Papers by Author: Takanori Ueno

Abstract: We developed the 3-D local hybrid method to evaluate the 3-D stress field inside the specimen from displacement data on the free surface obtained from the 2-D intelligent hybrid method. When a uniform load was applied to the structure with a surface crack, high accuracy was already acquired in stress analyses. The 3-D local hybrid method was newly applied to structure with a surface crack which is subjected to bending load. It is expected that the accuracy depends on local model size. In this study, the width, the thickness and the height of the local model were changed widely, and analyses were carried out. Then the size of the local model necessary for the analyses was examined. Assessment of analyses was performed by comparing J integral value of a full model and the local model.

Abstract: We developed the 3-D local hybrid method to evaluate the 3-D stress field inside the specimen from displacement data on the free surface obtained from the 2-D intelligent hybrid method. When a uniform load was applied to the structure with a surface crack, high accuracy was already acquired in stress analyses. The 3-D local hybrid method was anew applied to a structure with a surface crack which is subjected to bending load. It is expected that the accuracy depends on local model size. In this study, the width, the thickness and the height of the local model were changed widely, and analyses were carried out. Then the size of the local model necessary for the analyses was examined. Assessment of analyses was performed by comparing J integral value of a whole model and a local model.

Abstract: A Ni-30 mass% Fe alloy with dispersed coarse oxide particles, ranging from 1 to 3 μm in diameter, was multi-directionally forged (MDF) at temperatures between 773 K and 873 K at a true strain rate of 1 x 10-3 s-1 in vacuum. For comparison, a particle-free Ni-Fe alloy was also prepared and MDFed. At 873 K, an obvious flow softening occurred during MDF especially in the alloy with dispersed particles, while work hardening followed by steady-state flow appeared at 773 K in both alloys. With increasing cumulative strain, the average grain size became gradually finer. However, the evolved microstructure was quite different depending on temperature and dispersion of particles. At 873 K, in the alloy with particles, equi-axed fine grains of about 1.3 μm in average was uniformly evolved at a cumulative strain of Σε = 2.4, while at 773 K the microstructure was still inhomogeneous. The above experimental results suggest important role of coarse particles to stimulate grain refinement.

Abstract: The interior stress field of the surface crack specimen subjected to a uniform tensile load has been successfully analyzed by the 3-D local hybrid method. In this study, it was examined whether the 3-D local hybrid method was applicable to the specimen subjected to the bending load. It has been understood that the decision of the optimal size of the local model is indispensable in the improvement of accuracy from the previous research. Then, the width and thickness of the local model were changed widely, and analyses were carried out to find the optimal hybrid local model size. Moreover, it was examined how to decide the optimal size of the hybrid local model with various crack length and aspect ratio of the specimen. The optimal size of the hybrid local model was examined from the comparison with the J integral of the whole model.