Development of An Extended Molecular Dynamics Capable of Simulating EmergentProcess and Its Application to Brittle/Ductile Transition Phenomena

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1. The concept of Renormalization Group Molecular Dynamics (RGMD) has been proposed. The RGMD consists of Renormalized Molecular Dynamics (RMD) for simulating macroscopic phenomena and Inverse RMD (IRMD) for simulating microscopic phenomena that occur in the RMD. The RMD and IRMD interact each other such that emergent processes can be simulated.2. New inter-particle potentials to be used in the RMD have been constructed based on energy conservation principle in renormalization process. The derived potentials can reproduce size effect of material strength as well as the decrease of strength at high temperature.A method to compute transformations from atomic arrangement in clusters to cluster arrangement around the cluster has been proposed to evaluate the inter-particle potentials described in (3) numerically. The results of numerical examples for carious cases show that the proposed method can construct transformations with satisfactory accuracy.4. The necessity of introducing viscosity in computing particle motion in the RMD has been clarified based on the physical phenomena through which viscosity appears. Then an extended MD algorithm for computing particle motion with viscosity has been developed. The result of simulation obtained using this algorithm with regard to tensile test of a copper specimen on micrometer size shows brittle fracture under pulling speed at 100m/s. This result is consistent with experimental ones obtained by impact tensile test.