Kyushu University Academic Staff Educational and Research Activities Database
List of Presentations
Masanobu Kubota Last modified date:2018.03.15

Professor / Hydrogen Materials Compatibilty and Fracture (April 2014 - Current), Air Liquide Industrial Chair on Hydrogen Structural Materials and Fracture (Oct. 2010 - March 2014) / Hydrogen Materials Compatibility Division / International Institute for Carbon-Neutral Energy Research


Presentations
1. 久保田 祐信, MACADRE ARNAUD PAUL ALAIN, Hydrogen Compatibility of Ultra-Fine Grain Austenitic Stainless Steel, International Colloquium on Environmentally Preferred Advanced Generation Grid evolution global summit "HYDROGEN" (ICEPAG2017), 2017.03, 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.
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2. Short crack growth behavior of oil well pipe material.
3. 森 諒, 久保田 祐信, MACADRE ARNAUD PAUL ALAIN, The effect of machined layer on fatigue strength of ultra-fine grain austenitic stainless steel and the microstructure change due to machining, 2017 I2CNER ANNUAL SYMPOSIUM: APPLIED MATH CHALLENGES IN ENERGY & THE NEXT‐GENERATION, 2017.02.
4. 久保田 祐信, 薦田 亮介, Structural Materials used in Hydrogen at Elevated Temperature, 2017 I2CNER ANNUAL SYMPOSIUM: APPLIED MATH CHALLENGES IN ENERGY & THE NEXT‐GENERATION, 2017.02.
5. 薦田 亮介, 久保田 祐信, Jader Furtado, Fretting Fatigue in Hydrogen Containing ppm-levels of Oxygen
, 2017 I2CNER ANNUAL SYMPOSIUM: APPLIED MATH CHALLENGES IN ENERGY & THE NEXT‐GENERATION, 2017.02.
6. Fatigue Limit of SCM435 and XM-19 in High Pressure Hydrogen.
7. Characterization of Hydrogen Embrittlement of High-Nitrogen Stainless Steel Pipe for High-Pressure Gaseous Hydrogen
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8. Effect of flatness of the contacting surfaces on fretting fatigue properties.
9. The effect of machining on the fatigue properties of ultra-fine grain austenitic stainless steel.
10. Effect of Injection Molding Conditions on Strength Properties of Short Carbon Fiber.
11. 久保田 祐信, 薦田 亮介, Jader Furtado, Fretting fatigue in hydrogen and the effect of oxygen impurity, The 15th Asian Coference on Experimental Mechanics (ACEM2016), 2016.11, Fretting is a coupled problem of fatigue and frictional contact. It brings unique phenomena that enhance the hydrogen-induced degradation of fatigue strength. Therefore, the role of hydrogen in the fretting fatigue is seriously considered by both manufacturers and users of hydrogen equipment. 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.
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12. 髙﨑 大裕, 久保田 祐信, 薦田 亮介, 吉田 修一, 奥 洋介, 牧野 泰三, 杉野 正明, Effect of Contact Pressure on Fretting Fatigue Failure of Oil-Well Pipe Material
, The 15th Asian Coference on Experimental Mechanics (ACEM2016), 2016.11, Fretting fatigue is a combination of fatigue and a kind of wear. Since the fretting fatigue strength is significantly lower than plain fatigue strength, fretting fatigue is one of the most important factors in the design of components. In resent oil-well development, drilling casing technology becomes popular. As shown in Fig. 1, the thread joint between pipes might suffer from fretting fatigue. In the results of full-scale fatigue test of thread joint, there were two failure modes [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..
13. 加藤 孝憲, 牧野 泰三, 久保田 祐信, 堀川 晋之介, Effect of Small Defects on Fatigue Strength of Railway Wheel Steels, 18th International Wheelset Congress (18th IWC), 2016.11, 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..
14. 薦田 亮介, Nobutomo Morita, Fumiya Nakashima, 久保田 祐信, 澤田 廉士, Development of new measurement method applying MEMS technology for relative slip range during fretting fatigue test in hydrogen , 2016 International Hydrogen Conference, 2016.09, 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..
15. 久保田 祐信, Akihide Nagao, University of Illinois at Urbana Champaign, Harvard University, University of Illinois at Urbana Champaign, University of Thessaly, Sandia National Laboratories, Livermore, SOFRONIS PETROS, Constitutive equations of hydrogen-enhanced plasticity for quantitative understanding of the mechanisms of hydrogen-assisted fracture, 2016 International Hydrogen Conference, 2016.09, 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.
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16. Fatigue Strength Evaluation of High-Nitrogen Stainless Steel Welds for High-Pressure Hydrogen Piping
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17. Mechanism of reduction in fretting fatigue strength in hydrogen by addition of ppm-level oxygen.
18. 久保田 祐信, 薦田 亮介, Jader Furtado, The effect of oxygen impurities on fretting fatigue of austenitic stainless steel in hydrogen gas, 2016 International Hydrogen Conference, 2016.09, 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..
19. Mechanism of fretting fatigue of thread joint for oil well pipes.
20. The effect of machining on the fatigue properties of ultra-fine grain austenitic stainless steel.
21. Fatigue strength and fatigue life essentially involve scatter. This lecture introduced how to deal with that scatter by citing standards and past studies..
22. Nobutomo Morita, 薦田 亮介, Fumiya Nakashima, 久保田 祐信, Eiji Higurashi, Renshi Sawada, Evaluation of Local Relative Slip in a narrow space in Hydrogen Gas Using MEMS Optical Encoder, 2016 International Conference on Optical MEMS and Nanophotonics (IEEE OMN2016), 2016.08, 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..
23. 奥 洋介, 杉野 正明, 牧野 泰三, 久保田 祐信, 髙﨑 大裕, Fatigue evaluation on premium threaded connections for OCTG, 8th International Symposium on Fretting Fatigue (ISFF8), 2016.04, 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. .
24. 薦田 亮介, 久保田 祐信, Characterization of the effect of hydrogen on the microstructure change at the adhered spot during fretting fatigue, 8th International Symposium on Fretting Fatigue (ISFF8), 2016.04, 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. .
25. 久保田 祐信, 片岡 俊介, 近藤 良之, A quantitative approach to evaluate fretting fatigue limit using a pre-cracked specimen, 8th International Symposium on Fretting Fatigue (ISFF8), 2016.04, 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..
