| 久保田 祐信（くぼた まさのぶ） | データ更新日：2024.04.05 |
教授 ／
カーボンニュートラル・エネルギー国際研究所
物質変換科学ユニット
水素適合材料・破壊学（機械工学科・機械工学専攻, 2014.4 - Current）, エア・リキード水素構造材料・破壊学（機械工学科・機械工学専攻, 2010.10 - 2014.3）
| 1. | Shunsuke Umezaki, Masanobu Kubota, Ryosuke Kmoda, Naho Inoue, Hiroshi Okano, Tomoharu Ishida, Shusaku Takagi, Effect of Hydrogen Blending on Fatigue Crack Growth Behavior in Natural Gas , 第10回構造物の安全性・信頼性に関する国内シンポジウム（JCOSSAR2023）, 2024.10, Hydrogen and natural gas blending can be considered as an important energy technology in terms of utilization of the existing infrastructure, which is the magnitude of a cost impact to the deployment of hydrogen infrastructures, and smooth transition of energy systems. In this study, fatigue crack growth tests were carried out in air, hydrogen, methane/20% hydrogen mixtures and three kinds of natural gas/20% hydrogen mixtures with different impurity oxygen concentrations in order to characterize the effect of hydrogen on fatigue crack growth properties in natural gas in conjunction with the effect of impurity oxygen. The pressure of gases except for air was 1 MPa. The material was JIS SCM435 low-alloy steel. In the hydrogen and the methane/20% hydrogen mixtures, the fatigue crack growth rates were accelerated. The acceleration was less in the methane/hydrogen mixtures compared with that in the hydrogen. It is presumed that the less hydrogen effect was due to reduced partial hydrogen pressure in the methane/20% hydrogen mixtures. This was confirmed by the crack growth test in 0.2 MPa hydrogen resulting in the same crack growth rate in the mixture. Regarding the experiments in the natural gas/20% hydrogen mixtures, the acceleration of fatigue crack growth rate occurred, but it was partially inhibited. This result was due to the oxygen contained in the natural gas. The inhibitory effect increased with increasing oxygen concentration. The predictive model of hydrogen-assisted crack growth in the presence of oxygen by Somerday et al. was well adapted to the results of this study.. |
| 2. | 村上 幸太郎, 駒崎 慎一, 久保田 祐信, オーステナイト系ステンレス鋼SUS 304 のスモールパンチ試験特性に及ぼす高温水素ガス雰囲気の影響, 2024.06, We developed a small punch (SP) test system enables SP testing in a hydrogen atmosphere at elevated temperatures in order to utilize the SP testing for the remaining life assessment of mechanical components used in advanced high temperature hydrogen techno logies, such as SOFC and SOEC. Type 304 stainless steel was subjected to the SP and SP creep test s with a small disk type specimen. A small disk specimen with a diameter of 8 mm and thickness of 0.5 mm was tested in hydrogen and argon gases. The absolute g as pressure and temperature at which the SP test wa s carried out were 0.12 MPa and 600℃, respectively . The experimental results showed that the 0.2% proof stress and tensile strength in hydrogen and argon gases, which were predicted based on the SP test results, were consi s tent with those obtained from the tensile tests. T he SP creep rupture time tended to be shorter in hydrogen gas than argon gas , and the equivalent fracture strain (rupture ductility) was slightly higher in hydrogen gas . The results obtained in the SP creep test were also qualitatively in agreement with those in the standard uniaxial creep test.. |
| 3. | 久保田祐信, 納山尚樹, 笛田宗広, 栄中, 近藤良之
, フレッティング疲労に及ぼす水素ガス環境の影響, 材料, https://doi.org/10.2472/jsms.54.1231, 54, 12, 1231-1236, 2005.12, The objective of this study is to clarify the effect of hydrogen gas environment on fretting fatigue strength of the materials, which will be used for the mechanical system for hydrogen utilization. It is important to take fretting fatigue into account for strength design, since many fatigue failure accidents have occurred at joints or contact parts between components. The test materials were austenitic stainless steel SUS 304 and corrosion resisting aluminum alloy A6061. Fretting fatigue tests and also fretting wear tests were done in hydrogen gas, nitrogen gas and air. Fretting fatigue strength in hydrogen gas environment was lower than that in air for both materials. Tangential force coefficient in hydrogen gas was larger than that in air. The appearance of fretting pit and microcrack was quite different among environments. Absorption of hydrogen was detected in contact pad of fretting wear test fretted in hydrogen gas environment. Fretting fatigue life of the stainless steel was decreased due to hydrogen pre-charge..  |
| 4. | K. Vijayvargia, P. Sofronis, M. Dadfarnia, M. Kubota, A. Staykov, K. Wada, J. A. Pugh, T. J. Eason, Three-dimensional constraint-based void-growth model for high temperature hydrogen attack, International Journal of Fracture, https://doi.org/10.1007/s10704-023-00739-2, 243, 203-228, 2023.10, High temperature hydrogen attack (HTHA) is degradation of steels exposed to hydrogen gas at high temperatures and pressures. Currently, the design practice against HTHA is based on the Nelson curves which are phenomenological in nature and do not account for the underlying failure mechanisms. It is expected that void growth is accelerated by the triaxial stresses associated with microstructural flaws. To this end, we propose a three-dimensional, axisymmetric, constraint-based void-growth model extending the ‘‘one dimensional’’ model of Dadfarnia et al. The proposed methodology can be viewed as providing a step toward improving the current design practice against HTHA while maintaining the simplicity of the original Nelson curve approach.. |
| 5. | Ryosuke Komoda, Masanobu Kubota, Aleksandar Staykov, Patrick Ginet, Francoise Barbier, Jader Furtado, Laurent Prost, Akihide Nagao, Mitigation of hydrogen environment embrittlment of carbon steels A106 and A333 by addition of CO to H2 gas and its gas pressure dependence, Proceedings of the Fourth International Conference on Metals & Hydrogen (SteelyHydrogen2022), A01, 2022.10, The addition of carbon monoxide (CO) to hydrogen (H2) gas can mitigate hydrogen environment embrittlement (HEE) of steels. The effect of gas pressure on the mitigation of HEE by CO was investigated in this study by a concerted effort of fracture toughness tests in H2 gas containing CO and molecular dynamics (MD) simulations of surface chemical reactions of H2 and CO with iron (Fe) surface. The addition of CO to H2 gas completely prevented HEE under certain conditions. The CO concentration to achieve complete HEE prevention increased with an increase in the gas pressure, in other words, the CO mitigation effect was reduced by an elevated（圧力に対してelevateは使える？） gas pressure. The MD simulations revealed that the dissociation rate of dihydrogen molecules to atomic hydrogen on the Fe surface significantly increased with an increase in the gas pressure, whereas the adsorption rate of CO on the Fe surface was almost independent of the gas pressure. These simulation results suggested that the increase in the gas pressure promoted the hydrogen uptake into the material relatively in the presence of CO（意味不明）. This is a reason for the gas pressure dependence of the CO mitigation effect observed in the fracture toughness tests.. |
| 6. | Ryosuke Komoda, Masanobu Kubota, Aleksandar Staykov, Patrick Ginet, Jader Furtado, Laurent Prost, Akihide Nagao, Loading dependence of mitigation effect of CO on hydrogen embrittlement of pure iron and low carbon steel, Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference, 3038-3043, 2022.06, The mitigation effect of carbon monoxide (CO) on hydrogen embrittlement (HE) was studied in terms of the loading rate dependence by fracture toughness tests, fatigue crack growth tests, and density functional theory (DFT) simulations. The experimental results demonstrated that the mitigation effect is reduced with a decreasing loading rate in the lower crack growth rate region. The DFT simulations revealed that this is caused by the incomplete coverage of the iron surface by CO. Oppositely, the mitigation effect increased with the decreasing loading rate in the higher crack growth rate region due to a lack of CO adsorption on the iron surface.. |
| 7. | Masanobu Kubota, Ryosuke Komoda, Yuki Nakamura, Improvement of fretting fatigue strength by carbon monoxide and catalyst activation under chemomechanical effects of fretting, Theoretical and Applied Fracture Mechanics, https://doi.org/10.1016/j.tafmec.2022.103460, 121, 103460, 2022.10, It is known that the fretting fatigue strength in hydrogen (H2) gas is lower than that in air. The objective of this study is to mitigate the hydrogen effect during the fretting fatigue test in H2 gas by adding carbon monoxide (CO) to the H2 environment. The expected CO effect was reduction in the hydrogen uptake into the material following deactivation of the catalytic surface where H2 molecules dissociate into H atoms. However, an unexpected result, which was unique in fretting, was obtained. The fretting fatigue test using JIS SUS304 austenitic stainless steel was performed in H2, argon (Ar), 2 vol% CO mixed H2, and 2 vol% CO mixed Ar gases. The fretting fatigue strengths in the CO-mixed gases were significantly improved. For instance, the fretting fatigue life at σa = 240 MPa was 8.8 × 10^5 cycles in the H2 and 10^7 cycles or longer in the CO mixed H2. The cause of the improved fretting fatigue strength was the formation of amorphous carbon between the contacting surfaces during the fretting. The carbon reduced the tangential force coefficient between the contacting surfaces from around 0.6 in the H2 to 0.2 or less in the CO mixed H2. The reduced tangential force resulted in improvement of the fretting fatigue strength. Although the detailed mechanisms of the carbon deposition were unclear, it is plausible that the catalytic action of the metal surface for the CO decomposition into C and O was activated by the effect of fretting, such as removal of the surface oxide layer and other chemomechanical effects. . |
| 8. | Nan Zhang, Ryosuke Komoda, Kazuki Yamada, Masanobu Kubota, Aleksandar Staykov, Ammonia mitigation and induction effects on hydrogen environment embrittlement of SCM440 low-alloy steel, International journal of hydrogen energy, https://doi.org/10.1016/j.ijhydene.2022.03.006, 47, 33, 15084-15093, 2022.04, The effect of ammonia (NH3) contained in hydrogen (H2) gas on hydrogen environment embrittlement (HEE) of SCM440 low-alloy steel was studied in association with the NH3 concentration, loading rate, and gas pressure. NH3 worked as both mitigator of the HEE and inducer of hydrogen embrittlement (HE) depending on the testing conditions. The mitigation of the HEE was achieved by the deactivation of the iron (Fe) surface for H2 dissociation caused by the preferential adsorption of NH3 on the Fe surface, which is enhanced by the increase in the NH3 concentration and decrease in the H2 gas pressure. NH3 induced HE was caused due to creating hydrogen by the NH3 decomposition. Since the NH3 decomposition rate is low, the induction effect was observed when the loading rate was low. The effect of NH3 was determined by the competition of the mitigation and induction effects.. |
| 9. | 久保田 祐信, 和田 健太郎，山下 透 , 工業用純鉄SUY-1およびオーステナイト系ステンレス鋼SUS310Sを用いた高温水素中のクリープ強度に関する基礎的研究, ボイラ研究, 431, 24-31, 2022.02, 高温水素機器の普及を見越して水素中クリープ試験を実施した．水素中クリープ特性に関する研究は過去にも行われているが，水素がクリープ変形に影響を与える機構や，高温水素機器という新しい製品の安全性に対してさらなる研究が必要である．オーステナイト系ステンレス鋼SUS310Sと工業用純鉄SYU-1を供試材とした．いずれの材料も，水素中では定常クリープ域のひずみ速度がアルゴン中と比べて増加し，その結果としてクリープ寿命が減少した．SUY-1の破断した試験片の外観や破面の様相に，水素による顕著な差違は見られないことから，水素はクリープ変形の機構を変えずに変形を加速する役割のあることが示唆された．SUS310Sについても，先行して研究が進められているSUS304と結果は類似しており，水素の影響機構としてもSUS304と同じもの，つまり，水素による空孔濃度増加による転位上昇の促進が考えられる．. |
