Calculation and Analysis of Isentropic Release Path of OFHC Copper Under the Assumption of Fluid Model

The research of isentropic release curve is significant for equation of state(EOS) and shock wave released on the free surface of sample. In this paper, the isentropic release curves were calculated by employing linear and quadratic Hugoniot relation as the reference of Grüneisen EOS. The calculated pressure-particle graph showed that the relative deviation among two isentropic release curves and mirror reflection of the principal Hugoniot increases gradually with the releasing process and initial releasing pressure. The comparisons for OFHC copper released into air showed that the experiments can be described well by the isentropic release curves which calculated with quadratic Hugoniot relation. And it is reasonable that the process of OFHC copper released into air at free surface is approximated to isentropic release. The error of free surface velocity approximated as twice of particle velocity is larger than 5% at initial releasing pressure of 180GPa. It is invalided at sufficiently high pressures on the Hugoniot that release behavior of OFHC copper is approximated by a simple mirror reflection of the principal Hugoniot in the pressure-particle velocity plane.