26. Fatigue Crack Growth Behavior of Ultra-Fine Grain Austenitic Stainless Steel.
27. Fatigue Limit of SCM435 Low-Alloy Steel in 115 MPa Hydrogen Gas.
28. 久保田 祐信, Matsuoka Saburo, 薦田 亮介, Fatigue Limit in High-Pressure Hydrogen Gas, Joint HYDROGENIUS and I2CNER International Wprkshop on Hydrogen -Materials Interactions 2016, 2016.02, (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. .
29. 薦田 亮介, Jader Furtado, 久保田 祐信, Fretting Fatigue in Hydrogen Gas and the Effect of Impurities, I2CNER Annual Symposium 2016 Computational Solutions to Fundamental Problems in Carbon-Neutral Energy Research, 2016.02.
30. 森 功一, 久保田 祐信, MACADRE ARNAUD PAUL ALAIN, Fatigue Properties of Ultra-Fine Grain Austenitic Stainless Steel and the Effect of Hydrogen
, I2CNER Annual Symposium 2016 Computational Solutions to Fundamental Problems in Carbon-Neutral Energy Research, 2016.02.
31. 久保田 祐信, 薦田 亮介, Matsuoka Saburo, High-Cycle Fatigue Properties in High-Pressure Hydrogen Gas
, I2CNER Annual Symposium 2016 Computational Solutions to Fundamental Problems in Carbon-Neutral Energy Research, 2016.02.
32. 久保田 祐信, 長尾 彰英, May L Martin, N Vasios, Mohsen Dadfarnia, Nilolaos Aravas, SOFRONIS PETROS, Brian Somerday, Single Crystal Project, I2CNER Annual Symposium 2016 Computational Solutions to Fundamental Problems in Carbon-Neutral Energy Research, 2016.02.
33. 山本 侑生, 松本 拓哉, Toshihiro Tsuchiyama, 久保田 祐信, Development of weld joint for XM-19 high-pressure hydrogen tubing
, I2CNER Annual Symposium 2016 Computational Solutions to Fundamental Problems in Carbon-Neutral Energy Research, 2016.02.
34. Fatigue Strength Evaluation of High-Nitrogen Stainless Steel Pipe Welds.
35. Application of MEMS Technology to Measurement of Relative Slip during Fretting Fatigue Test in Hydrogen.
36. Fatigue crack initiation behavior of ultra-fine grain austenitic stainless steel.
37. Effect of contact pressure on fretting fatigue failure modes of oil-well pipe materials.
38. 薦田 亮介, 久保田 祐信, Fretting fatigue properties in hydrogen contacting ppm-levels of oxygen, I2CNER Institute Interest Seminar, 2015.11.
39. 松本 拓哉, 久保田 祐信, 松岡 三郎, Patrick Ginet, Jader Furtado, Francois Barbier, THRESHOLD STRESS INTENSITY FACTOR FOR HYDROGEN-ASSISTED CRACKING OF CR-MO STEEL USED AS STATIONARY STORAGE BUFFER OF A HYDROGEN REFUELING STATION, International Conference on Hydrogen Safety (ICHS2015), 2015.10, In order to determine appropriate value for threshold stress intensity factor for hydrogen-assisted cracking, KIH, constant-displacement and rising-load tests were conducted in high-pressure hydrogen gas for JIS-SCM435 low alloy steel (Cr-Mo steel) used as stationary storage buffer of a hydrogen refuelling station with 0.2 % proof strength and ultimate tensile strength equal to 772 MPa and 948 MPa respectively. Thresholds for crack arrest under constant displacement and for crack initiation under rising load were identified. The crack arrest threshold under constant displacement was 44.3 MPa·m1/2 to 44.5 MPa·m1/2 when small-scale yielding and plane-strain criteria were satisfied and the crack initiation threshold under rising load was 33.1 MPa·m1/2 to 41.1 MPa·m1/2 in 115 MPa hydrogen gas. The crack arrest threshold was roughly equivalent to the crack initiation threshold although the crack initiation threshold showed slightly more conservative values. It was considered that both test methods could be suitable to determine appropriate value for KIH for this material..
40. 久保田 祐信, 森 功一, MACADRE ARNAUD PAUL ALAIN, Study on Hydrogen Compatibility in Fatigue of Ultra-Fine Grain Austenitic Stainless Steel, European Congress and Exhibition on Advanced Mterials and Processes 20415 (EUROMAT 2015), 2015.09, 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..
41. 久保田 祐信, 薦田 亮介, Jader Furtado, Fretting Fatigue Properties in Hydrogen Containing Impurities, European Congress and Exhibition on Advanced Mterials and Processes 20415 (EUROMAT 2015), 2015.09, 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..
42. Effect of Molding Conditions on Strength Properties of Short Carbon Fiber Reinforced PPS Plastic.
43. Mechanisms that reduce fretting fatigue strength in hydrogen.
44. Effect of hydroen on microstructure change of the material at adhesion between contacting surfaces during fretting fatigue in hydrogen.
45. Effects of Annealing and Injection Molding Conditions on Tensile Properties of Short Carbon Fiber Reinforced PPS Plastic
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46. Effects of Annealing and Injection Molding Conditions on Tensile Properties of Short Carbon Fiber Reinforced PPS Plastic.
47. 久保田 祐信, MACADRE ARNAUD PAUL ALAIN, 森 功一, Fatigue Properties of Ultra-Fine Grain Austenitic Stainless Steel and the Effect of Hydrogen
, Joint HYDROGENIUS and I2CNER International Wprkshop on Hydrogen -Materials Interactions 2015, 2015.02, 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.
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48. High-cycle fatigue properties of work-hardened oxygen-free cupper in high-pressure hydrogen.
49. 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.
50. Effect of annealing on tensile properties of short carbon fiber reinforced PPS.
51. Consideration of fatigue mechanism in ultra-fine grain austenitic steel having a 1μm grain size
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52. Fracture toughness of hydrogen charged low alloy steels.
53. 森 功一, 久保田 祐信, MACADRE ARNAUD PAUL ALAIN, Fatigue properties of ultra-fine grain austenitic stainless steel and effect of hydrogen, Third Japan - China joint symposium on fatigue, 2014.11, 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..