| 10. | LinTian, Christine Borchers, Masanobu Kubota, Petros Sofronis, Reiner Kirchheim, Cynthia A. Volkert, A study of crack initiation in a low alloy steel, Acta Materialia, https://doi.org/10.1016/j.actamat.2021.117474, 223, 11747, 2022.01, Taking advantage of in-situ fracture testing method inside a transmission electron microscope (TEM), crack evolution in a low alloy steel under low triaxiality conditions is studied and the interaction between cementite particles and the crack is revealed. It is found that the ferrite matrix is the major void initiation site due to the low stress triaxiality in the thin TEM sample (plane stress condition), which contrasts the behavior under plane strain conditions in bulk specimens, where voids are typically found to initiate by decohesion at the particle/matrix interface. This work reveals that fracture behavior proceeds differently under low triaxiality conditions, such as the shear lip region of fractured bulk sample, and demonstrates the possibility to avoid interface decohesion and thereby to enhance ductility in steels.. |
| 11. | Andrew Chapman,Elif Ertekin, Masanobu Kubota, Akihide Nagao, Kaila Bertsch, Arnaud Macadre, Toshihiro Tsuchiyama, Takuro Masamura, Setsuo Takaki, Ryosuke Komoda, Mohsen Dadfarnia, Brian Somerday, Alexander Tsekov Staykov, Joichi Sugimura, Yoshinori Sawae, Takehiro Morita, Hiroyoshi Tanaka, Kazuyuki Yagi, Vlad Niste, Prabakaran Saravanan, Shugo Onitsuka, Ki-Seok Yoon, Seiji Ogo, Toshinori Matsushima, Ganbaatar Tumen-Ulzii, Dino Klotz, Dinh Hoa Nguyen, George Harrington, Chihaya Adachi, Hiroshige Matsumoto, Leonard Kwati, Yukina Takahashi, Nuttavut Kosem, Tatsumi Ishihara, Miho Yamauchi, Bidyut Baran Saha, Md. Amirul Islam, Jin Miyawaki, Harish Sivasankaran, Masamichi Kohno, Shigenori Fujikawa, Roman Selyanchyn, Takeshi Tsuji, Yukihiro Higashi, Reiner Kirchheim, and Petros Sofronis, Achieving a Carbon Neutral Future through Advanced Functional Materials and Technologies, Bulletin of The Chemical Society of Japan, https://doi.org/10.1246/bcsj.20210323, 95, 1, 73-103, 2022.01, Current greenhouse gas emissions suggest that keeping global temperature increase below 1.5 degrees, as espoused in the Paris Agreements will be challenging, and to do so, the achievement of carbon neutrality is of utmost importance. It is also clear that no single solution can meet the carbon neutral challenge, so it is essential for scientific research to cover a broad range of technologies and initiatives which will enable the realization of a carbon free energy system. This study details the broad, yet targeted research themes being pioneered within the International Institute for Carbon-Neutral Energy Research (I2CNER). These approaches include hydrogen materials, bio-mimetic catalysts, electrochemistry, thermal energy and absorption, carbon capture, storage and management and refrigerants. Here we outline the state of the art for this suite of technologies and detail how their deployment, alongside prudent energy policy implementation can engender a carbon neutral Japan by 2050. Recognizing that just as no single technological solution will engender carbon neutrality, no single nation can expect to achieve this goal alone. This study represents a recognition of conducive international policy agendas and is representative of interdisciplinary, international collaboration.. |
| 12. | Ryosuke Komoda, Masanobu Kubota, Aleksandar Staykov, Patrick Ginet, Francoise Barbier, Jader Furtado, Laurent Prost, Akihide Nagao, Effect of gas pressure on hydrogen environment embrittlement of carbon steel A106 in carbon monoxide mixed hydrogen gas, Metallurgical and Materials Transactions A, Accepted 14th Oct., 2021, 2021.10, The addition of a small volume fraction of carbon monoxide (CO) gas to pure gaseous H2 potentially mitigates the susceptibility of steel to hydrogen environment embrittlement (HEE). The effect of environmental gas pressure on the mitigation of HEEs by a mixture of H2 and CO was examined in this study. Fracture toughness tests of an ASTM A106 pipe carbon steel were carried out in H2 gas containing CO. The environmental gas pressures at which the fracture toughness tests were conducted were 0.6, 1.0 and 4.0 MPa. The addition of a certain concentration of CO to H2 gas completely prevented HEE. The CO concentration achieving complete HEE prevention increased with an enhancement of the environmental gas pressure. Molecular dynamics (MD) simulations were further conducted to interpret the experimental results based on the interactions of H2 and CO with the Fe surface in conjunction with the effect of gas pressure. The MD simulations revealed that the dissociation rate of dihydrogen molecules to atomic hydrogen on the Fe surface significantly increased with an elevation of the gas pressure, whereas the adsorption rate of CO on the Fe surface was almost independent of the gas pressure. These results suggest that the increase in the gas pressure relatively promotes hydrogen uptake into the material in the presence of CO, which accounts for the experimental results showing that the CO concentration achieving complete HEE prevention increased with the elevation of the gas pressure.. |
| 13. | Daisuke Takazaki, Toshihiro Tsuchiyama, Ryosuke Komoda, Mohsen Dadfarnia, Brian P. Somerday, Petros Sofronis, Masanobu Kubota
, Effect of Hydrogen on Creep Properties of SUS304 Austenitic Stainless Steel, Corrosion, 77, 3, 256-265, 2021.03, The objective of this study is to derive mechanistic insight into the degradation of metals in high-temperature hydrogen in order to enable the safety of evolving hydrogen technologies that operate at elevated temperature. Creep testing was performed in argon and hydrogen gases under absolute pressure of 0.12 MPa at 873 K. The material was JIS SUS304 austenitic stainless steel. Results revealed that the creep life (time to failure) and creep ductility (strain to failure) of the SUS304 in hydrogen gas and in argon displayed opposite trends. While the creep life (time to failure) of the SUS304 in hydrogen gas was significantly shorter than that in argon, creep ductility (strain to failure) was higher in hydrogen. Associated with the relatively higher creep ductility, evidence of transgranular microvoid coalescence was more prevalent on fracture surfaces produced in hydrogen compared to those produced in argon. In addition, analysis of the steady-state creep relationships in hydrogen and argon indicated that the same creep mechanism operated in the two environments, which was deduced as dislocation creep. Regarding the mechanisms governing reduced creep life in hydrogen, the effects of decarburization, carbide formation, and the hydrogen-enhanced localized plasticity mechanism were investigated. It was confirmed that these effects were not responsible for the reduced creep life in hydrogen, at least within the creep life range of this study. Alternately, the plausible role of hydrogen was to enhance the vacancy density, which led to magnified lattice diffusion (self-diffusion) and associated dislocation climb. As a consequence, hydrogen accelerated the creep strain rate and shortened the creep life.. |
| 14. | Zahra S. Hosseini, Mohsen Dadfarnia, Akihide Nagao, Masanobu Kubota, Brian P. Somerday, Robert O. Ritchie, Petros Sofronis, Modeling the Hydrogen Effect on the Constitutive Response of a Low Carbon Steel in Cyclic Loading, Journal of Applied Mechanics, DOI: 10.1115/1.4049076, 88, 3, 031001-1-031001-14, 2021.03, Hydrogen-accelerated fatigue crack growth is a most severe manifestation of hydrogen embrittlement. A mechanistic and predictive model is still lacking partly due to the lack of a descriptive constitutive model of the hydrogen/material interaction at the macroscale under cyclic loading. Such a model could be used to assess the nature of the stress and strain fields in the neighborhood of a crack, a development that could potentially lead to the association of these fields with proper macroscopic parameters. Toward this goal, a constitutive model for cyclic response should be capable of capturing hardening or softening under cyclic straining or ratcheting under stress-controlled testing. In this work, we attempt a constitutive description by using data from uniaxial strain-controlled cyclic loading and stress-controlled ratcheting tests with a low carbon steel, Japanese Industrial Standard (JIS) SM490YB, conducted in air and 1 MPa H2 gas environment at room temperature. We explore the Chaboche constitutive model which is a nonlinear kinematic hardening model that was developed as an extension to the Frederick and Armstrong model, and propose an approach to calibrate the parameters involved. From the combined experimental data and the calibrated Chaboche model, we may conclude that hydrogen decreases the yield stress and the amount of cyclic hardening. On the other hand, hydrogen increases ratcheting, the rate of cyclic hardening, and promotes stronger recovery. . |
| 15. | Masanobu Kubota, Mio Fukuda, Ryosuke Komoda, Effect of Hydrogen on Fatigue Limit of SCM435 Low-Alloy Steel, Procedia Structural Integrity , 10.1016/j.prostr.2019.12.056, 19, 520-527, 2019.12, The objective of this study is to gain a basic understanding of the effect of hydrogen on the fatigue limit. The material was a low-alloy steel modified to be sensitive to hydrogen embrittlement by heat treatment. A statistical fatigue test was carried out using smooth and deep-notched specimens at a loading frequency of 20 Hz. The environment was laboratory air and hydrogen gas. The hydrogen gas pressure was 0.1 MPa in gauge pressure. The fatigue limit of the smooth specimen was higher in the hydrogen gas than that in air, although the material showed severe hydrogen embrittlement during the SSRT. The fatigue limit of the deep-notched specimen in the hydrogen gas was the same as that in air. For the smooth specimen, the fatigue limit was determined by whether or not a crack was initiated. For the deep-notched specimen, the fatigue limit was determined by whether or not a crack propagated. The results can be interpreted as that hydrogen has no significant effect on crack initiation in the high-cycle fatigue regime and affected the threshold of the crack propagation.. |
| 16. | Aleksandar Staykov, Ryosuke Komoda, Masanobu Kubota, Patrick Ginet, Françoise Barbier, Jader Furtado, Coadsorption of CO and H2 on an Iron Surface and Its Implication on the Hydrogen Embrittlement of Iron, Journal of Physical Chemistry C, 10.1021/acs.jpcc.9b06927, 123, 50, 30265-30273, 2019.12, [URL], We investigated the competitive coadsorption of carbon monoxide and hydrogen gas on an iron surface with a 110 facet using density functional theory. Our study discusses the hydrogen dissociation reaction on a fresh iron surface and a surface with varying carbon monoxide coverage. Additionally, we investigated the carbon monoxide surface adsorption as a function of the carbon monoxide surface coverage. Our results show different trends for the carbon monoxide adsorption and hydrogen dissociation on surfaces with low and high CO coverage. Those opposite trends were related to the charge of the surface iron atoms and the available surface electron density which is necessary to facilitate the carbon monoxide adsorption and catalyze the hydrogen dissociation reaction. The subsurface diffusion of predissociated surface hydrogen atoms has been included in the model. It was found that the atomistic hydrogen diffusion into the material is also related to the carbon monoxide surface coverage. Our theoretical results confirmed that a small amount of carbon monoxide as an impurity in the hydrogen gas can mitigate the effect of hydrogen embrittlement by significantly reducing the rate of hydrogen dissociation on the iron surface and thus reduce the hydrogen uptake into the bulk of the material. To verify the theoretical results, we carried out a fracture toughness test of pure iron in a high-purity H2, CO and H2 mixture, and N2 gases. This material suffered from hydrogen embrittlement, in other words, reduction in the fracture toughness due to hydrogen. We could derive the complex dependence on the hydrogen embrittlement manifestation as a function of the H2/CO gas mixture ratio and gas exposure time.. |
