Shock wave compression and release of hexagonal-close-packed metal single crystals: Inelastic deformation of c-axis magnesium

Abstract

To understand inelastic deformation mechanisms for shocked hexagonal-close-packed (hcp) metals, shock compression and release wave profiles, previously unavailable for hcp single crystals, were measured for c-axis magnesium crystals. The results show that the elastic-inelastic loading response is strongly time-dependent. Measured release wave profiles showed distinct peaked features, which are unusual for inelastic deformation during unloading of shocked metals. Numerical simulations show that pyramidal slip provides a reasonably good description of the inelastic loading response. However, {101¯2} twinning is needed to explain the unloading response. The results and analysis presented here provide insight into the relative roles of dislocation slip and deformation twinning in the response of shocked hcp metals.

Shock compression of metal single crystals modeled via Finsler-geometric continuum theory

“…Weyl parameter k corresponds to the volume change predicted via (4) at saturation with G(ξ) scaling the reference volume [16,18,19]. The only parameter not known independently a priori is γ 0 , which is set to its listed value to provide agreement with test data [8] as reported next.…”

“…Results for k = 0 omit the density change from dislocations. Experimental data correspond to planar impact tests on single crystals [8]. The isentrope for purely elastic uniaxial strain compression corresponds to ξ = 0 throughout the deformation process.…”

“…The order parameter is linked simultaneously to inelastic shear slip on six primary pyramidal systems [8,26] and volume change associated with nonlinear elastic dislocation core fields [27,28,29]. Other slip and twinning systems are not activated for this crystal orientation and loading mode.…”

“…Analytical solutions are derived in terms of a set of algebraic equations that may be solved simultaneously, albeit not in closed form. In addition to modeling the response of the nominal material and verifying results versus experimental data [8], effects of changes in several fundamental material properties on dynamic shock stress, shear strength, and dislocation density are investigated.…”

“…Approaches to modeling the response of anisotropic single crystalline metals to planar shock loading include analytical models [1,2,3], steady wave models [4,5], finite difference models [6,7,8], and fully resolved finite element models [9,10,11]. These approaches all tend to adopt continuum crystal plasticity theory [12,13,14] to describe the constitutive response, whereby a flow rule is used to specify the relationship between shear strength and the rate of plastic flow attributed to dislocation glide, for example.…”