54. 松本 拓哉, Patrick Ginet, 久保田 祐信, Matsuoka Saburo, Jader Furtado, Francois Barbier, Use of Back Face Strain Gage Technique to Obtain Crack Arrest Threshold Stress Intensity Factor of Cr-Mo Steel used as Stationary Storage Buffer of a H2 Refueling Station, International Conference on Hydrogen Storage, Embrittlement and Applications (HySEA2014), 2014.10, 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..
55. 久保田 祐信, Jader Furtado, 薦田 亮介, Effect of Addition of Oxygen and Water Vapor on Fretting Fatigue Properties in Hydrogen
, International Conference on Hydrogen Storage, Embrittlement and Applications (HySEA2014), 2014.10, Fretting fatigue, which is composite phenomenon of friction and fatigue, is one of major concerns in the design of components. Since hydrogen can influence both friction and fatigue, fretting fatigue in hydrogen equipment is seriously worried by industries. When considering service conditions of hydrogen equipment, hydrogen can contain some amount of impurities. For example, the purity of hydrogen for PEM fuel cell is designated by ISO standard as 99.99% [1]. Such impurities may affect fretting fatigue properties. Therefore the fretting fatigue in hydrogen containing impurities was studied. In this study, very small amount of oxygen was mixed to hydrogen. In addition, humidified hydrogen was also used. Prior to fretting fatigue test, control method of the oxygen level in hydrogen was established (Fig. 1). During the test, the gases were kept flowing at a flow rate of 0.2ml/min.
Figure 2 shows the results of the fretting fatigue test of JIS SUS304 austenitic stainless steel. The addition of oxygen significantly reduced the fretting fatigue strength in hydrogen (■,◆,○,▽) compared with that in vacuum (◎). The fretting fatigue strength in the oxygen-hydrogen mixture was different depending on the oxygen level. The humidification of hydrogen also significantly reduced the fretting fatigue strength (■,▲). Adhesion between contacting surfaces is key factor to understand the fretting fatigue in hydrogen [2]. The addition of oxygen or humidity changed adhesion properties because of production of oxidized fretting wear particles. This is one of the possible reasons for the change of the fretting fatigue strength.
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56. 久保田 祐信, 森 功一, MACADRE ARNAUD PAUL ALAIN, Fatigue Properties of Ultra-Fine Grain Austenitic Steel and Evaluation of the Effect of Hydrogen, International Conference on Hydrogen Storage, Embrittlement and Applications (HySEA2014), 2014.10, 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..
57. 森 功一, 久保田 祐信, MACADRE ARNAUD PAUL ALAIN, Fatigue properties of ultra-fine grain austenitic stainless steel and the effect of hydrogen, The seventh Kyushu University - KAIST joint workshop on frontier in mechnics engineering, 2014.09, In recent years, use of hydrogen energy is promoting in helping to solve the energy and global climate change problems. But it is necessary to optimize the cost and safety of hydrogen energy system in order to accelerate deployment. One of the possible ways is development of high strength steel without compromising performance in hydrogen. The objective of this study is to characterize fatigue properties of ultra-fine grain austenitic steel. In addition, the effect of hydrogen is also studied. The material was ultra-fine grain 16Cr-10Ni steel whose grain size was 1m. As a reference, coarse grain 16Cr-10Ni steel, SUS316 and SUH660 were used. The grain size was 21m, 76m and 10m. The fatigue test of the hydrogen-charged and uncharged materials was carried out with a stress ratio of -1 at a frequency of 15Hz. The environment was air and the temperature is ambient. The fatigue limit of the ultra-fine grain steel was significantly improved. The crack growth resistance of the ultra-fine grain steel was also remarkably improved. Furthermore, the fatigue strength and crack growth rate were not significantly influenced by hydrogen. The crack path of the ultra-fine grain is very smooth, whereas that of the SUS316 and SUH660 was meandering. There is a big difference of the development of slip bands between the ultra-fine grain and other materials. It may suggests that there is an inherent mechanism improving fatigue properties resulted from ultra-fine grain..
58. 薦田 亮介, 吉開 巨都, 久保田 祐信, Jader Furtado, Effect of internal hydrogen on fretting fatigue strength of austenitic stainless steels and consideration on interaction of internal and environmental hydrogen , The seventh Kyushu University - KAIST joint workshop on frontier in mechnics engineering, 2014.09, Fretting fatigue, which is composite phenomenon of friction and fatigue, is one of major concerns in the design of components. It is well-known that hydrogen degrades materials strength, and friction behavior changes depending on environment. Therefore, the companies producing hydrogen equipment seriously worry about fretting fatigue in hydrogen. The authors have reported significant reduction in fretting fatigue strength of austenitic stainless steels due to environmental hydrogen. When considering long-term operation of hydrogen equipment, the research on the effects of absorbed hydrogen is also necessary. In this study, fretting fatigue strength of hydrogen-charged austenitic stainless steels was studied. In addition, interaction of internal hydrogen and environmental hydrogen was also studied. The internal hydrogen reduced the fretting fatigue strength. The reduction in the fretting fatigue strength became more significant with increase in hydrogen content. 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 environmental hydrogen synergistically worked to reduce the fretting fatigue strength of the austenitic stainless steels. The one of the reasons for this reduction in fretting fatigue strength is that internal and environmental hydrogen assist fretting fatigue crack initiation..
59. 久保田 祐信, 堀川 晋之介, 加藤 孝憲, 牧野 泰三, Small crack propagation properties of three railroad wheel materials, The seventh Kyushu University - KAIST joint workshop on frontier in mechnics engineering, 2014.09, Small crack effect that small crack has faster crack growth rate and lower crack growth threshold than long crack is one of the most important factors in design. Railroad wheels are typical machine component suffering from fatigue. In this research, the small crack propagation properties of three railroad wheel materials were investigated. The materials were sampled from real railroad wheels, which were made of Class A, B, and C medium carbon wheel steels designated by AAR M107 Standard. The mechanical properties and ferrite fraction were different between materials. Pre-crack specimens in which the pre-crack length was 50m and 170m were prepared. The crack growth test was done under cyclic bending moment with a stress ratio of zero. The crack length and crack closure behavior were measured by unloading elastic compliance method. The results showed that there was no significant difference in the growth rate of small crack between the materials. The threshold stress intensity factor for crack growth was also almost the same for the materials. To clarify the reason why there was no significant difference in crack growth behavior despite the difference of microstructure and mechanical properties, crack path and local hardness of pearlite grains were investigated. It was found that the crack mostly passed through pearlite grains, and the hardness of pearlite grain has small difference between three materials. Therefore, it can be presumed that the crack growth behavior of the materials was dominated by the properties of pearlite grains, and it resulted the similar crack growth behavior..
