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

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.

DOI： http://dx.doi.org/10.1016/j.triboint.2016.10.017

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

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

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．

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

Fatigue properties of work-hardened oxygen-free cupper in high-pressure hydrogen

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

Fundamental Mechanisms Causing Reduction in Fretting Fatigue Strength by Hydrogen
(Effect of Hydrogen on Small Crack Initiation at the Adhered Spot)

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

Fundamental Mechanisms Causing Reduction in Fretting Fatigue Strength by Hydrogen
(Effect of Hydrogen on Small Crack Initiation at the Adhered Spot)

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

"Effects of Multiple Overloads and Hydrogen on High-Cycle Fatigue Strength of Notched Specimen of Austenitic Stainless Steels" in the transactions of the Japan Society for Mechanical Engineers, Ser. A

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

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.

DOI： 10.1299/jmmp.5.753

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

Mechanism of reductin of fretting fatigue limit in hydrogen gas in SUS304

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

DOI： 10.1299/jmmp.4.816

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

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

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

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

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

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

Fretting Fatigue Strength of SCM435H Steel and SUH660 Heat Resistant Steel in Hydrogen Gas Environment

Language：English   Publishing type：Research paper (international conference proceedings)  

Mechanism of Reduction of Fretting Fatigue Limit in Hydrogen Gas Environment

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

Effect of Stress Relief Groove on Fretting Fatigue Strength and Index for the Selection of Optimal Groove Shape

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

Fretting Fatigue Properties of SCM435H and SUH660 in Hydrogen Gas Environment by Masanobu KUBOTA, Yasuhiro TANAKA and Yoshiyuki KONDO, Transactions of Japan Society of Mechanical Engineers, Vol .73, No. 736, pp. 1382-1387 (2007.12)

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

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Others   Publishing type：Research paper (international conference proceedings)  

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

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

Effect of hydrogen gas environment on fretting fatigue strength

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

Effect of Under Stress on Fretting Fatigue Crack Initiation of Press-Fitted Axle,
Masanobu KUBOTA, Sotaro NIHO, Chu SAKAE and Yoshiyuki KONDO,
JSME International Journal,
Vol. 46, No. 3, pp.297-302, July 2003

DOI： 10.1299/jsmea.46.297

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

The Analysis of Fretting Fatigue Failure in Backup Roll and its Prevention,
Masanobu KUBOTA, Hidenori ODANAKA, Chu SAKAE, Yoshihiro OHKOMORI, and Yoshiyuki KONDO,
ASTM STP 1425,
pp. 434-445, March 2003

DOI： 10.1520/STP10775S

Language：English   Publishing type：Research paper (international conference proceedings)  

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,
Vol. 2, pp.220-225, October, 2002 (Hawaii, USA)

DOI： 10.1299/jsmea.46.297

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

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, American Society for Testing and Materials,
pp. 477-490, Jan. 2000.

DOI： 10.1520/STP14749S

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

Crack Propagation Properties on HIP-Treated Cast Aluminum Alloys,
M. Kubota, T. Ochi, A. Ishii and R. Shibata
Material Science and Research International,
Vol. 4, No. 3, pp.193-199, 1998.

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

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.

Language：Japanese   Publisher：The Society of Materials Science, Japan  

<p>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 technologies, such as SOFC and SOEC. Type 304 stainless steel was subjected to the SP and SP creep tests 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 gas pressure and temperature at which the SP test was 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 consistent with those obtained from the tensile tests. The 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.</p>

DOI： 10.2472/jsms.73.512

Scopus

CiNii Research

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

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.

Publisher：International Journal of Hydrogen Energy  

This paper provides a comprehensive review of the authors’ recent achievements in mitigating hydrogen embrittlement (HE) in iron (Fe) and steels using carbon monoxide (CO) in gaseous H2. CO contained in H2 gas preferentially adsorbs on the Fe surface, and effectively suppresses hydrogen dissolution into the material, resulting in mitigating HE. Fracture toughness test results under various conditions demonstrated the effectiveness of CO in mitigating HE, with its impact influenced by factors such as loading rate, gas pressure, strength, and chemical composition. The CO mitigation effect diminishes with the lower loading rate, higher gas pressure, higher strength, and increased chromium content. The mechanisms underlying the effects of these factors on the susceptibility to HE are theoretically elucidated based on the surface reactions of the H2 and CO molecules with the Fe surface through density functional theory and molecular dynamics simulations.

DOI： 10.1016/j.ijhydene.2024.04.071

Scopus

Publisher：International Journal of Hydrogen Energy  

Fracture by hydrogen accelerated fatigue crack growth is a severe type of environmental failure. Although fatigue crack growth has been the subject of intense investigation over several decades, a complete mechanistic and predictive model is still lacking. Such a crack growth model is even more rare in the case of hydrogen in view of the lack also of constitutive models for material deformation under cycling loading that account for the hydrogen effect. In this study, we present a model for fatigue crack propagation induced by alternating crack tip plastic blunting and re-sharpening, which in the presence of hydrogen can be accelerated by hydrogen enhanced dislocation motion and generation. The Chaboche constitutive model, which is a nonlinear kinematic hardening model capable of capturing many features of material behavior under cyclic loading, is used for the calculation of the stress and strain fields at the propagating crack tip. The Chaboche model is calibrated using a sequence of experimental data from uniaxial strain-controlled cyclic loading tests and uniaxial stress-controlled ratcheting tests with a low carbon steel, JIS SM490YB, in the absence and presence of hydrogen. The numerical simulation results indicate that the proposed crack propagation model can predict Paris law behavior and can successfully demonstrate acceleration of fatigue crack growth in the presence of hydrogen. Significantly, the profiles of the steady-state opening stress and strain ahead of the fatigue crack tip in a compact tension (C(T)) specimen were found to have sections over which they vary as ln(1/r) with distance r from the crack tip, consistent with the crack-tip strain field for a non-stationary crack.

DOI： 10.1016/j.ijhydene.2024.05.351

Scopus

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

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.

DOI： https://doi.org/10.1007/s10704-023-00739-2

Publisher：International Journal of Fracture  

High temperature hydrogen attack (HTHA) is degradation of steels exposed to hydrogen gas at high temperatures and pressures. Hydrogen in steels reacts with carbon from carbides to produce methane gas bubbles typically on grain boundaries which grow and coalesce, leading to loss of strength and fracture toughness. Current design practice against HTHA is based on the Nelson curves which define the conditions for safe operation in a temperature/hydrogen-partial-pressure diagram. Nelson curves are phenomenological in nature and do not account for the underlying failure mechanism(s), material microstructure, carbide stability, and applied stresses. In light of experimental evidence of predominant cavitation ahead of cracks reported by Martin et al. (Acta Mater 140:300–304, 2017), 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. (Int J Fract 219:1–17, 2019). The present model is shown to yield satisfactory agreement with the available experimental data from hydrogen attack of 2¼Cr–1Mo steel at temperatures ranging from 500 to 600 °C. In addition, the model is used to construct Nelson type curves in the temperature/hydrogen-partial-pressure diagram. These curves represent failure times for given applied stresses and triaxiality. 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.

DOI： 10.1007/s10704-023-00739-2

Web of Science

Scopus

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>The small punch (SP) creep test was conducted using a newly developed testing machine capable of conducting SP test with a small disk type specimen in a high temperature hydrogen gas atmosphere. The test material used was Type 304 austenitic stainless steel. The tests were carried out at a temperature of 600°C in a hydrogen and argon gas atmosphere with an absolute gas pressure of 0.12 MPa. The experimental results showed that the SP creep rupture time was shorter in the hydrogen gas atmosphere compared to the argon gas atmosphere. This difference in rupture decreased with decreasing applied SP load. Consequently, there was no significant difference at the load level of 486 N, which was the lowest SP load in this test. It was found that the <i>F</i>/<i>σ</i> value, which was necessary parameter for comparing SP results with traditional uniaxial creep rupture results, decreased with decreasing applied SP load. The <i>F</i>/<i>σ</i> value for hydrogen gas atmosphere was consistent larger than that for argon gas atmosphere, and this larger value was closely associated with higher rupture ductility in the hydrogen gas atmosphere.</p>

DOI： 10.1299/jsmemm.2023.mm1208

CiNii Research

Language：Japanese   Publisher：Steering Committee on Japan Conference on Structural Safety and Reliability  

<p>The objective of this study is to characterize the effect of hydrogen on the creep properties of pure iron. Elucidation of mechanism that hydrogen affects creep deformation is essentially important to ensure the safety of evolving high-temperature hydrogen technologies. The material was JIS SUY-1 industrial pure iron, because its simple chemical composition and pure single phase may facilitate the consideration of the mechanism. Creep testing was carried out in argon and hydrogen gases at 873 K. The absolute gas pressure at which the creep tests were carried out was 0.12 MPa. The estimated hydrogen concentration in the specimen at the relevant conditions was estimated to be 0.70 mass ppm. Hydrogen accelerated the creep strain rate resulting in a significant reduction in the creep life. The fracture profile shows double cup fracture and fracture surface was dimple in both argon and hydrogen environments. There were no significant differences in the shape and size of the dimples depending on the environment. This observation indicated that hydrogen accelerated the creep deformation without changing the creep deformation mechanism. This consideration is similar to the creep of SUS304 stainless steel in hydrogen, which we previously carried out. A similar mechanism that hydrogen may increase the vacancy density, leading to enhanced dislocation climb, may be adopted.</p>

DOI： 10.60316/jcossar.10.0_341

CiNii Research

Language：English   Publisher：Steering Committee on Japan Conference on Structural Safety and Reliability  

<p>Hydrogen and natural gas blending can be considered an important energy technology in terms of utilization of the existing infrastructure, which has a significant cost impact on the deployment of hydrogen infrastructures, and the smooth transition of energy systems. In this study, fatigue crack growth tests were carried out in air, hydrogen (H₂), 20% H₂ mixed methane (CH₄) and 20% H₂ mixed natural gases. Three kinds of natural gases with different oxygen (O₂) impurity concentrations were used in order to characterize the effect of hydrogen on the fatigue crack growth behavior in natural gas in conjunction with the effect of the O₂ impurity. The pressure of the gases except for air was 1 MPa. The test material was JIS SCM435 low-alloy steel. In the H₂ and the 20% H₂ mixed CH₄, the fatigue crack growth rates were accelerated. The acceleration was less in the 20% H₂ mixed CH₄ compared to that in the H₂. It is presumed that the lower hydrogen effect was due to reduced partial H₂ pressure in the mixture. This was confirmed by the crack growth test in 0.2 MPa H₂ resulting in the same crack growth rate as in the mixture. Regarding the fatigue crack growth tests in the 20% H₂ mixed natural gases, acceleration of the fatigue crack growth rate and suppression of the acceleration due to oxygen were observed. The oxygen effect increased with the increase in the oxygen concentration and was well-evaluated by the predictive model of hydrogen-assisted crack growth in the presence of oxygen proposed by Somerday et al.</p>

DOI： 10.60316/jcossar.10.0_128

CiNii Research

Publisher：Proceedings of the International Offshore and Polar Engineering Conference  

Carbon monoxide (CO) contained in hydrogen gas mitigates hydrogen embrittlement (HE). This CO effect can be affected by the chemical composition of the steel surface. This study investigated the effect of chromium (Cr) on Cr-rich and Cr-low materials. During the fracture toughness test, the CO effect was significantly less for the SUS430 ferritic stainless steel (16.17% Cr) compared to that for the A333 carbon steel (0.03% Cr). The mechanism that Cr reduced the CO mitigation effect was considered by DFT calculations of the interaction of CO with the steel surface. It revealed that the CO adsorption on the Fe site is greater than that on the Cr site.

Scopus

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

Publisher：Theoretical and Applied Fracture Mechanics  

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 × 105 cycles in the H2 and 107 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.

DOI： 10.1016/j.tafmec.2022.103460

Web of Science

Scopus

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

Publisher：International Journal of Hydrogen Energy  

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.

DOI： 10.1016/j.ijhydene.2022.03.006

Web of Science

Scopus

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

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.

DOI： https://doi.org/10.1016/j.ijhydene.2022.03.006

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

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．

Publisher：Acta Materialia  

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.

DOI： 10.1016/j.actamat.2021.117474

Web of Science

Scopus

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

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.

DOI： https://doi.org/10.1016/j.actamat.2021.117474

Publisher：Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science  

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.

DOI： 10.1007/s11661-021-06491-3

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Scopus

Publisher：Bulletin of the Chemical Society of Japan  

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.

DOI： 10.1246/bcsj.20210323

Web of Science

Scopus

Publisher：Proceedings of the International Offshore and Polar Engineering Conference  

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.

Scopus

Publisher：Minerals, Metals and Materials Series  

It is expected that high-temperature hydrogen technologies, such as the solid oxide fuel cell and high-temperature water electrolysis, will play important roles in the hydrogen society. In this study, creep tests of JIS SUS304, SUS304L and SUS310S austenitic stainless steels and SUY-1 pure iron were carried out in hydrogen and argon at 873 K. For all the materials, the creep rate in the secondary creep region in hydrogen environment was increased. It resulted in reduction of the creep life. In argon, the fracture surface of the SUS304 changed from dimple to intergranular fracture with the increase in the creep life. In hydrogen, this change was delayed. Regarding the mechanism, it was confirmed that the effect of carbide formation, HELP and HTHA were not activated in this study. Instead, enhanced dislocation climb mediated by an increased vacancy density is a plausible mechanism, although further investigation is needed.

DOI： 10.1007/978-3-030-92381-5_146

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Scopus

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

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.

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

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.

DOI： DOI: 10.1115/1.4049076

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

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.

DOI： 10.1021/acs.jpcc.9b06927

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

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.

DOI： 10.1016/j.prostr.2019.12.056

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

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.

DOI： 10.1016/j.ijhydene.2019.09.146

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

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.

DOI： 10.18178/ijmerr.8.5.713-718

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

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.

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

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

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.

Language：English   Publishing type：Research paper (international conference proceedings)  

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

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.

DOI： https://doi.org/10.1016/j.ijfatigue.2017.03.024

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

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.

DOI： http://dx.doi.org/10.1016/j.triboint.2016.10.021

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

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.

DOI： http://dx.doi.org/10.1016/j.ijhydene.2016.05.124

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

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

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.

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

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

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.

DOI： http://dx.doi.org/10.1016/j.ijhydene.2014.12.129

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

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.

Language：English   Publishing type：Research paper (international conference proceedings)  

The fatigue properties of ultra-fine grain austenitic steel (UFG), which has a 1m 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 21m. 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.

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

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.

DOI： http://dx.doi.org/10.1016/j.triboint.2014.02.025

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

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.

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

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.

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

Language：English   Publishing type：Research paper (international conference proceedings)  

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.

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

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.

DOI： 10.1299/kikaia.78.674

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

"Effect of Contact Conditions on Growth of Small Crack in Fretting Fatigue" in the transactions of the Japan Society for Mechanical Engineers, Ser. A

DOI： http://dx.doi.org/10.1299/kikaia.78.1

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

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.

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

The crack growth threshold, ΔK_th, 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 ΔK_th with the change in ρ was dependent on R. Under R = -1, there was a reduction in ΔK_th when the notch root radius was greater than 0.5mm. On the other hand, for R = 0 and high R, ΔK_th was almost constant regardless of ρ. Although ΔK_th 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 ΔK_th 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.

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

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.

