under conventional loading of rotating bending (50 Hz). The growth of a crack retarded at about 500 µm in surface length under ultrasonic loading, while at about 20 µm under rotating bending. Although striations being a typical fracture mechanism were observed under conventional loading, most of fracture surface was covered with many facets under ultrasonic loading. These facets were also observed under rotating bending in nitrogen gas. The difference in growth mechanism depending on the loading frequency and the retardation of a crack growth under ultrasonic loading may be caused by the environment at the crack tip due to high crack growth rate under ultrasonic loading..
12. Norio Kawagoishi, Kohji Kariya, Qiang Chen, Masahiro Goto, Yuzo Nakamura, Growth mechanism of shear mode fatigue crack of age-hardened al alloy, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.60.890, 60, 10, 890-897, 2011, 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%, 50%, 75% and 85%, 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..
13. Norio Kawagoishi, Takuro Fukudome, Kohji Kariya, Qiang Chen, Masahiro Goto, Fatigue strength of age-hardened & extruded al alloy under high humidity (rotating bending and ultrasonic loading), Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.76.1651, 76, 772, 1651-1658, 2010.01, 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 7075T 6 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..
14. Norio Kawagoishi, Eiji Maemura, Qiang Chen, Masahiro Goto, Kazuhiro Morino, Effect of grain size on ultrasonic fatigue properties of Ni-base super alloy inconel 718, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 74, 7, 1000-1005, 2008.07, 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..
15. Effect of Grain Size on Ultrasonic Fatigue Properties of Ni-Base Super Alloy Inconel 718.
16. Takanori Nagano, Norio Kawagoishi, Michihiko Moriyama, Qiang Chen, Etsuichi Nagashima, Influence of shot peening on fatigue strength of maraging steels with different hardness, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.56.1126, 56, 12, 1126-1132, 2007.12, 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 107 cycles for surface fracture and 108 cycles 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..
17. K. Morino, N. Kawagoishi, Qiang Chen, Y. Matsuyama, Y. Nakamura, Fatigue crack growth resistance in Ni-base super alloy, Key Engineering Materials, 348-349, 541-544, 2007.08, Rotating bending fatigue tests were carried out to investigate the influence of grain size on the resistance to crack growth of Ni-base super alloy, Inconel 718, using the materials with grain sizes of about 20, 50,100 and 200 μ, at room temperature. The larger grain size, the smaller crack growth rate, though the static strength was decreased with increase in grain size. The growth rate of a small crack was uniquely determined by the term σa n (Small crack growth law), where σ a and a are the stress amplitude and the crack length, respectively, and n is a constant. The resistance to crack growth among materials was evaluated based on the law and showed a good correlation with tensile strength σB, meaning that fatigue life can be predicted by using only σB..
18. Nu Yan, Q. Y. Wang, Qiang Chen, J. J. Sun, Influence of loading frequency on fatigue behavior of high strength steel, Key Engineering Materials, 353-358, PART 1, 227-230, 2007, In order to investigate the influence of loading frequency on the fatigue behaviors of the high strength steel, ultrasonic fatigue tests were carried out for a high-carbon-chromium steel and the results were compared with those of fatigue tests using conventional rotary bending fatigue test machine with a frequency of 52.5Hz. The different of fatigue strength at ultrasonic frequency level and conventional frequency level is very small and the S-N curve obtained from 20 kHz or 52.5 Hz shows the step-wise shape. The fatigue crack occurred from inclusions on the subsurface site in the long life regime and the typical surface fracture occurred in the short life one though the loading frequency level is different. It is indicated that ultrasonic fatigue method is an effective method to investigate the fatigue properties in super-long life region..
