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Tsuru, Tomohito; Kaji, Yoshiyuki; Shibutani, Yoji*
Journal of Computational Science and Technology (Internet), 4(3), p.185 - 193, 2010/09
The minimum energy motions of pure edge and screw dislocations in aluminum were investigated by atomistic transition state analysis. While the Peierls-Nabarro model and its modifications duplicate the essential nature of a dislocation within a crystalline lattice, the atomic-level relaxation of the dislocation core should be considered to estimate the minimum energy barrier. In this study, the minimum energy barriers and core structures for the quasi-static motions of pure edge and screw dislocations were investigated by the parallelized nudged elastic band method with the embedded atom method potential. We found that the local potential energy is distributed asymmetrically around the dislocation line for the most stable state and that it is bilaterally symmetrical at the transition state of the dislocation motion. The short-ranged structural relaxation of the core rearrangement as well as the wide-ranging elastic stress field is of great importance in realistic dislocation motion.
Tsuru, Tomohito; Shibutani, Yoji*
Journal of Computational Science and Technology (Internet), 2(4), p.559 - 567, 2008/11
Abrupt growth of displacement has been recognized as one of the representative examples of nanoscale plastic behavior (nanoplasticity). This phenomenon corresponds to the early stage of plastic deformation and is greatly influenced by the collective dislocation emission. In the present paper a simplified model is constructed for the first displacement burst with use of the elastic theory based on both the Hertzian contact theory and the classical dislocation theory to evaluate the displacement burst in nanoindentation. As a result, it is shown that more than one hundred high-density dislocations are generated simultaneously and surface step corresponding to the Burgers vector of dislocation dipole of each emitted dislocation causes significant displacement burst.
Tsuru, Tomohito; Shibutani, Yoji*
Journal of Computational Science and Technology (Internet), 2(4), p.459 - 467, 2008/10
Unstable displacement burst or the abrupt growth of indent displacement after homogeneous elastic deformation observed in crystalline materials is a unique plastic deformation characteristic (nanoplasticity). In the present paper, a series of atomistic simulations of nanoindentation in single crystalline aluminum and copper are performed in analyzing the critical state for dislocation nucleation and interaction between dislocations beneath the indenter. With reference to the Hertzian solution based on isotropic linear elastic theory, both the anisotropic effect and nonlinear behavior of nanoindentation are discussed in detail. The discovery was made that the incipient yield process is strongly related to the triaxial stress state created beneath the indenter, and that energetically unfavorable interactions accompanied with cross slip induce the formation of prismatic dislocations.
Kushida, Noriyuki; Okuda, Hiroshi*
Journal of Computational Science and Technology (Internet), 2(1), p.81 - 91, 2008/00
Since the earth simulator consists of 640 SMP nodes, each of which has eight vector processors, there are three levels of hierarchical parallelization methods: inter-node, intra-node, and vectorization. In the present study, intra-node and vectorization were added on the inter-node parallelized FEM code, and the performance was examined. As a result, we achieved 30 times acceleration at maximum. Additionally, we achieved 10 TeraFLOPS, which was approximately 30% of peak performance, when we used 4,096 processors.
Kushida, Noriyuki; Okuda, Hiroshi*
Journal of Computational Science and Technology (Internet), 1(1), p.2 - 13, 2007/00
Stress singularity is usually observed in practical stress analysis, and it may lead to the deterioration of the convergence rate of the preconditioned conjugate gradient method(PCG). Until now, parallel PCG has been used without considering the practical issues; therefore, the deterioration was induced in the problem in which stress singularity was observed. The convergence acceleration method was developed in parallel PCG based on controlled domain decomposition. The acceleration method can be achieved by considering the spatial locality of stress singularity and preconditioning of conjugate gradient method. The convergence acceleration method reduces the 15 % of iteration of PCG as a maximum, where the singular area is included in one domain.
