Strength behavior of materials at high pressures

Strength is an important aspect of material behavior for armor performance, planetary science, and accurate property measurement under quasi-isentropic loading and static high pressure. The advent of time-resolved diagnostics allowed the elastic-plastic behavior of solids under shock loading to be detected for the first time. These early experiments revealed a two-wave structure of elastic and plastic shock waves for stresses above the elastic limit. However, the full stress state in the shocked state remained unknown because the conservation equations provide only the longitudinal stress. Since then, a variety of techniques has been used to determine strength in the shocked state. One of the most successful has been using shock/release and shock/reload to find the stress state and strength in the shocked condition. This technique has been applied to a variety of metals and ceramics at stresses of 100 GPa or higher. These experiments have revealed a rich set of behaviors, many of which are still not fully understood. Recently, there has been significant interest in isentropic loading where the material can be significantly cooler and strength even more important. In this paper, we present a current perspective on strength under high pressures, particularly in the dynamic regime, with emphasis on the techniques used to measure strength and their advantages and disadvantages. Results of strength measurements on several materials will be discussed, and interesting aspects of behavior will be highlighted. In addition, shock results will be contrasted with those under isentropic loading. Finally, some new directions in the study of strength will be outlined. (C) 2006 Elsevier Ltd. All rights reserved.