| 17. | Ryosuke Komoda, Kazuki Yamada, Masanobu Kubota, Patrick Ginet, Francoise Barbier, Jader Furtado, Laurent Prost, The inhibitory effect of carbon monoxide contained in hydrogen gas environment on hydrogen-accelerated fatigue crack growth and its loading frequency dependency, International Journal of Hydrogen Energy, 10.1016/j.ijhydene.2019.09.146, 44, 54, 29007-29016, 2019.11, [URL], The effect of carbon monoxide (CO) contained in H2 gas as an impurity on the hydrogen-accelerated fatigue crack growth of A333 pipe steel was studied in association with loading frequency dependency. The addition of CO to H2 gas inhibited the accelerated fatigue crack growth due to the hydrogen. The inhibitory effect was affected by the CO content in the H2 gas, loading frequency, and crack growth rate. Based on these results, it was revealed that the inhibitory effect of CO was governed by both competition between the rate of fresh surface creation by the crack growth and the rate of coverage of the surface by CO and time for hydrogen diffusion in the material to the crack tip with reduced hydrogen entry by CO.. |
| 18. | Masanobu Kubota, Ryosuke Komoda, Xuesong Cui, Hiroshi Wakabayashi, Yasuhisa Tanaka, Effects of hydrogen and weld defect on tensile properties of SUH660 and SUS316L welded joints, International Journal of Mechanical Engineering and Robotics Research, 10.18178/ijmerr.8.5.713-718, 8, 5, 713-718, 2019.09, [URL], The effect of hydrogen on the tensile properties of the SUH660 and SUS316L different materials welded joints was characterized in conjunction with the joint shape and weld defects. The butt welded joint specimen without weld defect fractured at the SUS316L base material, and did not cause hydrogen embrittlement (HE). However, the failure position of the spigot-lap welded joint specimen moved from the SUS316L base material to the weld part when hydrogen charging was applied. This resulted in a significant reduction of the elongation. It was presumed that the HE was induced by the stress concentration due to the weld shape. The weld defect induced HE in both joints. The weld defect was produced by incomplete penetration. It also caused incomplete mixing of the weld metal. Consequently, filler nickel segregated around the weld defect, then HE occurred.. |
| 19. | Ryosuke Komoda, Masanobu Kubota, Aleksandar Tsekov Staykov, Patrick Ginet, Francoise Barbier, Jader Furtado, Inhibitory effect of oxygen on hydrogen-induced fracture of A333 pipe steel, Fatigue and Fracture of Engineering Materials and Structures, 10.1111/ffe.12994, 42, 6, 1387-1401, 2019.06, [URL], The effect of oxygen contained in hydrogen gas environment as an impurity on hydrogen environment embrittlement (HEE) of A333 pipe steel was studied through the fracture toughness tests in hydrogen gases. The oxygen contents in the hydrogen gases were 100, 10, and 0.1 vppm. A significant reduction in the J-Δa curve was observed in the hydrogen with 0.1-vppm oxygen. Under given loading conditions, the embrittling effect of hydrogen was completely inhibited by 100 vppm of oxygen. In the case of the hydrogen with 10-vppm oxygen, initially the embrittling effect of hydrogen was fully inhibited, and then subsequently appeared. It was confirmed that 1-vppm oxygen reduced the embrittling effect of hydrogen. The results can be explained by the predictive model of HEE proposed by Somerday et al.. |
| 20. | Ryosuke Komoda, Kazuki Yamada, Masanobu Kubota, A comparison of inhibitory effects of carbon monoxide and oxygen on hydrogen-accelerated fatigue crack growth, 29th International Ocean and Polar Engineering Conference, ISOPE 2019 Proceedings of the 29th International Ocean and Polar Engineering Conference, ISOPE 2019, 4169-4174, 2019.01, This study investigated effects of addition of O2 and CO to H2 gas environments on a hydrogen-accelerated fatigue crack growth in a pipe steel. Both O2 and CO inhibited the hydrogen-accelerated fatigue crack growth. The inhibitory effect of O2 was well-interpreted by the mechanism proposed by Somerday et al. (2013). On the other hand, different mechanisms, which are the reaction rate of CO with the iron surface and time for hydrogen diffusion in the material, dominated the inhibitory effect of CO.. |
| 21. | Masanobu Kubota, Xuesong Cui, Ryosuke Komoda, Hiroshi Wakabayashi and Yasuhisa Tanaka , Effects of hydrogen and weld defect on tensile properties of SUH660 and SUS316L welded joints, Proceedings of 3rd International Conference on Design, Materials and Manufacturing (ICDMM2018), 2018.08, The effect of hydrogen on the tensile properties of the SUH660 and SUS316L different materials welded joints was characterized in conjunction with the joint shape and weld defects. The butt welded joint specimen without weld defect fractured at the SUS316L base material, and did not cause hydrogen embrittlement (HE). However, the failure position of the spigot-lap welded joint specimen moved from the SUS316L base material to the weld part when hydrogen charging was applied. This resulted in a significant reduction of the elongation. It was presumed that the HE was induced by the stress concentration due to the weld shape. The weld defect induced HE in both joints. The weld defect was produced by incomplete penetration. It also caused incomplete mixing of the weld metal. Consequently, filler nickel segregated around the weld defect, then HE occurred.. |
| 22. | Ryosuke Komoda, Masanobu Kubota, Aleksandar Staykov, Patrick Ginet, Francoise Barbier, Jader Furtado , Inhibition of hydrogen environment assisted cracking by small amount of oxygen contained in hydrogen gas, Proceedings of the 6th International Conference on Crack Path (CP2018), 2018.08, Fracture toughness tests of a pipe steel were conducted in hydrogen environment. The crosshead speed was 2.0 × 10-5 mm/s. The gas pressure was 0.6 MPa. The temperature was kept at 293 K. Two gas systems were used to investigate the small amount of oxygen on hydrogen environment assisted cracking (HEAC). One is a closed gas system, where hydrogen gas is stored in the gas chamber. In this system, oxygen content in the gas chamber gradually increased with time and reached 1 vppm during the test. Another is an open gas system, where high-purity hydrogen gas is continuously supplied into the gas chamber. In this system, the oxygen content in the gas chamber can be kept at 0.1 vppm. The fracture toughness in the hydrogen with 0.1 vppm oxygen was significantly lower than that in air. The fracture toughness in the hydrogen with the maximum oxygen content of 1 vppm was higher than that in the hydrogen with 0.1 vppm oxygen. 1 vppm oxygen partially inhibited the HEAC. Owing to detailed analysis of the fracture toughness test results, the critical oxygen content to appear the inhibitory effect of oxygen under the test conditions could be estimated as 0.3 vppm.. |
| 23. | Komoda, R., Kubota, M., Staykov, A., Ginet, P., Barbier, F., Furtado, J, Inhibition of hydrogen embrittlement of Cr-Mo steel by the addition of impurities to hydrogen environment and the effect of material strength, Proceedings of International Ocean and Polar Engineering Conference 2018 (ISOPE-2018), 2018.06, The effect of impurities, added to hydrogen environment, on hydrogen embrittlement (HE) was investigated in association with the effect of material strength. Addition of CO and O2 deactivated the HE. O2 prevented the HE with lower concentration than CO. Material with higher strength required larger amount of impurities to prevent the HE. Reduction of hydrogen uptake was the primary result of the addition of the impurities, but a certain amount of hydrogen uptake occurred when the HE was completely inhibited. Discussion regarding essential HE mechanisms for the fracture morphologies was required to interpret the effect of material strength.. |
| 24. | MasanobuKubota, ArnaudMacadre, KoichiMori and RyoMori, Fatigue Properties of Ultra-Fine Grain Austenitic Stainless Steel and the Effect of Hydrogen, MATEC Web of Conferences, 165, 2018.05, The fatigue properties of ultra-fine grain austenitic steel(UFG16-10), which has a 1 μm average grain size, were studied as part of the project aimed at the development of high-strength low-cost stainless steels for hydrogen service. The fatigue properties of the UFG16-10 werecompared with that of a coarse grain material with the same chemical composition (CG16-10) and two kinds of commercialsteels, JIS SUS316 and JIS SUH660. The fatigue strength of the UFG16-10was 2.8 times higher than that of the CG16-10. The effect of hydrogenon the fatigue limit of the UFG16-10was not significant. However, the fatigue life of the UFG16-10 was reducedby hydrogen in the short life regime. In the fatigue crack growth test, the UFG16-10showed a good crack growth resistance that was equivalent to that of the SUH660 and significantlyhigher than that of the SUS316. However, the crack growth rate was significantly accelerated by hydrogen. The cause of the hydrogen-assisted fatigue crack growth of the UFG16-10was transformation of the microstructure at the crack tip from austenite to strain-induced martensite.This wasalso the cause of the reducedfatigue life of the hydrogen-charged UFG16-10.. |
| 25. | Komoda, R., Morita, N., Nakashima, F., Kubota, M., Sawada, R., Development of new measurement method applying mems technology for relative slip range during fretting fatigue test in hydrogen, Proceedings of 2016 Hydrogen Confrerence, Edited by B.P. Somerday and P. Sofronis, ASME, 454-461, 2017.10. |
| 26. | Kubota, M., Komoda, R., Furtado, J, The effects of oxygen impurities on fretting fatigue of austenitic stainless steel in hydrogen gas, Proceedings of 2016 Hydrogen Confrerence, Edited by B.P. Somerday and P. Sofronis, ASME, 454-461, 2017.10. |
| 27. | 髙﨑 大裕, 久保田 祐信, 薦田 亮介, 奥 洋介, 杉野 正明, 牧野 泰三, Effect of contact pressure on fretting fatigue failure of oil-well pipe material, International Journal of Fatigue, https://doi.org/10.1016/j.ijfatigue.2017.03.024, 110, 1, 67-74, 2017.08, In a traditional way of oil-well development, casing pipes were laid into a hole drilled beforehand. Recently, a new technology that drilling and laying of casing pipes are simultaneously done by casing pipes a drill bit is at-tached to the top pipe has been developed. The thread joints connecting pipes receive bending rotating load during drilling, and then fretting fatigue is concerned at the thread joints. Based on the results of the full-scale fatigue test of a thread joint, there were two failure modes. The first one was fatigue failure at the thread corner. The second one is fretting fatigue fail-ure at the middle of the contact part of the threads. Fretting fatigue cracks frequently originate at the contact edge because of severe stress concentration. For this fretting fatigue failure mode, many approaches for quantitative evalua-tion of the fretting fatigue strength have been developed. On the other hand, the fretting fatigue crack dur-ing the full scale test of the thread joint was formed at the middle of the contact part. Similar failure mode can be seen in the fretting fatigue with relatively lower con-tact pressure, but quantitative understanding has not yet been achieved.. |
