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Fujihara, Hiro*; Toda, Hiroyuki*; Ebihara, Kenichi; Kobayashi, Masakazu*; Mayama, Tsuyoshi*; Hirayama, Kyosuke*; Shimizu, Kazuyuki*; Takeuchi, Akihisa*; Uesugi, Masayuki*
International Journal of Plasticity, 174, p.103897_1 - 103897_22, 2024/03
Times Cited Count：0 Percentile：0.02(Engineering, Mechanical)Hydrogen(H) embrittlement in high-strength aluminum(Al) alloys is a crucial problem. H accumulation at the interface of precipitates in Al alloy is considered to cause embrittlement. However, there is no quantitative knowledge regarding the interaction between H distribution and stress field near cracks. In this study, using a multi-modal three-dimensional image-based simulation combining the crystal plasticity finite element method and H diffusion analysis, we tried to capture the stress distribution near the crack, its influence on the H distribution, and the probability of crack initiation in the experimental condition. As a result, it was found that grain boundary cracks transition to quasi-cleavage cracks in the region where the cohesive energy of the semi-coherent interface of MgZn
precipitates decreases due to H accumulation near the tip. We believe the present simulation method successfully bridges nanoscale delamination and macroscale brittle fracture.
Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*
Keikinzoku, 73(11), p.530 - 536, 2023/11
In Al-Zn-Mg alloys, suppression of hydrogen embrittlement is necessary to improve their strength. In this study, the distribution of stress, strain, and hydrogen concentration in the actual fracture region was investigated using the crystal plasticity finite element method and hydrogen diffusion analysis based on a model derived from three-dimensional polycrystalline microstructural data obtained by X-ray CT. In addition, the distributions of stress, strain, and hydrogen concentration were compared with the actual crack initiation behavior by combining in-situ observation of tensile tests using X-ray CT and simulation. The results show that stress loading perpendicular to the grain boundary due to crystal plasticity dominates grain boundary crack initiation. It was also found that internal hydrogen accumulation due to crystal plasticity has little effect on crack initiation.
Ajita, Saya*; Nishimura, Hayato*; Hojo, Tomohiko*; Koyama, Motomichi*; Fujita, Kenichi*; Kakinuma, Hiroshi*; Akiyama, Eiji*; Shibayama, Yuki
no journal, ,
no abstracts in English
diffusion and trapping in dilute Fe alloys by longitudinal spin relaxation techniqueNishida, Nobuhiko*; Higemoto, Wataru; Ito, Takashi
no journal, ,
In the late 1970s and 1980s muon spin rotation experiments were performed elaborately to study muon diffusion and trapping in Fe and Fe alloys. Recently, we have found that the measurement of the longitudinal muon spin relaxation time in ferromagnetic Fe alloys is the effective technique to study the muon diffusion and trapping in Fe dilute alloys and to investigate how the hydrogen interacts with the principal alloying elements We revisit the 
SR studies of diffusion and trapping in Fe alloys. In some alloys, we found the temperature dependence of muon spin relaxation time exhibits the peaks and in some other alloys a hump in a broad temperature region.
