Atomistic simulation of transonic dislocations

Abstract

Recent work has been done on the analysis of elastic stress singularities, such as cracks and dislocations, which propagate at supersonic speeds. Gumbsch and Gao have performed atomistic simulations in which dislocations are created and travel at transonic velocities (speeds which are greater than the material's shear wave speeds but less than the longitudinal wave speed) close to the theoretical value corresponding to the radiation-free state for glide motion. Gao et al. have derived expressions for this radiation-free velocity in both isotropic and anisotropic media. We have performed molecular dynamics simulations showing dislocation nucleation at crystal surface ledges. Dislocations were nucleated at either sub- or transonic velocities, depending upon the ambient temperature, and accelerated to transonic speeds. This paper shows the velocity profiles for the emitted dislocations and compares velocities observed with a theoretical minimum-radiation speed derived by a Stroh-type anisotropic elasticity analysis performed by Barnett and Zimmerman. Our findings are particularly exciting considering these simulations were not specifically engineered for the purpose of creating transonic defects, but show agreement with theory nonetheless.