A polycrystalline ceramic may display high strength under dynamic compression but fails catastrophically during load reversal to tension.One plausible mechanism is that heterogeneous plasticity in some of the crystals under compression induces microdamage during load reversal.To examine this possibility quantitatively,we developed a computational method,in which the polycrystalline microstructure is realistically simulated using Voronoi crystals having grain boundary layer.Both anisotropic elasticity and plastic slip in limited crystallographic planes are considered in crystal modeling.The grain boundary material is treated as an isotropic glassy solid,which has pressure-dependent shear strength under compression and fractures in Mode I when the threshold is reached.The structural and material models have been implemented into ABAQUS/Explicit code.Model simulations have been performed to analyze the intragranular microplasticity,intergranular microdamage,and their interactions in polycrystalline alpha-6H silicon carbide subjected to dynamic unaxial-strain compression and then load reversal to tension.It is found that microplasticity is more favorable than intergranular shear damage during compression.However,both the microplasticity-induced heterogeneity and the grain boundary damage affect strongly microcracking during load reversal,which leads to fragmentation or spallation depending on the level of compression.The significance of these findings is discussed.
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