Effect of Grain Size and Shape on Shock-Induced Spallation in Polycrystalline Ceramics

The shock-induced spallation behavior of polycrystalline ceramics is strongly influenced by microstructural features such as grain size, grain shape, crystallographic texture, and grain boundary properties. In this study, we employ a microstructure-explicit and fracture process-explicit computational framework to investigate how these features impact the spall response of polycrystalline ceramics under dynamic loading conditions. Using the cohesive finite element method (CFEM), the model incorporates anisotropic bulk constitutive behavior, misorientation angle-dependent grain boundary properties, and explicit intergranular and transgranular fracture mechanisms to resolve complex crack paths and spall fracture patterns. The material system studied is silicon carbide (SiC), a high-strength ceramic widely used in impact-resistant applications. Simulation results reveal that spall strength increases with grain size, with larger grains exhibiting enhanced resistance to spall failure. Grain shape, particularly the aspect ratio, significantly affects spall strength, with elongated grains aligned in the shock-loading direction providing up to a two-fold increase in resistance compared to equiaxed grains. The level of grain texture also plays a crucial role, with stronger texture alignment improving spall resistance by promoting favorable fracture mechanisms. Detailed analyses of fracture mechanisms indicate that the interplay between intergranular and intragranular fracture governs energy dissipation during spallation. Intragranular fracture, particularly in grains with higher orientation-dependent fracture toughness, enhances the overall spall strength of the material. These findings provide critical insights into microstructural design strategies for improving the spall resistance of polycrystalline ceramics and offer a computational framework for optimizing microstructures in other ceramic and ceramic composite systems.