60. Effects of hardness and loading rate on fracture toughness of low alloy steels under continuous hydrogen charging
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61. Effects of hardness and loading rate on fracture toughness of low alloy steels under continuous hydrogen charging.
62. 久保田 祐信, 薦田 亮介, Jader Furtado, Basic Study on The Effect of Hydrogen on Fretting Fatigue, Society of Tribologists and Lubrication Engineers (STLE), 2014 Annual Meeting at Disney Contemporary Resort, 2014.05, 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.
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63. Fretting fatigue property in hydrogen including oxygen or water vapor.
64. Fatigue properties of ultra-fine grain austenitic stailness steel and the effect of hydrogen.
65. Factors affect fretting fatigue propertoes in hydrogn.
66. Effects of Ni Content and Hardness on the Fracture Toughness of Low Alloy Steels in the Presence of Hydrogen.
67. Fatigue properties of ultra fine grain austenitic stainless steel and effect of hydrogen.
68. Short crack growth behavior of railway wheel and axle materials.
69. The effect of impurities contained in hydrogen gas on fretting fatigue properties.
70. Discussion on contribution of adhesion to the reduction in fretting fatigue strength.
71. 久保田 祐信, 河上 紘大, High-cycle fatigue properties of carbon steel and work-hardened oxygen free copper in high pressure hydrogen, 11th International Fatigue Congress (Fatigue 2014), 2014.03, Commercialization of fuel cell vehicle (FCV) is scheduled for in 2015. In anticipation of the sales of FCV, construction of hydrogen stations is in progress. However, there are technical challenges to ensure safety at low cost. In this study, high-cycle fatigue properties in hydrogen, especially, the development of slip bands and crack initiation, were studied. The materials were 0.35% carbon steel and work-hardened oxygen free copper (OFC). The former is BCC material and the latter is FCC one. The hydrogen pressure was 10MPa. The fatigue limit of the carbon steel was slightly reduced in hydrogen. Commonly the fatigue limit of carbon steel is clearly shown by the horizontal part of the S-N curve. In hydrogen, there was a trend that the horizontal part of the S-N curve disappeared. The fatigue strength at 10^7 cycles of the OFC was higher in hydrogen than in air. The fatigue life of the OFC is extended in hydrogen. One of the causes was the delay of crack initiation and early propagation of crack. In this sense, hydrogen assisted fracture didn’t occur in the work-hardened OFC., However, the morphology of the slip bands in hydrogen was distinctively different from that in air. The sSlip bands in air wasbands in air were poorly developed, because there is almost no mobile dislocations due to work hardening. On the other hand, in hydrogen, extensive development of the slip band was found. It is presumed that hydrogen enhanced localized plastic deformation took a role to explain this phenomenon. .
72. 薦田 亮介, 久保田 祐信, Jader Furtado, Reduction in fretting fatigue strength of austenitic stainless steels due to internal hydrogen , 11th International Fatigue Congress (Fatigue 2014) , 2014.03, Fretting fatigue is one of the major factors in the design of mechanical components, because fretting fatigue strength is significantly lower than plain fatigue strength. The authors have reported a significant reduction inthein the fretting fatigue strength of austenitic stainless steels due to gaseous hydrogen. The mechanism that the fretting fatigue strength is reduced by hydrogen gas is adhesion between fretted surfaces and following crack nucleation.Thenucleation. The crack initiation limit in hydrogen gas is significantly lower than that in air. When considering long-term use of hydrogen equipment, it is necessary to consider not only the effect of gaseous hydrogen but also the effect of hydrogen diffusion into the material. Therefore,inTherefore, in this study, the effect of internal hydrogen on the fretting fatigue strength of austenitic stainless steels was studied in a well controlled hydrogen atmosphere as impurities in hydrogen can influence the phenomenon. For this purpose, hydrogen charged specimen was prepared. The internal hydrogen reduced fretting fatigue strength of austenitic stainless steels. In the case that the hydrogen-charged specimen was tested in hydrogengashydrogen gas, the reduction in the fretting fatigue strength was most significant. Gaseous hydrogen and internal hydrogen have an impact on the fretting fatigue strength independently and also synergistically. The hydrogen content in the material also affects the fretting fatigue strength.Increasestrength. Increase in hydrogen content causes more reduction in the fretting fatigue strength. The cause of the reduction in the fretting fatigue strength by the internal hydrogen is that internal hydrogen assists crack initiation under fretting fatigue condition..
73. 久保田 祐信, Jader Furtado, 薦田 亮介, 吉開 巨都, Fretting fatigue properties under the effect of hydrogen and the mechanisms that cause the reduction in fretting fatigue strength, Joint HYDROGENIUS & I²CNER International Workshop on Hydrogen-Materials Interactions, 2014.01, 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.
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74. 久保田 祐信, High-cycle fatigue properties of work-hardened copper in 10MPa hydrogen gas, Joint HYDROGENIUS & I²CNER International Workshop on Hydrogen-Materials Interactions, 2014.01, 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.
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75. Impact statement technique of the mean stress at the time of the fatigue strength design of the short fibers CFRP product.
76. Effect of internal hydrogen on fretting fatigue strength of austenitic stainless steels.
77. Fatigue properties of ultra-fine grain austenitic stainless steel and effect of hydrogen.
78. Short-crack growth behavior of railway wheel materials.
79. Effect of Displacement Velocity on Elastic Plastic Fracture Toughness of SM490B Carbon Steel Plate in 0.7 MPa Hydrogen Gas.
80. Crack Arrest Threshold Stress Intensity Factor of SCM435 Steel for a Storage Cylinder of a 35 MPa Hydrogen Refueling Station in High-Pressure Hydrogen Gas.
81. Fatigue properties of ultra-fine grain austenitic stainless steel and effect of hydrogen.
82. Concerning fretting fatigue, examples of failure accident, design method, counter measures, history, cutting-edge research and so on were introduced..
83. Study on rapid fracture of large hydrogen buffers for hydrogen stations by hydrogen embrittlement and its prevention.
84. Jader Furtado, 薦田亮介, 久保田 祐信, Fretting fatigue properties under the effect of hydrogen and the mechanisms that cause the reduction in fretting fatigue strength, 13th International Conference on Fracture (ICF-13), 2013.06, 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..
