| 1. |
Osamu TAKAKUWA, Investigation of material compatibility to high-pressure hydrogen-gas, International Conference on Flow Dynamics 2020, 2020.10. |
| 2. |
Osamu TAKAKUWA, Yuhei OGAWA, Hisao MATSUNAGA, Temperature dependence of hydrogen-assisted fatigue crack growth of ferrite-pearlite steel in gaseous environment, Joint Research Symposium -Hydrogen-Material Interactions-, 2020.01. |
| 3. |
Hisao MATSUNAGA, Osamu TAKAKUWA, Junichiro YAMABE, Recent Progress in the Study on Strength Properties of Metallic Materials in High-Pressure Hydrogen Environments, The 8th World Hydrogen Technologies Convention (WHTC2019), 2019.06. |
| 4. |
Peculiar Temperature Dependence of Hydrogen-Assisted Fatigue Crack Growth of Low-Carbon Steel in Gaseous Hydrogen, Osamu TAKAKUWA, Yuhei OGAWA, Junichiro YAMABE, Hisao MATSUNAGA, Japan-Korea-China Joint Workshop on Hydrogen Materials 2019, 2019.04. |
| 5. |
Hisao MATSUNAGA, Osamu TAKAKUWA, Junichiro YAMABE, Recent Activities for Hydrogen Compatibility of Materials Used in Hydrogen Stations in Japan, International Workshop on Standards and Codes for Hydrogen Infrastructure Safety, 2018.11. |
| 6. |
Domas Birenis, Yuhei Ogawa, Hisao Matsunaga, Osamu Takakuwa, Junichiro Yamabe, Øystein Prytz, Annett Thøgersen, Hydrogen-assisted fatigue crack propagation in a pure BCC iron. Part II
Accelerated regime manifested by quasi-cleavage fracture at relatively high stress intensity range values, 12th International Fatigue Congress, FATIGUE 2018, 2018.05, Hydrogen effect on fatigue performance at relatively high values of stress intensity factor range, ΔK, of pure BCC iron has been studied with a combination of various electron microscopy techniques. Hydrogen-assisted fatigue crack growth rate is manifested by a change of fracture features at the fracture surface from ductile transgranular in air to quasi-cleavage in hydrogen gas. Grain reference orientation deviation (GROD) analysis has shown a dramatic suppression of plastic deformation around the crack wake in samples fatigued in hydrogen. These results were verified by preparing site-specific specimens from different fracture features by using Focused Ion Beam (FIB) technique and observing them with Transmission Electron Microscope (TEM). The FIB lamella taken from the sample fatigued in air was decorated with dislocation cell structure indicating high amount of plasticity, while the lamella taken from the quasi-cleavage surface of the sample fatigued in hydrogen revealed a distribution of dislocation tangles which corresponds to smaller plastic strain amplitude involved at the point of fracture. These results show that a combination of critical hydrogen concentration and critical stress during fatigue crack growth at high ΔK values triggers cleavage-like fracture due to reduction of cohesive force between matrix atoms.. |
| 7. |
Yuhei Ogawa, Domas Birenis, Hisao Matsunaga, Osamu Takakuwa, Junichiro Yamabe, Øystein Prytz, Annett Thøgersen, Hydrogen-assisted fatigue crack propagation in a pure BCC iron. Part I
Intergranular crack propagation at relatively low stress intensities, 12th International Fatigue Congress, FATIGUE 2018, 2018.05, The role of hydrogen on intergranular (IG) fracture in hydrogen-assisted fatigue crack growth (HAFCG) of a pure iron at low stress intensity was discussed in terms of the microscopic deformation structures near crack propagation paths. The main cause of IG fracture was assumed to be the hydrogen-enhanced dislocation structure evolution and subsequent microvoids formation along the grain boundaries. Additionally, the impact of such IG cracking on the macroscopic FCG rate was evaluated according to the dependency of IG fracture propensity on the hydrogen gas pressure. It was first demonstrated that the increased hydrogen pressure results in the larger area fraction of IG and corresponding faster FCG rate. Moreover, gaseous hydrogen environment also had a positive influence on the FCG rate due to the absence of oxygen and water vapor. The macroscopic crack propagation rate was controlled by the competition process of said positive and negative effects.. |
| 8. |
Osamu TAKAKUWA, Yuhei OGAWA, Junichiro YAMABE, Hisao MATSUNAGA, Hydrogen-Assisted Fracture in Pre-Charged Precipitation-Hardened Iron-Based Superalloy A286, Korea-China-Japan Joint Workshop on Hydrogen Materials 2018, 2018.04. |
| 9. |
Osamu TAKAKUWA, Junichiro YAMABE, Hisao MATSUNAGA, Saburo MATSUOKA, Compatibility of Type 304 Stainless Steel to High-Pressure Hydrogen Gas, HYDROGENIUS, I2CNER & HydroMate Joint Research Symposium 2018, 2018.02. |
| 10. |
Yuhei OGAWA, Domas BIRENIS, Hisao MATSUNAGA, Osamu TAKAKUWA, Junichiro YAMABE, Interpretation of Hydrogen-Assisted Fatigue Crack Propagation in a Pure BCC Iron Based on Crack Tip Plasticity Evolution, HYDROGENIUS, I2CNER & HydroMate Joint Research Symposium 2018, 2018.02. |
| 11. |
