Molecular-Level Analysis of Shock-Wave Physics and Derivation of the Hugoniot Relations for Fused Silica

Abstract

Equilibrium and non-equilibrium molecular-dynamics simulations are employed in this study to investigate various aspects of shock waves in fused silica (a pure SiO2 amorphous material used in transparent-armor applications). Equilibrium molecular-dynamics simulations are used first to validate that the initial (unshocked) fused silica possesses the appropriate mass density and microstructure (as characterized by its partial Si-Si, Si-O, and O-O radial distribution functions). Next, non-equilibrium molecular-dynamics simulations are employed, within a continuously contracting computational-cell scheme, to generate planar longitudinal (uniaxial motion) shocks of different strengths. By examining and quantifying the dynamics of shock-wave motion, the respective shock-Hugoniot relations (i.e., functional relations between various material-state variables in the material states produced by the shocks of different strengths) are determined. This methodology suggested that irreversible non-equilibrium deformation/damage processes play an important role in the mechanical response of fused silica to shock loading and that the “equilibrium” procedures for Hugoniot determination based on the equation of state and the Rankine-Hugoniot equation may not be fully justified. Finally, the non-equilibrium molecular-dynamics simulations were used to identify the main microstructure modifying/altering processes accompanying the shock-wave motion through fused silica.