85. Fundamental Mechanism Causing Reduction in Fretting Fatigue Strength of SUS304.
86. 宮澤金敬, 三輪昌人, 近藤 良之, 久保田 祐信, DEVELOPMENT OF THE HYBRID JOINT AND TORSIONAL FRETTING FATIGUE STRENGTH IMPROVEMENT IN THE POWER TRANSMISSION SHAFT, Seventh International Symposium on Fretting Fatigue, 2013.04, 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..
87. 久保田 祐信, 薦田亮介, 足立裕太郎, 近藤 良之, Jader Furtado, EFFECT OF HYDROGEN AND IMPURITIES ON FRETTING FATIGUE PROPERTIES
, Seventh International Symposium on Fretting Fatigue, 2013.04, 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..
88. 薦田亮介, 久保田 祐信, 近藤 良之, Jader Furtado, THE MECHANISM CAUSING REDUCTION IN FRETTING FATIGUE STRENGTH DUE TO HYDROGEN, Seventh International Symposium on Fretting Fatigue, 2013.04, 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..
89. Effects of Notch Root Radius, Stress Ratio and Material Hardness on Fatigue Crack Growth Threshold for a Short Crack at Deep Notch Root
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90. Effects of Notch Root Radius, Stress Ratio and Material Hardness on Fatigue Crack Growth Threshold for a Short Crack at Deep Notch Root
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91. Short crack growth behavior of railway wheel materials.
92. Improvement of the Fretting Fatigue Strength of the Small Diameter Power-Transmitting Shaft by Hybrid Joint
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93. Effect of hydrogen on fatigue and fretting fatigue of oxygen-free copper.
94. The Effect of Small Amount of Oxygen on Fretting Fatigue Strength of Austenitic Stainless Steel in Hydrogen Gas.
95. 足立裕太郎, 久保田 祐信, 近藤 良之, Jader Furtado, Effect of Hydrogen on Fatigue Strength of Mechanical Joint, Kyushu University-KAIST Joint Seminar 2010, 2012.09, the effect of hydrogen on fretting fatigue strength of SUS304 and mechanisms were investigated. In hydrogen, fretting damaging mechanism was changed from oxidation dominant process to adhesion dominant process. Local adhesion between contacting surface produced many small cracks due to severe stress concentration in the vicinity of the adhered spot. On the other hand, the formation of such small cracks was affected by hydrogen. Critical maximum shear stress to crack initiation was significantly lower in hydrogen than in air.
When oxygen was mixed to the hydrogen, the fretting fatigue strength was increased. Addition of oxygen mitigated the effect of hydrogen on fretting fatigue strength. The friction coefficient in the oxygen-mixed hydrogen was lower than that in hydrogen. This indicated adhesion was mitigated. And crack initiation limit in the oxygen-mixed hydrogen was equivalent to that in air.
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96. 青木達郎, 池宮秀也, 久保田 祐信, 近藤 良之, EFFECT OF HYDROGEN ON FRACTURE TOUGHNESS OF LOW ALLOY STEELS
, 2012 Hydrogen Conferencce, 2012.09, 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. .
97. 久保田 祐信, 足立裕太郎, 白石悠貴, 薦田亮介, Jader Furtado, 近藤 良之, EFFECT OF HYDROGEN AND ADDITION OF OXYGEN ON FRETTING FATIGUE PROPERTIES
, 2012 Hydrogen Conferencce, 2012.09, The fretting fatigue strength of SUS304 is more significantly reduced in hydrogen as compared to air. One of the causes is adhesion between the contacting surfaces and formation of many small cracks. In the adhesion mimicked fatigue test, hydrogen participates to 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 is reduced in this mixture as compared to pure hydrogen. The critical maximum shear stress range to crack initiation was higher in the oxygen-hydrogen mixture than in pure hydrogen. These are the possible reasons for the increase in the fretting fatigue strength in the oxygen-hydrogen mixture. .
98. Quantitative understanding on the effect of contact pad shape on fretting fatigue strength using pre-cracked specimen
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99. 瀬尾明光, 久保田 祐信, 近藤 良之, Effects of Notch Root Radius and Stress Ratio on the Fatigue Crack Propagation Threshold for the Short Crack at the Notch Root
, 19th European Conference on Fracture (ECF-19), 2012.08, The crack growth threshold, Kth, for the short crack at the root of a long notch including the effects of notch root radius,  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 Kth with the change in was dependent on R. Under R = -1, there was a reduction in Kth when the notch root radius was greater than 0.5mm. On the other hand, for R = 0 and high R, Kth was almost constant regardless of . Although Kth was different depending on the stress ratio and notch root radius, the effective crack growth threshold (Keff)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 Kth 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..
100. 久保田 祐信, 白石悠貴, 薦田亮介, 近藤 良之, Considering the Mechanisms Causing Reduction of Fretting Fatigue Strength by Hydrogen
, 19th European Conference on Fracture (ECF-19), 2012.08, The fretting fatigue test of austenitic stainless steels, JIS SUS304 and SUS316, was carried out in 0.12MPa hydrogen. The fretting fatigue strength of both materials was reduced by the hydrogen. One of the causes was adhesion between the fretting surfaces which was predominant in hydrogen. Two types of specimens, which had a surface roughness of Ra = 0.420m and 0.008m, were prepared to examine the role of adhesion to reduce the fretting fatigue strength. 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. The fretting fatigue strength decreased when adhesion occurred. Thus, it can be presumed that adhesion resulted in the reduction of the fretting fatigue strength. Strain-induced martensite was found in the region of the adhered part. It can be presumed that severe cyclic strain occurred at the adhered position. .
101. Fatigue Crack Propagation Threshold for the Short Crack at Notch Root.
102. Effects of weld defect and hydrogen on high-cycle fatigue strength of rolled steels for welded structure SM400A welded
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103. High-cycle fatigue properties of S35C carbon steel in 10 MPa hydrogen gas.
104. Study on the Mechanism Causing Redaction of Fretting Fatigue Strength due to Hydrogen Gas.
105. The Effect of Impurities Containing Hydrogen Gas on Fretting Fatigue Strength of Austenitic Stainless Steels
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106. Role of adhesion to cause reduction of fretting fatigue strength in hydrogen gas.