| 28. | 久保田 祐信, 片岡 俊介, 髙﨑 大裕, 近藤 良之, A Quantitative Approach to Evaluate Fretting Fatigue Limit Using a Pre-Cracked Specimen, Tribology International, http://dx.doi.org/10.1016/j.triboint.2016.10.017, 108, 48-56, 2017.04, A pre-cracked specimen, which has a 70-μm-deep crack, was used for the fretting fatigue test to understand the reasons for the change in the fretting fatigue limit due to changes in the contact pressure, position of the precrack, and foot length of the contact pad. The threshold stress intensity factor range to crack propagation of the pre-crack, ΔKth, was obtained by the crack growth test. The stress intensity factor range of the pre-crack under fretting conditions was then evaluated by a finite element analysis to estimate the fretting fatigue limit of the pre-crack specimen. The effects of these variables on the fretting fatigue limit were quantitatively explained by the results of the FEM and ΔKth of the short crack.. |
| 29. | 奥 洋介, 杉野 正明, Yoshinori Ando, 牧野 泰三, 薦田 亮介, 髙﨑 大裕, 久保田 祐信, Fretting Fatigue on Thread Root of Premium Threaded Connections, Tribology International, http://dx.doi.org/10.1016/j.triboint.2016.10.021, 108, 111-120, 2017.04, Identification of the fatigue failure mode of the premium threaded connection for Oil Country Tubular Goods pipes was conducted via full-scale fatigue tests. A through-wall crack was found at the imperfect thread root of the male embodiment, but the crack initiation site depended on the stress level. At relatively higher stress amplitude region, the crack originated from the thread rounded corner by stress concentration. At relatively lower stress amplitude region, the crack originated at the middle of the thread root because of fretting fatigue. To investigate the fretting fatigue mechanism in the threaded connection, a fundamental fretting fatigue test was conducted. This test achieved the fretting fatigue failure at the middle of the contact surface under large gross slip condition.. |
| 30. | 松本 拓哉, 久保田 祐信, 松岡 三郎, Patrick Ginet, Jader Furtado, Francois Barbier, Threshold stress intensity factor for hydrogen-assisted cracking of Cr-Mo steel used as stationary storage buffer of a hydrogen refueling station, International journal of hydrogen energy, http://dx.doi.org/10.1016/j.ijhydene.2016.05.124, 42, 7422-7428, 2017.03, In order to determine appropriate value for threshold stress intensity factor for hydrogen assisted cracking (KIH), constant-displacement and rising-load tests were conducted in high-pressure hydrogen gas for JIS-SCM435 low alloy steel (Cr-Mo steel) used as stationary storage buffer of a hydrogen refuelling station with 0.2% proof strength and ultimate tensile strength equal to 772 MPa and 948 MPa respectively. Thresholds for crack arrest under constant displacement and for crack initiation under rising load were identified. The crack arrest threshold under constant displacement was 44.3 MPa m1/2 to 44.5 MPa m1/2 when small-scale yielding and plane-strain criteria were satisfied and the crack initiation threshold under rising load was 33.1 MPa m1/2 to 41.1 MPa m1/2 in 115 MPa hydrogen gas. The crack arrest threshold was roughly equivalent to the crack initiation threshold although the crack initiation threshold showed slightly more conservative values. It was considered that both test methods could be suitable to determine appropriate value for KIH for this material. . |
| 31. | 髙﨑 大裕, 久保田 祐信, 薦田 亮介, 吉田 修一, 奥 洋介, 牧野 泰三, 杉野 正明, Effect of Contact Pressure on Fretting Fatigue Failure of Oil-Well Pipe Material, Proc. the Asian Conference on Experimental Mechanics 2016 (ACEM 2016), 2016.11, Fretting fatigue is a combination of fatigue and a kind of wear. Since the fretting fatigue strength is significantly lower than plain fatigue strength, fretting fatigue is one of the most important factors in the design of components. In resent oil-well development, drilling casing technology becomes popular. As shown in Fig. 1, the thread joint between pipes might suffer from fretting fatigue. In the results of full-scale fatigue test of thread joint, there were two failure modes. The first one was the fatigue failure at the thread corner radius, which has been already quantitatively evaluated. The second one is the fretting fatigue failure at the inner contact surface, which has not been studied yet. The objective of this study is to clarify the mechanism of the fretting fatigue failure at the inner contact surface. For this purpose, a fretting fatigue test with different contact pressure was carried out.. |
| 32. | 久保田 祐信, 薦田 亮介, Jader Furtado, Fretting fatigue in hydrogen and the effect of oxygen impurity, Proc. the Asian Conference on Experimental Mechanics 2016 (ACEM 2016), 2016.11, Fretting is a coupled problem of fatigue and frictional contact. It brings unique phenomena that enhance the hydrogen-induced degradation of fatigue strength. Therefore, the role of hydrogen in the fretting fatigue is seriously considered by both manufacturers and users of hydrogen equipment. The fretting fatigue limit in hydrogen was significantly lower than that in air, whereas the fatigue limit of the conventional fatigue test was the same for the both tests. The results clearly demonstrate that the fretting had some specific effects that enhance hydrogen-induced degradation of fatigue strength.. |
| 33. | Nobutomo Morita, 薦田 亮介, Fumiya Nakashima, 久保田 祐信, Eiji Higurashi, 澤田 廉士, Evaluation of Local Relative Slip in a narrow space in Hydrogen Gas Using MEMS Optical Encoder, Proc. International Conference on Optical MEMS and Nanophotonics (IEEE OMN 2016), 2016.08, The sensing technology to measure local m-order displacement is requested in mechanical property testing. The sensor size should be sufficiently small to install the sensor on specimen, and the sensor characteristic should not be affected by the environment in order to evaluate the change in mechanical properties in different environments. In this paper, we will report evaluation of local relative slip range in fretting fatigue testing using our developed MEMS optical encoder and grating scale. An alignment method of the sensor is also developed.. |
| 34. | Masanobu Kubota, Ryosuke Komoda, Test machine for fretting in hydrogen environment, Toraibarojisuto/Journal of Japanese Society of Tribologists, 61, 3, 187-190, 2016. |
| 35. | 薦田 亮介, 久保田 祐信, Jader Furtado, Effect of addition of oxygen and water vapor on fretting fatigue properties of an austenitic stainless steel in hydrogen, Tribology International, http://dx.doi.org/10.1016/j.ijhydene.2014.12.129, 40, 16868-16877, 2015.12, JIS SUS304 fretting fatigue test was done in high-purity hydrogen, an oxygenehydrogen mixture and humidified hydrogen. The fretting fatigue strength in hydrogen was drastically changed depending onthe oxygen level. Basedonthe XPS(X-ray photoelectron spectroscopy) analysis of the fretted surface, it was found that the fretting removed the original protection layer of the stainless steel, however, the addition of water vapor or ppm-level of oxygen produced an oxide layer on the fretted surface during the fretting that surpassed the removal effect of the initial oxide layer by fretting. In fact, a strong adhesion between the contacting surfaces occurred and no fretting wear particles were observed in the high-purity hydrogen. On the other hand, oxidized fretting wear particles were found in the oxygen-hydrogen mixture. Based on the geometry of contact used in this study, a severe concentration of the contact pressure arouse at the contact edge. This produces a compressive stress field in the specimen where the crack growth was suppressed. This stress concentration was relieved when fretting wear occurs. Therefore, the change in the fretting fatigue strength in hydrogen by the addition of oxygen is closely related to the change in the wear behavior.. |
| 36. | 久保田 祐信, 薦田 亮介, 水素雰囲気におけるフレッチング疲労 , トライボロジスト, 60, 10, 651-657, 2015.10, フレッチング疲労に及ぼす水素の影響はかなり古くから調べられている様子であるが，研究の数は少なく，また燃料電池技術を核とした水素エネルギー利用に即した研究が必要である．ここでは，著者らの研究を中心に，オーステナイト系ステンレス鋼の低圧の水素ガス中フレッチング疲労，水素チャージ材の大気中フレッチング疲労などについて強度特性と機構を解説する．. |
| 37. | 松本 拓哉, 久保田 祐信, 松岡 三郎, Patrick Ginet, Jader Furtado, Francois Barbier, Threshold stress intensity factor for hydrogen-assisted cracking of Cr-Mo steel used as stationary storage buffer of a hydrogen refueling station, Proc. International Conference on Hydrogen Safety (ICHS2015), 2015.10, In order to determine appropriate value for threshold stress intensity factor for hydrogen-assisted cracking, KIH, constant-displacement and rising-load tests were conducted in high-pressure hydrogen gas for JIS-SCM435 low alloy steel (Cr-Mo steel) used as stationary storage buffer of a hydrogen refuelling station with 0.2 % proof strength and ultimate tensile strength equal to 772 MPa and 948 MPa respectively. Thresholds for crack arrest under constant displacement and for crack initiation under rising load were identified. The crack arrest threshold under constant displacement was 44.3 MPa·m1/2 to 44.5 MPa·m1/2 when small-scale yielding and plane-strain criteria were satisfied and the crack initiation threshold under rising load was 33.1 MPa·m1/2 to 41.1 MPa·m1/2 in 115 MPa hydrogen gas. The crack arrest threshold was roughly equivalent to the crack initiation threshold although the crack initiation threshold showed slightly more conservative values. It was considered that both test methods could be suitable to determine appropriate value for KIH for this material.. |
| 38. | 森 功一, 久保田 祐信, MACADRE ARNAUD PAUL ALAIN, Fatigue properties of ultra-fine grain austenitic stainless steel and effect of hydrogen, Proc. Third Japan-China Joint Fatigue Symposium , 2014.11, The fatigue properties of ultra-fine grain austenitic steel (UFG), which has a 1m average grain size, were studied. The effect of hydrogen was also investigated using hydrogen-charged material. The fatigue strength of the UFG was 2.8 times higher than that of coarse grain material which has an average grain size of 21m. The effect of hydrogen charge on the fatigue strength of the UFG was not significant. The fatigue crack growth resistance of the UFG is remarkably improved compared with that of SUS316. The crack path of the UFG was very straight, while that of the coarse grain materials was meandering and branching. The development of slip bands at the crack tip was extremely reduced in the UFG than in the coarse grain materials. It was presumed that the significant improvement of the fatigue properties of the UFG was achieved by the fact that the ultra-fine grains suppressed the slip deformation at the crack tip, and as a conse-quence, the crack opening displacement might decrease. . |
| 39. | 薦田 亮介, 久保田 祐信, 近藤 良之, Jader Furtado, Effect of oxygen addition on fretting fatigue strength in hydrogen of JIS SUS304 stainless steel, Tribology International, http://dx.doi.org/10.1016/j.triboint.2014.02.025, 76, 92-99, 2014.08, The mechanisms that cause a significant reduction in the fretting fatigue strength of SUS304 stainless steel in gaseous hydrogen is discussed focusing on the adhesion between contact surfaces and crack nucleation. The reduction in the fretting fatigue strength in hydrogen was partially mitigated by the prevention of the adhesion by the addition of oxygen. To characterize the effect of hydrogen on the fretting fatigue crack nucleation, fatigue tests carried out in air and in hydrogen, and finite element analyses were conducted. The crack nucleation limit in both tests was significantly lower in hydrogen than in air. The role of hydrogen in the fretting fatigue crack nucleation is another cause of the reduced fretting fatigue strength of SUS304 steel in hydrogen.. |