Jean Gabriel Sezgin, Osamu Takakuwa, Hisao Matsunaga, Junichiro Yamabe, Assessment of the contribution of internal pressure to the structural damage in a hydrogen-charged Type 316L austenitic stainless steel during slow strain rate tensile test, 22nd European Conference on Fracture, ECF 2018, 2018.01, The aim of this study is to provide a quantification of the internal pressure contribution to the SSRT properties of H-charged Type-316L steel tested in air at room temperature. Considering pre-existing penny-shaped voids, the transient pressure build-up has been simulated as well as its impact on the void growth by preforming J
Ic
calculations. Several void distributions (size and spacing) have been considered. Simulations have concluded that there was no impact of the internal pressure on the void growth, regardless the void distribution since the effective pressure was on the order of 1 MPa during the SSRT test. Even if fast hydrogen diffusion related to dislocation pipe-diffusion has been assessed as a conservative case, the impact on void growth was barely imperceptible (or significantly low). The effect of internal pressure has been experimentally verified via the following conditions: (I) non-charged in vacuum; (II) H-charged in vacuum; (III) H-charged in 115-MPa nitrogen gas; (IV) non-charged in 115-MPa nitrogen gas. As a result, the relative reduction in area (RRA) was 0.84 for (II), 0.88 for (III), and 1.01 for (IV), respectively. The difference in void morphology of the H-charged specimens did not depend on the presence of external pressure. These experimental results demonstrate that the internal pressure had no effect on the tensile ductility and void morphology of the H-charged specimen.. |
| 12. |
Domas Birenis, Yuhei Ogawa, Hisao Matsunaga, Osamu Takakuwa, Øystein Prytz, Junichiro Yamabe, Annett Thøgersen, Hydrogen-assisted fatigue crack propagation in a commercially pure BCC iron, ASME 2018 Pressure Vessels and Piping Conference, PVP 2018, 2018.01, Hydrogen effect on fatigue performance of commercially pure BCC iron has been studied with a combination of various electron microscopy techniques. The fatigue crack growth (FCG) in gaseous hydrogen was found to consist of two regimes corresponding to a slightly accelerated regime at relatively low stress intensity factor range, ΔK, (Stage I) and the highly accelerated regime at relatively high ΔK (Stage II). These regimes were manifested by the intergranular and quasi-cleavage types of fractures respectively. Scanning electron microscopy (SEM) observations demonstrated an increase in plastic deformation around the crack wake in the Stage I, but considerably lower amount of plasticity around the crack path in the Stage II. Transmission electron microscopy (TEM) results identified dislocation cell structure immediately beneath the fracture surface of the Stage I sample, and dislocation tangles in the Stage II sample corresponding to fracture at high and low plastic strain amplitudes respectively.. |
| 13. |
Osamu Takakuwa, Michio Yoshikawa, Saburo Matsuoka, Junichiro Yamabe, Saburo Okazaki, Hisao Matsunaga, Temperature dependence of fatigue crack growth in low-alloy steel under gaseous hydrogen, ASME 2018 Pressure Vessels and Piping Conference, PVP 2018, 2018.01, In order to elucidate the temperature dependence of hydrogen-enhanced fatigue crack growth (FCG), the FCG test was performed on low-alloy Cr-Mo steel JIS-SCM435 according to ASTM E647 using compact tension (CT) specimen under 0.1 - 95 MPa hydrogen-gas at temperature ranging from room temperature (298 K) to 423 K. The obtained results were interpreted according to trap site occupancy under thermal equilibrium state. The FCG was significantly accelerated at RT under hydrogen-gas, that its maximum acceleration rate of the FCG was 15 at the pressure of 95 MPa at the temperature of 298 K. The hydrogen-enhanced FCG was mitigated due to temperature elevation for all pressure conditions. The trap site with binding energy of 44 kJ/mol dominated the temperature dependence of hydrogen-enhanced FCG, corresponding approximately to binding energy of dislocation core. The trap site (dislocation) occupancy is decreased with the temperature elevation, resulting in the mitigation of the FCG acceleration. On the basis of the obtained results, when the occupancy becomes higher at lower temperature, e.g. 298 K, hydrogen-enhanced FCG becomes more pronounced. The lower occupancy at higher temperature does the opposite.. |
| 14. |