DOI： 10.1299/kikaia.77.208

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

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

"Effect of Heat Treatment on the Hydrogen Enhanced Fatigue Crack Propagation of Low Carbon Steel S25C" in the journal of the Japan Society of Materials Science

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

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

Effects of Small Defect and Hydrogen on Fatigue Strength of Weld-Jointed Tube in Austenitic Stainless Steel

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

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

Effect of Loading Rate and Tempering Temperature on Fracture Toughness of Hydrogen-Charged Low Alloy Steel SCM440

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

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.

DOI： 10.4028/www.scientific.net/KEM.465.515

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

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.

DOI： 10.1299/kikaia.77.1747

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

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.

DOI： 10.4028/www.scientific.net/KEM.465.519

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

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

Effects of hydrogen concentration, specimen thickness, loading frequency and temperature on the hydrogen enhanced crack propagation of low alloy steel

Language：English   Publishing type：Research paper (international conference proceedings)  

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

Language：English   Publishing type：Research paper (international conference proceedings)  

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

DOI： 10.1299/jmmp.4.830

Language：English   Publishing type：Research paper (international conference proceedings)  

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

Effect of absorbed hydrogen and environmental hydrogen on short fatigu ecrack propagation near thershold in low alloy steel

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

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

Study on crack opening displacement and hydrogen enhanced crack propagation of low alloy steel

Publishing type：Research paper (international conference proceedings)  

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

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

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

Applied Stress Estimation from the Fatigue Fracture Surface in the Near Threshold Region of Fatigue Crack Propagation

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

Language：English   Publishing type：Research paper (international conference proceedings)  

Single Overload Effect in Short Crack

Language：English   Publishing type：Research paper (international conference proceedings)  

Effect of Notch Shape and Absorbed Hydrogen on the Fatigue Fracture below Fatigue Limit

Language：English   Publishing type：Research paper (international conference proceedings)  

Fatigue Strength Reduction of Notched Component in Hydrogen Gas after Multiple Overloading

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

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

Crack Propagation Behavior of SCM440H Low Alloy Steel Enhanced by Hydrogen under Long-term Varying Load and Static Load

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

Effect of Absorbed Hydrogen on the Near Threshold Fatigue Crack Growth Behavior of Short Crack

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

Effect of Absorbed Hydrogen on the Near Threshold Fatigue Crack Growth Behavior of Short Crack
(Examination on Low Alloy Steel, Carbon Steel and A286 Alloy)

Publishing type：Research paper (scientific journal)  

Effect of Notch Shape and Absorbed Hydrogen on the Fatigue Fracture below Fatigue Limit

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

Effect of Absorbed Hydrogen on the Near Threshold Fatigue Crack Growth Behavior of Short Crack

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

Effect of Load Variation on the Transition of Crack Path in Delayed Failure of 12Cr Steel

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

Applicability of Applied Stress Estimation Method Based on the Micro Hardness of Fatigue Fracture Surface of Stainless Steel without Striations

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

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

DOI： 10.2472/jsms.57.316

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

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.

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

Effect of Absorbed Hydrogen on Torsional Fatigue Behavior of Stainless Steels (Examination by Continuous Cathodic Polarization), Transactions of Japan Society of Mechanical Engineers, Vol. 73, No. 736, pp.1351-1357 (2007.12)

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

Effect of stress relief groove shape on fretting fatigue strength and index for the selection of groove shape
by Yoshiyuki KONDO, Shunsuke KATAOKA, Masanobu KUBOTA and Chu SAKAE, Journal of the Society of Materials Science "Zairyo", Vol.56, No.12, pp.1156-1162 (2007.12).

Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

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

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

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

Language：English   Publishing type：Research paper (international conference proceedings)  

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

Evaluation of Fatigue Crack Propagation Property on the Wheelseat of Normalized Axles for Narrow Gauge Line Vehicle

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

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

DOI： 10.1007/1-4020-4972-2_608

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

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.

DOI： https://doi.org/10.2472/jsms.54.1231

Repository Public URL： https://hdl.handle.net/2324/7162363

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

Effect of crack length, stress ratio and hydrogen on fatigue crack propagation threshold of high-strength steel

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

DOI： 10.1111/j.1460-2695.2005.00896.x

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

DOI： 10.1520/STP11509S

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

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

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

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

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

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 ΔK_th 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.

DOI： 10.1111/j.1460-2695.2004.00750.x

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

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

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

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 σ_wf1. Rotating bending fatigue tests were performed using a 40 mm diameter press fitted axle assembly. Two step variable stresses consisting of σ_wf1 and half or one third of σ_wf1 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 n_L/n_H. The sum of the number of cycles of higher stress at crack initiation N_H 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.

DOI： 10.1299/jsmea.46.297

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

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

DOI： 10.1046/j.1460-2695.2003.00656.x

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

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

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

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

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 (2001. 12) (in Korean)

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

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

K Hirakawa and M Kubota,
On the fatigue design method for high-speed railway axles,
Journal of Rail and Rapid Transit,
Proc Instn Mech Engrs, Vol. 215, Part F2,
pp. 73-82, 2001

DOI： 10.1243/0954409011531413

Publishing type：Research paper (international conference proceedings)  

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 (Hawaii, USA).

Language：English   Publishing type：Research paper (international conference proceedings)  

On The Fatigue Design Method for High Speed Railway Axles,
K. Hirakawa and M. Kubota,
Proc. of 12th International Wheelset Congress,
pp.477-482, 1998 (Qingdao, China).

DOI： 10.1243/0954409011531413

Language：English   Publishing type：Research paper (international conference proceedings)  

Effects of Matrix-Structures on Low Cycle Fatigue Properties in Ductile Cast Irons,
Y. Ochi and M. Kubota,
Proc. of Low Cycle Fatigue and Elasto-Plastic Behviour of Materials,
pp.339-344, 1998 (Garmiscg-Partenkirchen, Germany).

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

The Analysis and Prevention of Failure in Railway Axles,
K. Hirakawa, K. Toyama and M. Kubota,
International Journal of Fatigue,
Vol. 20, No. 2, pp. 135-144, 1998.

DOI： 10.1016/S0142-1123(97)00096-0

Language：English   Publishing type：Research paper (international conference proceedings)  

Non-Destructive Inspection of Fretting Fatigue Cracks,
T. Okamoto, M. Kubota and K. Hirakawa,
Proc. of International Conference on Materials and Mechanics '97 (ICM&M '97),
pp.379-384 (Shinbashi, Tokyo).

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

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 N_ac 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 N_ac and the propagation rate after N_ac. It was clear that the fatigue life of ductile cast iron was goverened by the scatter of N_ac.

DOI： 10.2472/jsms.46.1155

Language：English   Publishing type：Research paper (international conference proceedings)  

The Analysis and Prevention of Failure in Railway Axles,
K. Hirakawa, K. Toyama and M. Kubota,
Proc. JSME International Symposium on Product Liability and Failure Prevention,
pp. 47-59, 1996 (Umi-no-Naka-Michi, Japan).

DOI： 10.1016/S0142-1123(97)00096-0

Language：English   Publishing type：Research paper (international conference proceedings)  

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 (Kyongju, Korea).

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

Microscopic Observation of Initiation and Propagation Behavior of Small Crack on HIP-Treated AC4CH in High Cycle Fatigue,
M. Kubota, Y. Ochi, A. Ishii and R. Shibata,
Journal of Material Testing Research Association of Japan,
Vol.46, No. 1, pp.42-47 (Jan. 1996)

Language：English   Publishing type：Research paper (international conference proceedings)  

Improvement of High Cycle Fatigue Strength in Advanced Cast Aluminum Alloys by HIP Treatment,
M. Kubota, Y. Ochi, A. Ishi and R. Shibata,
Proc. of International Symposium on Advanced Technology in Experimental Mechanics ’95(ATEM ’95),
pp.171-176, 1995 (Aoyama Gakuin Univ., Tokyo).

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

Improvement of High Cycle Fatigue Properties by HIP Treatment for Cast Alminum Alloy,
Trans. JSME, Ser. A,
Vol. 61, No. 591, pp.2342-2348 (July 1995)

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

Effect of Microstructures on Low-Cycle Fatigue Properties and Surface Crack Propagation Behavior in Ductile Cast Irons
Trans. JSME, Ser. A,
Vol. 60, No. 571, pp.619-625 (March 1994)

Event date： 2020.12

Language：English   Presentation type：Oral presentation (general)  

Venue：KPC Headquater   Country：Kuwait  

Steels, stainless steels and other metallic materials are necessary to construct hydrogen chain from hydrogen production to end use via hydrogen storage and transportation. These structural materials for hydrogen service is used under severe conditions in terms of material strength. Because ultra-high pressure (70 MPa for fuel cell vehicles and 82 MPa for hydrogen refueling stations) is used to store and transport hydrogen efficiently (Liquid hydrogen is future option). In addition, hydrogen can degrade material strength (it is called hydrogen embrittlement). Actually, hydrogen embrittlement is difficult problem, because resistance of steel against hydrogen embrittlement is achieved by either alloying of a lot of amount of expensive rare earth metals and lowering material strength. These measures directly increase cost of materials. The materials for hydrogen service should be selected based on scientific knowledge about hydrogen embrittlement while seeing cost of materials. Japan have developed hydrogen technologies with industry and academia based on their strategy road map. The roadmap includes development and research of structural materials. In this presentation, recent history and accomplishments of the national projects of Japan for high-pressure hydrogen materials are introduced. In addition, material science that enables optimization of cost and performance of high-pressure hydrogen containment systems without compromising safety that I2CNER is pursuing is also introduced.

Event date： 2020.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Wuhan International Convention Center, Wuhan, China   Country：China  

The objective is to gain a basic understanding of the effect of hydrogen on the fatigue limit. The material was low-alloy steel adjusted 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 pressure of hydrogen gas was 0.1 MPa in gauge pressure. The fatigue limit of the smooth specimen was higher in 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 hydrogen gas was the same as that in air. For the smooth specimen, the fatigue limit was determined by whether or not crack initiated. For the deep-notched specimen, the fatigue limit was determined by whether or not crack propagate. The results can be interpreted as that hydrogen have no significant effect on crack initiation in high-cycle fatigue regime and affected the threshold of crack propagation.

Event date： 2020.1

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

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 carried out in argon and hydrogen gases under absolute pressures 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) displayed opposite trends in hydrogen compared to argon, i.e. creep life was significantly reduced while creep ductility was higher in hydrogen. Associated with the higher creep ductility, evidence of transgranular microvoid coalescence was more prevalent on fracture surfaces produced in hydrogen gas. Regarding the mechanisms governing reduced creep life in hydrogen, the effects of decarburization and carbide formation were investigated. It was confirmed that these effects were minor contributors to the reduced creep life at least within the creep life range of this study. Alternately, it was postulated that hydrogen-stabilized vacancy formation enhanced self-diffusion, leading to accelerated creep strain rate and shortened creep life in hydrogen.

Event date： 2019.3

Language：English   Presentation type：Oral presentation (general)  

Venue：San Antonio, Texas   Country：United States  

Hydrogen accelerated fatigue crack growth is a mode of environmental failure for which a mechanistic model is still lacking. In this work we attempt to develop a fatigue crack propagation model in the Paris regime on the assumption that the underlying mechanism is crack-tip plastic blunting and re-sharpening. In particular, we attempt to predict Paris law behavior by accounting for the material constitutive behavior in response to cyclic loading and using inputs that can be obtained from macroscopic experiments such as the uniaxial cyclic straining. The model is tested against predictions of the response due to overload and varying hydrostatic constraint. Lastly we investigate the role of hydrogen on crack propagation by considering the effect of hydrogen on the hardening response and the kinetics of hydrogen uptake.

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学，熊本   Country：Japan  

Effects of coating and lubrication on fretting fatigue properties of oil-well pipe material

Event date： 2018.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都テルサ，京都   Country：Japan  

The Effect of Carbon Monoxide Inhibitor against the Accelerated Fatigue Crack Growth in Gaseous Hydrogen and its Loading Frequency Dependency

Event date： 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Ryuku University, Okinawa   Country：Japan  

This document explains and demonstrates how to prepare your camera-ready manuscript for Trans Tech Publications. The best is to read these instructions and follow the outline of this text. The text area for your manuscript must be 17 cm wide and 25 cm high (6.7 and 9.8 inches, resp.). Do not place any text outside this area. Use good quality, white paper of approximately 21 x 29 cm or 8 x 11 inches (please do not change the document setting from A4 to letter). Your manuscript will be reduced by approximately 20% by the publisher. Please keep this in mind when designing your figures and tables etc.

Event date： 2018.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高知工科大学   Country：Japan  

Effect of material strength on inhibitory effect of carbon monoxide on hydrogen-assisted fracture

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Hotel Crown Plaza Hefei, China   Country：Japan  

Fretting fatigue is a form of contact fatigue, which frequently occurs on the mating surfaces of joined structures subjected to a fatigue load, which could be one of the major concerns in the design of machines and structures due to the significant reduction in the fatigue strength. Fretting fatigue strength of austenitic stainless steels was significantly reduced in hydrogen gas. Since hydrogen could influence both the fatigue and the phenomena occurring at the contacting surfaces such as friction, fretting wear, oxidation, etc., the mechanisms that causes the reduction in the fretting fatigue properties are very complicated. When considering the service conditions of hydrogen-containment systems, some amount of impurities in the hydrogen should be accepted. The objective of this study is to clarify the effects of hydrogen and oxygen addition to hydrogen on the fretting fatigue strength. For the fretting fatigue test, a controlled method to add ppm-level oxygen to a hydrogen environment was firstly established. The fretting fatigue tests were carried out in high-purity hydrogen (0.088 vol. ppm O2) and in oxygen/hydrogen mixtures with 5, 35 and 100 vol. ppm O2 concentrations. The material was JIS SUS304 austenitic stainless steel. The fretting fatigue strength was significantly lower in hydrogen gas than in air. Fretting removed surface oxide layer. It caused two primary consequences, enhancement of hydrogen entry and local adhesion between contacting surfaces. The adhesion resulted severe cyclic plastic strain at the adhered spot. It facilitated formation of small cracks. In addition, microstructural change from austenite to martensite was also induced by the cyclic plastic strain. The reduced fretting fatigue strength in hydrogen was synergistically caused by chemical, physical and mechanical processes. The fretting fatigue strength in the oxygen/hydrogen mixtures was significantly lower than that in the high-purity hydrogen. Since addition of oxygen to hydrogen environment usually mitigate the effect of hydrogen, the results obtained were opposite. The fretting fatigue strength in the oxygen/hydrogen mixtures slightly changed depending on the oxygen level. Based on the X-ray photoelectron spectroscopy analysis of the fretted surface, it was found that an oxide layer was produced on the fretted surface in the oxygen/hydrogen mixture by overcoming the removal action of the fretting. It resulted weakening of the adhesion between contacting surfaces, and larger slip between contacting surfaces was produced. As the result, stress conditions at the contact part were changed. As the result that the oxidation behavior was changed, the fretting fatigue strength was reduced by the addition of oxygen.

