Reshock response of shock deformed aluminum

Abstract

The effects of shock loading on compressive yield strength are presented for several aluminum materials. These include commercially pure aluminum 1060, ultrapure aluminum, pure aluminum single crystal of [100] and [111] orientations, and aluminum alloy 6061-T6. The yield strength of these materials was measured by a cyclic shock loading technique in which the sample was first shocked to longitudinal stresses ranging from 4to22GPa, followed by complete release and then reshocked to final states of 4–31GPa. The results reveal that the yield strength of 6061-T6 alloy, as determined through measurement of its Hugoniot elastic limit during reshocking, remains unchanged after first shock loading and release. In contrast, the yield strength of all pure aluminum materials was found to increase during reshocking. In addition, plastic strain hardening was observed in all reshock wave profiles after the initial elastic response, as observed through substantially higher reshock wave speeds. This results in substantially higher reshock Hugoniot stresses than predicted by the original Hugoniot of aluminum at the same compression. The compressive yield strength at the reshock Hugoniot stress was estimated by comparing the first and second Hugoniot states and correcting for thermal effects. The results suggest that strain hardening during second shock compression is independent of first shock amplitudes over the range of 6–22GPa and appears to saturate for a first shock stress greater than 6GPa. The temperature correction for the Hugoniot mean stress shows that the increased temperature produced by second shock compression significantly reduces the flow strength during reshocking and makes the resultant strength strongly dependent on loading history.