Intergranular and transgranular fracture play a critical role in determining the fracture behavior and toughness of polycrystalline materials, such as metals and ceramics. These mechanisms are strongly governed by microstructural features, including grain size, grain shape, crystallographic orientations, and grain boundary properties. We present a microstructure-explicit and fracture process-explicit model for elucidating the relationships between the fracture mechanisms, microstructural features, and macroscopic fracture behavior of ceramics under dynamic loading conditions. The cohesive finite element method (CFEM) is employed, incorporating anisotropic bulk constitutive and fracture behaviors of grains and misorientation angle-dependent grain boundary properties, enabling the explicit resolution of complex crack paths and patterns. The material system considered is SiC. Simulations under impact loading reveal dependencies of spall strength on grain size and grain shape. Specifically, the spall strength increases with grain size, reaches a peak at a grain size of approximately 10 µm and decreases when grain size further increases. The grain shape, characterized by the aspect ratio, also exhibits a strong influence on the spall strength, with grains elongated in the direction of impact loading providing an up to two-fold increase in the spall strength over aspect ratios up to 10. Analyses of microstructure fracture mechanisms reveal that the interplay between intergranular fracture and intragranular fracture is responsible for the observed trends and the underlying processes of grain/grain boundary dissipation and what is commonly referred to as crack bridging in the microstructure. It is found that the promotion of intragranular fracture, particularly in grain fracture sites with high orientation-dependent fracture energies, is essential for strength enhancement. The findings can provide insights for designing tougher ceramics by optimizing microstructures.
2025-04-09 09:00:00
