Abstract
The measured unloading and reloading wave profiles in shocked metals have long been known to show deviations from the usual elastic-plastic response used to model shocked metals. To gain insight into inelastic deformation mechanisms during unloading and reloading from the shocked state and to avoid complexities associated with material heterogeneities present in polycrystalline metals, this work has focused on the shock wave response of single crystals. Here, we report on wave propagation simulations to examine the unloading and reloading response of aluminum single crystals shocked along [100], [110], and [111] orientations to 21 GPa peak stresses. The simulations utilized a dislocation dynamics based, time-dependent anisotropic material description to model shock-induced elastic-plastic deformation. The calculated profiles provide good overall agreement with measured unloading and reloading wave profiles [H. Huang and J. R. Asay, J. Appl. Phys. 101, 063550 (2007)] for all three crystal orientations and for two different peak stresses. Our single crystal simulations show that differences between the profiles calculated using simpler elastic-plastic models and the measured profiles can be understood in terms of time-dependent material inelastic response. Therefore, the general applicability of previous time-independent analysis methods to infer shear strength from unloading and reloading wave profiles is questionable. Our simulations also show that dislocation mechanisms governing the unloading response of shocked Al single crystals differ from those governing the reloading response. Overall, our findings show that a dislocation-based approach provides a useful physical description to explain unloading and reloading of shocked Al single crystals. More generally, the present work demonstrates that understanding and modeling the unloading and reloading response of shocked metals may require the incorporation of time-dependent inelastic deformation response.
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