Avalanche-like discontinuous plasticity, called intermittent plasticity, is the emergence of unpredictable sudden large-scale plastic deformations, which are characterized by peculiar statistical distributions, i.e., power-law distributions . A remarkable feature of the avalanche plasticity is that the intermittency becomes pronounced strongly in micro-scale samples [2-4]. Thus, suppressing this intermittent behavior will be significant in synthesizing and designing the nano-scale structural materials. Atomistic structures such as grain boundaries (GBs), stacking faults (SFs), vacancies, and other lattice defects might inhibit the intermittency. Actually, it has been demonstrated that GBs play a role as an obstacle to the propagation of the avalanche plasticity . This role might be closely related to mechanical properties of polycrystalline materials. However, theoretical approaches are still quite preliminary, because the role is fully atomistic scale behaviors. To investigate the behaviors, e.g., the dislocation-grain boundary interaction, defect nucleation, dislocation entanglements and so on, molecular dynamics (MD) simulations with realistic interatomic interaction are indispensable.
In our previous MD simulation study, avalanche behaviors of dislocations in single metallic crystals have been successfully reproduced by molecular dynamics simulations of constant strain rate uniaxial tensile deformation . We also applied the numerical method to metallic poly-crystal models simplified by symmetric tilt GBs  and metallic glasses. The numerical results show that avalanche-like motions of dislocations and those of shear transformations of atoms in local areas. The statistical distributions of plastic deformations in our simulations follow power-law distributions which are qualitatively consistent with the previous experimental studies. Our MD simulations also demonstrate that GBs suppress the instability of the plasticity; GBs reduce frequency of system-spanning large scale slips. This fact implies that designs of atomistic structures, such as GBs or SFs, will be significant in synthesizing of nano-scale structural materials. In addition to the plastic manner in bulk solids, a potential of MD simulations for nano metallic materials cooperating to 3D tomography observations by transmission electron microscopes is discussed.
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