Event date： 2017.3

Language：English   Presentation type：Oral presentation (general)  

Venue：University of California, Irvine Henry Samueli School of Engineering Complex, CA, USA   Country：United States  

A certain kind of austenitic stainless steel shows a good resistance against hydrogen-induced degradation of material strength. However, basically the yield strength of single austenitic phase materials is not so high. For hydrogen equipment, high strength is very beneficial in terms of cost of the material and performance of the equipment. Therefore, the development of high-strength austenitic stainless steels is strongly desired. Alloying and following precipitation hardening are useful to obtain high strength, but these methods are not always good in terms of material cost. On the other hand, grain refinement is a promising method to improve the mechanical strength of metals. The idea of this study is the combination of austenitic stainless steel and grain refinement in order to obtain both high strength and hydrogen compatibility.
The material was synthesized by a thermo-mechanical treatment invented by Takaki et al [Takaki, 1988]. The grain size was adjusted during reaustenization of the microstructure so that its average size was 1 m. The yield strength was 596 MPa. It was almost twice higher than that of commercial austenitic stainless steels. The improvement of the yield strength by the grain refinement was significant.
Fatigue tests were carried out to obtain the fatigue strength and identify the crack origin. In addition, fatigue crack growth tests were also carried out to obtain the crack growth behavior. The effect of hydrogen on the fatigue properties was evaluated with hydrogen charged material. The reference materials were JIS SUS316 and JIS SUH660. The fatigue limit of the 1 m grain size material was approximately 2.8 times higher than that of the SUS316. The hydrogen charge didn’t affect the fatigue limit, but reduced the fatigue life in the short life region.
The crack origin was a non-metallic inclusion. It was surprising that the size of the inclusion was 2 m. Usually an inclusion acts as the crack origin when the material hardness is higher than HV400 and its size is several tens of m. The hardness of the 1 m grain size material was less than HV300. Therefore, the experimental fact that the crack initiated from a 2 m inclusion was beyond the knowledge about engineering metals.
Generally, the crack growth resistance is deteriorated by grain refinement because the crack path becomes smooth. However, this material showed a good crack growth resistance which was equivalent to the SUH660. It was found that the crack tip opening displacement (CTOD) during crack growth was distinctively smaller compared to those of the reference materials. Furthermore, the plastic zone size at the crack tip was also considerably smaller than those of the reference materials. According to classic crack growth mechanisms, the CTOD is proportional to the plastic zone size and the CTOD governs the crack growth rate. Therefore, a possible mechanism for the good crack growth resistance is the barrier of the grain boundary of the small grains against the dislocation motion and the following suppression of plastic deformation at the crack tip.
The hydrogen charge caused an acceleration of the crack growth, and this result is consistent with the reduced fatigue life of the hydrogen charged material. The reason for the acceleration of the crack growth was the transformation of microstructure from austenite to strain-induced martensite during crack growth. The grain refinement significantly improved the both static and fatigue strength. However, there is room for improvement in hydrogen compatibility.

Event date： 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Ramada Plaza Jeju Hotel, Jeju, Korea   Country：Korea, Republic of  

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. Figure 1 shows the result of the conventional fatigue test and the fretting fatigue test of SUS304 austenitic stainless steel in 0.1 MPa hydrogen gas and air. 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 esults clearly demonstrate that the fretting had some specific effects that enhance hydrogen-induced degradation of fatigue strength.

Event date： 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Ramada Plaza Jeju Hotel, Jeju, Korea   Country：Korea, Republic of  

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 [1]. The first one was the fatigue failure at the thread corner radius, which has been already quantitatively evaluated [2]. 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.

Event date： 2016.9 - 2017.9

Language：English  

Venue：Jackson Lake Lodge, Moran, Wyoming   Country：United States  

Although the phenomenon of hydrogen-induced degradation of metals and alloys is well documented, there remains a paucity of information with regard to 3-D constitutive material model in the presence of hydrogen. Such constitutive material models that account for the hydrogen effects on the microplasticity of crystals are central to the challenges for material performance prognosis under in-service conditions. Once such a constitutive model is developed and tested under monotonic and cyclic loading conditions, it can be used in a general purpose finite element code to investigate such issues as the role of maximum stress in promoting accelerated fatigue crack growth in the presence of hydrogen.
The objective of this work is the development of a single crystal plasticity model that accounts for the hydrogen effect on dislocation activity along individual slip systems and the interactions between slip systems under varied crystal orientations and loading triaxialities. Toward this objective, a concerted experimental and simulation effort has been mounted by an international team of researchers from the academia, industry, and national laboratories.
In the experimental part of this study, a special tensile test fixture has been designed to carry out uniaxial tension, which can accommodate rotation of the tensile axis and allow for tension free from bending moments. The shape of the specimen has been chosen using computational plasticity so as to minimize stress concentration effects close to the specimen grips. To monitor the response of specific crystal orientations the specimen is mounted and stressed in a way that slip proceeds sequentially from a given single system to multiple slip systems as the load increases. A non-contact strain measurement system is employed in order to avoid imposing any deformation constraints on the specimen. The material used for experiments in this study is single crystal nickel, which has a FCC structure. The computational part of the study involves the development of a single crystal plasticity model accounting for the hydrogen effects on slip along individual systems and their interactions. At the preliminary stages of this investigation, the model of Bassani and Wu has been adopted and modified to account for the hydrogen effects.

Event date： 2016.9 - 2017.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Jackson Lake Lodge, Moran, Wyoming   Country：United States  

Fretting fatigue is a form of contact fatigue, which frequently occurs on the mating surfaces of joined structures subjected to a fatigue load, which could be one of the major concerns in the design of machines and structures due to the significant reduction in the fatigue strength. For the fretting fatigue in hydrogen, a significant reduction in the fretting fatigue strength has been reported in austenitic stainless steels. Since hydrogen could influence both the fatigue and the phenomena occurring at the contacting surfaces such as friction, fretting wear, oxidation, etc., the mechanisms that cause the reduction in the fretting fatigue properties are very complicated. When considering the service conditions of hydrogen-containment systems, some amount of impurities in the hydrogen should be accepted. The objective of this study is to clarify the effect of oxygen added to hydrogen on the fretting fatigue strength of an austenitic stainless steel. For the fretting fatigue test, a controlled method to add ppm-level oxygen to a hydrogen environment was established. The fretting fatigue tests were carried out in high-purity hydrogen (0.088 vol. ppm O2) and in oxygen/hydrogen mixtures with 5, 35 and 100 vol. ppm O2 concentrations. The material was JIS SUS304 austenitic stainless steel. The fretting fatigue strength in the oxygen/hydrogen mixtures was significantly lower than that in the high-purity hydrogen. The fretting fatigue strength in the oxygen/hydrogen mixtures slightly changed depending on the oxygen level. Based on the X-ray photoelectron spectroscopy analysis of the fretted surface, it was found that the oxide layer of the stainless steel was removed by the fretting in the high-purity hydrogen. The removal of the oxide layer could contribute strong adhesion between contacting surfaces. On the other hand, an oxide layer was produced on the fretted surface in the oxygen/hydrogen mixture by overcoming the removal action of the fretting. It resulted weakening of the adhesion between contacting surfaces, and larger slip between contacting surfaces was produced. As the result, stress conditions at the contact part were changed. Therefore, the change in the oxidation behavior is closely related to the reduction of the fretting fatigue strength by the addition of oxygen.

Event date： 2016.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Finatec at University of Brasilia   Country：Brazil  

As the general feature of fretting fatigue, non-propagating cracks are frequently found in the unbroken specimens or structural members of machines. Based on this fact, the fretting fatigue limit can be evaluated by the critical stress to crack propagation of a small crack under fretting conditions. In this context, a pre-cracked specimen was prepared for the fretting fatigue test. In the fretting fatigue test using a pre-cracked specimen, the fretting fatigue limit decreased, then increased with an increase in the contact pressure. The threshold stress intensity factor to crack propagation of the small crack, ΔKth, was obtained by the crack growth test. The stress intensity factor range of the pre-crack under fretting conditions, ΔK, was evaluated by a finite element analysis. It was clarified that the change in the fretting fatigue limit with a change in the contact pressure is quantitatively explained by comparison of ΔK to ΔKth. Based on this result, the effect of the position of the pre-crack on the fretting fatigue limit was also both experimentally and analytically investigated.

Event date： 2015.11 - 2015.12

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：Hilton Atlanta Airport   Country：United States  

Hydrogen is necessary to establish a sustainable and environmentally-friendly society. However, hydrogen could degrade materials strength. Therefore, one of the key issues to deploy high-pressure hydrogen containment systems is how to optimize the cost, performance and safety of those systems. For this issue, many studies on hydrogen-affected fracture are under way in order to identify fundamental mechanisms, develop predictive performance models, develop next generation materials, reduce regulations, develop design methods, identify appropriate material testing standards in high-pressure hydrogen environment, and so on.
Fretting fatigue is a kind of fatigue at the contact part between mechanical components. As can be expected from the fact that fretting is sometimes termed as fretting corrosion, it involves some chemical reactions, which might have a great impact on fatigue properties. Since hydrogen could influence both fatigue and the phenomena occurring at the contact surface such as friction, wear, oxidation, etc., the effects of hydrogen on fretting fatigue are very complicated. In fact, fretting fatigue strength of austenitic stainless steels is significantly lower in hydrogen than in air. As a result, the industries related to hydrogen-containment systems are deeply concerned about fretting fatigue in hydrogen. Figure 1 shows an example of fretting found in a high-pressure hydrogen containment system, which occurred at the contact part between 100MPa hydrogen packing and its holder.
When considering service conditions of hydrogen-containment systems, some amount of impurities in hydrogen should be accepted. For example, the purity of hydrogen for PEM fuel cell is designated by ISO standard as 99.99%. On the other hand, positive use of impurities is expected based on the report in which the addition of small amounts of oxygen to hydrogen inhibited hydrogen-affected fracture. The objective of this study is to clarify the effect of oxygen and water vapor added to hydrogen on fretting fatigue strength of an austenitic stainless steel.
For the fretting fatigue test, a controlled method for the addition of ppm-level oxygen to hydrogen environment was established. Fretting fatigue tests in hydrogen containing 0.088, 5, 35 and 100 volume-ppm oxygen were carried out using the test apparatus shown in Fig. 2. The fretting fatigue strength in the oxygen-hydrogen mixture was different depending on the oxygen level as shown in Fig. 3. In the fretting fatigue test in hydrogen with humidification, it was found that the humidification of hydrogen significantly reduced the fretting fatigue strength.
Based on the XPS (X-ray photoelectron spectroscopy) analysis of the fretted surface (Fig. 4), 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.
In addition, the reasons for the change in the fretting fatigue strength in hydrogen due to the addition of impurities were examined from the view point of the change in mechanical stress conditions.

Event date： 2015.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Warsaw University of Technology   Country：Poland  

This study is aiming to develop higher yield strength austenitic steels without compromising performance in hydrogen by a method of grain refinement. Austenitic stainless steels are superior in hydrogen compatibility than ferritic and martensitic steels. However, austenitic steels have the drawback of relatively low proof strength. It causes increase of thickness of tubes, and it results increase cost and decrease of flow rate.
The material was prepared by thermo-mechanical treatment using reversion from strain-induced martensite to austenite, which has been developed by Takaki et al [1]. Two materials, which have 1m and 21m of average grain size, were prepared. The microstructure is shown in Fig.1. The yield strength was 596MPa for the material with 1m grain size and the proof strength was 156MPa for the material with 21m grain size.
Fatigue test of hydrogen charged and uncharged materials was done with a stress ratio of -1 at a loading frequency of 15Hz in air. Crack growth tests were also performed. The fatigue limit of the 1m grain size material was significantly higher than that of the 21m grain size material. But the fatigue life in the short life region was significantly reduced by hydrogen charge.
It seems that there is no precedent, the crack growth resistance of the ultra-fine grain material was good compared to that of commercial austenitic stainless steels. However, the hydrogen charge accelerated crack growth. This was consistent with the reduction of fatigue life. Based on the observation of morphology of crack, slip bands and crack opening displacement, a possible toughening mechanism, which is inherent in ultra-fine grain austenitic stainless steel was considered.

Event date： 2014.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Disney Contemporary Resort, FL   Country：United States  

The effect of hydrogen on the fretting fatigue strength of SUS304 austenitic stainless steels and the mechanisms were studied. The fretting fatigue strength is significantly lower in hydrogen gas than in air. The fretting fatigue strength is decreased by hydrogen charge. Addition of oxygen partially increased the fretting fatigue strength in gaseous hydrogen. Adhesion between the contacting surfaces is one of the causes of the reduced fretting fatigue strength in hydrogen. The adhesion causes increase in stress, severe plastic deformation and microstructure change.Initiation limit of fretting fatigue cracks was reduced by hydrogen. This is also one of the causes of the reduced fretting fatigue strength in hydrogen.

Event date： 2014.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡大学   Country：Japan  

Factors affect fretting fatigue propertoes in hydrogn

Event date： 2014.1

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

The effect of hydrogen on the fretting fatigue strength of austenitic stainless steels and the mechanisms were studied.
The fretting fatigue strength is significantly lower in hydrogen gas than in air.
The fretting fatigue strength is decreased by hydrogen charge.
Adhesion between the contacting surfaces is one of the causes of the reduced fretting fatigue strength in hydrogen in terms of stress concentration, severe plastic deformation and microstructure change.

Event date： 2014.1

Language：English  

Venue：九州大学伊都キャンパス   Country：Japan  

High-cycle fatigue properties of work-hardened oxygen-free copper in 10MPa hydrogen gas were studied.
(1) The fatigue limit in hydrogen increased compared to that in air.
(2) The increased fatigue strength was caused by the delay of the crack growth.
(3) Hydrogen participated in the slip deformation. Hydrogen activates dislocations which are immobile in air.
(4) Crack initiation and development of slip bands occurred at lower stress amplitude in hydrogen than in air. The possible mechanism is HELP.

Event date： 2013.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山大学   Country：Japan  

Fatigue properties of ultra-fine grain austenitic stainless steel and effect of hydrogen

Event date： 2013.6

Language：English   Presentation type：Oral presentation (general)  

Venue：China National Convention Center (CNCC), Beijing   Country：China  

Fretting fatigue, which is a composite phenomenon of metal fatigue and friction, is one of the major factors in the design of mechanical components as it significantly reduces fatigue strength. Since hydrogen can influence both fatigue and friction, fretting fatigue is one of the important concerns in designing hydrogen equipment. The authors carried out the fretting fatigue tests on austenitic stainless steels in order to characterize the effect of hydrogen and to explain the mechanism responsible for hydrogen embrittlement. In this study, the significant reduction in fretting fatigue strength due to hydrogen is shown including other factors influencing the fretting fatigue strength such as surface roughness, hydrogen content and the addition of oxygen. The cause of the reduction in the fretting fatigue strength in hydrogen is local adhesion between the contacting surfaces and subsequent formation of many small cracks. Furthermore, hydrogen enhances crack initiation under fretting fatigue conditions. Transformation of the microstructure from austenite to martensite is another possible reason. A hydrogen charge also reduces the fretting fatigue strength. The cause is the reduction in the crack growth threshold, Kth, due to hydrogen.

Event date： 2013.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Christ Church, Oxford University   Country：United Kingdom  

Downsizing and reduction of the weight of components is a critical issue for automotive parts manufacturers in the face of strong demand for a reduction of the environmental burden caused by automobiles. Improving the efficiency of the car air conditioning compressor significantly contributes to improved fuel efficiency, but requires downsizing of the compressor’s power transmission shaft. At the same time, the fatigue strength of shaft has to be improved in order to transmit a given level of power through a smaller component. Currently, the spline used for the compressor transmission shaft is the part most prone to fretting fatigue, so an investigation was carried out revealing that the fretting fatigue strength of the downsized spline was insufficient to meet design requirements. Therefore, a new type of joint, a hybrid joint, was developed that combined the press-fit and spline. The structure of the hybrid joint is shown in Fig. 1. The hybrid joint prevented fretting fatigue failure of the downsized spline, resulting in a significant improvement in fatigue strength. In order to use the hybrid joint in the actual product, factors with a bearing on its fatigue strength, particularly the contact pressure and the contact length in the press-fit part, were studied. Contact pressure is one of the major factors influencing fretting fatigue strength of the press-fit part. Since the diameter of the shaft used in this study is relatively small, the contact pressure significantly changes by the degree of interference, which is the difference between shaft diameter and inner diameter of boss.

