Modeling From Molecular Dynamics Simulations of Ejecta Production Induced by Shock-Loaded Metallic Surfaces

The capability of molecular dynamics (MD) simulations to capture the physics of fragmentation is used to investigate the production of an ejecta cloud from shock-loaded metallic surfaces. A three-dimensional tin crystal with an initial sinusoidal interfacial perturbation is set in contact with a vacuum and shock-loaded in such a way that it melts directly upon receiving the shock. Upon reflection of the shockwave by the wavy free surface, two-dimensional sheets of liquid metal are ejected, which stretch and break up, forming ejecta of various sizes. A model derived from the simulations provides an analytical form of the temporal evolution of the ejected areal density as a function of the position in the cloud, and also shows that the average size of the particles progressively increases as they are created closer to the free surface. This model is based on the propagation of a fragmentation zone from the edge of the sheets to the free surface; this zone corresponds to the portion of the sheet whose thickness has been reduced to below a critical value during the stretching. Although it is derived from nanometer scale systems, our model may help in the analysis of experiments. © 2017, Society for Experimental Mechanics, Inc.