19. Q. Y. Wang, N. Kawagoishi, Qiang Chen, Fatigue and fracture behaviour of structural Al-alloys up to very long life regimes, International Journal of Fatigue, 10.1016/j.ijfatigue.2005.09.017, 28, 11, 1572-1576, 2006.11, Very long life fatigue and near-threshold fatigue crack growth behaviour of 7075 and 6061 Al-alloys in T6 condition were investigated using accelerated fatigue testing at 19.5 kHz on a piezoelectric machine. Significant interfacial voids were observed in the two Al-alloys during crack initiation and early fatigue crack growth process. Fatigue failure in Al-alloys could be ascribed to: the formation of a number of fatigue voids, their growth and coalescence, and the subsequent formation and propagation of macroscopic cracks. Moreover, fatigue crack growth rates of small cracks in these alloys were found to be greater than those of large cracks for the same stress intensity factor range..
20. Norio Kawagoishi, Jun Ogawa, Qiang Chen, Masahiro Goto, Kazuhiro Morino, Effect of loading frequency on fatigue strength of Ni-based super alloy, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 72, 10, 1542-1549, 2006.10, 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 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..
21. Q. Y. Wang, M. R. Sriraman, N. Kawagoishi, Qiang Chen, Fatigue crack growth of bonded composite repairs in gigacycle regime, International Journal of Fatigue, 10.1016/j.ijfatigue.2006.02.028, 28, 10 SPEC. ISS., 1197-1201, 2006.10, Fatigue induced from various aeromechanical sources can reach gigacycle regime due to vibratory stress cycles at high frequencies. Composite repairs offer various advantages over mechanical fastening or riveting, including improved long-term durability behavior and reduced corrosion. In this study, by using ultrasonic frequency cyclic loading, fatigue crack growth tests in gigacycle regime were conducted on notched 7075 and 6061 aluminum alloy substrates (in T6 condition) with and without bonded Boron/epoxy patches. A considerable increase in the fatigue life was observed with more number of patch plies. The effect of patch configuration and thickness on enhancing the fatigue strength by orders of magnitude has been demonstrated..
22. Effect of Loading Frequency on Fatigue Strength of Ni-Based Super Alloy.
23. Norio Kawagoishi, Masahiro Oki, Masahiro Goto, Qiang Chen, Qingyuan Wang, Crack growth behavior of Al alloy 7075-T6 under ultrasonic fatigue, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 72, 9, 1356-1363, 2006.09, 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 σa and a crack depth at the transition of crack growth direction bT was expressed by σa nbT=constant. These results were explained from the time dependent environmental effect and texture of microstructure..
24. N. Kawagoishi, Qiang Chen, M. Oki, Q. Y. Wang, Crack growth behavior of Al alloy under ultrasonic fatigue, Key Engineering Materials, 324-325 I, 327-330, 2006, 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. This was mainly caused by the retardation of crack initiation. Growth direction of a crack changed from a tensile mode to a shear one in ultrasonic fatigue, though fracture occurred by the growth of a tensile mode in rotating bending. The growth direction of a shear mode crack was inclined about 55 degrees to the tensile axis. The relation between an applied stress σa and a crack depth at transition of growth direction b T was expressed by σa n bT=C, where C and n are constants. These results were discussed from the points of view of the time dependent environmental effect and the texture of material..
25. Propagation behavior of an internal crack of a radical nitrided bearing steel.
26. Qiang Chen, N. Kawagoishi, Q. Y. Wang, N. Yan, T. Ono, G. Hashiguchi, Small crack behavior and fracture of nickel-based superalloy under ultrasonic fatigue, International Journal of Fatigue, 10.1016/j.ijfatigue.2005.07.022, 27, 10-12, 1227-1232, 2005.10, Fracture and small crack behavior in the very high cycle domain of 10 9 cycles were investigated with a nickel-based superalloy under ultrasonic fatigue in ambient air at room temperature. The influence of ultrasonic frequency is examined by comparing the results with those in conventional low frequency fatigue. It is found that fatigue strength increases as frequency is raised up to 19.5 kHz and the most of fatigue life is consumed in nucleating and propagating small cracks up to 100 μm. Transition of fracture mode from transgranular ductile fracture to cleavage-dominated fracture occurs beyond a critical stress intensity factor range of approximately 21MPam, leading to the catastrophic failure under ultrasonic fatigue..
