Papers by Author: Toshihiko Sasaki

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Authors: Toshihiko Sasaki, Osama Yaguchi, Yuichi Kobayashi
Abstract: In order to study on the effects of grinding of rail head on rolling contact fatigue of rails, residual stress measurements were conducted for rails processed under different grinding conditions. In this study, residual stresses in rails used for a service line were measured with the method of X-ray stress measurement. The triaxial stress analysis was conducted using a new method for an area detector type X-ray stress analysis proposed by the authors. Four grinding conditions were used to rail specimens. The distributions of residual stresses in the surface layer of the rail head were obtained. It was found that the tensile residual stresses were generated at the field-side of the ground rai1, and that the triaxial stress state was formed in the surface of the rail head widely.
Authors: Mitsuyoshi Nakatani, Masamitsu Abe, Hidekazu Murakawa, Toshihiko Sasaki
Abstract: There are few reports that evaluated quantitatively the effect of the PWHT (Post Weld Heat Treatment) on the weld residual stress relaxation. We studied the residual stress for butt welding of thick plate. We conducted the experiment and the thermo-elastic-plastic finite element analysis. We became to be able to estimate the residual stress distribution of the butt weld. Also we clarified the effect of the PWHT on the weld residual stress.
Authors: Toshihiko Sasaki, Yohei Miyazawa, Masanari Yoshida, Kazuto Fukuda
Abstract: In this study, the authors made an experiment to observe the residual stress state in the surface of the engineered parts (for example, shot-peened steel) by X-ray stress measurement. An evaluation method was proposed for the stress gradient from the information on the X-ray Debye ring obtained with an area detector. The method utilized the fact that the X-ray penetration depth is a function of the central angle of the Debye ring α. It varies due to a section of Debye ring. It also depends on the incidence angle of X-rays and the wavelength used. Mean stress over the whole penetration depths of X-rays, which is defined as the Laplace stress, was measured by the cosα method[1, 2] by using this characteristic, and the real space stress[3-5] gradient was evaluated.
Authors: Shunichi Takahashi, Toshihiko Sasaki, Yukio Sato, Kengo Iwafuchi, Hiroshi Suzuki, Yukio Morii, Yasuto Kondo, Ryoichi Monzen, Yukio Hirose
Abstract: As an important industrial problem, the rolling contact fatigue damage is accumulated in rails during the repeated passage of trains over the rails, and rail failures may occur from the cracks grown in the rails. In order to prevent such rail failures, the estimation of the behavior of internal rail cracks is required based on the exact engineering analysis model as well as conducting rail test to search rail defects. The purposes of this paper are to apply the neutron stress measurement to rails, and to obtain residual stress state in the rails for the above purpose. The rail samples used were those that have been used in service line in Japan for about six years (222 million gross tons). The neutron measurement was conducted using the Residual Stress Analyzer (RESA) of the Japan Atomic Energy Agency (JAEA). The present measurement of stresses in rails by the neutron diffraction method was the first attempt in Japan.
Authors: Toshihiko Sasaki, Yohei Miyazawa, Shunichi Takahashi, Ryohei Matsuyama, Katsunari Sasaki, Koichi Hiratsuka
Abstract: The X-ray stress measurement with synchrotron radiation (SR) and an image plate (IP) was conducted using the facility of the Photon Factory (PF) of the High Energy Accelerator Research Organization (KEK). The influence of 2θ on stress measurement with the cosα method was investigated. The experiments were conducted under the conditions of 2θ=170 deg, 156.4 deg and 127 deg respectively. It was found that the hypothesis on the relation between the accuracy and the diffraction angle in the X-ray method is not valid in case of the cosα method.
Authors: Toshihiko Sasaki
Abstract: In order to study the method of the neutron stress measurement using the cosα method, a numerical simulation study was performed and the result was compared with author's former experiment. The results of the simulation study agreed with those obtained in the previous experiment, which suggests the validity of the present method for neutron stress measurement.
Authors: Toshihiko Sasaki, Junichi Akita, Yasutomo Sone, Yuichi Kobayashi
Abstract: Measurement of shearing stresses, τxz and τyz, by X-ray diffraction technique with two-dimensional detector was studied. The principle which was developed for an area detector type X-ray triaxial stress analysis was adopted for this purpose. In the present method, Debye ring was measured first and its whole part was used for determining shearing stresses. One Debye ring is enough to determine shearing stresses without accurate diffraction data such as lattice spacing in stress free. The result of the simulation showed that the present method is useful for the evaluation of shearing stresses by X-ray diffraction technique.
Authors: Yohei Miyazawa, Osama Yaguchi, Toshihiko Sasaki
Abstract: In this study, the authors investigated the application of the area detector type method for the purpose of evaluating residual stress in tools having a V-groove. The specimen used was a shot-peened forming rack. This alternative method uses a diffraction ring and single incidence X-ray to clarify precisely and effectively complex stresses and stresses in narrow parts of the tools such as the teeth on the surface of the rack. In addition, the authors evaluated stress gradients generated after shot peening using synchrotron radiation (SR).
Authors: Yasutomo Sone, Junichi Suzumura, Naoya Kamura, Toshihiko Sasaki
Abstract: A periodical unevenness of the running surface of rails is formed on ascending slope of submarine railway tunnel. One of the causes has been concluded due to the combination of a low friction and wheel load variation induced by some kinds of iron oxides and oxyhydroxides with various coefficients of friction on the rail, though it has not been made clear yet. In this study, X-ray diffraction and Raman scattering spectroscopic analysis were attempted to identify iron rusts on the rail as a process to solve the periodic unevenness of the rail suffering many railway companies.
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