MOLECULAR DYNAMICS SIMULATIONS OF DISLOCATION DYNAMICS

Dislocations are of fundamental importance in plasticity and mechanical deformation of solids. Knowledge of their properties and their interaction with the lattice and other defects is required for understanding of numerous phenomena related to mechanical response. In this work we exploit the power of molecular dynamics simulations to study the short time and length scales characteristic of dislocation motion and which are difficult to access by experimental means. Simulations were performed for FCC copper ideal, single crystal with full periodic boundary conditions, incorporating a dislocation dipole with zero net Burgers vector. Kinematics were studied by accelerating dislocations at constant stress and temperature until achieving a terminal velocity. The relation between stress and terminal velocity at cryogenic and room temperatures for both screw and edge dislocations was obtained. While applying high stresses, a breakdown of the viscous behavior is observed such that terminal velocity shifts from linearity with the applied stress into asymptotic approaching to the first sound velocity of the crystal. At even higher stress we observe a shift into the transonic regimes. For screw dislocations we have also simulated the thermally activated process of cross-slip, creating statistical data from which the activation parameters are calculated.