Shock Waves, Fragmentation, and Hypervelocity Impacts by Molecular Dynamics

Abstract

A wide variety of nonequilibrumi processes can be investigated from the atomistic viewpoint by the method of molecular dyniamics (MD), where the equations of motion of thousands of interacting atoms are solved on the computer. MD simulations of shock waves in three-dimensional fluids have shown conclusively that shear-stress relaxation is achieved through the atomic rearrangement of transverse viscous flow, for which Navier-Stokes hydrodynamics has been shown to be accurate. MD simulations of homogeneous adiabatic expansion have provided significant insight into the process of fragmentation for hot dense fluids, in that the fragment distribution is exponential in fragment mass; moreover, the average mass can be reasonably estimated by a simple model based on energy balance. Finally, both compression and expansion are involved when a high-velocity sphere impacts and penetrates a thin wall; atomistic (MD) simulations of this highly nonequilibrium flow resemble in many ways the continuum (hydrodynamic) simulations, especially when the number of atoms in the simulation is sufficiently large.