Effects of temperature and strain on the resistance to high-rate deformation of copper in shock waves

Elastic-plastic shock compression, unloading, and the stepwise shock compression of copper were investigated at room temperature, 710 degrees C, and 850 degrees C to expand the measurement range of high-rate deformations. The dependences of the dynamic yield stress on the temperature and pressure of shock compression were determined from an analysis of the free-surface velocity histories. Although the initial resistance to high-rate deformation increases anomalously with increasing temperature, even a small strain in the shock wave can change the sign of the temperature dependence of the flow stress. Using these data, the dependence of the plastic strain rate on the shear stress in shock waves and temperature was obtained in the range 10(5)-10(7)s(-1). It was found that at room temperature, the ratio between the shear stress and the plastic shear strain rate in a shock wave practically does not depend on the loading history, whereas at 850 degrees C, the parameters of the plastic flow in the second shock wave deviates significantly from the initial dependence for lower stresses and higher strain rates.