Event date： 2013.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Christ Church, Oxford University   Country：United Kingdom  

Hydrogen is the most promising candidate as a new energy carrier in the very near future. Fretting fatigue in hydrogen containment equipment should be considered in order to ensure safety. The authors have reported a significant reduction in the fretting fatigue strength due to hydrogen [1]. One of the causes of the reduced fretting fatigue strength in hydrogen is small cracks that emanate from a locally adhered spot between contacting surfaces. The objective of this study is to establish a quantitative understanding of the effect of hydrogen on the initiation of the small cracks under fretting fatigue conditions.

Event date： 2013.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Christ Church, Oxford University   Country：United Kingdom  

The authors have reported that the reduction in fatigue strength due to fretting can be significantly enhanced in hydrogen. In this study, the mechanisms enhancing hydrogen embrittlement by fretting were investigated. Impurities in hydrogen can be considered as an influencing factor on the fretting fatigue strength in hydrogen. The effect of oxygen addition was also studied.

Event date： 2012.2

Venue：九州大学伊都キャンパス   Country：Japan  

Event date： 2012.2

Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

Event date： 2011.7

Presentation type：Oral presentation (general)  

Venue：九州工業大学　戸畑キャンパス   Country：Japan  

A study on the damage caused by repetitive open-close movement in a high-pressure hydrogen gas valve

Event date： 2011.7

Presentation type：Oral presentation (general)  

Venue：九州工業大学　戸畑キャンパス   Country：Japan  

Effects of Notch Root Radius and Stress Ratio on the Behavior of Short Crack at Notch Root

Event date： 2011.7

Presentation type：Oral presentation (general)  

Venue：九州工業大学　戸畑キャンパス   Country：Japan  

Effects of Multiple Overloads and Hydrogen on High-Cycle Fatigue Strength of Notched Specimen of Austenitic Stainless Steel and Prediction of Reduction of Fatigue Limit

Event date： 2011.6

Presentation type：Oral presentation (general)  

Venue：Corvallis, Oregon, USA   Country：Armenia  

Event date： 2011.6

Presentation type：Oral presentation (general)  

Venue：Corvallis, Oregon, USA   Country：Armenia  

Event date： 2011.5

Presentation type：Oral presentation (general)  

Venue：大阪大学コンベンションセンター   Country：Japan  

Effect of 10MPa Hydrogen gas environment on high-cycle fatigue properties of carbon steels

Event date： 2011.3

Presentation type：Oral presentation (general)  

Country：Japan  

"Effect of Hydrogen on Fretting Fatigue Strength of SUS316L Austenitic Stainless Steel" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University

Event date： 2010.11

Presentation type：Oral presentation (general)  

Venue：東京大学   Country：Japan  

Effectiveness of combination of press-fit for improvement of fatigue strength of splined shaft

Event date： 2010.11

Presentation type：Oral presentation (general)  

Venue：東京大学   Country：Japan  

Effect of Hydrogen on Fretting Fatigue in Austenitic Stainless Steels

Event date： 2010.9

Presentation type：Oral presentation (general)  

Venue：名古屋工業大学   Country：Japan  

Improvement of Fretting Fatigue Strength by Hybrid Joint

Event date： 2010.4

Presentation type：Oral presentation (general)  

Venue：西南交通大学・成都・中国   Country：China  

Event date： 2010.3

Presentation type：Oral presentation (general)  

Venue：Califolnia Institute of Technology, CA, USA   Country：United States  

Event date： 2009.11

Presentation type：Oral presentation (general)  

Venue：Pacifico Yokohama, Yokohama   Country：Japan  

Event date： 2009.11

Presentation type：Oral presentation (general)  

Venue：富山市・富山国際会議場   Country：Japan  

Mechanism of Reduction of Fretting Fatigue Limit in Hydrogen Gas in SUS304

Event date： 2009.9

Presentation type：Oral presentation (general)  

Venue：岩手大学   Country：Japan  

Optimization of Shape of Stress-relief Groove for Improvement of Fretting Fatigue Strength

Event date： 2009.5

Presentation type：Oral presentation (general)  

Venue：愛媛大学   Country：Japan  

Effect of Hydrogen on the Reduction of Fatigue Strength by Multiple Overloading

Event date： 2008.10

Presentation type：Oral presentation (general)  

Venue：Northwestern University, Evanston, Illinois   Country：United States  

Mechanism of Reduction of Fretting Fatigue Limit in Hydrogen Gas Environmet

Event date： 2007.11

Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：東京大学　山上会館   Country：Japan  

Contact Mechanics and Evaluation of Fretting Fatigue Strength

Event date： 2007.9

Presentation type：Oral presentation (general)  

Venue：岐阜大学   Country：Japan  

The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines

Event date： 2007.9

Presentation type：Oral presentation (general)  

Venue：ACROS Fukuoka   Country：Japan  

Event date： 2007.9

Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：東京工業大学　百年記念館フェライト会議室   Country：Japan  

Fretting and Fatigue

Event date： 2007.9

Presentation type：Oral presentation (general)  

Venue：関西大学   Country：Japan  

Evaluation of Fretting Fatigue Strength and Fatigue Design Method

Presentation type：Oral presentation (general)  

Venue：岐阜大学   Country：Japan  

The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines

Presentation type：Oral presentation (general)  

Venue：Atlanta   Country：United States  

Presentation type：Oral presentation (general)  

Venue：九州大学　伊都キャンパス   Country：Japan  

Evaluation of Fatigue Strength of Fine Copper Wire for Electric Equipment

Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

Effect and Elucidation of Mechanism of Hydrogen Gas Environment on Fretting Fatigue Strength of Hydrogen Utilization Machines’ materials

Presentation type：Oral presentation (general)  

Venue：Montreal   Country：Canada  

Presentation type：Oral presentation (general)  

Venue：Montreal   Country：Canada  

The cause of the derailment of ICE train which occurred in 1998 at Eschede was the fatigue failure of a wheel tyre. Figure 1 shows the structure of the rubber sprung wheel. It was discussed that fretting fatigue between the rubber block and inner side of the tire affected the initiation of incipient crack. To clarify the effect of rubber contact on the fatigue strength of the tyre, the authors made fretting fatigue experiments under rubber contact conditions.
At first, fundamental fretting fatigue test was made using a servo-hydraulic fatigue machine. The specimen consisted of a 15mm diameter bar with two parallel flats where rubbers contacted. The specimen is made of medium carbon steel. Using bridge type fretting pads, which hold rubbers to contact with the flat parts of specimen, fretting testing was made. Two cylindrical rubbers, which were taken from the rubber block of a resilient wheel. Contact pressure was 24MPa at the first set-up of testing, which was the similar value of the related wheel assembling pressure calculated by FEM method. Two kind of the fatigue stress amplitude were applied to the specimens. The one was 90MPa, which is the fretting fatigue strength of this carbon steel fretted with steel. The second amplitude was 200MPa, which is twice a large as the fretting fatigue strength. No damage by the contact of rubber was obtained.
Secondly, three-dimensional elastic stress analysis on a rubber-sprung single-ring railway wheel was made using a general-purpose Finite Element Method (ABACUS program). Figure 2 shows the FEM model. Since the rubber is a super-elastic material, Mooney-Revlin Model was used in the calculation. It was found that the wheel tyre is subjected to a cyclic stress in one revolution of the wheel and the maximum stress occurs at the centre of inner surface of the tyre where the fatigue crack initiated.
Finally, fatigue tests of full size wheel-set were made as shown in Fig. 3 to confirm the fatigue resistance of the wheel at high load levels for up to 20millions of cycles of loading. After 20 millions of cycles of 280kN, which is 3.5time higher load than the static wheel load, no fretting damage could be observed.
It was concluded that the no effect of rubber contact on the fretting fatigue strength of a rubber-sprung single-ring railway wheel was observed.

Presentation type：Oral presentation (general)  

Venue：関西大学千里山キャンパス   Country：Japan  

Fretting fatigue and Design Method
Masanobu Kubota

Presentation type：Oral presentation (general)  

Venue：ACROS Fukuoka, Fukuoka   Country：Japan  

Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：百年記念館・東工大   Country：Japan  

Fretting and Fatigue
Masanobu Kubota

Event date： 2024.7 - 2024.8

Language：English   Presentation type：Oral presentation (general)  

Venue：THE HYATT REGENCY BELLEVUE BELLEVUE, WASHINGTON, USA   Country：United States  

Hydrogen gas pipelines are expected to serve as a large-scale and cost-efficient transportation to promote the utilization of hydrogen energy. Ensuring their safe operation requires a thorough understanding of the various strength characteristics that degrade in the presence of hydrogen gas and the incorporation of this knowledge into the strength design. Among these characteristics, understanding fatigue crack growth is crucial for accurately predicting the crack growth life. It has been reported that various factors can influence the degree of crack acceleration in hydrogen gas, such as gas pressure, temperature, and gas impurities. However, many aspects of the acceleration characteristics under changing conditions remain unknown. In this study, we conducted fatigue crack growth tests using compact tension specimens of the pipeline steel, X60, to investigate the effects of temperature and oxygen impurity on hydrogen-induced crack acceleration. It is worth noting that significant degradation of fatigue crack growth resistance did not appear in hydrogen gas even at low temperatures down to −30°C, as compared to room temperature. Additionally, this study confirmed the inhibitory effect of oxygen impurity on mitigating crack acceleration. In our presentation, we will demonstrate some interesting findings related to the crack growth properties and then discuss the roles and mechanisms of each influencing factor in determining the acceleration characteristics.

Event date： 2024.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Jesus College, Oxford   Country：United Kingdom  

In-situ fracture testing in an environmental transmission electron microscope has been used to perform dynamic defect-level studies of crack tip propagation in Cr-Mo low alloy steel lamellae. The first stage of crack propagation involves extensive plasticity and thinning ahead of the crack tip, whether hydrogen gas is present in the microscope chamber or not [1]. However, subsequent stages are strongly changed by the presence of H2. In the absence of hydrogen gas, extensive plasticity continues, leading to crack tip blunting, void nucleation, crack bridging and necking [1]. In contrast, the crack tip in hydrogen gas remains sharp and propagates by the formation and linking up of {100} facetted zig-zag micro-cracks, without much associated plasticity. The behaviour can be explained by dislocation activity that concentrates tensile stresses on {100} planes followed by hydrogen-enhanced decohesion (HELP followed by HEDE). Alternatively, or additionally, the observed fracture behavior can be understood in terms of the relative rates of dislocation interaction and dislocation generation near the crack tip. A specific scenario will be presented for the formation of zig-zag cracks by hydrogen-enhanced local plasticity (HELP) on slip planes in the TEM lamellae. We will discuss possible electron beam effects and extrapolate our observations and models to the geometries and high triaxiality conditions present during fracture of hydrogen embrittled bulk specimens.

Event date： 2024.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Zagreb, Croatia   Country：Croatia  

Hydrogen gas pipelines are poised to become a large-scale and cost-efficient means of transportation, enhancing the utilization of hydrogen energy. Ensuring their safe opera-tion necessitates a comprehensive understanding of the various strength properties that might degrade in the presence of hydrogen gas [1]. It is critical to incorporate this knowledge into the design for strength. From this perspective, it is essential to investi-gate various strength properties, including (i) tensile properties, (ii) fatigue life, (iii) fa-tigue crack growth, and (iv) fracture toughness. These elements are crucial for maintain-ing material integrity under service conditions. It has been observed that several factors, including gas pressure, temperature, and impurities, can influence degradation in a hy-drogen gas environment. However, the specifics of hydrogen-induced degradation are still largely unexplored.

In this study, we performed a series of experiments to assess the impact of hydrogen gas on the pipeline steel X60. These experiments included slow strain rate tensile (SSRT) tests, bending fatigue tests, fatigue crack growth tests, and fracture toughness tests. The tests were conducted in hydrogen gas at a pressure of 10 MPa and tempera-tures ranging from −30°C to room temperature. Furthermore, our study revealed that oxygen impurity has an inhibitory effect on the acceleration of crack growth.

The results indicate that there is no critical degradation in any of the properties tested, suggesting that these issues do not significantly hinder the material’s application in ser-vice. In our presentation, we will share some intriguing findings related to the strength properties and discuss the roles and mechanisms of each factor that influences degrada-tion.

Event date： 2024.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：琉球大学   Country：Japan  

現在の世界のエネルギーの多くは，有限な化石燃料に依存している．従来，化石燃料からエネルギーを取り出
す際に地球温暖化の原因となっている二酸化炭素（CO2）を排出し，環境に悪影響を及ぼしてきた．そのため，化
石燃料を用いる場合はCO2を回収・資源化する技術を共に用いたり，再生可能エネルギーを利用したりして，大
気中のCO2 濃度を増加させないカーボンニュートラルを達成する必要がある(1)．そのような流れの中で，水素エ
ネルギーの利用はカーボンニュートラルを達成する上で有効な方法の一つである(2)．H2 は地球上に豊富に存在す
る元素であることから持続可能なエネルギーキャリアとして期待されているが，H2ガスは密度が低いため，効率
的・経済的な貯蔵・運搬が極めて重要な課題となっている．そのため，液体の化合物として水素を運ぶことがで
きるアンモニア（NH3）を水素キャリアとして用いる方法(3)が検討されている．
NH3 は高温での脆化(4)，液体アンモニアによる応力腐食割れ(5)などの材料強度劣化を引き起こすことが知られて
おり，安全にNH3 を利用するため，NH3 が材料強度に及ぼす影響を明らかにしていく必要がある．Zhang らによ
る最近の研究により，NH3 を添加したH2 中では，NH3 がH2 よりも鉄表面に優先的に吸着するため，水素脆化に
よる破壊靭性値の低下が抑制されることが明らかにされている．しかし，NH3 を添加したN2 中では，鉄表面に吸
着したNH3 が分解してH2 を供給するため，NH3 が水素脆化による破壊靭性値の低下を促進することが明らかに
されている(6)．このように破壊靭性試験ではNH3 の水素脆化の抑制と促進の二つの相反する作用が確認されたが，
疲労き裂進展特性に及ぼすNH3 の影響は明らかでない．そこで本研究では，NH3 を添加したH2 ガス中での水素
脆化特性に関して一層知見を深めていくために，NH3 を含むH2 ガス，N2 ガス中で疲労き裂進展試験を実施した．

Event date： 2024.1

Language：English  

Venue：Kyushu University Ito campus   Country：Japan  

Event date： 2024.1

Language：English  

Venue：Kyushu University Ito campus   Country：Japan  

Event date： 2023.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：佐賀大学   Country：Japan  

