| 講演要旨： |
The influence of stress applied perpendicularly to a slip plane during the shear deformation of a crystal on the ideal shear strength is important in many deformation processes. As an example, one can consider the nanoindentation process as a combination of shear and compressive deformations in the vicinity of the indentor. Previous studies [1] based on the empirical Lennard-Jones potential suggested nearly linear dependence of the theoretical shear strength on the normal tensile and compressive loadings. The aim of this study is to verify those results using ab initio approach.
Fig.1: The energy surface for <110>{111} shear. Atomistic simulations of the shear deformation in fcc metals is performed using first principle method based on pseudo-potentials Vanderbilt ultrasoft pseudo-potentials [2] and plane wave basis set [3]. The fcc crystals are subjected to shear deformations in two common slip systems: <110>{111} and <112>{111}. The crystal energy is computed as a function of two independent parameters: the normalized interplanar distance (the plane distance divided by the equilibrium lattice parameter) and plane shift (see Fig.1). The latter quantity is scaled so that its values of 0 and (1/2)1/2 correspond to the cubic (fcc) state for <110> direction and, similarly, values of 0 and (3/2)1/2 correspond to the cubic state for <112> direction. The corresponding value of the normalized interplanar distance for the cubic state is (1/3)1/2. Such generalized energy surface allows us to evaluate both the shear and the normal stresses at any strain.
- [1] A. Kelly, W.R. Tyson and A.H. Cottrell, Phil. Mag. 15, 135 (1967).
- [2] D. Vanderbilt, Phys. Rev. B 41, 7892 (1990).
- [3] G. Kresse and J. Furthműller, Phys. Rev. B 54, 11169 (1996).
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