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Hojo, Tomohiko*; Koyama, Motomichi*; Kumai, Bakuya*; Zhou, Y.*; Shibayama, Yuki; Shiro, Ayumi*; Shobu, Takahisa; Saito, Hiroyuki*; Ajita, Saya*; Akiyama, Eiji*
ISIJ International, 65(2), p.284 - 296, 2025/02
neutron diffraction measurement during tensile deformationYamashita, Takayuki*; Morooka, Satoshi; Gong, W.; Kawasaki, Takuro; Harjo, S.; Hojo, Tomohiko*; Okitsu, Yoshitaka*; Fujii, Hidetoshi*
ISIJ International, 64(14), p.2051 - 2060, 2024/12
Shibayama, Yuki; Hojo, Tomohiko*; Koyama, Motomichi*; Akiyama, Eiji*
International Journal of Hydrogen Energy, 88, p.1010 - 1016, 2024/10
Times Cited Count：1 Percentile：0.00(Chemistry, Physical)
ders band propagation in an Fe-5Mn-0.1C medium Mn steel clarified through scanning electron microscopyKoyama, Motomichi*; Yamashita, Takayuki*; Morooka, Satoshi; Yang, Z.*; Varanasi, R. S.*; Hojo, Tomohiko*; Kawasaki, Takuro; Harjo, S.
Tetsu To Hagane, 110(3), p.205 - 216, 2024/02
Times Cited Count：0 Percentile：0.00(Metallurgy & Metallurgical Engineering)
neutron diffraction measurement during tensile deformationYamashita, Takayuki*; Morooka, Satoshi; Gong, W.; Kawasaki, Takuro; Harjo, S.; Hojo, Tomohiko*; Okitsu, Yoshitaka*; Fujii, Hidetoshi*
Tetsu To Hagane, 110(3), p.241 - 251, 2024/02
Times Cited Count：0 Percentile：0.00(Metallurgy & Metallurgical Engineering)ders deformation in an Fe-5Mn-0.1C medium-Mn steelKoyama, Motomichi*; Yamashita, Takayuki*; Morooka, Satoshi; Sawaguchi, Takahiro*; Yang, Z.*; Hojo, Tomohiko*; Kawasaki, Takuro; Harjo, S.
Tetsu To Hagane, 110(3), p.197 - 204, 2024/02
Times Cited Count：1 Percentile：54.79(Metallurgy & Metallurgical Engineering)Okitsu, Takayuki*; Hojo, Tomohiko*; Morooka, Satoshi; Miyamoto, Goro*
Tetsu To Hagane, 110(3), p.260 - 267, 2024/02
Times Cited Count：0 Percentile：0.00(Metallurgy & Metallurgical Engineering)Matsuno, Takashi*; Fujita, Taiki*; Matsuda, Tomoko*; Shibayama, Yuki; Hojo, Tomohiko*; Watanabe, Ikumu*
Journal of Materials Processing Technology, 322, p.118174_1 - 118174_16, 2023/12
Times Cited Count：7 Percentile：72.06(Engineering, Industrial)The impact of high stress triaxiality on work hardening in transformation-induced plasticity (TRIP) steel has been widely acknowledged, particularly through measurements of the austenite fraction. Understanding this TRIP behavior is crucial for predicting material fracture in press-forming processes. However, the actual flow stresses under high-stress-triaxiality conditions remain largely undetermined. To address this gap, we developed a new tensile testing method using tiny notched round bars to investigate stress-triaxiality-induced work hardening in TRIP steels. The specimens were analyzed using two-dimensional micrometry to allow finite element analyses to identify the flow stress. Additionally, we conducted in situ tensile tests in which their crystal lattice stresses were monitored using synchrotron X-ray diffraction (XRD) to realize mechanism analyses of the unexpected work-hardening behavior identified by the developed tensile testing method. Our combined approach revealed a mutual, unstable increase in the flow stress and stress triaxiality in the TRIP-aided bainitic ferrite steel, which reduced the hardening exponent coefficients and thus induced a higher stress triaxiality. In contrast, the TRIP-aided martensitic steel exhibited a weakening behavior, characterized by a significant decrease in the hardening exponent coefficients in the case of the sharpest notch. XRD analyses showed that microstructural heterogeneity led to an extraordinarily high hydrostatic stress in the austenite phase, accounting for these contrasting behaviors. This finding challenges the established consensus on TRIP steels and suggests the need for a revised framework for their application in press-forming, taking into account stress-triaxiality conditions.
ders band propagation in an Fe-5Mn-0.1C medium Mn steel clarified through scanning electron microscopyKoyama, Motomichi*; Yamashita, Takayuki*; Morooka, Satoshi; Yang, Z.*; Varanasi, R. S.*; Hojo, Tomohiko*; Kawasaki, Takuro; Harjo, S.
ISIJ International, 62(10), p.2043 - 2053, 2022/10
Times Cited Count：10 Percentile：66.38(Metallurgy & Metallurgical Engineering)ders deformation in an Fe-5Mn-0.1C medium-Mn steelKoyama, Motomichi*; Yamashita, Takayuki*; Morooka, Satoshi; Sawaguchi, Takahiro*; Yang, Z.*; Hojo, Tomohiko*; Kawasaki, Takuro; Harjo, S.
