Study Of The Sound Velocity And The Unloading Path Under High Pressure Of Transparent Window Materials

The symmetry-impact technique is used in this experiment in order to generate the loading-unloading process in the single crystal LiF. VISAR(Velocity Interferometer System for Any Reflector) diagnostic is used to get the particle velocity-time profile obtained from the experiment. Impedance match method is used to get the unloading path behind the shocking from the experimental data.The feasibility for the sound velocity and unloading path under high pressure by using VISAR diagnostic is validated. From the particle velocity-time profile, the unloading path under 27.7 GPa, 38.5 GPa and 53.7 GPa is calculated. The experimental data indicate there is a good linearity between the Lagrangian longitudinal sound velocity and the particle velocity with the fitted formula c1L = 7.66+2.84? There is no evidence of shock-induced melting or phase transition for LiF in our pressure range. There occur the strain hardening and the strain rate hardening in Single crystal LiF under compression. And there is obvious thermal soften by instant adiabatic temperature hoisting. The LiF unloading path and velocity profiles show a clear transformation from the elastic release to the plastic unloading. The experiential equations of the unloading path of LiF is given, which is the basis of the work for measuring the unloading path of other material by using LiF as the window.Numerical simulation also confirm this analysis that the fluid elastic-plastic model can approximately describe the shock compression and release process of single crystal LiF in the teens GPa range, but for precise description, especially in the initial release stage, more detail constitutive model is needed.