27. Norio Kawagoishi, Nu Yan, Masahiro Goto, Qiang Chen, Qingyuan Wang, Yoshihisa Ohzono, Fracture mechanism in fatigue of Ni-base superalloy Inconel 718 at elevated temperatures, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 71, 9, 1226-1233, 2005.09, 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..
28. Norio Kawagoishi, Qiang Chen, Nu Yan, Qingyuan Wang, Masahiro Goto, Ultrasonic fatigue properties of an age-hardened Al alloy 6061-T6, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 70, 8, 1139-1145, 2004.08, 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..
29. Q. Y. Wang, N. Kawagoishi, Qiang Chen, R. M. Pidaparti, Fatigue life enhancement of defective structures by bonded repairs, Structural Engineering and Mechanics, 10.12989/sem.2004.18.3.277, 18, 3, 277-286, 2004.01, Defective metallic components and structures are being repaired with bonded composite patches to improve overall mechanical and fatigue properties. In this study, fatigue crack growth tests were conducted on pre-cracked 7075/T6 Aluminum substrates with and without bonded Boron/epoxy patches. A considerable increase in the fatigue life and a decrease in the stress intensity factor (SIF) were observed as the number of patch plies increased. The experimental results demonstrate that the patch configurations and patch thickness can enhance fatigue life by order of magnitude. Quantitative comparisons between analytical and experimental data were made, and the analytical model based on a modified Rose's analytical solution appears to best estimate the fatigue life..
30. Q. Y. Wang, N. Kawagoishi, Qiang Chen, Fatigue voids in structural Al-alloys under high-frequency cyclic loading, Journal of Materials Science, 10.1023/B:JMSC.0000008091.55395.ee, 39, 1, 365-367, 2004.01, The fatigue behavior of 7075/T6 and 6061/T6 aluminum alloys in the very long life regime was investigated by using piezoelectric accelerated fatigue tests at 19.5 KHz. The mechanism of fatigue crack initiation and propagation by void formation and growth was identified using scanning electron microscopy (SEM)..
31. Q. Y. Wang, N. Kawagoishi, T. Li, Qiang Chen, Super long life fatigue in nitrided high strength steels, Key Engineering Materials, 274-276, I, 217-222, 2004, In order to investigate the effect of radical nitriding on fatigue behavior of high-strength steels, very long life fatigue tests were carried out for two kinds of steels, 18Ni Maraging steel and SUJ2 bearing steel, by using conventional and ultrasonic machines, respectively. It was shown that radical nitriding played the principal role in the subsurface crack initiation. Fatigue strength of Maraging steel appears to be significantly enhanced by radical nitriding, however, radical nitriding has a destructive effect on the fatigue behavior of SUJ2 steel..
32. Q. Y. Wang, N. Kawagoishi, N. Yan, Qiang Chen, Super-long life fatigue behavior of structural aluminum alloys, Key Engineering Materials, 261-263, II, 1287-1294, 2004, The objective of this study is to determine very long life fatigue and near threshold fatigue crack growth behaviors of 7075/T6 and 6061/T6 Al-alloys using piezoelectric accelerated fatigue at 19.5KHz. The experimental results show the fatigue failure can occur beyond 107, even 109 cycles, and endurance limits could not be obtained in the Al-alloys until 109 cycles. Fatigue voids are noticed on fatigue fracture in both alloys. By using scanning electron microscopy (SEM), the crack initiation and propagation behaviors have been examined. Fatigue crack growth rates of small cr acks in the Al-alloys are found to be greater than those of large cracks at the same stress intensity factor range..
33. Norio Kawagoishi, Qiang Chen, Nu Yan, Qingyuan Wang, Eiji Kondo, Ultrasonic Fatigue Properties of a High Strength Extruded Al Alloy, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 69, 12, 1672-1677, 2003.12, 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..