先進高温水素機器の余寿命評価へのSP試験法の適用性を検討するため，オーステナイト系ステンレス鋼SUS304を対象に，SP試験とSPクリープ試験を実施し，変形・強度・破壊特性に及ぼす高温水素ガス雰囲気の影響に関する基礎的検討を行った．得られた知見をまとめて以下に示す．
1. SP試験の結果，室温ではアルゴンガス雰囲気中に比べ水素ガス雰囲気中のほうがumは幾分小さかった．反対に，600℃では水素ガス雰囲気中のumはアルゴンガス雰囲気中に比べわずかに大きくなった．
2. SP試験後の破面観察を行ったところ，600℃においては，アルゴンガス雰囲気中および水素ガス雰囲気中ともに巨視的には延性に富んだ破壊形態を示していた．一方，室温において，アルゴンガス雰囲気中では600℃と同様延性破壊であったのに対して，水素ガス雰囲気中においては脆性的な破壊の様相を呈していた．
3. SPクリープ試験の結果，水素ガス雰囲気中のほうがアルゴンガス雰囲気中に比べクリープ破断時間が幾分短くなった．また，SUS304の破断時間は荷重低下とともに両雰囲気中の差異は減少する傾向にあった．
4. SPクリープ試験後の破面観察を行ったところ，アルゴンガス雰囲気中および水素ガス雰囲気中ともに，試験荷重の低下に伴い破壊がより脆性的になっていた．村上幸太郎　[院],　駒崎慎一,　九州大学アイスナー　久保田祐信

Event date： 2023.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ新潟コンベンションセンター   Country：Japan  

先進高温水素機器の余寿命評価へのSP 試験法の適用性を検討するため，温度600℃600℃，圧力0.98 MPa の高温水素ガス雰囲気中でSP 試験が可能な試験装置を新たに設計・製作した．その後，オーステナイト系ステンレス鋼SUS304 を対象に，温度600℃600℃，圧力0.12 MPa にてSP 試験とSP クリープ試験を実施し，変形・破壊特性に及ぼす高温水素ガス雰囲気の影響に関する基礎的検討を行った．加えて，同一ロット材で報告されている水素ガス雰囲気中単軸引張およびクリープ試験結果との関係について調査した．得られた知見をまとめて以下に示す．
1. S P 試験の結果，室温においてはアルゴンガス雰囲気中に比べ水素ガス雰囲気中のほうが最大荷重とそのときの変位は幾分小さかった．反対に，600600℃では水素ガス雰囲気中の最大荷重とそのときの変位はアルゴンガス雰囲気中に比べわずかに大きくなった．
2. S P 試験の結果に基づいて推定したアルゴンおよび水素ガス雰囲気中の0 耐力と引張強さは，引張試験で得られたものと良く一致していた．
3. SP クリープ試験の結果，水素ガス雰囲気中のほうがアルゴンガス雰囲気中に比べ変形が助長されクリープ破断時間が幾分短くなった．また，相当破壊ひずみは試験荷重の低下とともに減少する傾向にあり，破断延性はアルゴンガス雰囲気中に比べ水素ガス雰囲気中のほうがわずかに高かった．
4. 欧州推奨の方法で算出したF σ 値には環境の影響がほとんど現れなったのに対して，実験的に求めたF σ 値はアルゴン雰囲気中と水素雰囲気中で大きく異なり，前者のほうが大きな値となった．また荷重の増加とともにF σ 値が大きくなった．これらは，破断延性が増すことと対応していると考えられる．

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：日本学術会議   Country：Japan  

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.

Event date： 2023.10

Language：English   Presentation type：Oral presentation (general)  

Venue：日本学術会議   Country：Japan  

The objective of this study is to deepen the understanding of the creep in hydrogen for the safety of evolving high-temperature hydrogen technologies. The material was JIS SUY-1 industrial pure iron. Its simple chemical composition and pure single phase may facilitate the consideration of the mechanism that how hydrogen affect creep deformation. Creep testing was carried out in argon and hydrogen gases at 873 K. The absolute gas pressure at which the creep tests were carried out was 0.12 MPa. The estimated hydrogen concentration in the specimen at the relevant conditions was estimated to be 0.70 mass ppm. Hydrogen accelerated the creep strain rate, resulting in a significant reduction in the creep life. The fracture profile shows double cup fracture and fracture surface was dimple in both argon and hydrogen environments. This observation indicated that the same creep deformation mechanism can be activated in both environments. The relationship between the creep life and minimum creep strain rate in hydrogen conformed with that in argon. This means that the creep life was controlled by minimum creep strain rate regardless of the testing environment. This result also imply that hydrogen accelerated the creep deformation without changing the creep deformation mechanism. According to the creep deformation mechanism map produced by Frost and Ashby, the creep deformation mechanism in this study was estimated to be power-law creep. The deformation in power-law creep is dominated by dislocation climb, in which vacancy diffusion takes important role. It is reported that hydrogen reduce vacancy formation energy of alpha iron. Therefore, hydrogen may increase the vacancy concentration, leading to enhanced dislocation climb. The analysis of minimum creep strain rate based on the analytical model formula indicates that the plausible role of hydrogen was to decrease creep activation energy. This consideration is consistent with our past study on SUS304.

Event date： 2023.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場   Country：Japan  

T
he small punch (SP) creep test was conducted using a newly developed testing machine that enable d SP test with a
small disk type specimen in a high temperature hydrogen gas at mosphere. The test material used w as Type 304 austenitic
stainless steel, and the test s were carried out at a temperature of 600°C in a hydrogen and argon gas atmosphere (absolute
pressure is 0.12 MPa). The experimental results showed that the SP creep rup ture time was shorter in hydrogen gas
atmosphere than argon gas one . However, th is difference in rupture time tended to be smaller with decreasing applied SP
load, and there was no significant difference at the load level of 4 86 N. It was also found that the F σ value, which was
necessary to convert the SP load ( F ) to the equivalent stress σ for comparison between SP and uniaxial creep rupture
data , decreased with decreasing applied SP load. The F σ value for hydrogen gas atm o sphere was always larger than that
for argon gas one , and this large r value was closely associated with higher rupture ductility in hydrogen gas atmosphere.

Event date： 2023.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Park City, Utah   Country：Japan  

Identifying the atomic scale mechanisms for hydrogen embrittlement in steels remains a much discussed yet elusive goal. On the one hand, microscopy investigations show that hydrogen enhances dislocation motion, while on the other, the quasi-cleavage morphology of the fracture surfaces and early fracture confirm the embrittling role of hydrogen. Taking advantage of an in-situ fracture testing method in an environmental transmission electron microscope, we attempt to reconcile these apparently contradictory trends using dynamic studies of crack tip propagation in Cr-Mo low alloy steel lamellae. The first stage of crack propagation in the lamellae involves extensive plasticity and thinning ahead of the crack tip, whether hydrogen gas is present or not in the microscope chamber [1]. However, subsequent stages are strongly changed by pressures as low as 2 mbar of H2. In the absence of hydrogen gas, extensive plasticity continues, leading to crack tip blunting, void nucleation, crack bridging and necking [1]. In contrast, the crack tip in hydrogen gas remains sharp and propagates by the formation and linking up of {100} facetted staircase micro-cracks, without much associated plasticity. We propose an explanation for this behavior, which is based on the effect of H segregation on dislocation formation and mobility energies, and provides a consistent understanding of the observations of hydrogen embrittlement in steel.

Event date： 2023.9

Language：English   Presentation type：Oral presentation (general)  

Venue：東京都立大学 南大沢キャンパス   Country：Japan  

The fracture toughness test was conducted under various gas environments, including hydrogen (H2), nitrogen (N2), and ammonia (NH3) impurity mixed with H2 or N2 of the SCM440 low-alloy steel. NH3 showed mitigation of the hydrogen embrittlement (HE) when the loading rate was relatively high. However, the mitigation effect decreased with the decrease in the loading rate. It was found that NH3 acted as both a mitigator of the HE and a cause of the HE depending on the loading rate. The underlying mechanism was elucidated using density functional theory (DFT) calculations, revealing intricate atomic-level interactions.

Event date： 2023.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Technische Universität Wien, Vienna, Austria   Country：Austria  

Event date： 2023.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Norwegian University of Science and Technology   Country：Norway  

INPEX, which is the largest Oil and Gas Exploration and Production company in Japan, investigate the feasibility of hydrogen transportation through their natural gas pipeline as a part of their contributions toward the net-zero greenhouse gas emission by 2050. For this purpose, INPEX and Kyushu University started a joint research project on hydrogen embrittlement (HE) properties of pipeline steels. HE properties of API X60 steel, which are widely used in the INPEX pipelines, will be holistically studied under the testing conditions relevant to their actual usage environment. This is the first project in Japan in terms of the consideration of HE of large-scale natural gas pipeline in-operation in Japan. Although HE of pipeline steels has extensively been studied across the world, we expect unique and important results through this project. For instance, the study on the fatigue limit is very limited compared with the study on fatigue crack propagation in high-pressure hydrogen environment. This project includes fatigue test in high-pressure hydrogen gas up to 107 cycles. Also, the hydrogen effect will be studied in conjunction with the temperature effect. We aim not only for ensuring safe hydrogen transportation through natural gas pipeline but also developing relevant laws and regulations toward the future.

Event date： 2023.6

Language：English   Presentation type：Oral presentation (general)  

Venue：ottawa   Country：Canada  

Carbon monoxide (CO) contained in hydrogen gas mitigates hydrogen embrittlement (HE). This CO effect can be affected by the chemical composition of the steel surface. This study investigated the effect of chromium (Cr) on Cr-rich and Cr-low materials. During the fracture toughness test, the CO effect was significantly less for the SUS430 ferritic stainless steel (16.17% Cr) compared to that for the A333 carbon steel (0.03% Cr). The mechanism that Cr reduced the CO mitigation effect was considered by DFT calculations of the interaction of CO with the steel surface. It revealed that the CO adsorption on the Fe site is greater than that on the Cr site.

Event date： 2023.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：つくば国際会議場   Country：Japan  

水素ガス中の不純物は，水素脆化に対して影響を有するものがある．例えば，酸素，一酸化炭素は疲労き裂進展や破壊靭性試験で水素の影響を軽減したり，完全に防止したりする効果が報告されている．アンモニアについては，低合金鋼の破壊靭性試験において，負荷速度が比較的高速の場合は水素脆化の抑制効果が，負荷速度が比較的低速の場合は水素脆化の誘発効果があることが報告されている．不純物が水素脆化に影響を及ぼす機構については，第一原理計算や分子動力学計算によって明らかにされている．例えば，酸素の水素脆化抑制効果に対しては，酸素が水素よりも鉄表面と強い相互作用を持ち，また，鉄表面に吸着した酸素は水素が鉄表面に近づく際に必要な活性化エネルギーを顕著に増加させるため，水素が鉄表面に吸着できなくなることで水素脆化が抑制される．一酸化炭素については，鉄表面を100%被覆することができないことが明らかにされており，このことは，一酸化炭素が完全な水素脆化の抑制効果を示さない実験結果と一致する．このように，不純物の水素脆化に対する効果は不純物と鉄表面の化学反応に起因して生じるために，温度は一つの影響因子と考えられる．そこで，本研究の目的は，不純物として加えた酸素が水素脆化を抑制する効果に対して温度がどのように作用するのかを明らかにすることとした．

Event date： 2023.3

Language：English   Presentation type：Oral presentation (general)  

Venue：San Diego Convention Center & Hilton San Diego Bayfront. San Diego, California, USA   Country：Armenia  

High temperature hydrogen attack (HTHA) is degradation of carbon steels whereby internal hydrogen reacting with carbides forms methane gas bubbles typically on grain boundaries which grow and coalesce, leading to loss of strength and toughness. Current design practice against HTHA is based on Nelson curves which define the conditions for safe operation in a temperature/hydrogen-partial-pressure diagram. Nelson curves are phenomenological and do not account for the underlying failure mechanism(s), microstructure, carbide stability, and applied stresses. To this end, we present a micromechanical model for predicting void growth and coalescence in carbon steels due to methane pressure and external loads. The methane gas pressure was calculated by combining kinetics-based modeling with density functional theory. The effect of hydrogen on the constitutive response was quantified by determining the activation parameters that govern the deformation during HTHA. The micromechanical model is used to construct physically-based Nelson-type curves indicating lifetime under given applied stresses.

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学   Country：Japan  

試験温度やガス圧力の面でより広い実験条件の適用が可能である見込みの中空試験片を用いた高温水素中でのクリープ試験の手法を確立するために，オーステナイト系ステンレス鋼 JIS SUS304を供試材とし，温度873 K， 絶対圧力0.12 MPaの水素ガス中およびアルゴン中で中空試験法によるクリープ試験を行った．併せて，中空試験片内部のガス環境の作成方法の検討を実施した．その結果，ガス置換のみでは中空試験片内部を水素ガス純度をその影響評価に十分なまでに上げられないこと，真空引きをガス置換の間に挟めば水素ガスの純度を十分に高くすることができることが分かった．

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学   Country：Japan  

SP試験法の先進高温水素機器への適用性を検討するため，600℃の高温水素ガス雰囲気中で SP 試験が可能な新たな試験装置を設計・ 製作するとともに， SUS304鋼の同雰囲気中での SP クリープ特性を調べた．その結果，アルゴンガス雰囲気中に比べ， 水素ガス雰囲気中ではクリープ破断時間が減少し破断延性（相当破壊ひずみ）が増加することがわかった．このような結果は，標準の単軸クリープ試験の結果と定性的によく一致していた．加えて，SPクリープ試験と標準単軸クリープ試験の対応関係すなわち荷重 /応力換算について検討した ところ，欧州で推奨されている最小変位速度到達時の変位に基づいた荷重 /応力換算方法では水素ガス雰囲気中の SPクリープ破断試験データを単軸クリープ破断試験データに良好に対応付けることができなかった． 他方，相当破壊ひずみに基づいた方法で換算した結果，アルゴンガス雰囲気中の SPクリープ破断試験結果がわずかに短寿命側に位置するものの，両雰囲気中における単軸クリープ破断試験結果との対応は 比較的良好であった．

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宮崎大学工学部   Country：Japan  

フレッティング面のCO 分解触媒作用の支配的元素特定のため，SM490YB 鋼を用いてフレッティング疲労試
験を行い，SUS304 鋼の場合との比較を行った．本研究により以下の事が明らかとなった．
1. SM490YB 鋼のフレッティング面においてもSUS304 鋼の場合と同様にCO の分解触媒作用が確認された．
2. SM490YB 鋼のフレッティング面における炭素粉末の生成量はSUS304 鋼の場合と比較して少量であった．
3. CO 分解触媒作用に強い影響を及ぼす元素はNi であると考えられる．

Event date： 2023.1 - 2023.2

Language：English  

Venue：九州大学伊都キャンパス   Country：Japan  

The NH3 decomposition rate (NH2 → NH + H) decreased as NH3 concentration increased resulting in hindering NH3-derived hydrogen supply. As a result, insufficient time for NH3 further decomposition lead to lower H atom coverage on Fe surface even though NH3 concentration was increased.

Event date： 2022.12

Language：English   Presentation type：Oral presentation (general)  

Venue：KDDI維新ホール   Country：Japan  

In this study, we found that NH3 has an induction effect of HE. NH3 induced HE only at the slower loading rate because hydrogen production by NH3 decomposition with the help of Fe surface catalytic action is very slow reaction, whereas adsorption of NH3 on the Fe surface is very fast. The NH3-derived hydrogen atom coverage on Fe (110) surface was decreased with increased NH3 concentration because the NH3 decomposition rate (Ⅲ) was dramatically decreased due to lack of vacant site that is needed for decomposition. As the result that hydrogen supply decreases with an increase in NH3 concentration, NH3 induced He showed negative NH3 concentration dependence.