| 40. | 薦田 亮介, 吉開 巨都, 久保田 祐信, Jader Furtado, Reduction in Fretting Fatigue Strength of Austenitic Stainless Steels due to Internal Hydrogen, Advanced Materials Research, 891-892, 891-896, 2014.03, Fretting fatigue is one of the major factors in the design of hydrogen equipment. The effect of internal hydrogen on the fretting fatigue strength of austenitic stainless steels was studied. The internal hydrogen reduced the fretting fatigue strength. The reduction in the fretting fatigue strength became more significant with an increase in the hydrogen content. The reason for this reduction is that the internal hydrogen assisted the crack initiation. When the fretting fatigue test of the hydrogen-charged material was carried out in hydrogen gas, the fretting fatigue strength was the lowest. Internal hydrogen and gaseous hydrogen synergistically induced the reduction in the fretting fatigue strength of the austenitic stainless steels. In the gaseous hydrogen, fretting creates adhesion between contacting surfaces where severe plastic deformation occurs. The internal hydrogen is activated at the adhered part by the plastic deformation which results in further reduction of the crack initiation limit.. |
| 41. | 久保田 祐信, High-Cycle Fatigue Properties of Carbon Steel and Work-Hardened Oxygen Free Copper in High Pressure Hydrogen, Advanced Materials Research, 891-892, 575-580, 2014.03, The high-cycle fatigue properties of 0.35 % carbon steel and work-hardened oxygen-free copper in 10MPa hydrogen were studied. The fatigue limit of the carbon steel in hydrogen was almost the same as that in air. The fatigue strength at 107 cycles of the copper was higher in hydrogen than in air. The fatigue life of both materials is longer in hydrogen than in air. The reason was the delays in the crack initiation and the early propagation of the cracks in hydrogen. For both materials, the detrimental effect on the fatigue strength due to the hydrogen environment was small, however, it was determined that hydrogen participates in the slip deformation. The morphology of the slip bands was specific in hydrogen. In the copper, the slip bands, which are non-viable in air, developed in hydrogen.. |
| 42. | 青木 辰郎, 池宮 秀也, 久保田 祐信, Yoshiyuki Kondo, EFFECT OF HYDROGEN ON FRACTURE TOUGHNESS OF LOW ALLOY STEELS , Proceedings of 2012 Hydrogen Conference, 173-181, 2014.02, A fracture toughness test in air under continuous hydrogen charge was performed using four kinds of low alloy steels. The reduction in fracture toughness JIC was characterized in terms of the effect of material, hardness and loading rate. The reduction in JIC was significant when a slower loading rate was used and a harder material was used. However, the 3.5NiCrMoV steel showed relatively less reduction in JIC compared with other materials even when the hardness was higher than that of other materials. The fracture surface was changed from dimpled to quasi-cleavage when the reduction in JIC was significant. . |
| 43. | 久保田 祐信, 足立裕太郎, 白石 悠貴, 薦田 亮介, Jader Furtado, EFFECT OF HYDROGEN AND ADDITION OF OXYGEN ON FRETTING FATIGUE PROPERTIES, Proceedings of 2012 Hydrogen Conference, 391-399, 2014.02, The fretting fatigue strength of SUS304 was more significantly reduced in hydrogen than in air. One of the causes was adhesion between the contacting surfaces and formation of many small cracks. In the adhesion mimicked fatigue test, hydrogen assisted in the crack initiation. This is another reason for the reduced fretting fatigue strength in hydrogen. The effect of oxygen addition to hydrogen was also investigated. An increase in the fretting fatigue strength was found in the oxygen-hydrogen mixture. The friction force coefficient was reduced in the oxygen- hydrogen mixture. The critical maximum shear stress range to crack initiation was higher in the oxygen-hydrogen mixture than in only hydrogen. These are the possible reasons for the increase in the fretting fatigue strength in the oxygen-hydrogen mixture.. |
| 44. | 河上紘大, 副島孝, 久保田 祐信, 高圧水素中における無酸素銅加工硬化材の疲労特性, 銅と銅合金, 52, 1, 245-250, 2013.08, The effects of hydrogen on the high-cycle fatigue properties of a work-hardened oxygen-free copper (OFC) was investigated. The fatigue strength in 10MPa hydrogen was increased compared to that in air. The cause of the increased fatigue strength in the hydrogen was the delay of crack initiation and the decrease of crack growth rate due to the absence of oxygen and water vapor. In this sense, hydrogen embrittlement didn’t occur in this material. However, hydrogen significantly enhanced the development of slip bands. The morphology of slip bands during the fatigue test in hydrogen was definitely different from that observed in air. Based on the detailed observation of the slip bands, it is presumed that the possible cause of the enhanced slip deformation during the fatigue in hydrogen is enhanced localized plastic deformation (HELP).. |
| 45. | 松本 拓哉, 伊藤賀久岳, 平林 佐那, 久保田 祐信, 松岡 三郎, 0.7MPa 水素ガス中における炭素鋼鋼板SM490B の弾塑性破壊靭性に及ぼす変位速度の影響, 日本機械学会論文集（A 編）, 79, 804, 1210-1225, 2013.08, The elastic-plastic fracture toughness, JIc, of SM490B carbon steel plate was investigated in air and 0.7 MPa hydrogen gas. JIc tests were conducted in accordance with the JSME standard, JSME S001 (1981). JIc was much smaller in hydrogen at a displacement velocity of V = 2 × 10–3 mm/s (JIc = 10.0 kJ/m2) than in air at V = 2 × 10–3 mm/s (JIc = 248.6 kJ/m2). JIc in air does not satisfy the validity requirement. In hydrogen, surprisingly, a further decrease in V did not decrease JIc, but increased it. JIc in hydrogen at V = 2 × 10–5 mm/s was 60.9 kJ/m2. The large and small values of JIc in air and hydrogen corresponded to the fracture morphology. In air at V = 2 × 10–3 mm/s, a critical stretched zone, SZWc, was formed at the tip of the fatigue pre-crack, followed by dimples. In hydrogen at V = 2 × 10–3 mm/s, quasi-cleavage instead of SZWc and dimples were formed at the pre-crack tip. In hydrogen at V = 2 × 10–5 mm/s, SZWc was formed at the precrack tip, followed by dimples again. This elastic-plastic fracture toughness behavior was analyzed assuming HESFCG (hydrogen-enhanced successive fatigue crack growth), which is proposed by the authors to explain the acceleration of fatigue crack growth rate in the presence of hydrogen. The elastic plastic fracture toughness test shown in 0.7 MPa hydrogen gas at V = 2 × 10–3 mm/s is the same as that shown in a fatigue crack growth test in 0.7 MPa hydrogen gas at a number of cycles of n = 1 and stress ratio of R = 0; and thus JIc in 0.7 MPa hydrogen gas at V = 2 × 10–3 mm/s is not the real elastic-plastic fracture toughness. We conclude that the real elastic-plastic fracture toughness in 0.7 MPa hydrogen gas can be determined by fracture toughness testing in 0.7 MPa hydrogen gas at V = 2 × 10–5 mm/s.. |
| 46. | 薦田亮介, 久保田 祐信, 近藤 良之, Jader Furtado, 水素ガス中フレッティング疲労における疲労強度低下の基本的機構（凝着部に発生する微小き裂の発生条件に及ぼす水素の影響）, 日本機械学会論文集A編, 79, 801, 536-545, 2013.05, The authors have reported a significant reduction in fretting fatigue strength of austenitic stainless steels due to hydrogen. One of the causes of the reduced fretting fatigue strength in hydrogen is adhesion between contacting surfaces and following formation of small cracks which emanate from the adhered spots. The objective of this study is to understand the effect of hydrogen on the initiation of the small cracks under fretting fatigue conditions. Since the adhesion between contacting surfaces during fretting in hydrogen is very localized, a small contact length was used in this test in order to facilitate understanding by avoiding such localization. The fretting fatigue test of an austenitic stainless steel SUS304 was performed in air and 0.13MPa hydrogen. In the fretting fatigue test, hydrogen participates in the initiation of the fretting fatigue crack. It can be presumed that high strain at the contact edge activates hydrogen assisted fracture in terms of dislocation mobility. Adhesion mimic test, in which a small contact area was welded, was also performed. As the result, the crack initiation limit evaluated by the maximum range of shear stress was significantly lower in hydrogen than in air. Hydrogen assists small crack initiation under fretting fatigue conditions. This is one of the possible causes of the significant reduction of fretting fatigue strength in hydrogen.. |
| 47. | 久保田祐信，佐久間亨，山口純一郎，近藤良之, オーステナイト系ステンレス鋼の切欠き材の高サイクル疲労強度に及ぼす過大応力と水素の影響, 日本機械学会論文集（A 編）, 77, 782, 1747-1759, 2012.10, SUS304，SUS316L鋼の切欠き材に水素チャージを施し，0.6MPa水素ガス環境中でN=200回の繰返し過大応力負荷後に高サイクル疲労試験を実施し，過大応力負荷と水素が高サイクル疲労強度低下に及ぼす影響を検討した．高サイクル疲労強度は過大応力負荷によって低下した．その原因は過大応力により発生した微小き裂である．SUS304では水素の影響により疲労強度低下が助長されたが，SUS316Lでは水素の影響は見られなかった．切欠き底の微小き裂進展挙動を評価し，さらにKthとき裂長さの関係を用いて，任意の負荷条件，切欠き先端半径に対して影響を予測する方法を提案した．. |
| 48. | Masanobu Kubota, Yutaro Adachi, Yoshiyuki Kondo, Observation of surface damage in a valve for hydrogen gas and leakage conditions, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.78.674, 78, 789, 674-678, 2012.06, [URL], A basic study to upgrade long-term reliability and durability of a high-pressure hydrogen gas valve was carried out in anticipation of increase of the use of hydrogen utilization machines and infrastructures. The morphology of the surface damage in the sealing components, the damaging mechanism and the relation between development of the damage and leakage were investigated. The surface damage in hydrogen gas was caused by surface plastic flow and transfer of material. In addition, fatigue crack and following delamination were caused by repetitive contact. Small amount of the surface damage didn't cause leakage. When the surface damage reached a certain amount of depth or width, steep increase of the leakage was caused. Although the meaning of the limitation of the depth or width of the surface damage to cause the rapid increase of leakage is not fully understood, it was recognized that holistic studies to minimalize surface damage including contact conditions, shape of the sealing components and material are required in terms of wear but also in terms of fatigue.. |
| 49. | 片岡 俊介，小野 裕章，久保田 祐信，近藤 良之, フレッティング疲労における微小き裂進展に及ぼす接触条件の影響, 日本機械学会論文集（A 編）, http://dx.doi.org/10.1299/kikaia.78.1, 78, 785, 1-13, 2012.01, As the general features of fretting fatigue, initiation of fretting fatigue crack is in the very early stage of the fretting fatigue life and there are small non-propagating cracks in the test specimen that doesn’t fracture at the fretting fatigue limit. In accordance with these experimental facts, fretting fatigue problem can be considered as a propagation problem of small crack. Thus, a pre-cracked specimen was used in the fretting fatigue test in this study. The objective was to consider the determinant factors of fretting fatigue strength. In the fretting fatigue test, the fretting fatigue limit of the pre-cracked specimen was once reduced and after increased with increase of the contact pressure. The reason was understood by the stress intensity factor of the pre-crack obtained by a finite element analysis. In this study, the fretting fatigue limit can be predicted by the comparison of ΔK of the pre-crack and the propagation threshold of the pre-crack ΔKth. The effect of the relative location of the pre-crack to the contact edge on the fretting fatigue strength was also discussed by both fretting fatigue test and FEM analysis.. |