Junichiro Yamabe, Osamu Takakuwa, Tohru Awane, Saburo Matsuoka, Hydrogen-assisted degradation of high-strength stainless steel with a newly developed aluminum-based coating in high-pressure hydrogen gas environment, ASME 2017 Pressure Vessels and Piping Conference, PVP 2017, 2017.01, The paper presents the hydrogen-entry, tensile, and fatigue properties of a precipitation-hardened martensitic stainless steel, JIS-SUS630, with a newly developed coating, whose thickness ranges from 10 to 20 μm. The newly developed coating consists of alumina, aluminum, and ferroaluminum, and has an excellent resistance to hydrogen entry in 100-MPa hydrogen gas at 270°C. The hydrogen entry in the coated specimen occurred under a diffusion-controlled process and the effective hydrogen diffusivity was approximately one thousandth of that of the base steel. Although the hydrogen diffusivity of JIS-SUS630 was two orders of magnitude larger than that of JIS-SUS304, the effective hydrogen diffusivity of the coated JIS-SUS630 was nearly equal to that of the coated SUS304. In our previous study with secondary-mass ion spectroscopy (SIMS), the coating's excellent resistance to hydrogen entry was attributed to interfacial hydrogen trapping between the aluminum and ferroaluminum layers. The experimental result obtained in this study suggested that the excellent resistance to hydrogen entry demonstrated by the developed coating can be attributed to the reduction in the permeation area induced by the interfacial trapping of hydrogen. The tensile tests of a smooth, round-bar specimen and fatigue tests of a circumferentially notched specimen with exposure to 100-MPa hydrogen gas at 270°C were performed in air at room temperature (RT). The test results showed that the tensile and fatigue properties of the coated specimens were not degraded by hydrogen exposure, whereas those for the non-coated specimens were significantly degraded. Hydrogen-pressure cycle tests of the coated, tubular specimens with an inner notch were also carried out with 95-MPa hydrogen gas at 85°C, demonstrating that the fatigue life of the tubular specimen was improved by the developed coating.. |
| 15. |
Osamu Takakuwa, Junichiro Yamabe, Hisao Matsunaga, Yoshiyuki Furuya, Saburo Matsuoka, Recent progress on interpretation of tensile ductility loss for various austenitic stainless steels with external and internal hydrogen, ASME 2017 Pressure Vessels and Piping Conference, PVP 2017, 2017.01, Slow-strain rate tensile (SSRT) tests on various metals having γ-Fe phase; Type 304 and 316L stainless steels, HP160 high strength stainless steel, and A286 Fe-based super alloy were conducted in external hydrogen and with internal hydrogen. The external hydrogen indicates non-charged specimens tested in high-pressure hydrogen-gas environment, whereas the internal hydrogen indicates hydrogen-charged specimens, with uniform distribution of hydrogen, tested in inert gas. The hydrogen distribution was calculated based on the measured hydrogen diffusivity and solubility. The fracture morphologies were observed by scanning electron microscopy (SEM). For Types 304, 316L, and HP160 the relative reduction in area (RRA of the steels was successfully reproduced by the nickel equivalent, Nieq, showing the higher Nieq, the lager RRA. Furthermore, at a low Nieq, the RRA of the steel with external hydrogen was nearly equal to that with internal hydrogen. In contrast, at a high Nieq, the RRA of the steel with internal hydrogen was slightly degraded by hydrogen, RRA ∼ 0.8, whereas that in external hydrogen was not degraded, RRA ∼ 1. For A286, despite a high Nieq, the RRA of the alloy with internal hydrogen was significantly degraded by hydrogen, RRA ∼ 0.5. The fracture morphologies were categorized into four types: quasi-cleavage fracture associated with hydrogen-assisted surface cracks; ordinary void formation with no hydrogen effect; small-void formation associated with void sheet enhanced by hydrogen; facet formation induced by hydrogen. These categorized morphologies could be interpreted in terms of hydrogen distribution (internal or external hydrogen), austenitic stability (a low or high Nieq), and microstructure (solution or precipitation-hardened treatment).. |
| 16. |
Osamu Takakuwa, Yuta Mano, Hitoshi Soyama, Effect of hydrogen on the micro- and macro-strain near the surface of austenitic stainless steel, 2014 International Conference on Materials Science and Engineering Technology, MSET 2014, 2014.01, The objective of this study is to evaluate the effect of hydrogen on the micro- and macro-strain of austenitic stainless steel using X-ray diffraction. When hydrogen is trapped in lattice sites, it can affect both the micro- and macro-strain. The micro-strain was evaluated through fitting profiles to measured X-ray diffraction profile using a fundamental parameter method. The macro-strain, i.e., the residual stress, was evaluated by a 2D method using a two-dimensional PSPC. The experimental samples were charged with hydrogen by a cathodic charging method. The results revealed that the induced residual stress was equi-biaxial and compressive, and that the micro-strain increased. Both of these varied rapidly with increasing hydrogen charging time. Saturation occurred at a compressive stress of around 130 MPa. On reaching saturation, the hydrogen charging was terminated and desorption of hydrogen began at room temperature. Then, the strains decreased and the compressive stress reverted, ultimately, to a tensile stress of 180 MPa. Martensitic transformation occurred due to hydrogen charging and this had a significant effect on the X-ray diffraction profile.. |