Event date： 2022.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学   Country：Japan  

フレッティング面のCO分解触媒作用の支配的元素特定のため， SM490YB鋼を用いてフレッティング疲労試験を行い，SUS304鋼の場合との比較を行った．本研究により以下の事が明らかとなった．
1. SM490YB鋼のフレッティング面においてもSUS304鋼の場合と同様にCOの分解触媒作用が確認された．
2. SM490YB鋼のフレッティング面における炭素粉末の生成量はSUS304鋼の場合と比較して少量であった．
3. CO分解触媒作用に強い影響を及ぼす元素はNiである可能性が高い．

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Venue：沖縄県市町村自治会館   Country：Japan  

The objective of this study is to gain a better understanding on the hydrogen effect on the creep properties in order to establish the science enables to secure the advanced high-temperature hydrogen technologies. Creep testing was carried out in argon and hydrogen gases at 873 K. The absolute gas pressure at which the creep tests were performed was 0.12 MPa. The material was JIS SUY-1 industrial pure iron. It was used as a model material having bcc crystalline structure. Pure single-phase microstructure may be beneficial to elucidate the central role of hydrogen in the creep deformation in the presence of hydrogen. Hydrogen accelerated the creep strain rate resulting in significant reduction in the creep life. Based on the creep deformation mechanism map by Frost and Ashby, the creep in this experiment was driven by power-low creep. The specimens formed double cup fracture and exhibited dimple fracture surface regardless of the environment and creep life. There was no significant difference in the fracture profile and fracture surface morphology. These observations indicated no change in the creep deformation mechanism in hydrogen. This was the similar to the creep of SUS304 stainless steel in hydrogen. Similar mechanism that hydrogen may enhance the vacancy density, which led to magnified lattice diffusion and associated dislocation climb may be adopted.

Event date： 2022.11

Language：English   Presentation type：Oral presentation (general)  

Venue：沖縄県市町村自治会館   Country：Japan  

The utilization of hydrogen is one of the keys to achieving sustainable development goals. During the transition toward a hydrogen society, the repurposing of existing non-hydrogen energy systems to a hydrogen one is very important in terms of costs and smooth reforming of energy and industrial structures. In this context, the mixing of hydrogen with natural gas can be one of the important technologies. In this study, fatigue crack growth testing was carried out in air, hydrogen, methane / hydrogen mixed gases in order to characterize the effect of hydrogen on the fatigue crack growth behavior in natural gas. The test material was JIS SCM435 low alloy steel. Two materials, which have different strength levels, were used. Both materials showed acceleration of the fatigue crack growth rate in only hydrogen and the mixed gases. The extent of the acceleration was less in the mixed gas compared with that in hydrogen. It is presumed that the hydrogen effect was less pronounced by the reduced partial hydrogen pressure in the mixed gas. Also, the extent of the acceleration was less in the lower strength material than in the higher strength one. It was confirmed that methane had no detrimental effect on the fatigue crack growth behavior of both materials.

Event date： 2022.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Augustinian Monastery, Belgium   Country：Belgium  

The addition of carbon monoxide (CO) to hydrogen (H2) gas can mitigate the hydrogen environment embrittlement (HEE) of steels. The effect of gas pressure on the mitigation of the HEE of low carbon steels by the addition of 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 the surface chemical reactions of H2 and CO with the iron (Fe) surface. The degree of mitigation of the HEE depended on the gas pressure and CO concentration; the CO concentration to achieve complete HEE prevention was enhanced with an increase in the gas pressure, in other words, the CO mitigation effect was reduced by the increased gas pressure. The MD simulations revealed that the dissociation rate of dihydrogen molecules to atomic hydrogen on the Fe surface was significantly enhanced 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 suggest that the hydrogen uptake into a steel is more effectively prohibited in a lower pressure H2 gas containing CO, which accounts for the gas pressure dependence of the CO mitigation effect observed in the fracture toughness tests.

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：弘前大学   Country：Japan  

Development of Small Punch Creep Testing Technique in High-Temperature Hydrogen Gas Atmosphere

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Hydrogen Embrittlement Properties of Low Alloy Steels in H2 added CH4 Gas

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Hydrogen Embrittlement Properties of Low Alloy Steels in H2 added CH4 Gas

Event date： 2022.2 - 2022.3

Language：English  

Venue：オンライン   Country：United States  

Recent experimental studies of the microstructure beneath fracture surfaces of ferritic steel, lath martensitic steel, stainless steel, and nickel specimens fractured in hydrogen suggest that the dislocation structure and hydrogen transported by mobile dislocations play important roles in the evolution of the fracture process/event. After reviewing this plasticity-mediated hydrogen-induced failure, we present a model for hydrogen/deformation interactions to quantify the effect of hydrogen on the fracture resistance of a low alloy martensitic steel through the use of a statistically-based micromechanical model for the critical local fracture event, which relates the influence of hydrogen on dislocation interactions and internal interfaces in affecting decohesion to the onset of macroscopic failure. The results demonstrate that hydrogen induced failures are complex phenomena that can be explained by a combination of HELP and decohesion and require factors such as stress, strain, and hydrogen concentration to all act in concert to bring about failure.

Event date： 2022.2 - 2022.3

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：United States  

Creep in hydrogen was studied to ensure safety of evolving high-temperature hydrogen technologies such as SOFC and SOEC.

Event date： 2022.1 - 2022.2

Language：Japanese  

Venue：九州大学伊都キャンパス   Country：Japan  

水素によってSUY-1のクリープひずみ速度が加速しクリープ寿命が顕著に低下した．
水素中とアルゴン中どちらの環境でも破壊形態はダブルカップ型，破面はディンプルであった．
転位クリープにおける最小クリープひずみ速度の定式を用いた解析により，もっともらしい水素の役割はクリープ活性化エネルギーを低下させることであると推察される．

Event date： 2022.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Effect of Hydrogen on Creep Strength Properties

Event date： 2022.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

I2CNER research on Mitigation of hydrogen embrittlement by addition of impurities to hydrogen gas was reviewed.

Event date： 2022.1

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Malaysia  

High-temperature hydrogen technology is one of the keys to establish carbon-neutral society. To ensure the safety of materials subjected to high temperature hydrogen, basic understanding of the material properties in hydrogen at elevated temperature is necessary. The objective of this study is to deepen mechanistic insight of the creep in hydrogen.
Creep testing was performed in argon and hydrogen gases at 873 K. The absolute gas pressure at which the creep test was carried out was 0.12 MPa. The materials were JIS SUY-1 commercial pure iron and SUS310S austenitic stainless steel. The pure iron was used as a model material having BCC crystalline structure to study the mechanism that hydrogen affects creep properties. Regarding FCC material, we studied SUS304 [1]. The SUS310S was a candidate material for high temperature hydrogen equipment and component.
Figure 1 shows the creep curves of each material. For both materials, hydrogen accelerated the creep strain rate at the steady state creep region, and it resulted the reduction in the creep life. Regarding fracture profiles, the SUY-1 showed double cup fracture following a significant decrease in the cross-sectional area during creep testing, and the SUS310S showed cup-and-cone like fracture, which was similar to the SUS304 we studied previously. The fracture surface of the SUY-1 was dimple for both creep tests in argon and hydrogen. This implies that hydrogen didn’t change the creep deformation mechanism but accelerated the deformation. As the results of the examination of the fracture surface and fracture profiles of the SUS310S, it was found that formation of surface cracks was suppressed in hydrogen. This observation is consistent with the experimental result that elongation in hydrogen is larger than that in argon. Since these trends were similar to the SUS304, the same mechanism that hydrogen reduced the creep life of the SUS304, which was enhanced dislocation climb mediated by enhanced vacancy density, can be adopted to the SUS310S.

Event date： 2022.1

Language：English   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Malaysia  

Hydrogen takes a key role in decarbonization in energy and industrial sectors. During transition toward hydrogen society, blue hydrogen and mixed hydrogen and fossil fuel will be used, although use of green hydrogen is an ultimate goal. In this context, assessment of hydrogen embrittlement properties in hydrogen-mixed gases is necessary. In this study, slow strain rate tensile tests were carried out in air, hydrogen, methene and methene and hydrogen mixed gases. The material was JIS SCM435 low alloy steel. Two materials, which were relatively higher strength one and lower strength one, were prepared. Both materials showed a decrease in reduction of area in hydrogen and the mixed gases. There was no significant difference between the results in air and that in methane. The fracture surface in air and methane was dimple. Quasi-cleavage fracture surface was observed in hydrogen and methane and hydrogen mixed gases. For the fractured specimens tested in hydrogen and the mixed gases, small cracks were observed on the surface. It was presumed that the reduction in area was caused by accelerated surface crack propagation of these small cracks due to hydrogen. The effect of hydrogen in the mixed gas was less than that in hydrogen. It is considered that reduction in the partial hydrogen pressure diminished the effect of hydrogen. Also, the area of quasi-cleavage fracture surface is less in the mixture than in hydrogen gas. The effect of hydrogen was more pronounced in the high-strength materials.

Event date： 2022.1

Language：English  

Country：Japan  

Effect of ammonia on hydrogen embrittlement was studied. As a result, we found both NH3 effects of hydrogen embrittlement mitigation and induction. The plausible reason was NH3's faster reaction with Fe surface than H2 for the mitigation and NH3 decomposition to H and other compounds by the help of Fe catalyst.

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Mitigation of hydrogen effect on fretting fatigue by addition of carbon monoxide

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学   Country：Japan  

Mitigation of hydrogen effect on fretting fatigue by addition of carbon monoxide

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋⼤学 東⼭キャンパス (オンライン開催)   Country：Japan  

The objective of this study is to accumulate creep data in hydrogen of various materials in order to consider the mechanisms that hydrogen affects creep properties. Creep testing was performed in argon and hydrogen gases at 873K. The materials were JIS SUS304, SUS304L and SUS310S austenitic stainless steels and JIS SUY-1 commercial pure iron. For all materials, the creep life was reduced in hydrogen compared to that in argon to a greater or lesser extent. The creep ductility in hydrogen was higher than that in argon except for the pure iron. The mechanism that hydrogen reduced the creep life of the SUS304 we considered was the accelerated dislocation climb mediated by hydrogen increased vacancy concentration. According to the literatures, decarburization, carbide formation and hydrogen enhanced localized plasticity (HELP) were investigated. It was confirmed that these mechanisms were not activated in our creep test for the SUS304.

Event date： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：電気通信大学*コロナにより開催中止，講演論文集は発行   Country：Japan  

Effect of Hydrogen on Creep Properties of SUS304 was studied. In creep test of SUS304 at 600 degree C in hydrogen gas, the creep life was significantly reduced by accelerated creep rate at steady-state creep region. Transition of fracture mode from dimple to intergranular cracking was delayed in hydrogen. It was confirmed that effects of decarburization and formation of carbide were minor in this test. The plausible mechanism that hydrogen reduced creep life was promotion of recovery.

Event date： 2021.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Evaluation of environmentally friendly grease for fretting fatigue of oil-well pipe materials

Event date： 2021.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Creep tests of SUS304 and SUS310S austenitic stainless steels and SUY-1 commercial pure iron were carried out at 873 K in hydrogen and argon gases. 1. For all materials, the creep life was significantly reduced in hydrogen compared with that in argon. 2. In the fracture surface of the SUS304, Hydrogen decreased the percentage of intergranular fracture. 3. The most probable mechanism for how hydrogen accelerated the creep deformation of the SUS304 is the promoted dislocation crimb due to hydrogen increasing the vacancy concentration.

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学戸畑キャンパス   Country：Japan  

Difference of Controlling Mechanisms of CO and O2 Inhibitory Effects to Hydrogen-Assisted Fatigue Crack Growth

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学戸畑キャンパス   Country：Japan  

Effect of Manganese Phosphate Coating on Fretting Fatigue Strength of Oil-Well Pipe Material under Grease Lubrication

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学戸畑キャンパス   Country：Japan  

Difference of Controlling Mechanisms of CO and O2 Inhibitory Effects to Hydrogen-Assisted Fatigue Crack Growth

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学戸畑キャンパス   Country：Japan  

Difference of Controlling Mechanisms of CO and O2 Inhibitory Effects to Hydrogen-Assisted Fatigue Crack Growth

Event date： 2020.11 - 2020.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Korea, Republic of  

Fretting fatigue strength of SUS304 in H2 and the effect of O2 addition to the H2 environment were studied. The FF strength in H2 was significantly lower than that in air. Surface oxide layer was removed during fretting in the high-purity H2. It resulted two primary consequences, which are enhancement of hydrogen uptake and adhesion between contacting surfaces. Localized severe cyclic plastic strain was caused by the adhesion. As a result, microstructural change was caused. These are also responsible for the reduced FF strength in H2.

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

Effect of hydrogen on creep properties was investigated. The materials were JIS SUS304, SUS304L, SUS310S and pure iron. All materials showed reduction in the creep life due to hydrogen.

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

Study on fatigue crack growth behavior of small crack of low alloy steel in hydrogen gas : Method to evaluate the effect of hydrogen on fatigue crack growth test of small crack was established.

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

To characterize the effect of NH3 contained in H2 gas on hydrogen environment embrittlement JIS SCM440 Cr-Mo steel, fracture toughness tests were conducted in H2, N2, and NH3 added H2 or N2 mixtures. The effects of gas pressure and loading rate were discussed. (1) 1000 vppm NH3 mitigated the HEE at crosshead speed was 2.0 × 10-3 mm/s and gas pressure was 0.1 MPa. (2) The mitigation effect of NH3 decreased with the decrease in the crosshead speed and increase in the gas pressure. (3) NH3 caused HEE by hydrogen supply by its decomposition at crosshead speed was 2.0 × 10-5 mm/s.

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福井大学   Country：Japan  

Elucidation of the effect of ppm-levels of oxygen addition to the environment on fretting fatigue properties in hydrogen gas and its mechanism

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Cetim, Senlis   Country：France  

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.

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス, 福岡   Country：Japan  

Effect of High-temperature Hydrogen on Material Strength of SUS304 and Ti-6Al-4V

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Online (Shanghai was planned, but switched to online due to pandemic)   Country：China  

Ammonia (NH3) was added to hydrogen gas as an impurity, and then hydrogen embrittlement (HE) of SCM440 low alloy steel was investigated through fracture toughness tests. NH3 showed inhibition of the HE when the loading rate was relatively high. But the inhibitory effect decreased with the decrease in a loading rate. Also the inhibitory effect decreased with an increase in the gas pressure. It was found that NH3 acted as both an inhibitor of the HE and a cause of the HE depending on the loading rate.

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ, 新潟   Country：Japan  

The objective of this study is to clarify the effect of high-temperature hydrogen on creep properties for advanced hydrogen energy technologies such as SOFC, SOEC, RFC and hydrogen gas turbine. A significant ductility loss due to hydrogen occurred at 25 ℃. On the other hand, no ductility loss occurred at 100 ℃ and higher temperatures.
The creep life was significantly reduceed in hydrogen. In Ar, dimple and intergranular fracture surfaces were observed at σ = 310 MPa. Most of the fracture surface was covered by intergranular cracking when σ = 270 MPa. In H2, the major fracture surface was dimple at σ = 310 MPa, and dimple and intergranular fracture surfaces at σ = 270 MPa. The change in the fracture surface and the change in the slope of the creep curve saggested multiple reasons that hydrogen affects creep life corresponding to creep life.