| 50. | Akimitsu Seo, Masanobu Kubota, Yoshiyuki Kondo, Effects of notch root radius and stress ratio on the fatigue crack propagation threshold for the short crack at the notch root, 19th European Conference on Fracture: Fracture Mechanics for Durability, Reliability and Safety, ECF 2012 19th European Conference on Fracture Fracture Mechanics for Durability, Reliability and Safety, ECF 2012, 2012.01, The crack growth threshold, ΔKth, for the short crack at the root of a long notch including the effects of notch root radius, ρ, and stress ratio, R, were investigated in this study. The pre-crack, with a depth of 0.15mm, was introduced at the root of a 2mm deep notch which had the root radius changed from 0.015mm to 15mm. A crack propagation test using the unloading elastic compliance method was carried out with the stress ratios of -1, 0 and 0.62-0.72 (high R). The material was normalized 0.25 % carbon steel. The change in ΔKth with the change in ρ was dependent on R. Under R = -1, there was a reduction in ΔKth when the notch root radius was greater than 0.5mm. On the other hand, for R = 0 and high R, ΔKth was almost constant regardless of ρ. Although ΔKth was different depending on the stress ratio and notch root radius, the effective crack growth threshold (ΔKeff)th was constant under all the test conditions. Therefore, the change in the crack growth behavior of the short crack at the notch root was dominated by the crack closure. The reduction in ΔKth in the relatively dull notch for R = -1 could also be explained by the change in the development of the crack closure during crack growth.. |
| 51. | Masanobu Kubota, Yuki Shiraishi, Ryosuke Komoda, Yoshiyuki Kondo, Jader Furtado, Considering the mechanisms causing reduction of fretting fatigue strength by hydrogen, 19th European Conference on Fracture: Fracture Mechanics for Durability, Reliability and Safety, ECF 2012 19th European Conference on Fracture Fracture Mechanics for Durability, Reliability and Safety, ECF 2012, 2012.01, The fretting fatigue test of austenitic stainless steels, JIS SUS304 and SUS316, was carried out in 0.12MPa hydrogen and air. The fretting fatigue strength of both materials was reduced by hydrogen. One of the possible causes was adhesion between the fretting surfaces which was predominant in hydrogen. The effect of specimen finishing on adhesion was also verified. For this purpose, two surface roughness were prepared with Ra = 0.420μm and 0.008μm. During the fretting fatigue test of these specimens in air, adhesion occurred in the smoother surface specimen but did not occur in the rougher surface specimen. As a result, the fretting fatigue strength decreased when adhesion occurred. Therefore, it can be considered that adhesion resulted in the reduction of the fretting fatigue strength in smoother specimens in air and in 0.12MPa hydrogen. Strain-induced martensite was found in the region of the adhered part, possibly due to the severe cyclic strain occurred locally at the adhered region.. |
| 52. | Kanetaka MIYAZAWA, Masato MIWA, Akihiro TASHIRO, Tatsuro AOKI Masanobu KUBOTA and Yoshiyuki KONDO, Improvement of Torsional Fretting Fatigue Strength of Splined Shaft Used for Car Air Conditioning Compressors by Hybrid Joint, Journal of Solid Mechanics and Materials Engineering, 10.1299/jmmp.5.753, 5, 12, 753-764, 2011.12, To improve the fatigue strength of the splined shaft used for a car’s air conditioning compressor, press fit was added to the innermost part of the spline. This shaft connection consisting of a spline and press fit is called a "hybrid joint" in this study. A torsional fretting fatigue test was performed focusing on the effect of the amount of interference on the fatigue strength. The fatigue strength of the splined shaft was drastically increased by the hybrid joint. The fatigue strength of the hybrid joint was at most 8 times higher than that of the conventional spline-joint shaft. The fatigue strength as well as the failure mode of the hybrid-jointed specimens were changed depending on the amount of interference. The reason was that the relative slip was significantly reduced with an increase in the amount of interference. The specimen consisted of a shaft, a boss and a bolt. The hybrid joint prevented loosening of the bolt, while loosening of the bolt was found to occur in the conventional spline-joint shaft.. |
| 53. | Masanobu Kubota, Kanetaka Miyazawa, Masato Miwa, Akihiro Tashiro, Tatsuro Aoki, Yoshiyuki Kondo, Improvement of torsional fretting fatigue strength of splined shaft used for car air conditioner's compressor by hybrid joint, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.77.208, 77, 773, 208-217, 2011.11, [URL], To improve the fretting fatigue strength of splined shaft used for compressor of car air conditioner, press-fit joint was combined with the spline joint. Torsional fretting fatigue strength of the combined jointed shaft was evaluated focusing on the effect of press-fit interference which must be secured when the combined joint is applied to the production process. Torsional fretting fatigue strength of the splined shaft was drastically increased by the combination of press-fit. The improvement was achieved by sharing transmitted torque between press-fit and spline. While fretting fatigue failure occurred at the press-fitted part when the press-fit interference was relatively small, the combined jointed shaft had four times higher fatigue strength than the conventional splined shaft. The increase of press-fit interference prevented the fretting fatigue failure and brought further increase of the fatigue strength, since amount of relative slip was significantly reduced by the increase of contact pressure.. |
| 54. | Masanobu Kubota, Kyohei Kuwada, YasuhiroTanaka, YoshiyukiKondo, Mechanism of reduction of fretting fatigue limit caused by hydrogen gas in SUS304 austenitic stainless steel, Tribology International, 44, 1495-1502, 2011.10. |
| 55. | Tatsuro AOKI, Hideya IKEMIYA, Masanobu KUBOTA, and Yoshiyuki KONDO, Fracture Toughness of Low Alloy Steels in Absorbed Hydrogen Condition, 2nd Japan-China Joint Symposium on Fatigue of Engineering Materials and Structures, 65-68, 2011.10. |
| 56. | 近藤 良之，久保田 祐信, 熱処理で硬化した低炭素鋼S25Cの長周期応力下の水素誘起疲労き裂進展, 材料, 60, 10, 898-904, 2011.10, The effect of heat treatment of S25C on the fatigue crack propagation rate enhanced by hydrogen was investigated under long term varying loading. The Vickers hardness was changed by heat treatment between 155 and 255. Stress hold at maximum stress was inserted in the 0.1Hz sinusoidal stress wave. The acceleration of crack propagation rate occurred irrespective of hold time in every material. However, the mean value of crack propagation rate decreased when hold time increased. The instantaneous crack propagation rate in time domain was dependent on the passage of time after the start of stress hold. The crack propagation rate was high at the beginning for several tens of second and it was reduced down to less than one hundredth after ten minutes. The time-dependent crack propagation was not maintained continuously in all materials whose Vickers hardness was between 155 and 255. As a consequence, the possibility of damage suffered by time-dependent crack growth is negligibly small even in the hardest material that can be reached by heat treatment on S25C.. |
| 57. | Masanobu Kubota, Toru Sakuma, Junichiro Yamaguchi and Yoshiyuki Kondo, Effects of hydrogen and multiple overloads on the fatigue strength of notched component , Proceedings of International Conference on Advanced Technology in Experimental Mechanics 2011 (ATEM11), 2011.09. |
| 58. | Shunsuke KATAOKA, Hiroaki ONO, Masanobu Kubota and Yoshiyuki KONDO , Mechanism of improving fretting fatigue strength by stress relief groove, Proceedings of International Conference on Advanced Technology in Experimental Mechanics 2011 (ATEM11), 2011.09. |
| 59. | 松本 圭純，久保田 祐信，近藤 良之, オーステナイト系ステンレス鋼における溶接接合管材の疲労強度に及ぼす微小欠陥と水素の影響, 日本機械学会論文集，Ａ編, 7７, 781, 1554-1558, 2011.09. |
| 60. | Koshiro Mizobe, Yuki Shiraishi, Msanobu Kubota and Yoshiyuki Kondo , EFFECT OF HYDROGEN ON FRETTING FATIGUE STRENGTH OF SUS304 AND SUS316L AUSTENITIC STAINLESS STEELS, Proceedings of the JSME/ASME 2011 International Conference on Materials and Processing (ICM&P2011), 2011.06. |
| 61. | Kanetaka MIYAZAWA, Masato MIWA, Akihiro TASHIRO, Tatsuro AOKI, Msanobu KUBOTA and Yoshiyuki KONDO , INPROVEMENT OF TORSIONAL FRETTING FATIGUE STRENGTH OF SPLINED SHAFT USED FOR CAR AIR CONDITIONING COMPRESSORS BY HYBRID JOINT, Proceedings of the JSME/ASME 2011 International Conference on Materials and Processing (ICM&P2011), 2011.06. |
| 62. | 池宮 秀也，久保田 祐信，近藤 良之, 水素侵入した低合金鋼SCM440 の破壊じん性に及ぼす負荷速度と焼戻し温度の影響, 日本機械学会論文集，Ａ編, 7７, 7７５, 483-494, 2011.03. |
| 63. | Koshiro Mizobe, Masanobu Kubota and Yoshiyuki Kondo, Behavior of short fatigue crack at notch root, Key Engineering Materials, 10.4028/www.scientific.net/KEM.465.515, 465, 515-518, 2011.01, It has been recognized that the threshold stress intensity factor range ΔKth of a short crack is lower than that of a long crack. The short crack behavior in plain specimen has been studied by many researchers. However, the behavior of a short crack at the root of a long notch is not yet clear. The crack closure behavior is considered to be affected by the constraint at notch root and it is dependent on the length and the root radius of notch. In this study, fatigue tests on specimens with short pre-crack at long notch were done and the difference in crack closure behavior was studied. As a result, short crack effect appeared in any notch root radius. In a sharp notch, the crack opening point easily reached its stable condition after a small amount of crack extension. On the contrary in a dull notch, the opening point was lower than the stable condition and consequently short crack effect lasted in relatively wide range of crack extension. The small crack effect of notched specimen was discussed based on crack closure behavior.. |
| 64. | Yoshiyuki Kondo, Koshiro Mizobe, Masanobu Kubota, Effects of Hydrogen Concentration, Specimen Thickness and Loading Frequency on the Hydrogen Enhanced Crack Propagation of Low Alloy Steel, Key Engineering Materials, 10.4028/www.scientific.net/KEM.465.519, 465, 519-522, 2011.01, Crack propagation of SCM440H low alloy steel under varying load is enhanced by absorbed hydrogen. Substantial acceleration of crack propagation rate up to 1000 times was observed compared with that of uncharged material. The role of factors affecting enhanced acceleration was investigated by changing hydrogen concentration absorbed in metal, specimen thickness and loading frequency. Results are as follows. (1) 0.2 mass ppm diffusible hydrogen in metal was enough to cause enhanced acceleration. The predominant fracture mode showing acceleration was quasi cleavage. (2) In the case of thin specimen thinner than 0.8mm, the tri-axiality of stress is weak, and the enhanced crack propagation did not appear. However, the introduction of side-groove to 0.8mm specimen in order to increase the tri-axiality resulted in enhanced acceleration. (3) Lower loading frequency resulted in higher crack propagation rate in cycle domain. The crack propagation rate in time domain was almost constant irrespective of loading frequency. Enough concentration of hydrogen, tri-axiality and low loading frequency resulted in enhanced acceleration of fatigue crack propagation.. |
| 65. | Masanobu Kubota, Toru Sakuma, Junichiro Yamaguchi, Yoshiyuki Kondo, Effects of Multiple Overloads and Hydrogen on High-Cycle Fatigue Strength of Notched Specimen of Austenitic Stainless Steels, Nihon Kikai Gakkai Ronbunshu, A Hen/Transactions of the Japan Society of Mechanical Engineers, Part A, 10.1299/kikaia.77.1747, 77, 782, 1747-1759, 2011.01, [URL], To safely use of hydrogen utilization machines after large earthquakes, the effect of multiple overloads and hydrogen on high-cycle fatigue strength of SUS304 and SUS316L austenitic stainless steels were evaluated. Three kinds of notched fatigue test specimens which have different notch root radius were used. The fatigue strength of both materials was significantly reduced by multiple overloads. The cause was small cracks formed by the overloads. In SUS304, the reduction of fatigue strength became more significant by hydrogen. The cause was that hydrogen accelerated propagation of the small cracks during overloading. On the other hand, fatigue strength of SUS316L was insusceptible to hydrogen. Propagation of the small cracks existing notch root was evaluated by plastic strain range at notch root and Manson-Coffin rule in order to consider application of this study for design.. |