107. Effect of contact pad shape on growth of short crack in fretting fatigue.
108. Development of high fatigue strength splined shaft for car air conditioning compressor
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109. Report on progress of development of HYDROBLOCKER.
110. Damage characterization in high-pressure hydrogen valve.
111. 水素ガス中フレッティング疲労の疲労限度低下メカニズムにおける接触面間の凝着の寄与の解明
Elucidating the role of adhesion in the reduced fretting fatigue strength in hydrogen.
112. Effect of Hydrogen on Fretting Fatigue in SUS316 Austenitic Stainless Steel.
113. A study on the damage caused by repetitive open-close movement in a high-pressure hydrogen gas valve.
114. 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
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115. Effects of Notch Root Radius and Stress Ratio on the Behavior of Short Crack at Notch Root.
116. Effect of 10MPa Hydrogen gas environment on high-cycle fatigue properties of carbon steels.
117. "Effect of contact pressure on growth of small crack under fretting fatigue conditions" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University.
118. "High-cycle fatigue properties of carbon steels in 10 MPa hydrogen gas" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University.
119. "Effect of Multiple Overloads and Hydrogen on High-Cycle Fatigue Strength of Notched Component of Low Alloy Steel" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University.
120. "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.
121. "Role of adhesion to cause reduction of fretting fatigue strength in hydrogen gas" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University.
122. "The Effect of Impurities Containing Hydrogen Gas on Fretting Fatigue Strength of Austenitic Stainless Steels" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University.
123. "Study on the mechanism causing reduction of fretting fatigue strength due to hydrogen gas" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University.
124. "High-cycle fatigue properties of S35C carbon steel in 10 MPa hydrogen gas" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University.
125. "Effects of weld defect and hydrogen on high-cycle fatigue strength of rolled steels for welded structure SM400A welded" presented at JSME Kyushu branch annual technical meeting 2011 took place in Ito campus, Kyushu University.
126. "Development of high fatigue strength splined shaft forcar air conditioning compressor" presented at the 43th graduation study workshop organized by JSME Kyushu Student Council. .
127. "Effect of contact pad shape on growth of short crack in fretting fatigue" presented at the 43th graduation study workshop organized by JSME Kyushu Student Council. .
128. "Improvement of fatigue strength of splined shaft used for car air conditioning compressor" presented at the 42th graduation study workshop organized by JSME Kyushu Student Council. .
129. "Behavior of short crack at notch root" presented at the 42th graduation study workshop organized by JSME Kyushu Student Council. This presentation won a prize for good presentation..
130. "Behavior of hydrogen enhanced fatigue crack propagation under long-term varying stress" presented at the 42th graduation study workshop organized by JSME Kyushu Student Council.
131. "Effect of contact conditions on growth of small crack in fretting fatigue" presented at the 42th graduation study workshop organized by JSME Kyushu Student Council.
132. "Study on conditions causing leakage in valve for high-pressure hydrogen gas" presented at the 42th graduation study workshop organized by JSME Kyushu Student Council.
133. Development of novel metal sealing for ultra-high pressure hydrogen gas.
134. Report on "Reserch committee for construction of modeling, analyzing, evaluation CAE system on joint structures".
135. Effectiveness of combination of press-fit for improvement of fatigue strength of splined shaft.
136. Effects of small defect and hydrogen on fatigue strength of weld-jointed tube.
137. Effect of Hydrogen on Fretting Fatigue in Austenitic Stainless Steels.
138. Effect sof heat treatment on the hydrogen enhanced crack propagation of low carbon steel (S25C).
139. Effect of hydrogen on fatigue behavior of stainless steels under two-step multiple variable stresses.
140. Experiences of study on fretting fatigue and future plot .
141. Improvement of Fretting Fatigue Strength by Hybrid Joint.
142. Effect of loading rate and tempering temperature on fracture toughness of hydrogen charged low alloy steel.
143. Effect of pre-crack length and notch root radius on propagation of small crack existing notch root near thershold .
144. Effect of absorbed hydrogen on fretting fatigue strength.
145. Effect of Multiple Overloading and Hydrogen on Fatigue Strength of Notched Component.
146. Effect of Absorbed Hydrogen, Environment and Stress Ratio on Short Fatigue Crack Propagation
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147. Influence of Hydrogen and Loading Rate on Fracture Toughness of Low Alloy Steel.
148. Effect of Hydrogen on Fatigue Behavior of Stainless Steels under Two-step Multiple Variable Stress .
149. Torsional fretting fatigue properties of splined shafts.
150. Fretting fatigue strength of SUS304 containing high concentration hydrogen in hydrogen gas.
151. Fatigue properties of weld joint for high pressure hydrogen gas tubing.
152. Behavior of short crack at notch root.
153. Mechanism of Reduction of Fretting Fatigue Limit in Hydrogen Gas in SUS304.
154. Mechanism of redution of fretting fatigue strengh by hydrogen gas and effect of hydrogen concentration.
155. Optimization of Shape of Stress-relief Groove for Improvement of Fretting Fatigue Strength.
156. Effect of Hydrogen on the Reduction of Fatigue Strength by Multiple Overloading.
157. Crack Propagation Behavior of SCM440H Low Alloy Steel Enhanced by Hydrogen under Long-term Varying Load and Static Load.
158. Effect of hydrogen and improvemnton of fatigue strength of work-hardened SUS316L.
159. Fretting fatigue strength of stainless steels containing high concentrations of hydrogen.
160. Study on Fatigue Design Criterion for the Components in Hydrogen Utilization Machines Considering the Multiple Overload Produced by Earthquakes
.
161. Mechanism for the reduction of fretting fatigue strength of stainless steel in hydrogen gas.
162. Effect of stress relief groove on fretting fatigue strength and index for the selection of optimal groove shape.
163. Contact mechanics and evaluation of fretting fatigue strength.
164. Investigation of critical crack size that causes retardation by single overload.
165. Effect of hydrogen on fretting fatigue strength.
166. Reduction of fatigue strength due to hydrogen and its improvement in work-hardened small diameter tube of SUS316L.
167. Effect of Hydrogen on High-Cycle Fatigue Strength after Multiple Overloads.
168. Mechanism of Reduction of Fretting Fatigue Limit in Hydrogen Gas Environmet.
169. Fretting fatigue strength of stainless steels with high hydrogen concentration.
170. Effect of Hydrogen on Propagation and Closure Behavior of Short Crack in Low Alloy Steel.
171. Effect of Notch Shape and Absorbed Hydrogen on the Fatigue Fracture below Fatigue Limit
.
