Extended Rice-Walsh equation of state for metals based on shock Hugoniot data for porous samples

摘要

The dimensionless material parameter R introduced by Wu and Jing into the Rice-Walsh equation of state (EOS) deduced from the shock Hugoniot data for porous Al and Cu was shown to be well approximated by a function of pressure alone. This data processing was extended to several metals including Mo, Ni, Co, Cr, Pb, Ta, W, and Fe using porous shock data basically published by Russian researchers. It was again found that the parameter R/p for all metals decays smoothly with shock pressure p and displays small experimental scatter in the high pressure region. It is then possible to construct the Rice-Walsh EOS using the empirically determined function R{p) and its known full-density shock Hugoniot and to reproduce porous shock Hugoniot for these metals. For most degrees of porosity, the agreement between the porous data and the calculated Hugoniots using the empirical function described was very good, while anomalous Hugoniots of Mo and Ni with extremely high porosity exhibit appreciable discrepancies. In this paper, the Wu-Jing parameter as a function of pressure together with thermal contribution was introduced to extend the Rice-Walsh EOS to explain Hugoniots with extremely high porosities. Extended EOS was also formulated with newly introduced thermal variables, which enabled the calculation of the cold compression curve for these metals. The present analysis suggested that the Rice-Walsh type EOS is, in most cases, a preferable choice for analysis with its simple form, pressure-dependent empirical Wu-Jing parameter and its compatibility with porous shock data. Extended Rice-Walsh EOS is only necessary for anomalous Hugoniots.