Effect of irreversible phase change on shock-wave propagation

Abstract

New release adiabat data for vitreous GeO_2 are reported up to ∼25 GPa using the VISAR technique. Numerical modeling of isentropic release wave induced dynamic states achieved from one dimensional strain–stress waves is consistent with a phase change that induce an increase in zero-pressure density from 3.7–6.3 Mg/m^3 starting at ∼8 GPa. The first release adiabat data for SiO_2 ( fused quartz) are presented (obtained with immersed foil technique) . Above 10 GPa, the SiO_2 release isentropes, in analogy with GeO_2, are steeper than the Hugoniot in the volume-pressure space, indicating the presence of an irreversible phase transition (to a stishovite-like phase). We simulate propagation of shock-waves in GeO_2, in spherical and planar symmetries, and predict enhanced attenuation for shock pressures ( p) above the phase change initiation pressure (8 GPa) . The pressure from a spherical source decays with propagation radius r, p ∼ r^x, where x is the decay coefficient. Modeling hysteresis of the phase change gives x = −2.71, whereas without the phase change, x = −1.15. An analytical model is also given.