Papers by Author: Yasuo Ochi

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Authors: Katsuaki Furukawa, Yasuo Ochi
Authors: Sheng Long Zhu, Masataka Mizuno, Yutaka Kagawa, Yasuo Ochi
Authors: Yasuo Ochi, Kiyotaka Masaki, Takashi Matsumura, Yuji Sano, Koichi Akita, Kentaro Kajiwara
Abstract: In order to investigate effects of low energy laser peening (LP) without protective coating on surface fatigue crack growth behavior, rotating bending fatigue tests were carried out on cast Al-Si-Mg aluminum alloy with a pre-cracked round bar type specimens. As the results, the fatigue crack growth was restrained by the compressive residual stress induced by laser peening treatment. And also, the three dimensional (3D) image of surface fatigue cracks was reconstructed by using a micro computed tomography (μCT) with phase contrast technique. It was also shown that the surface crack growth was restrained for the laser peened materials.
Authors: Toshio Sakuma, Yuji Mihara, Yasuo Ochi, M. Ozawa, K. Okita, N. Okabe
Abstract: Ti-Ni-Nb shape memory alloy has a wide transformation hysteresis, and has been used as coupling devices and so on. However systematic researches of the influence of the amount of Nb addition on transformation temperatures are few. The purpose of this work is to clarify the influences of pre-strain and Nb content on transformation temperatures in Ti-Ni-Nb shape memory alloys. The specimens were Ti-Ni-Nb alloys (Ni/Ti=1.0, Nb=0-15at%), annealed at 1223 K for 0.3 ks. The variation of transformation temperatures with pre-strain and Nb content were investigated experimentally. The variation of As, Ms and transformation temperature hysteresis with pre-strain and Nb content will be discussed in relation to the elastic strain energy and the volume fraction of slip-deformed martensite.
Authors: Yuji Sano, T. Adachi, Koichi Akita, I. Altenberger, M.A. Cherif, Berthold Scholtes, Kiyotaka Masaki, Yasuo Ochi, Tatsuo Inoue
Abstract: Laser peening without protective coating (LPwC) has been applied to metallic materials using low energy pulses of a Q-switched and frequency-doubled Nd:YAG laser. Compressive residual stresses of several hundred megapascals were imparted on the surface of the materials. Redistribution of the residual stress in the top surface due to thermal loading was evaluated non-destructively by synchrotron radiation of SPring-8. Accelerating stress corrosion cracking (SCC) tests showed that LPwC prohibited SCC of sensitized materials. LPwC largely prolonged the fatigue lives of titanium alloys, aluminum alloys and austenitic stainless steels.
Authors: Yasuo Ochi, Kiyotaka Masaki, Takashi Matsumura, M. Wadasako
Abstract: The rotating bending fatigue tests in high cycle region were carried out on alumina short fiber reinforced aluminum alloy composites (MMCs) at room and elevated temperatures of 200, 350, 400 and 450°C. The four kind of MMCs with 0%, 10%, 18% and 25% volume fraction were prepared in order to investigate the effects of alumina short fiber volume fraction on the fatigue property such as the fatigue strength, the crack initiation and propagation behaviors. As results, it was found that the fatigue strength at 107 cycles decreased with increase in the test temperature, but increased with an increase in alumina short fiber volume fraction at room and elevated temperatures. The crack initiation sites were large size alumina short fibers; some kind of cluster of short fibers and large size alumina particles (i.e. shots). And the crack growth paths were related to the distribution of the short fibers.
Authors: Kiyotaka Masaki, Yasuo Ochi, Takashi Matsumura
Abstract: In order to investigate the effect of SP treatment on the high cycle fatigue properties such as fatigue strength, crack initiation and propagation behaviors, rotating bending fatigue tests on shot-peening (SP) treated AC4CH aluminum alloy were carried out. The fatigue properties of the SP-treated material were compared with fatigue properties of the non-peened material, the hot isostatic pressure (HIP) treated material and the semi-liquid (SL) die casting material. the main conclusions obtained were, (1) The fatigue properties of SP-treated material is most excellent in all materials. (2) The fatigue life property of AC4CH alloys is significantly affected by fatigue crack initiation behavior. The reason why the SP-treated material has longer fatigue life than those of other material is that it has no cast defects near the surface by the effect of SP treatment. (3) The reason of fatigue life improvement by SP treatment is decrease of fatigue crack propagation rate.
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