34. Q. Y. Wang, N. Kawagoishi, Qiang Chen, Effect of pitting corrosion on very high cycle fatigue behavior, Scripta Materialia, 10.1016/S1359-6462(03)00365-8, 49, 7, 711-716, 2003.10, The effects of pitting corrosion on very high cycle fatigue behavior of aluminum alloys were discussed. The results indicated that the presence of pre-existing corrosion pits, produced by 1-day, 4-day and 7-day immersion in salt water significantly reduces the fatigue life of the alloy by a factor of 10-100. It was also found that the pittings accelerated crack initiation and promoted multiple-site damage..
35. Qingyuan Wang, N. Kawagoishi, Qiang Chen, R. M. Pidaparti, Evaluation of the probability distribution of pitting corrosion fatigue life in aircraft materials, Acta Mechanica Sinica/Lixue Xuebao, 19, 3, 247-252, 2003.06, Corrosion and fatigue properties of aircraft materials are known to have a considerable scatter due to the random nature of materials, loading, and environmental conditions. A probabilistic approach for predicting the pitting corrosion fatigue life has been investigated which captures the effect of the interaction of the cyclic load and corrosive environment and all stages of the corrosion fatigue process (i.e. the pit nucleation and growth, pit-crack transition, short- and long-crack propagation). The probabilistic model investigated considers the uncertainties in the initial pit size, corrosion pitting current, and material properties due to the scatter found in the experimental data. Monte Carlo simulations were performed to define the failure probability distribution. Predicted cumulative distribution functions of fatigue life agreed reasonably well with the existing experimental data..
36. Qiang Chen, Norio Kawagoishi, Hironobu Nisitani, Ken Ichi Otsubo, Qingyuan Wang, Eiji Kondo, Ultrasonic fatigue properties of Ni-base superalloy, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 69, 3, 626-632, 2003.03, 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 (19.5 kHz) 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..
37. N. Yan, N. Kawagoishi, Qiang Chen, Q. Y. Wang, H. Nisitani, E. Kondo, Fatigue properties of inconel 718 in long life region at elevated temperature, Key Engineering Materials, 243-244, 321-326, 2003, The fatigue properties of Inconel 718 in long life region up to 108 cycles were investigated under rotating bending at room temperature and 500°C. The early propagation of a crack was suppressed by oxide induced crack closure. Consequently, fatigue strength was higher at 500°C than at room temperature. Surface fracture occurred at high stress levels and internal fracture occurred in long life region beyond 107 cycles at 500°C. Correspondingly, S-N curve at 500°C presented in a step-wise shape, compared to the conventional one-step shape at room temperature. Intergranular cracking was observed at the origins of internal fracture at 500°C..
38. Q. Y. Wang, C. Bathias, N. Kawagoishi, Qiang Chen, Effect of inclusion on subsurface crack initiation and gigacycle fatigue strength, International Journal of Fatigue, 10.1016/S0142-1123(02)00037-3, 24, 12, 1269-1274, 2002.12, The effect of inclusions on crack initiation and propagation in gigacycle fatigue was investigated experimentally and analytically in six high strength low alloy steels. Fatigue testing was performed at very high numbers of cycles through ultrasonic fatigue tests at 20 kHz. Inclusions at subsurface are common sites for fatigue crack nucleation in these alloys when cycles to failure was > 107 cycles. A significant change in the slope of the S-N curve was observed accompanying the transition from surface to subsurface crack initiation. A deterministic model has been developed to predict the total fatigue life, i.e. crack initiation life and crack propagation life, from the measured inclusion sizes. The predicted fatigue strength agreed reasonably well with the experimental results. It is a tendency that smaller inclusions are associated with longer fatigue life. The results demonstrated that the portions of life attributed to subsurface crack initiation between 107 and 109 cycles are > 99%..
39. Norio Kawagoishi, Qiang Chen, Ken Ichi Otsubo, Nu Yan, Eiji Kondo, Qingyuan Wang, Fatigue properties of Ni-base superalloy in long life region at elevated temperature, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 68, 8, 1192-1197, 2002.08, 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 cracking were observed at the origin of internal fracture..
