Quasielastic release in shock-compressed solids

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Abstract
Shock‐ and release‐wave measurements are reported for 6061‐T6 aluminum [J. R. Asay and L. C. Chhabildas, in Shock Waves and High‐Strain‐Rate Phenomena in Metals, edited by M. A. Meyers and L. E. Murr (Plenum, New York, 1981), pp. 417–431], oxygen‐free‐electronic copper, and a Si‐bronze alloy. Significant departure from ideal elastic‐plastic response is observed in all three materials. Experimentally determined release‐wave profiles show evidence for the onset of reverse plastic flow immediately upon release from the shocked state. This phenomenon is analyzed in terms of internal stresses acting on straight dislocation pileups and pinned dislocation loops created by the shock‐compression process. Following shock compression and prior to release, the internal stresses are opposed by the applied shear stress; that is, they exactly balance each other and no plastic flow occurs. As the applied stress is reduced in the unloading wave, reverse plastic flow occurs immediately due to internal reverse stresses acting on these pileups and pinned loops. This effect reduces the longitudinal modulus, and hence, the release‐wave speed in what we normally think of as the ‘‘elastic‐wave’’ regime. Interpretations of quasielastic release‐wave data and calculations are expressed in terms of micromechanical concepts.