172. Single Overload Effect in Short Crack.
173. Fatigue Strength Reduction of Notched Component in Hydrogen Gas after Multiple Overloading.
174. Fretting fatigue strength of stainless steels containing high concentration of hydrogen.
175. Single Overload Effect in Short Crack
.
176. Fatigue Strength of Notched Specimen in Hydrogen Gas after Overload.
177. An Approach to understand the Mechanism of Fatigue Strength Reduction caused by Absorbed Hydrogen
.
178. Fretting fatigue strength on high pressurized hydrogen gas exposed specimen.
179. Prevention of reduction of fretting fatigue strength in hydrogen gas environment by DLC coating and nitriding.
180. Effect of Hydrogen on the crack closurebehabior of Short Crack near Threshold Region.
181. Fretting Fatigue Failure in Localized Contact Condition.
182. Contact Mechanics and Evaluation of Fretting Fatigue Strength .
183. Observations of Initiation and Propagation of Crack and Wear under Fretting Condition in Hydrogen Gas Environment.
184. Effect of Hydrogen on Small Fatigue Crack Propagation Behavior near Threshold Region of A286 Alloy
.
185. The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines
.
186. Fretting and Fatigue.
187. Effect of Hydrogen Gas Environment on Fretting Fatigue Strength in Long-Life Region.
188. Evaluation of Fretting Fatigue Strength and Fatigue Design Method.
189. Small-notched Fatigue Under Two Step Loading Below Fatigue Limit.
190. The effect of hydrogen gas environment on fretting fatigue strength of materials used for hydrogen utilization machines
.
191. Fretting and Fatigue
Masanobu Kubota.
192. Fretting fatigue and Design Method
Masanobu Kubota.
193. Effect of Hydrogen Gas Environment on Fretting Fatigue Strength in Long-Life Region
Kyohei KUWADA,Yasuhiro TANAKA, Masanobu KUBOTA, and Yoshiyuki KONDO
.
194. Small-notched Fatigue Under Two Step Loading Below Fatigue Limit
Hikaru EDA, Masanobu KUBOTA and Yoshiyuki KONDO.
195. An Approach to understand the Mechanism of Fatigue Strength Reduction caused by Absorbed Hydrogen
Tomoe Sudo, Kano Daichi, Masanobu Kubota, Yoshiyuki Kondo
.
196. Effect of hydrogen on crack propagation of small fatigue crack in A286 steel.
197. Evaluation of Fretting Fatigue Strength at Connect and Joint Parts of Machine Components in Hydrogen Gas Environment.
198. Effect and Elucidation of Mechanism of Hydrogen Gas Environment on Fretting Fatigue Strength of Hydrogen Utilization Machines’ materials.
199. Effect of Hydrogen on Fatigue Crack Propagation Rate and DKth of Austenitic Stainless Steel.
200. Effects of Hydrogen, Hardness and Microstructure on the DKth of Short Crack.
201. Effect of Hydrogen Charge on Fatigue Behavior of Pre-strained SUS316L with Small Defect.
202. Evaluation of the improvement of fretting fatigue strength by stress-relief groove.
203. Evaluation of Fatigue Strength of Fine Copper Wire for Electric Equipment
.
204. Investigations of the effect of stress relief groove on fretting fatigue strength and control parameters.
205. Effect of hydrogen gas environment on fretting fatigue strength of materials for machines and stractures.
206. Examinations of fatigue fracture surface analysis method for estimation of applied stress.
207. Effect of hydrogen charge on fatigue strength of small-cracked specimen of stainless steel.
208. Evaluation of applied stress in fatigue fracture surface analysis.
209. Effect of hydrogen and material hardness on propagation threshold of small crack in low alloy steel.
210. Effect of stress relief groove shape on fretting fatigue strength.
211. Continuous observation of crack by ultrasonic inspection in two cylinders rolling fatigue test.
212. Effect of hydrogen charge and material hardness on torsion fatigue of stinless steel.
213. Consideration about adequate autofrettage stress of aluminum gas cylinder liner focused on crack closure behavior.
214. Fretting wear and friction behavior in hydrogen gas envionment.
215. Fretting fatigue properties of stainless steel in hydrogen gas environment.
216. Effect of hydrogen gas on fretting fatigue strength of stainless steels.
217. Effect of hydrogen gas environment on fretting wear of stainless steels.
218. Effect of Shape of Fitted Part on Fatigue Strength of Railway Axle.
219. Small-notched Fatigue under Variable Amplitude Loading below Fatigue Limit Diagram.
220. Evaluation of effect of shape of fitted part on frettin gfatigue strength of railroad axles.
221. Effect of Stress Ratio and Hydrogen on the Fatigue Crack Propagation Behavior of High Strength Steel.
222. Effect of Hydrogen Environment on Fretting Fatigue
Prized.
223. Effects of Hydrogen and Stress Ratio on Fatigue Crack Growth of High Strength Steel.
224. Effect of hydrogen gas environment on fretting fatigue strength
Naoki NOYAMA, Masanobu KUBOTA,Munehiro FUETA, Chu SAKAE & Yoshiyuki KONDO
Materials and Processing Conference 2004
Kumamoto Univ, 2004.11.
225. On the mechanics of fretting fatigue and evaluation of its strength
Masanobu KUBOTA and Yoshiyuki KONDO
Work shop "W02 Processing and Reliability Evaluation of Fastening and Joint Part of Machines and Structures",
Mechanical Engineering Congress, 2004 Japan
Hokkaido University.
226. Effect of Continuous Hydrogen Charge Environment on Fatigue Fracture of High-Strength Steels
Satoshi OHYANAGI, Kazutomo YANAGIHARA, Masanobu KUBOTA, Chu SAKAE and Yoshiyuki KONDO
Mechanical Engineering Congress, 2004, Japan, JSME
Hokkaido University, 2004.
227. Evaluation of fatigue strength of fine cupper wire for electronic equipment
Masanobu KUBOTA, Hitoshi SATO, Chu SAKAE, Yoshiyuki KONDO
Mechanical Engineering Congress, 2004 Japan, JSME
Hokkaido University, 2004.
228. Fretting in hydrogen
Masanobu Kubota, Naoki Noyama, Chu Sakae, Yoshiyuki Kondo
4th International Symposium on Fretting Fatigue
Lyon, France 2004.5.
