Densification and devitrification of fused silica induced by ballistic impact: A computational investigation

Abstract

A molecular-level computational investigation is carried out to determine the dynamic response and material topology changes of fused silica subjected to ballistic impact by a hard projectile. The analysis was focused on the investigation of specific aspects of the dynamic response and of the topological changes such as the deformation of highly sheared and densifed regions, and the conversion of amorphous fused silica to SiO 2 crystalline polymorphs (in particular, α-quartz and stishovite). The topological changes in question were determined by carrying out a postprocessing atom-coordination procedure. This procedure suggested the formation of stishovite (and perhaps α-quartz) within fused silica during ballistic impact. To rationalize the fndings obtained, the all-atom molecular-level computational analysis is complemented by a series of quantum-mechanics density functional theory (DFT) computations. The latter computations enable determination of the relative potential energies of the fused silica, α-quartz and stishovite, under ambient pressure (i.e., under their natural densities) as well as under imposed (as high as 50 GPa) pressures (i.e., under higher densities) and shear strains. In addition, the transition states associated with various fused-silica devitrification processes were identified. The results obtained are found to be in good agreement with their respective experimental counterparts.