| 66. | Masanobu KUBOTA, Toru SAKUMA, Junichiro YAMAGUCHI and Yoshiyuki KONDO, Effect of Hydrogen Absorption on the Fatigue Strength Reduction caused by Multiple Overloads in Notched Component, Journal of Solid Mechanics and Materials Engineering, 2010.11. |
| 67. | 近藤 良之，久保田 祐信，溝部 浩志郎, 低合金鋼SCM440Hの長周期変動応力下の水素誘起き裂進展加速に及ぼす水素濃度，板厚，周波数の影響, 日本機械学会論文集，Ａ編, 76, 769, 1204-1213, 2010.09. |
| 68. | Yoshiyuki Kondo, Masanobu Kubota and Koshiro Mizobe, Mechanistic Role of Hydrogen on the Enhanced Crack Propagation of Low Alloy Steel SCM440H, Proceedings of the 18th European Conference on fracture (ECF18), 2010.08. |
| 69. | Yoshiyuki Kondo, Masanobu Kubota and Katsuya Shimada, Hydrogen Enhanced Crack Propagation of SCM440H Low-alloy Steel under Long-term Varying Load, Engineering Fracture Mechanics, 2010.07. |
| 70. | Koshiro MIZOBE, Masanobu KUBOTA, and Yoshiyuki KONDO, Behavior of Short Fatigue Crack at Notch Root, Proceedings of the Sixth International Conference on Materials Structure & Micromechanics of Fracture (MSMF-6), Brno, Czech, 2010.06. |
| 71. | Yoshiyuki KONDO, Masanobu KUBOTA and Koshiro MIZOBE, Effects of Hydrogen Concentration, Specimen Thickness, Loading Frequency and Temperature on the Hydrogen Enhanced Crack Propagation of Low Alloy Steel, Proceedings of the Sixth International Conference on Materials Structure & Micromechanics of Fracture (MSMF-6), Brno, Czech, 2010.06. |
| 72. | Yuta UEDA, Masanobu KUBOTA and Yoshiyuki KONDO, Effect of Absorbed and Environmental Hydrogen on Short Fatigue Crack Propagation near Threshold in Low Alloy Steel, Journal of solid mechanics and material engineering, 10.1299/jmmp.4.830, 4, 6, 830-839, 2010.06. |
| 73. | 久保田 祐信，田中 康宏，桑田 喬平，近藤 良之, SUS304の水素ガス中フレッティング疲労における疲労限度低下機構, 材料, 59, 6, 439-446, 2010.06. |
| 74. | Masanobu Kubota, Tsuyoshi Nishimura, Yoshiyuki Kondo, Effect of hydrogen concetration on fretting fatigue strength, Journal of solid mechanics and material engineering, 10.1299/jmmp.4.816, 4, 6, 816-829, 2010.06. |
| 75. | 植田 裕太，久保田 祐信，近藤 良之, 低合金鋼の下限界近傍の微小疲労き裂進展に及ぼす水素侵入と水素雰囲気の影響, 日本機械学会論文集，Ａ編, 76, 765, 602-609, 2010.05. |
| 76. | 近藤 良之，久保田 祐信，溝部 浩志郎, 低合金鋼の水素誘起き裂進展加速とき裂の開口状態について, 日本機械学会論文集，Ａ編, 76, 765, 594-601, 2010.05. |
| 77. | Yoshiyuki Kondo, Masanobu Kubota and Katsuya Shimada, Hydrogen Eenhanced Crack Propagation of SCM440H Low Alloy Steel under Long-term Varying Load, Engineering Fracture Mechanics, Avairable online, 2010.05. |
| 78. | Masanobu KUBOTA, Shunsuke KATAOKA and Yoshiyuki KONDO, Effect of Stress Relief Groove on Fretting Fatigue Strength and Index for the Selection of Optimal Groove Shape, International Journal of fatigue, 31, 3, 439-446, 2010.05. |
| 79. | Masanobu KUBOTA, kenj HIRAKAWA, The effect of rubber contact on the fretting fatiguestrength of railway wheel tire, Tribology International, 42, 9, 1352-1359, 2010.05. |
| 80. | Masanobu KUBOTA, Yasuhiro TANAKA, Kyohei KUWADA and Yoshiyuki KONDO, Hydrogen Gas Effect on Fretting Fatigue Properties of Materials Used in Hydrogen Utilization Machines, Tribology International, 42, 9, 1352-1359, 2010.05. |
| 81. | Masanobu KUBOTA, Toru SAKUMA, Junichiro YAMAGUCHI and Yoshiyuki KONDO, Effect of Hydrogen Absorption on the Fatigue Strength Reduction Caused by Multiple Overloads in Notched Component, Proceedings of 2010 M&M International Symposium for Young Researchers, Pasadena, CA, USA, 2010.03. |
| 82. | 主藤友恵，久保田祐信，近藤良之, 単一過大荷重による短い疲労き裂の進展遅延現象発生に対する限界き裂長さの検討, 材料, 58, 12, 1023-1029, 2009.12. |
| 83. | Yoshiyuki KONDO, Tomoe Sudo and Masanobu KUBOTA, Critical Crack Size that Causes Retardation of Short Fatigue Crack by Single Overload, Fatigue and Fracture of Engineering Materials and Structures, 32, 10, 856-864, 2009.10. |
| 84. | Yoshiyuki KONDO, Takuya OGAWA and Masanobu KUBOTA, Applied Stress Estimation from the Fatigue Fracture Surface in the Near Threshold Region of Fatigue Crack Propagation, Journal of Solid Mechanics and Materials Engineering, Vol.2, No.4, pp.537-548, 2009.10. |
| 85. | Yoshiyuki KONDO, Hikaru EDA and Masanobu KUBOTA, Effect of Small Notch and Absorbed Hydrogen on the Fatigue Fracture in Two-step Stress Test within Fatigue Limit Diagram, Fatigue and Fracture of Engineering Materials and Structures, 32, 9, 736-743, 2009.09. |
| 86. | Masanobu Kubota, Kenji Hirakawa, The effect of rubber contact on the fretting fatigue strength of railway wheel tire, Tribology International, Vol. 42, pp.1389-1398, 2009.09. |
| 87. | Masanobu Kubota, Yasuhiro Tanaka, Yoshiyuki Kondo, The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines, Tribology International, Vol. 42, pp. 1352-1359, 2009.09. |
| 88. | Masanobu KUBOTA, Jun-ichiro YAMAGUCHI and Yoshiyuki KONDO, Fatigue Strength Reduction of Notched Component in Hydrogen Gas after Multiple Overloading, European Conference on Fracture 17, Distributed by CD-ROM, 2009.09. |
| 89. | Yoshiyuki KONDO, Masanobu KUBOTA and Hikaru EDA, Effect of Notch Shape and Absorbed Hydrogen on the Fatigue Fracture below Fatigue Limit, European Conference on Fracture 17, Distributed by CD-ROM, 2009.09. |
| 90. | Tomoe SUDO, Masanobu KUBOTA and Yoshiyuki KONDO, Single Overload Effect in Short Crack, European Conference on Fracture 17, Distributed by CD-ROM, 2009.09. |
| 91. | Y. Kondo, H. Eda, M. Kubota, Effect of small notch and absorbed hydrogen on the fatigue fracture in two-step stress test within fatigue limit diagram, Fatigue and fracture of engineering materials, Vol. 32, pp.736-743, 2009.07. |
| 92. | 近藤良之，久保田祐信，嶋田勝也, 低合金鋼SCM440Hの長周期変動および静応力下の水素に助長されたき裂進展挙動, 日本機械学会論文集, 75巻754号，752-760, 2009.06. |
| 93. | Yoshiyuki KONDO, Hikaru EDA and Masanobu KUBOTA, Fatigue Failure under Varying Loading within Fatigue Limit Diagram, Materials Science Forum, Vol.567-568, pp.1-8, 2008.10. |
| 94. | Keiko SHISHME, Masanobu KUBOTA and Yoshiyuki KONDO, Effect of Absorbed Hydrogen on the Near Threshold Fatigue Crack Growth Behavior of Short Crack, Materials Science Forum, Vol.567-568, pp.409-412, 2008.10. |
| 95. | 近藤良之，久保田祐信，江田 光, 疲労限度以下の応力による2段2重変動応力下の疲労破壊に及ぼす微小切欠きの形状と水素の影響, 日本機械学会論文集（Ａ編）, 74巻746号, pp.1358-1365, 2008.10. |
| 96. | 近藤良之，久保田祐信，志々目佳子，山口純一郎, 微小疲労き裂の下限界近傍進展特性に及ぼす侵入水素の影響（低合金鋼，炭素鋼，析出強化型耐熱鋼A286についての検討）, 日本機械学会論文集（Ａ編）, 74巻，746号, pp.1366-1372, 2008.10. |
| 97. | 近藤良之，久保田祐信，永末知広, 12Cr鋼の遅れ破壊のき裂経路遷移に及ぼす応力変動の影響, 日本機械学会論文集（Ａ編）, 74巻745号, pp.1249-1255, 2008.09. |
| 98. | 近藤良之，小川琢也，久保田祐信, ストライエーションが観察されないステンレス鋼疲労破面の微小硬さによる作用応力推定の試み, 日本機械学会論文集（Ａ編）, 74巻745号, pp.1256-1261, 2008.09. |
| 99. | Masanobu KUBOTA, Yasuhiro TANAKA and Yoshiyuki.KONDO, Fretting Fatigue Strength of SCM435H Steel and SUH660 Heat Resistant Steel in Hydrogen Gas Environment, Tribotest, Vol. 14, pp.177-191, 2008.09. |
| 100. | Masanobu KUBOTA, Yasuhiro TANAKA, Kyouhei KUWADA and Yoshiyuki KONDO, Mechanism of Reduction of Fretting Fatigue Limit in Hydrogen Gas Environment, Proceedings of the 3rd International Conference on Material and Processing, Distributed by CD-ROM, 2008.09. |
| 101. | Masanobu KUBOTA, Shunsuke KATAOKA and Yoshiyuki KONDO, Effect of Stress Relief Groove on Fretting Fatigue Strength and Index for the Selection of Optimal Groove Shape, International Journal of Fatigue, Vol. 31, pp.436-446, 2008.07. |
| 102. | Yoshiyuki KONDO, Takuya OGAWA, Masanobu KUBOTA, Study on the parameters applicable to the stress estimation of fatigue fracture surface without striations, Journal of Solid Mechanics amd Materials Engineering, Vol. 2, No. 4, pp.537-548, 2008.04. |
| 103. | Masanobu Kubota, Report on ATEM'07, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.57.316, 57, 3, 2008.03, [URL]. |
| 104. | Tomoe Sudo, Masanobu Kubota, Yoshiyuki Kondo, Single overload effect in short crack, 17th European Conference on Fracture 2008: Multilevel Approach to Fracture of Materials, Components and Structures, ECF17 17th European Conference on Fracture 2008: Multilevel Approach to Fracture of Materials, Components and Structures, 2, 1024-1031, 2008, The effect of single overload on the retardation of fatigue crack propagation and crack arrest was examined on short crack less than a few hundred microns. The effect of stress ratio of baseline load was also investigated. The variation of crack closure stress caused by overload was measured. The retardation occurred even in short crack, which could be explained by the increase of crack closure stress caused by overload. The baseline stress ratio also affected the retardation. Retardation occurred even in 50 μm crack for baseline stress ratio R = 0. In the case of R = -1, however, no retardation occurred in short crack less than 100 μm since the increase of crack closure stress was restrained by the compressive stress of baseline load.. |
| 105. | 久保田 祐信，田中 康博，近藤 良之, SCM435H及びSUH660のフレッティング疲労特性に及ぼす水素ガス環境の影響, 日本機械学会論文集, Vol.73, No. 736, 1382-1387, 2007.12. |
| 106. | 近藤 良之，久保田 祐信，大熊 克紀，嶋田 勝也, ステンレス鋼のねじり疲労挙動に及ぼす水素侵入の影響（連続カソード分極下での検討）, 日本機械学会論文集, 第73巻第736号，1351-1357., 2007.12. |
| 107. | 近藤 良之，久保田 祐信，片岡 俊介，栄 中, フレッティング疲労強度向上に及ぼす応力逃がし溝形状の影響と溝形状選定条件, 日本材料学会「材料」, Vol.56, No. 12, pp.1156-1162, 2007.12. |
| 108. | Shunsuke Kataoka, Chu Sakae, Masanobu Kubota, Yoshiyuki Kondo, Effect of Stress Relief Groove Shape on Fretting Fatigue Strength, Key Engineering Materials, Vol.353-358, 2007, pp.856-859, 2007.11. |
| 109. | Masanobu Kubota, Shunsuke Kataoka, Yoshiyuki Kondo, Evaluation of optimal shape of stress relief groove for the improvement of fretting fatigue strength , Proceedings of ATEM07, Distributed by CD-ROM, 2007.09. |
| 110. | Yoshiyuki Kondo, Tomoe Sudo, Masanobu Kubota, Effects of absorbed hydrogen on stress-strain behavior of materials used in hydrogen environment, Proceedings of ATEM07, Distributed by CD-R, 2007.09. |
| 111. | Yoshiyuki Kondo, Ogawa Takuya, Masanobu Kubota, Estimation of applied stress in the near threshold region of fatigue crack propagation utilizing high frequency current impedance and hardness measurement, Proceedings of ATEM07, Dstributed by CD-ROM, 2007.09. |
| 112. | Kekio Shishime, Masanobu Kubota, Yoshiyuki Kondo, Effect of absorbed hydrogen on the near threshold fatigue crack growth behavior of short crack, Proceedings of MSMF-5, Brno, Czech, 2007.06. |
| 113. | Yoshiyuki Kondo, Hikaru Eda, Masanobu Kubota, Fatigue Failure under Varying Loading within Fatigue Limit Diagram, Proceedings of MSMF-5, Bruno,Czech, 2007.06. |
| 114. | Kenji HIRAKAWA, Masanobu KUBOTA, The effect of rubber contact on the fretting fatigue strength of railway wheel tire, Proceedings of 5th International Symposium on Fretting Fatigue, Session 8, No. 4, 2007.04. |
| 115. | Masanobu Kubota, Yasuhiro Tanaka, Kyohei Kuwada, Yoshiyuki Kondo, Hydrogen Gas Effect on Fretting Fatigue Properties of Materials Used in Hydrogen Utilization Machines, Proceedings of 5th International Symposium on Fretting Fatigue (ISFF5), Session 6, No. 4, 2007.04. |
| 116. | Yoshiyuki Kondo, Chu Sakae, Masanobu Kubota, Syaka Nagamatsu, Fatigue Strength of Small-Notched Specimens under Variable Amplitude Loading within Fatigue Limit Diagram, Fatigue and Fracture of Engineering Materials and Structures, Vol. 30, pp.301-310, 2007.04. |
| 117. | 栄中，今村裕輔，森田健敬，久保田祐信, ２円筒転がり試験における超音波探傷法によるき裂の連続観察, 日本機械学会論文集, ７３巻７２５号，102-108, 2007.01. |
| 118. | 近藤 良之，栄 中，久保田 祐信，永松 清佳，冨永 豊和, 応力振幅が疲労限度以下での切欠き材の変動応力疲労, 日本機械学会論文集, A編，72巻723号，pp.1759-1765, 2006.11. |
| 119. | Shunsuke Kataoka, Masanobu Kubota, Chu Sakae, Yoshiyuki Kondo, EFFECT OF STRESS RELIEF GROOVE SHAPE ON FRETTING FATIGUE STRENGTH, Asian Pasific Conference on Fracture and Strength (APCFS2006), PP.123, 2006.11. |
| 120. | M. Kubota, N. Noyama, C. Sakae and Y. Kondo, Fretting in Hydrogen gas, Tribology international, 39/10, pp.1241-1247, 2006.10. |