229. Fretting fatigue properties of SUS304 in hydrogen gas atmosphere
M Kubota, N Noyama, C Sakae, Y Kondo
53th Annual meeting, JSMS
Okayama University 2004.
230. Effect of hydrogen environment on fretting fatigue strength of SUS304
N Noyama, C Sakae, M. kubota, Y Kondo
57th Annual meeting, JSME Kyuhus branch
Saga University 2004.
231. Effect of chage of surface profile on fatigue strength evaluation of carburized gear material
M Iseki, T Yano, C Sakae, Morita, K Matsushita, M. kubota, Y Kondo
57th Annual meeting, JSME Kyuhus branch
Saga University 2004.
232. On the boundary between smooth and small defect
Kashiwagi, C Sakae, K Matsushita, M. kubota, Y Kondo
57th Annual meeting, JSME Kyuhus branch
Saga University 2004.
233. Fatigue under high-low mixed mode variable loading
H Kitahara, C Sakae, K Matsushita, M. kubota, Y Kondo
57th Annual meeting, JSME Kyuhus branch
Saga University 2004
Prized.
234. Effect of assemble method on the strength of dental inplant
Y Ikeda, C Sakae, K Matsushita, M. kubota, Y Kondo
57th Annual meeting, JSME Kyuhus branch
Saga University 2004
Prized.
235. Fretting Fatigue in Hydrogen Environment,
Masanobu Kubota, Naoki Noyama, Chu Sakae and Yoshiyuki Kondo,
The 5th International Symposium on Eco-Materials Processing & Design (ISEPD 2004),
Nagaoka, Jan. 2004
Prized: Young Researcher Award.
236. Estimation of applied stress of fatigue fracture surface using high-frequency current,
M. Kubota, Y. Kitahara, C. Sakae and Y. Kondo,
JSME M&M2003, Toyama Univ., Sep. 2003.
237. Effect of Relative Slip Amount on Initiation Site and Propagation Condition of Fretting Fatigue Crack,
S. Niho, M. Kubota, C. Sakae and Y. Kondo,
JSME Kyushu branch 56th Annual Meeting,
Kyushu Univ., March 2003.
238. Effect of Under Stress on Fretting Fatigue Crack Initiation of Press-Fitted Axle,
Masanobu Kubota, Sotaro Niho, Chu Sakae and yoshiyuki Kondo,
JSME/ASME International Conference on Material and Processing 2002,
Hawaii, Oct. 2002.
239. Study on Fretting Fatigue Crack Propagation Condition at Edge and Center of Contact Part,
S. Niho, M. Kubota, C. Sakae and Y. Kondo
JSME Mechanical Engineering Congress 2002, Tokyo Univ., Sep. 2002.
240. Fatigue Properties on Thin Cupper Wire for Electronic Equipment
M. Kubota, S. Matsuzawa, C. Sakae and Y. Kondo
JSMS 51th Annual Meeting, Kagawa, May 2002.
241. Effect of the understress on the initiation behavior of fretting fatigue cracks
M. Kubota, C. Sakae and Y. Kondo
The 9th Materials and Processing Conference (M&P2001), JSME
Ryukyu Univ., Nov. 2001
Prized: Excellent Presentation.
242. The Effect of Height of Bridge Pad Foot on Fretting Fatigue Strength
M. Kubota, K. Shiromaru, K. Maruyama, C. Sakae and Y. Kondo
JSME Annual meeting 2001, Fukui Univ., Aug. 2001.
243. Relationship between Forging Ratio and Fatigue Limit of High-Carbon Steel
M. Kubota, K. Yamamoto and C. Sakae
JSME Annual meeting 2001, Fukui Univ., Aug. 2001.
244. The analysis of fretting fatigue failure in buckup roll and its prevention
M Kubota, H. Odanaka, C. Sakae, Y. Ohkomori and Y. Kondo
Third International Symposium on Fretting Fatigue (Nagaoka, Japan) May , 2001.
245. Crack Initiation and Growth Properties of Shrink-Fitted Axle Assembly in Long-Life Fretting Fatigue
H. Odanaka, M. Kubota, C. Sakae and Y. Kondo
The 8th Materials and Processing Conference (M&P2000)
Waseda Univ., Nov. 2000.
246. Improvement of Fretting Fatigue Strength by NiB Plating
K. Shiromaru, M. Kubota, T. Makino and C. Sakae
JSME Annual meeting 2000, Meijo Univ., Aug. 2000.
247. The Analysis and Prevention of Failure in Steel Making Backup Roll
Y. Ohkomori, H. Odanaka, M. Kubota and C. Sakae
JSME Kyushu branch, July 2000.
248. Crack Initiation Behavior of Shrink-Fitted Axle in Long Life Fretting Fatigue
K. Shiba, H. Odanaka, R. Yamazawa, M. Kubota and C. Sakae.
249. On the Fatigue Design Method for High-Speed Railway Axles,
Kenji HIRAKAWA, Masanobu KUBOTA,
UK/Japan Railway Safety Seminor, October, 1999, Tokyo.
250. Problems on Standardized Fretting Fatigue Test Method,
M. Kubota, K. Tsutusi and K. Hirakawa
JSMS, 48th Annual Metting,
Kyushu Univ, May 1999.
251. Initiation and Propagation Behavior of Small Fatigue Cracks in HIP-Treated Aluminum Alloys: AC4CH,
Y. Ochi, M. Kubota and R. Shibata,
Small Fatigue Cracks Mechanics, Mechanisms and Applications,
Hawaii, Dec. 1998.
252. The Effect of Contact Conditions and Surface Treatments on the Fretting Fatigue Strength of Medium Carbon Steel
M. Kubota, K. Tsutsui, T. Makino and K. Hirakawa
2 nd International Symposium on Fretting Fatigue
University of Utah, USA, Sep. 1998.
253. Effect of Matrix-Structures on Low Cycle Fatigue Properties in Ductile Cast Irons,
Low-Cycle Fatigue and Elasto-Plastic Behavior of Materials (LCF4),
Germany, Sep. 1998.
254. The Effect of the Contact Edge Profile and Surface Treatment on the Fretting Fatigue Strength
K. Nakamura, K. Tsutsui, M. Kubota and K. Hirakawa
75th JSME Spring Annual Metting,
Tokyo Institute of Technology, March 1998.