Papers by Author: Tomohiro Takaki

Abstract: The novel coupling recrystallization model is proposed in this study. First, the deformation microstructure was simulated by the finite element method based on the strain gradient crystal plasticity theory. The calculated dislocation density and crystal orientation were transferred to the recrystallization phase-field simulation. The initial subgrain structures used in phase-field simulation were determined by a relationship between dislocation density and subgrain size with the dislocation density distribution calculated by crystal plasticity simulation. The so-called KWC phase-field model, which can introduce both subgrain rotation and grain boundary migration, was employed, and spontaneous nucleation and grain growth were simulated simultaneously.

Abstract: The establishment of the coupled numerical model which enable to simulate the spherulite formation and its mechanical behavior continuously is our final goal. In this paper, we have developed Phase-field model for spherulte growth of polymer by generalizing the model proposed by Granasy et. al.. The numerical simulations for single spherulite and multi-sperulites have been performed with isotropic interface energy.

Abstract: The integrated simulation model for microstructural design of Fe-C alloy using the phase-field method and the homogenization method is proposed. First, the phase-field simulation is performed to simulate the morphological change of the grain boundary ferrite to Widmanstätten ferrite. Then, in order to clarify the effects of the morphology of the ferrite phase on the micro- and macroscopic mechanical properties, the finite element analysis based on the homogenization method is conducted with the representative volume element obtained from the phase-field simulation. This numerical approach provides a powerful tool to investigate systematically the micro and macroscopic mechanical behavior with the morphological change of the ferrite phase in the Fe-C alloy.

Abstract: We have developed a phase-field model which can simulate the growth process of self-assembled SiGe/Si islands during deposition. The novel feature of this model is that it can reproduce the morphological transitions of islands, i.e., from single-faceted pyramid to multifaceted dome and from dome to barn, by taking a high anisotropy and a sixteen-fold anisotropy of surface energy into account. Two-dimensional simulations have been performed on a large computational model. As a result, island nucleation on the surface of a wetting layer, island morphological change and Ostwald ripening due to an interaction between two neighbor islands were well reproduced. The bimodal distribution of island size, which is a very important phenomenon in self-assembled quantum dots, could also be generated. Furthermore, it has been clarified that the bimodal distributions are largely affected by island morphological change from pyramid to dome. Furthermore, in order to discuss the mechanism of island growth, a simulation of single-island growth has been conducted and the variations of island size and energies have been estimated in detail. As a result, it is concluded that the island morphological transitions occur so as to reduce the elastic strain energy.