Papers by Author: Yuichi Kobayashi

Abstract: Measurement of shearing stresses, τ_xz and τ_yz, 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.

Abstract: Sensors of robots that act in unstructured environment sometimes do not provide complete observation, due to occlusion or limitation of sensing range. This paper presents a motion generation method for robot with multiple sensors with limited sensing ranges. The proposed method introduce extension of the action- observation mapping to outside of the sensing range of a sensor, based on the diffusion-based learning of Jacobian matrices between control input and observation variable. Multiple observation spaces can be integrated by finding correspondence between the virtual observation spaces. When a target observation variable is given to the robot, it can generate a motion from an observation space to- ward the target with another observation space using the extended observation space. The proposed framework is verified by two robot tasks, reaching motion toward the floor with a manipulator and navigation of mobile robot around the wall. In both cases, observation space by camera with limited view was extended and appropriate motion trajectories were obtained.

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.

Abstract: The influence of the peak determination method on the area detector type neutron stress measurement method was investigated. Two peak determination methods, the half value breadth method and the centroid method, were compared and discussed in this paper. Experiments and simulation studies were carried out respectively. The first experiment was conducted during the tensile stress test with a steel specimen having the thickness of 6mm, and the second experiment was conducted with steel specimens in the stress free state having the thickness between 1 mm to 20 mm. As a result of the experiments, it was found that the peak determination method has an affect on the area detector type neutron stress measurement. A numerical simulation study was also conducted and showed similar result as the experiments.