40. Norio Kawagoishi, Kazunori Fukada, Kazuhiro Morino, Qiang Chen, Eiji Kondo, Improvement of fatigue strength of maraging steel by nitriding, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.67.314, 67, 654, 314-320, 2001.01, 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 suface 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..
41. N. Kawagoishi, Qiang Chen, H. Nisitani, Fatigue strength of Inconel 718 at elevated temperatures, Fatigue and Fracture of Engineering Materials and Structures, 10.1046/j.1460-2695.2000.00263.x, 23, 3, 209-216, 2000.03, The strength of Inconel 718 under rotary bending fatigue is investigated at room temperature, 300, 500 and 600 °C in air. It is found that in the long-life region, the fatigue strength of a plain specimen is much higher at elevated temperatures than at room temperature, though the static strength decreases with the increase in temperature. The effect of temperature on the fatigue strength is examined in terms of the initiation and early growth behaviour of a small crack. The results are discussed in relation to the competition between the softening of the nickel matrix (γ phase) and the surface oxidation at elevated temperatures..
42. Eiji Kondo, Norio Kawagoishi, Hiroaki Okuma, Qiang Chen, Detection of Tool Wear using Characteristic Values of Dynamic Cutting Process
2nd Report, Adaptability of Characteristic Values to Variation of Measurement Conditions, Nippon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C, 10.1299/kikaic.66.1700, 66, 645, 1700-1705, 2000.01, 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..
43. Qiang Chen, N. Kawagoishi, H. Nisitani, Evaluation of fatigue crack growth rate and life prediction of Inconel 718 at room and elevated temperatures, Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing, 10.1016/S0921-5093(99)00555-9, 277, 1-2, 250-257, 2000.01, The fatigue crack growth behavior of Inconel 718 was investigated under rotating bending fatigue at room temperature, 300, 500, and 600°C in air. It has been found that the small crack growth rate could be evaluated by the small crack growth law at high stress levels, where the small-scale yielding conditions are exceeded and the Paris law is not applicable, irrespective of the temperature. The fatigue strength of plain specimens increased considerably in the long-life region at the elevated temperatures, because the early growth of a small crack in the range of 20-30 μm was suppressed. However, a crack grew faster at higher temperature after growing beyond about 50 μm due to the decrease of crack growth resistance. The fatigue life in the stable crack growth period can be predicted by the small crack growth law..
44. N. Kawagoishi, Qiang Chen, H. Nisitani, Significance of the small crack growth law and its practical application, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 10.1007/s11661-000-0228-6, 31, 8, 2005-2013, 2000.01, The effects of microstructure and specimen size on the fatigue crack growth rate of an annealed 0.42 C steel were investigated under uniaxial fatigue loading in air. Although a dramatic fluctuation of crack growth rate was found in the propagation process of microstructurally small cracks, the mean value of crack growth rate can be evaluated by a simple mechanical parameter, σa nl (l, crack length; n, constant), under high stress levels where small-scale yielding conditions are exceeded. This parameter is also effective for cracks larger than 1 to 2 mm under high stress levels, as long as the finite boundary effect of a specimen on the driving force of crack propagation is considered. The crack growth rate of the alloy was described as a function of stress amplitude and crack length in terms of two mechanical parameters, σa nl and ΔK. The applicable conditions of the two parameters were discussed and manifested..
45. N. Kawagoishi, Qiang Chen, E. Kondo, M. Goto, H. Nisitani, Influence of Cubic Boron Nitride Grinding on the Fatigue Strengths of Carbon Steels and a Nickel-Base Superalloy, Journal of Materials Engineering and Performance, 10.1361/105994999770346981, 8, 2, 152-158, 1999.01, The influence of cubic boron nitride (CBN) grinding on fatigue strength was investigated on an annealed carbon steel, a quenched and tempered carbon steel at room temperature, and a nickel-base superalloy, Inconel 718, at room temperature and 500°C. The results were discussed from several viewpoints, including surface roughness, residual stress, and work hardening or softening due to CBN grinding. The fatigue strength increased upon CBN grinding at room temperature, primarily because of the generation of compressive residual stress in the surface region. However, in the case of Inconel 718, this marked increase in the fatigue strength tended to disappear at the elevated temperature due to the release of compressive residual stress and the decrease of crack growth resistance at an elevated temperature..