Event date： 2020.10

Language：English   Presentation type：Oral presentation (general)  

Venue：朱鷺メッセ, 新潟   Country：Japan  

Due to the recent introduction of an advanced oil-well development technology in which the drilling and installation of pipes are simultaneously done, the pipes receive a rotating and bending fatigue loading. As a result, characterization of the fatigue properties of the pipes has become necessary. Since the pipes are connected by a threaded joint, the thread is the critical part of the connected pipes in terms of fatigue strength.
The surface of the thread is coated by manganese phosphate for ease of tightening. In addition, grease is also used for the tightening. According to the result of a full-scale fatigue test(1), the coating and lubrication improved the fatigue strength of the threaded joint. The objective of this study is to gain a better understanding of the effects the manganese phosphate coating and grease lubrication have on the fatigue strength of the thread joint for oil-well pipes.
A bridge-pad type fretting fatigue test was carried out. Two kinds of contact pads with different pad lengths, Lp, were used. The material of the test piece and pad was API L80 oilfield pipe steel. The surface of the pad was coated by manganese phosphate. The grease was API modified thread compound. The contact pressures, pc, were 50 MPa. The fretting fatigue test was carried out with a stress ratio of -1 at a loading frequency of 15 Hz at 20 ℃.
At a relatively high stress amplitude, there were no significant effects by both the coating and lubricant on the fretting fatigue life. At the relatively low stress amplitude, the effect of the coating was not seen, however, the lubricant showed a remarkable effect to extend the fatigue life.

Event date： 2020.1

Language：English  

Venue：九州大学伊都キャンパス   Country：Japan  

Event date： 2020.1

Language：English  

Venue：九州大学伊都キャンパス   Country：Japan  

Event date： 2020.1

Language：English  

Venue：九州大学伊都キャンパス   Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

Effect of Hydrogen on Creep Properties of SUS304

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

Effect of Manganese Phosphate Coating on Fretting Fatigue Strength of Oil-Well Pipe Material under Grease Lubrication

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

Difference of Controlling Mechanisms of CO and O2 Inhibitory Effects to Hydrogen-Assisted Fatigue Crack Growth

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州工業大学   Country：Japan  

Effect of sort of steel on impurity gas inhibitation to hydrogen-assisted crack growth

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Hawaiian Village Hotel, Honolulu, Hawaii   Country：United States  

Hydrogen uptake into the material is an essential process to cause accelerated fatigue crack growth in gaseous hydrogen. Dissociation of hydrogen molecules into hydrogen atoms is an important elemental processes of hydrogen uptake, and it requires catalytic action of iron surface. When hydrogen contains gas impurities that inhibit the catalytic action of iron surface for the splitting of hydrogen molecules, hydrogen uptake is prevented. As a result, hydrogen-assisted fatigue crack growth is inhibited. Since affinity of the gas impurity with iron surface depends on gas species, the inhibitory effect is different depending on the sort of gas impurity. The inhibitory effect of O2 is well understood as that a predictive model is provided.

In this study, fatigue crack growth test was carried out in hydrogen gases that contains O2 or CO as a gas impurity. Then, it was found that part of the CO-inhibitory effect could be interpreted by the similar mechanism of O2-inhibitory effect and another part of the CO-inhibitory effect was different from that of O2-inhibitory effect. Therefore, the results of CO and O2 were compared to gain better understanding of the inhibitory effect achieved by the addition of gas impurities.

The material was ASTM A333 grade 6 pipe steel. The test environments are high-purity hydrogen (< 0.1 vppm CO, < 0.1 vppm O2), CO added hydrogen, O2 added hydrogen, and air. The gas pressure was 0.11 MPa in absolute pressure. The fatigue crack growth test with a CT specimen was carried out with a stress ratio of 0.1 at the loading frequency of 20 or 0.02 Hz at room temperature.

The fatigue crack growth was accelerated in the high-purity hydrogen compared to that in air. Both impurities mitigated the acceleration of the crack growth. In the case that the loading frequency was 20 Hz, the magnitude of the inhibitory effect was changed depending on the gas impurity, however, the results could be explained by the similar mechanism that the inhibitory effect is determined by the competition of the rate of iron surface creation and the rate of covering iron surface with impurity. On the other hand, in the case of that the loading frequency was 0.02 Hz, the effect of CO could not be understood by only the competition. It was found that hydrogen diffusion took an important role in the inhibitory effect of CO when the loading frequency was low.

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Sorbonne University, Paris   Country：France  

We are challenging to developing a dream steel that has both hydrogen compatibility and high strength. The approach is grain refinement of austenitic stainless steel. Our final goal is to provide the basic science that enables optimization of the cost, performance, and safety of pressurized hydrogen containment systems. Therefore, amount of rare earth elements is reduced as much as possible. The material was 16Cr-10Ni-Fe austenitic stainless steel. It was synthesized in I2CNER by a thermo-mechanical treatment invented by Takaki et al [Takaki, 1988]. The grain size was adjusted to 1 m. The yield strength of the ultra-fine grain (UFG) austenitic steel was about 600 MPa. It was almost twice higher than that of the benchmark material (commercial hydrogen compatible austenitic stainless steels, 316). In the slow strain rate testing of the hydrogen-charged UFG steel, it was found that the grain refinement was effective not only for strengthening but also for improvement of hydrogen compatibility. Fatigue tests were also carried out to characterize fatigue life, fatigue crack propagation behavior and crack initiation behavior in the presence and absence of hydrogen. The fatigue limit of the UFG steel was 2.8 times higher than that of the benchmark. There was no significant effect of hydrogen on the fatigue limit. The crack propagation rate was better than that of the benchmark steel. According to the past studies, grain refinement deteriorates crack growth behavior. Our UFG steel showed unique and excellent properties. The mechanism of the improved crack growth resistance was also clarified from the viewpoint of crack closure in conjunction with grain refinement effect. The grain boundary of the UFG steel acted as a barrier to develop plastic zone at the crack tip. As a result, crack tip opening was reduced. Finally, the reduced crack growth rate was achieved. On the other hand, crack propagation rate was significantly accelerated by hydrogen, and it resulted reduced fatigue life. The cause was microstructure change from austenite to martensite at the crack tip during crack propagation. The crack origin was a non-metallic inclusion, which was 2 m in diameter. This is also unique in the UFG steel. Our final goal of this study is to develop 800 MPa yield strength hydrogen compatible steel. It requires further study.

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Tour Zamansky, Sorbone University Campus Pierre et Marie Curie, Paris,France   Country：France  

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo International Forum, Tokyo   Country：Japan  

The objective is to gain a better understanding of the effect of hydrogen on the fatigue limit in order to ensure safety of hydrogen equipment. When the safety factor is 4, the allowable stress becomes 1/4 of the ultimate tensile stress (UTS). The design is safe for fatigue failure based on an empirical equation, σw = 1/2 UTS (σw: Fatigue limit). However, if hydrogen reduces the fatigue limit, the risk of fatigue failure may arise.
High-cycle fatigue tests were carried out in air, H2 gas and N2 gas at a loading frequency of 20 Hz. The pressure of H2 and N2 was 0.1 MPa in gauge pressure. The material was JIS SCM435 Cr-Mo steel having HV600. This material suffered from severe hydrogen embrittlement in SSRT. A smooth specimen, deep notched one and H-charged deep notched one were used. To prevent dissipation of the charged hydrogen, copper plating was made to the H-charged specimen. The H-content after 10^7 cycles was 1 mass ppm. A staircase method (statistical method) was used to determine fatigue limit.
For the smooth specimen, the fatigue limit in hydrogen was higher than that in air. In this case, hydrogen uptake was very limited, and it made tangible the effect of absence of oxygen. The experimental result that the fatigue limit in N2 was the same as that in H2 was the evidence of this consideration. There were no non-propagating cracks in the unbroken specimens at 10^7 cycles. It suggested hydrogen had no effect on crack initiation at high-cycle regime. For the notched specimen, the fatigue limit in H2 was the same as that in air. The difference from the smooth specimen was caused by the stress condition at the notch root. A cyclic plastic deformation at the notch root enhanced interaction with hydrogen. Non-propagating cracks were found at 10^7 cycles. The mechanism that fatigue limit was achieved was also different from the smooth specimen. It suggested the crack growth threshold (DKth for long crack) affected by hydrogen. When comparing the results of copper plated specimens, the hydrogen charge had no significant effect on the fatigue limit.

Event date： 2019.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：室蘭工科大学，室蘭   Country：Japan  

The Effect of Addition of Oxygen and Carbon Monoxide on Hydrogen-Assisted Fatigue Crack Growth in conjunction with Loading Frequency

Event date： 2019.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：室蘭工科大学，室蘭   Country：Japan  

Effect of Hydrogen on Low-Cycle Fatigue Properties of SUS304

Event date： 2019.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Seville   Country：Spain  

Effects of surface treatments (copper plating and manganese phosphate coating) on the fretting fatigue strength of premium threaded connection for Oil Country Tubular Goods (OCTG) was characterized via the full-scale fatigue testing. A through-wall crack was found at the middle of the contact portion of the male thread root regardless of the surface treatments. The fretting fatigue strength with the copper plating was higher than that with the manganese phosphate coating. Based on the observation of the tested thread joints, it was found that copper plating was more effective to mitigate the fretting wear between the contacting surfaces of the engaging thread.

Event date： 2019.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Seville   Country：Spain  

The demands for the downsizing and weight reduction of mechanical components are very strong in the automotive industry. At the same time, reducing the production costs is also required. Regarding the power transmission shaft joint, downsizing may lead to a reduced mechanical strength. In this context, a simple method to improve the fretting fatigue strength of a splined shaft was studied.

Event date： 2019.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本大学，熊本   Country：Japan  

The Effectiveness of CO Chemical Coating in Conjunction with the Effect of Loading Frequency on the Hydrogen -Assisted Fatigue Crack Growth

Event date： 2018.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Swissotel Le Concorde, Bangkok   Country：Thailand  

The effect of the flatness of the contact surface within the machining tolerance on the fretting fatigue strength was investigated. The results are summarized as follows:
(1) When the contact pressure was 25 MPa, the fretting fatigue strength for the 7-μm flatness was significantly lower than that for the 0.2-μm flatness because of the partial contact. It was clarified that less flatness significantly reduced the fretting fatigue strength when the contact pressure was low.
(2) When the contact pressure was 100 MPa, the effect of the flatness on the fretting fatigue strength was relatively not significant because fretting wear resolved partial contact.

Event date： 2018.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Swissotel Le Concorde, Bangkok   Country：Thailand  

Hydrogen can induce ductility loss in tensile test, acceleration of crack growth, and reduction of fracture toughness. These phenomena are collectively called hydrogen embrittlement. There are several viable mechanisms of hydrogen embrittlement such as hydrogen-enhanced localized plasticity (HELP), hydride cleavage, and hydrogen-enhanced decohesion. Particularly for the HELP mechanism, understanding of the effect of hydrogen on the plastic deformation is important. Thus, a low cycle fatigue test was carried out to gain better understanding of the effect of hydrogen on the cyclic plastic deformation. The material was JIS SUS304 austenitic stainless steel. Hydrogen was charged to the specimen by a thermal method prior to the fatigue test. The resulted hydrogen content in the materials was 100 mass ppm. According to the hydrogen diffusion rate and hydrogen charging conditions, it is presumed that the distribution of hydrogen was uniform in the specimen. Low-cycle fatigue test was carried out with a strain rate of 1.3×10-3 /s. The low-cycle fatigue life was significantly reduced by the hydrogen charge. According to the past studies, the reason was strain-induced martensite produced at the crack tip. Regarding bulk deformation properties, the peak tensile stress of the hydrogen charged specimen was higher than that of the uncharged one. There was a significant difference in the cyclic work-hardening behavior between the hydrogen-charged and uncharged specimens. The uncharged specimen showed cyclic hardening in the last stage of its fatigue life. Contrary, the hydrogen-charged one showed cyclic softening. The cause of the hardening was transformation of microstructure from austenite to strain-induced martensite due to accumulated plastic strain. The transformation of the microstructure was significantly reduced in the hydrogen-charged specimen. Therefore, suppression of the formation of strain-induced martensite due to hydrogen was the cause of the softening.

Event date： 2018.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Swissotel Le Concorde, Bangkok   Country：Thailand  

1) The fatigue limit of the smooth specimen didn’t decrease in 0.1 MPa hydrogen gas.
2) There was no non-propagating crack at surface of the unbroken smooth specimen in any environments.
3) There was a significant difference in the morphologies of the slip bands observed on the surface of the unbroken smooth specimens by the effect of hydrogen.
4) The fatigue limit of the notched specimens slightly decreased in 0.1 MPa hydrogen gas.

Event date： 2018.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Verona   Country：Italy  

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.

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Sappro, Hokkaido   Country：Japan  

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 inactivated HE. O2 prevented the HE with lower dosage than CO. Higher strength material required larger amount of impurities to prevent the HE. Reduction of hydrogen uptake was the primary consequence of the addition of the impurities, but a certain amount of hydrogen uptake took place when the HE was fully inhibited. Discussion about essential HE mechanisms for the fracture morphologies was required to interpret the effect of material strength.

Event date： 2018.5 - 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Poitiers Futuroscope   Country：France  

The fatigue properties of ultra-fine grain austenitic steel (UFG16-10), which has a 1 micro-meter 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 were compared with that of a coarse grain material with the same chemical composition (CG16-10) and two kinds of commercial steels, JIS SUS316 and JIS SUH660. The fatigue strength of the UFG16-10 was 2.8 times higher than that of the CG16-10. The effect of hydrogen on the fatigue limit of the UFG16-10 was not significant. However, the fatigue life of the UFG16-10 was reduced by hydrogen in the short life regime. In the fatigue crack growth test, the UFG16-10 showed a good crack growth resistance that was equivalent to that of the SUH660 and significantly higher 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 UFG16-10 was transformation of the microstructure at the crack tip from austenite to strain-induced martensite. This was also the cause of the reduced fatigue life of the hydrogen-charged UFG16-10.

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

Effect of material strength and species of gas impurity on inhibition of hydrogen-induced fracture by gas impurities

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

Effect of Hydrogen on Fatigue Limit and Slip Bands of High-strength Steel

Event date： 2018.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宮崎シーガイヤコンベンションセンター   Country：Japan  

A quantitative approach to evaluate fretting fatigue limit using a pre-cracked specimen

Event date： 2018.2

Language：English   Presentation type：Oral presentation (general)  

Venue：Shiiki hall, Ito campus, Kyushu University   Country：Japan  

Fracture toughness of a Cr-Mo steel was significantly reduced in hydrogen environment. Carbon monoxide (CO) was added to the hydrogen environment as an impurity in order to mitigate hydrogen embrittlement. As a result, CO showed an inhibitory effect. However, the effectiveness was different depending on the material strength.