| 121. | 石塚弘道，久保田祐信，栄 中，近藤良之，佐藤康夫，牧野一成, 在来線車両用焼きならし車軸の疲労試験, 材料, 第55巻第6号, 2006.06. |
| 122. | Y. KONDO, C. SAKAE, M. KUBOTA and H. KITAHARA, Fretting Fatigue under Variable Amplitude Loading below Fretting Fatigue Limit, Fatigue and Fracture of Engineering Materials and Structures, 29, pp.183-189, 2006.01. |
| 123. | Y. Kondo, M. Kubota, K. Ohguma, Hydrogen and notch effects on torsional fatigue of stainless steel, 16th European Conference of Fracture Fracture of Nano and Engineering Materials and Structures - Proceedings of the 16th European Conference of Fracture, 10.1007/1-4020-4972-2_608, 1225-1226, 2006.01, [URL]. |
| 124. | 久保田祐信，納山尚樹，笛田宗広，栄 中，近藤良之, フレッティング疲労に及ぼす水素ガス環境の影響, 材料, 第54巻第12号，pp. 1231-1236, 2005.12. |
| 125. | 柳原一智，大柳聡，久保田祐信，栄 中，近藤良之, 高強度鋼の疲労き裂進展下限界条件に及ぼすき裂寸法，応力比および水素の影響, 材料, 第54巻第12号, 2005.12. |
| 126. | Y. KONDO, C. SAKAE, M. KUBOTA and K. YANAGIHARA, Non-propagating Crack Behavior at Giga-cycle Fretting Fatigue Limit, Fatigue and Fracture of Engineering Materials and Structures, 10.1111/j.1460-2695.2005.00896.x, 28, 6, 501-506, Vol.28, pp.501-506, 2005.01. |
| 127. | Y. KONDO, C. SAKAE, M. KUBOTA and M. KASHIWAGI, Interpretation of Material Hardness, Stress Ratio and Crack Size Effects on the ΔKth of Small Cracks Based on Crack Closure Measurement, Journal of ASTM International, Vol.2, No.4, Paper ID JAI 11990, 2005.01. |
| 128. | 近藤良之，栄 中，久保田祐信，北原寛樹，柳原一智, 北原寛樹，柳原一智, 全ての応力振幅が疲労限度以下での変動応力フレッティング疲労, 日本機械学会論文集（A編）, 第71巻第705号 ,pp.763-768, 2005.01. |
| 129. | Y. KONDO, C. SAKAE, M. KUBOTA and M. KASHIWAGI, Interpretation of Material Hardness, Stress Ratio and Crack Size Effects on the ΔKth of Small Cracks Based on Crack Closure Measurement, ASTM Special Technical Publications, STP1461, 10.1520/STP11509S, 1461, 415-429, Fatigue & Fracture Mechanics, 34th Volume, 2005.01. |
| 130. | 近藤良之，栄 中，久保田祐信，北原寛樹, 起動停止サイクルと振動応力のミクストモード疲労, 材料, Vol.53, No.10, pp.1130-1135, 2004.10. |
| 131. | 近藤良之，栄 中，久保田祐信，工藤隆夫, 微小き裂材の高応力比条件における(ΔKeff)thの急減, 材料, Vol.53, No.6, pp.661-666, 2004.06. |
| 132. | Y. Kondo, C. Sakae, Masanobu Kubota, T. Nagasue, S. Sato, Fretting fatigue limit as a short crack problem at the edge of contact, Fatigue and Fracture of Engineering Materials and Structures, 10.1111/j.1460-2695.2004.00750.x, 27, 5, 361-368, 2004.05, [URL], This paper proposes a local stress concept to evaluate the fretting fatigue limit for contact edge cracks. A unique S-N curve based on the local stress could be obtained for a contact edge crack irrespective of mechanical factors such as contact pressure, relative slip, contact length, specimen size and loading type. The analytical background for the local stress concept was studied using FEM analysis. It was shown that the local stress uniquely determined the ΔK change due to crack growth as well as the stress distribution near the contact edge. The condition that determined the fretting fatigue limit was predicted by combining the ΔK change due to crack growth and the ΔKth for a short crack. The formation of a non-propagating crack at the fatigue limit was predicted by the model and it was experimentally confirmed by a long-life fretting fatigue test.. |
| 133. | 近藤良之，栄 中，久保田祐信，柳原一智, ギガサイクル領域のフレッティング疲労限度とき裂の停留について, 日本機械学会論文集（Ａ編）, Vol.70, No.696, pp.1066-1071, 2004.01. |
| 134. | 柏木聖紘，工藤隆夫，久保田祐信，栄 中，近藤良之, 微小欠陥材の疲労強度に及ぼすき裂開閉口挙動の影響, 材料, Vol.52, No.11, pp.1345-1350, 2003.11. |
| 135. | Masanobu KUBOTA, Sotaro NIHO, Chu SAKAE and Yoshiyuki KONDO, Effect of Under Stress on Fretting Fatigue Crack Initiation of Press-Fitted Axle, JSME International Journal, 10.1299/jsmea.46.297, 46, 3, 297-302, Vol. 46, No. 3, pp.297-302, 2003.07. |
| 136. | Masanobu Kubota, Sotaro Niho, Chu Sakae, Yoshiyuki Kondo, Effect of understress on fretting fatigue crack initiation of press-fitted axle, JSME International Journal, Series A: Solid Mechanics and Material Engineering, 10.1299/jsmea.46.297, 46, 3, 297-302, 2003.07, [URL], Axles are one of the most important components in railway vehicles with regard to safety, since a fail safe design is not available. The problems of fretting fatigue crack initiation in a press fitted axle have not been completely solved even though up-to date fatigue design methods are employed. The objective of the present study is to clarify the effect of understress on fretting fatigue crack initiation behavior in the press fitted axle. Most of the stress amplitude given to the axle in service is smaller than the fretting fatigue limit based on the stress to initiate cracks under a constant load σwf1. Rotating bending fatigue tests were performed using a 40 mm diameter press fitted axle assembly. Two step variable stresses consisting of σwf1 and half or one third of σwf1 were used in the experiment. Crack initiation life was defined as the number of cycles when a fretting fatigue crack, which is longer than 30 μm, was found using a metallurgical microscope. Fretting fatigue cracks were initiated even when the variable stress did not contain the stress above the fretting fatigue crack initiation limit. The crack initiation life varied from 4.0 × 107 to 1.2 × 108 depending on the stress frequency ratio nL/nH. The sum of the number of cycles of higher stress at crack initiation NH was much smaller than the number of cycles to initiate cracks estimated from the modified Miner's rule. The value of the modified Miner's damage ranged from 0.013 to 0.185. To clarify the effect of variable amplitude on the fretting fatigue crack initiation, a comprehensive investigation related to relative slip, tangential force and fretting wear is necessary.. |
| 137. | Hisao MATSUNAGA, Yukitaka MURAKAMI, Masanobu KUBOTA, Joon-Hyun LEE, Fatigue Strength of Ti-6Al-4V Alloys Containing Small Artificial Defects, Material Science Research International, 9, 4, 263-269, Vol.9, No.4, pp.263-269, 2003.04. |
| 138. | Masanobu KUBOTA, Hidenori ODANAKA, Chu SAKAE, Yoshihiro OHKOMORI, and Yoshiyuki KONDO, The Analysis of Fretting Fatigue Failure in Backup Roll and its Prevention, ASTM STP 1425, 10.1520/STP10775S, 1425, 434-445, pp. 434-445, 2003.03. |
| 139. | Y. Kondo, C. Sakae, M. Kubota and T. Kudou, The Effect of Material Hardness and Mean Stress on the Fatigue Limit of Material Containing Small Defect, Fatigue and Fracture of Engineering Materials and Structures, 10.1046/j.1460-2695.2003.00656.x, 26, 8, 675-682, 26, pp.675-682, 2003.01. |
| 140. | 近藤良之，栄 中，久保田祐信，永末知広, フレッティング疲労における接触端部局所応力の意義について, 日本機械学会論文集（Ａ編）, Vol.69, No.678, pp.382-389, 2003.01. |
| 141. | Masanobu Kubota, Sotaro Niho, Chu Sakae and Yoshiyuki Kondo, Effect of Under Stress on Fretting Fatigue Crack Initiation of Press-Fitted Axle, Proc. of JSME/ASME International Conference on Materials and Processing 2002, 10.1299/jsmea.46.297, 46, 3, 297-302, Proc. of JSME/ASME International Conference on Materials and Processing 2002, 2002.10. |
| 142. | 近藤良之，栄 中，久保田祐信，永末知広，佐藤進一, 接触端部局所応力に基づくフレッティング疲労き裂成長限界の検討, 材料, Vol.51, No.9, pp.1017-1022, 2002.09. |
| 143. | 近藤良之，栄 中，久保田祐信，工藤隆夫, 微小欠陥材の疲労限度に及ぼす平均応力と硬さの影響, 日本機械学会論文集（Ａ編）, Vo.68, No.672, pp.1185-1191, 2002.01. |
| 144. | Sang-Woo Choi, Joon-Hyun Lee, M. Kubota and Y. Murakami, The characteristics of Ultrasonic Signals for Detecting Micro-Defects in Ti-6Al-4V Alloy, Journal of the Korean Society for Nondestructive Testing, Vol. 21, No. 6 (in Korean), 2001.12. |
| 145. | Sang-Woo Choi, Joon-Hyun Lee, M. Kubota and Y. Murakami, The Characteristics of Ultrasonic Signals for Detecting Micro-Defects in Ti-6Al-4V Alloy, Journal of the Korean Society for Nondestructive Testing, Vol. 21, No. 6 (in Korean), pp.591-597, 2001.01. |
| 146. | K Hirakawa and M Kubota, On the fatigue design method for high-speed railway axles, Journal of Rail and Rapid Transit, 10.1243/0954409011531413, 215, 2, 73-82, Vol. 215, Part F2, pp. 73-82, 2001.01. |
| 147. | Masanobu KUBOTA, Kentaro TSUTSUI, Taizo MAKINO, Kenji HIRAKAWA, The Effect of the Contact Conditions and Surface Treatments on the Fretting Fatigue Strength of Medium Carbon Steel, ASTM STP 1367, 10.1520/STP14749S, 1367, 477-490, 2000.01. |
| 148. | Yasuo OCHI, Masanobu Kubota, Ryouichi SHIBATA,, Initiation and Propagation Behavior of Small Fatigue Cracks in HIP-Treated Aluminum Alloy: AC4CH, Proceedings of Small Fatigue Cracks: Mechanics, Mechanisms and Applications, pp. 215-221, 1999.01. |
| 149. | K. Hirakawa and M. Kubota, On The Fatigue Design Method for High Speed Railway Axles, Proc. of 12th International Wheelset Congress, 10.1243/0954409011531413, 215, 2, 73-82, pp. 477-482, 1998.09. |
| 150. | Y. Ochi and M. Kubota, Effects of Matrix-Structures on Low Cycle Fatigue Properties in Ductile Cast Irons, Proc. of Low Cycle Fatigue and Elasto-Plastic Behviour of Materials, pp.339-344, 1998.09. |
| 151. | M. Kubota, T. Ochi, A. Ishii and R. Shibata, Crack Propagation Properties on HIP-Treated Cast Aluminum Alloys, Material Science and Research International, 4, 3, 193-199, Vol. 4, No. 3, pp. 193-199, 1998.09. |
| 152. | K. Hirakawa, K. Toyama and M. Kubota, The Analysis and Prevention of Failure in Railway Axles, International Journal of Fatigue, 10.1016/S0142-1123(97)00096-0, 20, 2, 135-144, Vol. 20, No. 2, pp. 135-144, 1998.02. |
| 153. | T. Okamoto, M. Kubota and K. Hirakawa, Non-Destructive Inspection of Fretting Fatigue Cracks, Proc. of International Conference on Materials and Mechanics '97 (ICM&M '97), pp.379-384, 1997.07. |
| 154. | Yasuo Ochi, Tomohisa Ogata, Masanobu Kubota, Akira Ishii, Initiation and propagation life distributions of fatigue cracks and the life evaluation in high cycle fatigue of ADI, Zairyo/Journal of the Society of Materials Science, Japan, 10.2472/jsms.46.1155, 46, 10, 1155-1160, 1997.01, [URL], Rotating bending fatigue tests were carried out on austempered ductile cast iron (ADI) in order to investigate the statistical properties of life distributions of crack initiation and propagation, and also the evaluation of fatigue life. The results are summarized as follows: (1) The size of crack initiation sites of the material was represented by a Weibull distribution without regarding to the kinds of crack initiation sites such as microshrinkage and graphite grain. The crack initiation life scattered widely, but the scatter became much smaller as soon as the cracks grew. (2) The crack propagation life Nac which was defined as the minimum crack propagation rate showed lower scatter than the crack initation life. (3) The fatigue life of the material was evaluated well by Nac and the propagation rate after Nac. It was clear that the fatigue life of ductile cast iron was goverened by the scatter of Nac.. |
| 155. | K. Hirakawa, K. Toyama and M. Kubota, The Analysis and Prevention of Failure in Railway Axles, Proc. JSME International Symposium on Product Liability and Failure Prevention, 10.1016/S0142-1123(97)00096-0, 20, 2, 135-144, pp. 47-59, 1996.10. |
| 156. | M. Kubota, Y. Ochi, S. Okazaki, A. Ishi and T. Hattori, High Cycle Fatigue Properties of HIP-Treated FDI Material, Proc. of Asian Pacific Conference for Fracture and Strength ’96(APCFS ‘96), pp.881-886, 1996.07. |
| 157. | 久保田祐信, 越智保雄, 石井明, 柴田良一, HIP処理AC4CHの高サイクル疲労における微小き裂の発生・進展挙動の微視的観察, 材料試験技術, Vol. 41, No. 1, pp. 42-47, 1996.01. |
| 158. | M. Kubota, Y. Ochi, A. Ishii and R. Shibata, Improvement of High Cycle Fatigue Strength in Advanced Cast Aluminum Alloys by HIP Treatment, Proc. of International Symposium on Advanced Technology in Experimental Mechanics ’95(ATEM ’95), pp.171-176, 1995.11. |
| 159. | 久保田祐信, 越智保雄, 石井明, 柴田良一, HIP処理による鋳造アルミニウム合金の高サイクル疲労特性の向上, 日本機械学会論文集Ａ編, Vol. 61, No. 591, pp.2342-2348, 1995.11. |
| 160. | 越智保雄, 石井明, 佐々木茂美, 坂口祐幸, 久保田祐信, 球状黒鉛鋳鉄の低サイクル疲労および表面き裂進展挙動に及ぼす基地組織の影響, 日本機械学会論文集, Vol. 60, No. 571, pp.619-625, 1994.03. |
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