面心立方晶の転位発生の分子動力学シミュレーションおよび前駆局所ひずみ集中の格子不安定条件による特性解析

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A molecular dynamics (MD) simulation was conducted on a thin wire of a single crystalline nickel subjected to tensile deformation in the [001] direction. When the applied strain, ε_<zz>, is smaller than 0.116,the crystal deforms uniformly and homogeneously, being perfectly elastic. A sudden drop in the applied load takes place at the moment of ε_<zz>=0.116 by a partial yielding. Dynamic process of the local strain concentration and the dislocation nucleation was analyzed through the measurement of a resolved shear strain, γ_<rss>, on every lattice plane in the direction of atom migration due to the partial dislocation : (1) When ε_<zz> reaches 0.116 at the first step of the present MD simulation, a high strain concentration region appears on the (010) surface, where the magnitude of γ_<rss> is larger than 0.13. (2) γ_<rss> increases during the relaxation time for the arrangement of atoms under a constant global strain of ε_<zz>=0.116,which is caused by the relaxation of the atomic potential energy. (3) A partial dislocation nucleates at the region when γ_<rss> reaches about 0.20. (4) The dislocation begins to glide on a (III) plane where γ_<rss> is most concentrated. It is noteworthy that the local strain increases during the relaxation of atomic arrangement before the dislocation nucleation, and that its concentration proceeds to nucleate the dislocation. In order to clarify the mechanism of the strain concentration on a smooth surface of the perfect crystal and the magnitude of the critical resolved shear strain : γ_<rss>=0.13,the crystal was subjected to an ideally homogeneous deformation, and its lattice instability criterion was evaluated based on the Born's concept. It was found that this homogeneously deformed lattice begins to be unstable in the direction of the resolved shear strain when γ_<rss> just reaches 0.13 being equal to the aforementioned crystal. Thus the localization of the resolved shear strain is attributed to the local lattice instability.
一般社団法人日本機械学会の論文
1998-10-25

面心立方晶の転位発生の分子動力学シミュレーションおよび前駆局所ひずみ集中の格子不安定条件による特性解析

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