ISIJ International, 62(10), p.2036 - 2042, 2022/10
Times Cited Count：18 Percentile：83.42(Metallurgy & Metallurgical Engineering)Hojo, Tomohiko*; Shibayama, Yuki; Ajita, Saya*; Koyama, Motomichi*; Akiyama, Eiji*
Materia, 61(7), p.413 - 418, 2022/07
no abstracts in English
Nishimura, Hayato*; Hojo, Tomohiko*; Ajita, Saya*; Shibayama, Yuki*; Koyama, Motomichi*; Saito, Hiroyuki*; Shiro, Ayumi*; Yasuda, Ryo*; Shobu, Takahisa; Akiyama, Eiji*
Tetsu To Hagane, 107(9), p.760 - 768, 2021/09
Times Cited Count：0 Percentile：0.00(Metallurgy & Metallurgical Engineering)no abstracts in English
Nishimura, Hayato*; Hojo, Tomohiko*; Ajita, Saya*; Shibayama, Yuki*; Koyama, Motomichi*; Saito, Hiroyuki*; Shiro, Ayumi*; Yasuda, Ryo*; Shobu, Takahisa; Akiyama, Eiji*
ISIJ International, 61(4), p.1170 - 1178, 2021/04
Times Cited Count：7 Percentile：39.62(Metallurgy & Metallurgical Engineering)Shibayama, Yuki; Hojo, Tomohiko*; Koyama, Motomichi*; Saito, Hiroyuki*; Shiro, Ayumi*; Yasuda, Ryo*; Shobu, Takahisa; Matsuno, Takashi*; Akiyama, Eiji*
ISIJ International, 61(4), p.1322 - 1329, 2021/04
Times Cited Count：7 Percentile：39.62(Metallurgy & Metallurgical Engineering)Hojo, Tomohiko*; Akiyama, Eiji*; Saito, Hiroyuki*; Shiro, Ayumi*; Yasuda, Ryo*; Shobu, Takahisa; Kinugasa, Junichiro*; Yuse, Fumio*
Corrosion Science, 177, p.108957_1 - 108957_9, 2020/12
Times Cited Count：27 Percentile：80.52(Materials Science, Multidisciplinary)Hydrogen assisted cracking on hemispherically-stretch-formed specimens of transformation induced plasticity-aided martensitic steel was investigated. Hydrogen charging induced cracking around the foot of the impression formed on the steel sheet, and the cracks propagated along the radial direction toward the hillside and the plains. Distributions of stress, plastic strain and volume fraction of retained austenite were analyzed employing the energy-dispersive X-ray diffraction method utilizing the synchrotron X-ray radiation at SPring-8. It was notable that the crack initiation took place in the region where the measured tensile stress was the highest. Influences of plastic strain and resulted martensitic transformation were also suggested.
Hojo, Tomohiko*; Kumai, B.*; Koyama, Motomichi*; Akiyama, Eiji*; Waki, Hiroyuki*; Saito, Hiroyuki*; Shiro, Ayumi*; Yasuda, Ryo*; Shobu, Takahisa; Nagasawa, Akihiko*
International Journal of Fracture, 224(2), p.253 - 260, 2020/08
Times Cited Count：17 Percentile：64.23(Materials Science, Multidisciplinary)In the study, the pre-strain effect on hydrogen embrittlement property of the ultra-high-strength transformation-induced plasticity -aided bainitic ferrite steel was investigated towards application for automobile frame parts. 3-10% tensile pre-strain suppressed hydrogen-induced mechanical degradation relative to total elongation while 12-15% pre-strained specimen did not exhibit elongation after hydrogen charging. The advantageous effect of the 3-10% pre-strain was attributed to the suppression of crack initiation related to retained austenite. The TRIP by pre-straining decreased the volume fraction of retained austenite before hydrogen charging, thereby reducing existing probabilities of preferential crack initiation sites and propagation paths. Conversely, high pre-strain such as 12-15% does not effectively work due to work hardening resulting in increases in hydrogen embrittlement susceptibility and a significant increase in hydrogen content due to the multiplication of dislocations.
-Fe
O solid solution thin films studied by soft X-ray magnetic circular dichroism and ab initio multiplet calculationsHojo, Hajime*; Fujita, Koji*; Ikeno, Hidekazu*; Matoba, Tomohiko*; Mizoguchi, Teruyasu*; Tanaka, Isao*; Nakamura, Tetsuya*; Takeda, Yukiharu; Okane, Tetsuo; Tanaka, Katsuhisa*
Applied Physics Letters, 104(11), p.112408_1 - 112408_5, 2014/03
Times Cited Count：9 Percentile：32.89(Physics, Applied)Ajita, Saya*; Nishimura, Hayato*; Hojo, Tomohiko*; Koyama, Motomichi*; Fujita, Kenichi*; Kakinuma, Hiroshi*; Akiyama, Eiji*; Shibayama, Yuki
no journal, ,
no abstracts in English
Koyama, Motomichi*; Hojo, Tomohiko*; Miyamoto, Goro*; Morooka, Satoshi; Yamashita, Takayuki; Sawaguchi, Takahiro*; Mine, Yoji*; Mayama, Tsuyoshi*; Okitsu, Takayuki*; Sakakibara, Mutsumi*; et al.
no journal, ,
no abstracts in English
ders band propagation in a medium Mn steelKoyama, Motomichi*; Hojo, Tomohiko*; Varanasi, R.*; Yamashita, Takayuki*; Morooka, Satoshi; Kawasaki, Takuro; Harjo, S.
no journal, ,
no abstracts in English
ders band propagation in a medium Mn steelKoyama, Motomichi*; Yamashita, Takayuki*; Morooka, Satoshi; Yang, Z.*; Varanasi, R.*; Hojo, Tomohiko*; Kawasaki, Takuro; Harjo, S.
no journal, ,
