Molecular dynamics simulations of dislocation dynamicsTuesday (27.09.2016) 15:00 - 15:15 Part of:
Dislocations are of fundamental importance in plasticity and mechanical deformation of solids and their properties are required for understanding of numerous phenomena related to mechanical response. Molecular dynamics simulations allow the study of dislocation motion at the short time and length scales which are difficult to access by experimental means, but require careful convergence for physical meaning. Highly converged simulations were performed on long dislocations in large FCC copper crystal supercells 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. The relation between stress and terminal velocity at cryogenic and room temperatures for both screw and edge dislocations was obtained. A transition from viscous behaviour to near sonic asymptotic behaviour was identified and the velocity dependence of the drag force was characterised. At higher stresses a shift into the transonic regimes occurs and the mechanism and stability of this transition is examined. The thermally activated process of cross-slip was simulated multiple times creating statistical data from which the kinetics and activation parameters were calculated. The effects of stresses in the cross slip and in the glide planes on the activation volumes were determined. Finally, the rate controlling step of the cross-slip process was identified.