Nonequilibrium Physical State of Copper under Shock Compression

Abstract

This paper touches upon a question of whether the physical state of shock-compressed copper is equilibrium. Answering this question requires that experimental data on defective electrical resistance are used to estimate point defect concentration. Quantitative information on the concentration of defects can be obtained if the type of occurring defects is known. A dependence between defect concentration in copper and a shock wave pressure is obtained in an assumption of the predominant formation of vacancies. It is shown that the number of defects monotonically increases with increasing shock wave pressure. The vacancy concentration calculated in this study (≈0.8% at a pressure of 20 GPa) exceeds the corresponding equilibrium value by ten orders of magnitude. Thus, the state of copper under shock compression is highly defective and highly nonequilibrium. The general features of the state of copper and silver are described by comparing data for shock-compressed metals. As demonstrated by comparing the data obtained immediately after the passage of a shock wave through a sample (in situ) with the known results for samples recovered after the experiment, the number of recorded defect concentrations in the first case is larger (up to two orders of magnitude). Thus, the method of stored samples does not provide objective information on the state of substance directly behind the shock front. The problem of constructing the equation of state under conditions of a nonequilibrium physical state is briefly discussed.