46. Initiation and growth behavior of a fatigue crack in inconel 718 at elevated temperatures.
47. Qiang Chen, Norio Kawagoishi, Hironobu Nisitani, Evaluation of notched fatigue strength at elevated temperature by linear notch mechanics, International Journal of Fatigue, 10.1016/S0142-1123(99)00081-X, 21, 9, 925-931, 1999, The notched fatigue strength of nickel-base superalloy Inconel 718 has been investigated under rotating bending loading at room temperature and 500 °C in air. The applicability of linear notch mechanics to the evaluation of notched fatigue strength at elevated temperature was assessed in terms of the fatigue limit for crack initiation and that for crack growth. The effect of temperature on the fatigue strength and notch sensitivity of Inconel 718 was examined. The results were discussed from the viewpoints of the softening of matrix and surface oxidation at elevated temperature..
48. Norio Kawagoishi, Yoshihisa Ozono, Qiang Chen, Masahiro Goto, Hideho Tanaka, Eiji Kondo, Effect of oxide films on a fatigue crack inititation and its early growth of Ni-base super alloy, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.64.839, 64, 620, 839-844, 1998.01, Rotating bending fatigue tests were carried out for Ni base super alloy Inconel 718 at room temperature and elevated temperatures of 300°C, 500°C and 600°C 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..
49. Norio Kawagoishi, Hiroshi Tachiya, Qiang Chen, Hironobu Nisitani, Masahiro Goto, Eiji Kondo, Notch sensitivity in fatigue of nickel-base superalloy at elevated temperatures, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.64.2869, 64, 627, 2869-2875, 1998.01, Rotating bending fatigue tests were carried out for nickel-base superalloy Inconel 718 in air at room temperature and the elevated temperatures of 300°C, 500°C and 600°C 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 σw1 and that for crack growth σw2, based on the Linear Notch Mechanics (LNM). It was found that the fatigue limits σw1, σw2 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..
50. Norio Kawagoishi, Qiang Chen, Hideho Tanaka, Ichiro Maeno, Jun ichi Kiyofuji, Characteristics of small crack growth in a nickel-base superalloy, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.63.1398, 63 A, 611, 1398-1402, 1997.01, 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 (σa0.2<0.5, σa: stress amplitude, (σ0.2:0.2% proof stress), the crack growth rate was determined by the stress intensity factor range ΔK; and at high stress levels (σa0.2>0.6), it was determined by the small crack growth law..
51. Norio Kawagoishi, Qiang Chen, Hironobu Nisitani, Masahiro Goto, Hideho Tanaka, Fatigue crack growth resistance in nickel-base superalloy at elevated temperatures, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.63.2298, 63, 615, 2298-2302, 1997.01, 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 = C1σa nl = C2aB)nl, at all the temperatures, where σB, σa and l are the tensile strength, the stress amplitude and the crack length, and C1, C2 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..
52. Norio Kawagoishi, Kensei Fujimura, Qiang Chen, Masaru Arikawa, Ichiro Maeno, Hideho Tanaka, Fatigue strength of specimens ground by a CBN wheel (In cases of carbon steels and a nickel-base super alloy), Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.63.1844, 63, 613, 1844-1848, 1997.01, 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..
53. Norio Kawagoishi, Qiang Chen, Hideho Tanaka, Ichiro Maeno, Jun ichi Kiyofuji, Fatigue strength of notched specimen in nickel-base superalloy at elevated temperatures, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.62.960, 62, 596, 960-965, 1996.01, 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..