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県青年会館（那覇）   Country：Japan  

Effect of addition of impurity to hydrogen accelerated-fatigue crack growth

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県青年会館（那覇）   Country：Japan  

Effect of material strength on the inhibition of hydrogen embrittlement by the addition of carbon monoxide to hydrogen environment

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県青年会館（那覇）   Country：Japan  

Effect of contact pressure on the fretting fatigue properties of the thread joint of oil-well pipes

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県青年会館（那覇）   Country：Japan  

Effect of Hydrogen on Tensile Strength Properties of Different Materials Welding Joint

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県青年会館（那覇）   Country：Japan  

Effect of hydrogen on cyclic deformation behavior in low-cycle fatigue

Event date： 2017.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：沖縄県青年会館（那覇）   Country：Japan  

Fatigue Limit of High-Strength Material in Hydrogen

Event date： 2017.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名城大学   Country：Japan  

Effect of hydrogen on fretting fatigue properties and the effect of impurities

Event date： 2017.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：琉球大学工学部   Country：Japan  

Short crack growth behavior of oil well pipe material

Event date： 2017.2

Language：English  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2017.2

Language：English  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2017.2

Language：English  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場   Country：Japan  

Fatigue Limit of SCM435 and XM-19 in High Pressure Hydrogen

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場   Country：Japan  

Effect of Injection Molding Conditions on Strength Properties of Short Carbon Fiber

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場   Country：Japan  

The effect of machining on the fatigue properties of ultra-fine grain austenitic stainless steel

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場   Country：Japan  

Effect of flatness of the contacting surfaces on fretting fatigue properties

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州国際会議場   Country：Japan  

Characterization of Hydrogen Embrittlement of High-Nitrogen Stainless Steel Pipe for High-Pressure Gaseous Hydrogen

Event date： 2016.11

Language：English   Presentation type：Oral presentation (general)  

Venue：InterContinental Century City,Chengdu, China   Country：China  

The fatigue strength of railway wheels is very important for the safe operations of all trains. Fatigue strength is usually evaluated using test specimens with machined and polished surfaces. However, the fatigue strength of the test specimens is not necessarily equivalent to that of the actual wheels. The main causes of the differences include surface conditions, residual stress, scale effect and so forth. This paper studied the effect of surface conditions because many types of wheels did not have smooth surfaces in the plate or in the rim. It is important to evaluate the effect of small defects on the fatigue strength of wheel steels since the actual wheels without a fine surface finish are considered to have small defects caused by coarse surface roughness. Thus, fatigue tests were conducted using round bar test specimens with smooth, notched and artificial small defect surfaces. Moreover, a unique small crack propagation test method was applied, and the crack propagation tests were conducted using plate test specimens. AAR Class-A, Class-B and Class-C wheel steels were used for these tests. The tests yielded three main results. Fatigue strength of the smooth and the notched test specimens increased with an increase in material hardness. Fatigue strength of the notched and of the small defect test specimens decreased compared to that of the smooth test specimens. The effect of material hardness did not clearly appear in the thresholds of small crack propagation, and those of the three steels were almost equivalent. The mechanism was explained based on the observation of crack growth path. Then, the fatigue limits of the notched and of the artificial small defect specimens were predicted using the Haddad equation by applying the fatigue limits of the smooth test specimens and the thresholds of small cracks. The predicted fatigue limits corresponded to the fully reversed fatigue limits obtained by the tests. Finally, the fatigue limits of the actual wheel plates were predicted by the same method to verify this method.

Event date： 2016.9 - 2017.9

Language：English  

Venue：Jackson Lake Lodge, Moran, Wyoming   Country：United States  

Fretting is a cyclic small amplitude relative slip motion between contacting surfaces of joined structures subjected to a vibration or fatigue load. Fretting fatigue is a fatigue occurring at a part where the fretting simultaneously occurs. Since fretting reduces the fatigue strength at the contacting part, fretting fatigue is one of the most important factors in the design of the contacting parts of machines and structures. In addition, hydrogen can affect fretting fatigue properties. Therefore, research studies are necessary to elucidate the mechanism of haw hydrogen changes the fretting fatigue properties. Evaluation of the fretting fatigue strength in hydrogen is also needed from an engineering point of view. For these purposes, relative slip measurements of the fretting are essentially important because the relative slip is a key factor that determines the fretting fatigue strength. However, there are some problems when measuring the relative slip during fretting fatigue in hydrogen, i.e., in terms of accuracy, size of the sensor, effect of hydrogen on the sensor stability, etc. In order to meet these challenges, we have developed a new measurement method using MEMS technology. The sensor consists of a microencoder chip and diffraction grating scale. The size of the microencoder chip is 2.8 mm square and 1.02 mm thick, and it has the high-resolution of 20 nm. Since the sensor is packed in the chip and sealed from the environment, the MEMS sensor is not affected by hydrogen. During the relative slip measurement, elastic deformation around the contacting part is not negligible because the relative slip of the fretting is at an equivalent level. Therefore, the effect of the elastic deformation was compensated by the direct measurement of the elastic deformation. As the result, the relative slip measurement during fretting fatigue in a hydrogen environment has been successfully developed. Using this MEMS sensor, we could discuss the mechanism based on the relative slip. For example, it was clarified that the relative slip during fretting fatigue in hydrogen is significantly lower than that in air. This is due to the local adhesion between the contacting surfaces produced during the fretting fatigue in hydrogen.

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

Fatigue Strength Evaluation of High-Nitrogen Stainless Steel Welds for High-Pressure Hydrogen Piping

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

The effect of machining on the fatigue properties of ultra-fine grain austenitic stainless steel

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

Mechanism of fretting fatigue of thread joint for oil well pipes

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

Mechanism of reduction in fretting fatigue strength in hydrogen by addition of ppm-level oxygen

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学工学部   Country：Japan  

Fatigue strength and fatigue life essentially involve scatter. This lecture introduced how to deal with that scatter by citing standards and past studies.

Event date： 2016.7 - 2016.8

Language：English   Presentation type：Oral presentation (general)  

Venue：National University of Singapore   Country：Singapore  

The sensing technology to measure local micro-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.

Event date： 2016.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Finatec at University of Brasilia   Country：Brazil  

In the present study, identification on the fatigue failure mode of the premium threaded connection for OCTG was conducted through the full-scale fatigue testing and the observation of tested samples by the optical microscope and scanning microscope. In high stress amplitude, the through wall crack originated by the stress concentration at the thread corner radius of the imperfect thread root of the male embodiment. In low stress amplitude, it originated from the centre on imperfect thread root of the male embodiment by the fretting fatigue. For the fretting fatigue, the fretting wear and fretting fatigue testing on test specimen were conducted in order to clarify the fretting mechanism on threaded connection.

Event date： 2016.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Finatec at University of Brasilia   Country：Brazil  

The fretting fatigue strength of austenitic stainless steels in hydrogen gas is lower than that in air. The authors clarified that the adhesion between contacting surfaces during fretting fatigue is the root cause of their reduction. In this study, to characterize the effect of hydrogen on the microstructure change at the adhered spot, a cyclic indentation test was performed using hydrogen-charged and uncharged specimens. Based on SEM observations and high-contrast SEM observations of the microstructure around the dimple produced by cyclic indentation, it was found that development of slip deformation was enhanced in the hydrogen-charged specimen.

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京理科大学   Country：Japan  

Fatigue Crack Growth Behavior of Ultra-Fine Grain Austenitic Stainless Steel

Event date： 2016.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京理科大学   Country：Japan  

Fatigue Limit of SCM435 Low-Alloy Steel in 115 MPa Hydrogen Gas

Event date： 2016.2

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学伊都キャンパス   Country：Japan  

(1) 140 MPa H2 resonant fatigue testing machine is developed for high-cycle fatigue test in high-pressure hydrogen. And then, high-cycle fatigue test in 115 MPa H2 was performed at a loading frequency of 20 Hz.
(2) The fatigue limit of the SCM435 Cr-Mo steel in 115MPa H2, which was obtained at f = 20Hz, was the same as that in air.
(3) The development of slip bands was significant in 115MPa H2, whereas it is not so in air. Hydrogen enhanced development of slip bands.
(4) The effect of hydrogen was confirmed at f = 20Hz.

Event date： 2016.2

Language：English  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2016.2

Language：English  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2016.2

Language：English  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2016.2

Language：English  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2016.2

Language：English  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ホルトホール大分   Country：Japan  

Fatigue Strength Evaluation of High-Nitrogen Stainless Steel Pipe Welds

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ホルトホール大分   Country：Japan  

従来より水素の影響を受けた材料の破壊に関する実験データが蓄積されているが，水素に助長された破壊を予測するモデルは確立されていない．そのため本研究では水素助長破壊の機構を説明する理論の一つである水素助長局所塑性変形理論（hydrogen-enhanced localized plasticity, HELP）に基づいて，水素の影響を受けた材料の変形挙動を予測する構成式を確立し，水素助長破壊の予測的モデルを構築することを目的とする．アプローチは実験とシミュレーションを合わせたものであり，本研究はその実験部分を担当するものである．ここでは材料の応力-ひずみ関係の取得とともに，塑性変形開始の明瞭な証拠としてすべり線の発生の観察を行う．すべりの解析を行うにあたり，できる限り単純なすべり系を用いることが必要であり,供試材としてはすべり系が比較的少ないFCC系の材料を用いる．また，駆動するすべり系を解析しやすい単結晶を用いる．材質は従来より水素に助長された変形の研究で使用され知見が蓄積されているニッケルを用いる．単結晶の引張では図1に示すように引張軸に対して試験片の回転や曲がりが生じるため，単純引張を実現するためにはそれらを許容できる特殊な構造の引張試験機が必要であり，本研究ではまず引張試験機の開発を行った．

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ホルトホール大分   Country：Japan  

Effect of contact pressure on fretting fatigue failure modes of oil-well pipe materials

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ホルトホール大分   Country：Japan  

Fatigue crack initiation behavior of ultra-fine grain austenitic stainless steel

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：ホルトホール大分   Country：Japan  

Application of MEMS Technology to Measurement of Relative Slip during Fretting Fatigue Test in Hydrogen

Event date： 2015.11

Language：English   Presentation type：Oral presentation (general)  

Venue：九州大学カーボンニュートラル・エネルギー国際研究所   Country：Japan  

Event date： 2015.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Yokohama Bay Sheraton Hotel & Towers   Country：Japan  

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.

Event date： 2015.9

Language：English  

Venue：Warsaw University of Technology   Country：Poland  

Fretting fatigue, which is composite phenomenon of metal fatigue and tribological action (fretting wear), is one of the most important factors in the design of mechanical component involving contact part, because fretting significantly reduces the fatigue strength of the contact part. In addition, hydrogen can cause further reduction of fretting fatigue strength [1].
The purity of hydrogen for fuel cell is provided by standard. For example, ISO specifies the purity of hydrogen for PEM fuel cell as 99.97% [2]. In this study, the effect of impurities contained in hydrogen gas on fretting fatigue properties was studied.
Figure 1 shows the change in the fretting fatigue strength of SUS304 austenitic stainless steel by the addition of water vapor or ppm-level oxygen as impurities. As shown in the figure, the fretting fatigue strength significantly reduced by the effect of impurities. Based on the XPS analysis of the fretted surface, it was found that the original oxide layer of the stainless steel was removed by the fretting in the high-purity hydrogen. However, the addition of the impurities produced an oxide layer on the fretted surface during the fretting. The production of the oxide layer increased fretting wear and it resulted the change in the geometry of the contact surface. As the result, the contact pressure at the contact edge was relieved. Until freting wear occurred, a compressive stress, which prevented crack growth, was produced in the specimen. That is, stress conditions, which crack growth is easy to occur, is produced by the addition of oxgen or water vapor.

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学工学部   Country：Japan  

Effect of Molding Conditions on Strength Properties of Short Carbon Fiber Reinforced PPS Plastic

Event date： 2015.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：神宮会館（伊勢市）   Country：Japan  

Mechanisms that reduce fretting fatigue strength in hydrogen

Event date： 2015.5

Language：Japanese  

Venue：山形大学米沢キャンパス   Country：Japan  

Effect of hydroen on microstructure change of the material at adhesion between contacting surfaces during fretting fatigue in hydrogen

Event date： 2015.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡大学工学部   Country：Japan  

Effects of Annealing and Injection Molding Conditions on Tensile Properties of Short Carbon Fiber Reinforced PPS Plastic

Event date： 2015.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡大学工学部   Country：Japan  

Effects of Annealing and Injection Molding Conditions on Tensile Properties of Short Carbon Fiber Reinforced PPS Plastic

Event date： 2015.2

Language：English  

Venue：九州大学伊都キャンパス   Country：Japan  

The fatigue properties of the ultra-fine grain austenitic steel (1mm average grain size, 16Cr-10Ni steel) were studied.

(1) The grain refinement significantly improved the fatigue strength.
(2) The effect of the hydrogen charge on the fatigue limit was not significant.
But the fatigue life in the short life region is significantly reduced by the hydrogen charge.
(3) The crack growth resistance of the UFG16-10 was remarkably good compared to that of
the commercial SUS316.
(4) The morphology of the crack of the UFG16-10 produces a lower crack growth resistance.
There was a toughening mechanism, which is caused by the ultra-fine grains.
(5) One of the possible mechanisms was the suppression of plastic deformation at the crack
tip by the ultra-fine grains and subsequent reduction in the crack opening displacement.

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学工学部   Country：Japan  

High-cycle fatigue properties of work-hardened oxygen-free cupper in high-pressure hydrogen

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学工学部   Country：Japan  

Fracture toughness of hydrogen charged low alloy steels

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学工学部   Country：Japan  

Consideration of fatigue mechanism in ultra-fine grain austenitic steel having a 1μm grain size

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学工学部   Country：Japan  

Effect of annealing on tensile properties of short carbon fiber reinforced PPS

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島大学工学部   Country：Japan  

Consideration of Effects of Minute Amounts of Oxygen and Water Vapor on Oxide Removal and Production Behavior at Fretted Surface of SUS304 in Hydrogen and Relation of Fretting Fatigue Strength

Event date： 2014.11

Language：English   Presentation type：Oral presentation (general)  

Venue：高山市民文化会館   Country：Japan  

The fatigue properties of ultra-fine grain austenitic steel (UFG), which has a 1 m 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 21 m. The effect of hydrogen charge charging 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 incompared to 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 consequence, the crack opening displacement might decrease.

Event date： 2014.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Hotel Rio Othon Palace, Rio de Janeiro   Country：Brazil  

To ensure the safety of hydrogen storage vessels in hydrogen refueling stations, it is required to carry-out a leak-before-break (LBB) assessment of the hydrogen storage cylinder in accordance to ASME BPVC 2013 Sec. VIII – Div. 3 Article KD-10. Two material properties are required: The KIH (threshold stress intensity factor for hydrogen assisted cracking) in accordance to ASTM E1681 or ISO 1111-4 (C method), and the KIC (plane strain fracture toughness), following ASTM E399 or E1820. The determination of KIH can be performed by constant displacement test or the rising force test method. However, there is still a matter of discussion which test method is more suitable for determining KIH. The aim of this work is to use the back-face strain (BFS) gage technique in order to determine the most appropriate value for KIH.

Event date： 2014.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Hotel Rio Othon Palace, Rio de Janeiro   Country：Brazil  

Although austenitic stainless steels are commonly used for gas components, they have the drawback of relatively poor proof strength. This study is aiming to acquire higher proof strength of austenitic steel without compromising performance in hydrogen through grain refinement in order to reduce cost and weight of hydrogen gas containment stainless steel components.
The material is 16Cr-10Ni austenitic steel having an average grain size of 1m. The material is prepared by thermo-mechanical treatment using reversion from strain-induced martensite to austenite, which has been established by Takaki et al [1]. Figure 1 shows the microstructure of the ultra-fine grain (UFG) austenitic steel used in this study. In the tensile test of the UFG material, clear yield point appeared by grain-refinement hardening. The yield strength of the UFG material was 632MPa.
In the fatigue test, coarse grain 16Cr-10Ni steel (CG, grain size 21m, 0.2 = 156MPa) and SUS316 (grain size 76m, 0.2 = 242MPa) were also used as reference. Thermal hydrogen charge was applied. The hydrogen content in the materials are shown with the result of the fatigue test. The fatigue test was done with a stress ratio of R = -1 at a loading frequency of f = 15Hz in air using blunt notch specimen (see Fig. 2). The fatigue strength of the CG16-10 steel was similar to that of the SUS316. The fatigue strength of the 16-10 austenitic steel was significantly improved by grain refinement. The effect of hydrogen on the fatigue strength of the UFG16-10 was not significant. The result demonstrated great potential to be high-strength hydrogen compatible material.

Event date： 2014.10

Language：English  

Venue：Hotel Rio Othon Palace, Rio de Janeiro   Country：Brazil