Elastic-plastic deformation and fracture of shock-compressed single-crystal and polycrystalline copper near melting

The Hugoniot elastic limit, the yield strength, and the spall strength of polycrystalline M1 copper and single-crystal (110) and (111) copper are determined during shock compression up to 8 GPa in the temperature range 20–1080$^\circ$C from an analysis of the free-surface velocity profiles recorded with VISAR laser velocimeter. The measurements show that all copper samples exhibit strong athermal hardening (increase in the Hugoniot elastic limit) near the melting temperature. Copper single crystals have a very low elastic limit in the temperature range up to 600$^\circ$C, this limit increases sharply as the temperature increases to 1000$^\circ$C, and it depends on the crystallographic orientation of a single crystal. The temperature dependence of the spall strength has a threshold character for all copper samples. Copper single crystals demonstrate higher resistance to spall fracture; however, near the melting temperature, the difference between the spall strengths of the copper single crystals and M1 copper becomes insignificant, 50% of the initial level.