| 17. |
Osamu Takakuwa, Yuta Mano, Hitoshi Soyama, Effect of indentation load on vickers hardness of austenitic stainless steel after hydrogen charging, ASME 2014 Pressure Vessels and Piping Conference, PVP 2014, 2014.01, In order to reveal the effect of indentation load on Vickers hardness of austenitic stainless steel after hydrogen charging, the Vickers hardness measurements have been conducted with three different indentation load of 0.49, 1.96 and 9.80 N on the surface of type 316L austenitic stainless steel after hydrogen charging. Relationship between plastic deformation behavior during indentation process and hydrogen absorption behavior was revealed. In the Vickers hardness test, Vickers hardness keeps same value though the indentation load varies. Needless to say, the value did not depend on magnitude of the indentation load before hydrogen charging in the present study. However, the Vickers hardness increased along with hydrogen charging time and, interestingly, the increase in the Vickers hardness due to the presence of hydrogen depends on magnitude of the indentation load. In the load of 0.49 N and 9.80 N, the Vickers hardness has a maximum value of 3.04 and 2.04 GPa which is 1.58 and 1.15 times larger than value of 1.73 and 1.70 GPa before hydrogen charging, respectively. The hydrogen-induced hardening behavior observed by the Vickers hardness tests employing different indentation load would be evaluated by the relationship between the plastic deformation depth and the hydrogen absorption depth.. |
| 18. |
H. Soyama, Osamu Takakuwa, A. Naito, Effect of nozzle shape for high injection pressure on aggressivity of cavitating jet, 21st International Conference on Water Jetting: Looking to the Future, Learning from the Past, 2012.12, A cavitating jet can be used for cutting and a material testing to evaluate cavitation erosion resistance of materials. In order to use the cavitating jet more efficiently, effect of nozzle shape should be investigated, as aggressivity of the jet was affected by the nozzle shape. In the present paper, erosion rate, intensity of luminescence and acoustic power were measured to evaluate the aggressivity of the jet from various types of the nozzle for high injection pressure. It was found that the aggressivity of the jet was drastically changed by the nozzle shape.. |
| 19. |
Osamu Takakuwa, Masaaki Nishikawa, Hitoshi Soyama, Suppression of fatigue crack growth in austenite stainless steel by cavitation peening, 9th International Conference on Fracture and Damage Mechanics, FDM 2010, 2011.01, Cavitation normally causes severe damage in hydraulic machinery such as pumps and turbines by the impact produced by cavitation bubbles collapsing. Although cavitation is known as a factor of erosion, Soyama et al. succeeded in utilizing impacts of cavitation bubble collapsing for surface modification by controlling cavitating jet in the same way as shot peening. The local plastic deformation caused by cavitation impact enhances the fatigue strength of metallic materials, and the surface modification technique utilizing cavitation impact is called "cavitation peening (CP)". It is well known that the peening improves fatigue strength by introducing compressive residual stress on the surface, but little attention has been paid to the behavior of fatigue crack growth of the material which was modified by CP. In the present study, the fatigue behavior of austenite stainless steel with and without CP was evaluated by a plate bending fatigue test, and the results revealed that the compressive residual stress introduced by CP suppresses fatigue crack growth rate by 70 % compared to that without CP.. |
| 20. |
H. Soyama, N. Yamada, Osamu Takakuwa, Y. Sekine, M. Mikami, Release of micro strain in tool alloy steel by a cavitating jet in air, 19th International Conference on Water Jetting, 2008.12, Cavitation impacts can be utilized to improve material properties such as fatigue strength. In case of such application, cavitation was produced by a cavitating jet. In order to investigate mechanism of surface modification, tool alloy steel was treated by a cavitating jet and the surface was analyzed by using X-ray diffraction methods, i.e., 2D method and a fundamental approach. Residual stress was measured by 2D method and micro strain, which is strain in the grain, was evaluated by a fundamental parameter approach. In the present paper, in order to enhance cavitation impacts, a cavitating jet in air was used for surface treatment of tool alloy steel. It was revealed that a cavitating jet in air can introduce compressive residual stress. It was also shown that micro strain introduced by heat treatment or mechanical finishing was released by a cavitating jet in air.. |
