Shock response of magnesium single crystals at normal and elevated temperatures

Abstract

Strength and elastic deformation of natural and synthetic diamond crystals shock compressed along [100] J.A series of magnesium single crystals, from 0.2 to 3 mm thick, were shock loaded in directions parallel and perpendicular to the c-axis of the hexagonal closed packed (hcp) structure and at 45 to the c-axis. Shock compression along the c-axis is associated with the largest Hugoniot elastic limit (HEL) for this material. Microscopic observation of recovered c-cut samples demonstrated intense twinning with a greater density of twins near the impact surface. The low-energy basal slip was activated by shock loading along the inclined direction and has the smallest HEL. In all cases, we observe the decay of the elastic precursor wave and growth of the HEL with increasing temperature. For the inclined shock compression after the HEL, two plastic waves were found where the stress level of the first plastic wave depends on the peak shock stress. Finally, the largest spall strength was along the transversal direction and the smallest in the off-axis direction. The fracture surface of the sample of transversal orientation contains numerous groves oriented along the base planes of the crystals. V C 2014 AIP Publishing LLC. [http://dx.

Analysis of nonlinear elastic aspects of precursor attenuation in shock-compressed metallic crystals

“…Remarks on experimental uncertainty and sparsity of test data are in order. Uncertainty in HEL data on Mg from [40] is reported as ±0.015 GPa, on the order of ±5% of the values of P corresponding to data points in figure 6(b). Corresponding error bars are not shown since these would be smaller than the data points themselves in the figure and would not be visible.…”

“…Conversely, a negative stress gradient corresponding to particle acceleration immediately behind the precursor front would inhibit its decay. The former situation (∂P/∂X>0) seems much more prevalent in data records from experiments [17][18][19][20]40] and nonlinear continuum simulations [14,15]. Physically, the drop in stress behind the precursor spike (figure 1(a)) has been attributed in ductile crystals to stress relaxation caused by multiplication of mobile dislocations [14,19,40,41].…”

“…Specifically, the intrinsic term will be represented via the solution for mobile edge dislocations at the precursor front derived in [16], suitably modified to account for the stress dependence of the shear modulus via (3.19) and the nonlinear elastic contribution in the denominator with c l /U calculated via the method described in section 3.3.1. The contribution from trailing rarefaction sources will be attributed to dislocation generation, noting that the stress gradient is thought to result from dislocation multiplication behind the front [14,19,40,41]. Recall that the linear decay equation (2.7) used in [13] is obtained from (4.1) by setting c l =U, reiterating that the contribution from trailing rarefaction sources vanishes identically in the linear model.…”

“…J D Clayton https://orcid.org/0000-0003-4107-6282 Figure 10. Precursor stress versus propagation distance compared with experimental data for Cu [13], Mg [40], and W [13]. For the nonlinear results, = · M 5 10 5 and =t 10 c 2 .…”

Atomistic study of shock Hugoniot of single crystal Mg

“…A fundamental understanding of deformation and failure response of HCP metals under dynamic loading conditions is therefore required in order to develop capability to withstand ballistic/blast impact. Experimentally, the response of Mg and Mg alloys under dynamic loading conditions has been studied using plate impact and laser shock experiments which focus on the spall strength of the material under different loading conditions [3,4,5,6,7]. While the experimental studies are able to investigate the spall strength at various shock pressures and strain rates, it is difficult to characterize and identify the micromechanisms that determine the deformation and failure response of the metal using experiments alone.…”