The effect of initial densification on the spallation damage of silica glass induced by planar impact

Densification, one of the main properties of silica glass, is very important in understanding the dynamics of materials. In this work, we investigate the effect of initial densification on the spallation damage of silica glass induced by planar impact with classical molecular dynamics simulations. At the same impact velocity, the higher the initial densification, the higher the shock pressure and shock wave velocity, but the lower shock temperature. As a result, the higher densified silica glass has higher spall stress. The spall strength from bulk decreases approximately linearly with the impact velocity, but it increases with initial densification to a certain extent and especially at higher impact velocity. The spall strength from the surface is underestimated at lower impact velocity and overestimated at higher impact velocity. Of course, that can be improved distinctly by the modified acoustic method. The microstructure analysis reveals that the higher densified silica glass causes a higher nucleation rate and wider spallation damage region. Except for shear transformation, tension transformation zones coalescence also happens in higher densified silica glass that has more porosity during spallation, reflecting the enhancement of spall ductility. In addition, spall damage of higher initial densified silica glass develops more rapidly and tends to form locally larger voids. After spallation, parts of 4-fold Si are converted to 3-fold Si and 5-fold Si, and initial densification can weaken the conversion.