Intragranular microplasticity and intergranular microdamage in polycrystalline hexagonal-structure ceramics subjected to a cycle of dynamic compression and tension are studied computationally using the Voronoi polycrystal modeling in conjunction with dynamic finite element analysis. The Voronoi polycrystal model allows explicit simulations of the topological heterogeneity and material anisotropy of the crystals. The constitutive modeling considers volume-compression-dependent crystal elasticity, crystal plasticity by basal slip, intergranular shear damage during compression, and mode-I cracking of grain boundaries during tension. Two sets of model parameters are obtained from the available experimental results on polycrystalline a-6H silicon carbide and on polycrystalline a-phase aluminum oxide, respectively. Numerical calculations are carried out for the two materials using the ABAQUS/Explicit code. The results show that the microplasticity is a more plausible mechanism for the inelastic response of the materials under impulsive compression. On the other hand, the spalling behavior of the shocked materials can be well predicted by the intergranular mode-I microcracking during load reversal from dynamic compression to tension, and is strongly affected by the heterogeneity resulted from the in-grain microplasticity and grain boundary shear damage under compression.
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