Microscale model for intergranular and transgranular damage and fracture in polycrystalline ceramics

Abstract

Intergranular and transgranular fracture play a critical role in determining the fracture behavior and toughness of polycrystalline materials. These mechanisms are governed by microstructural features, including grain size, grain shape, grain 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. This cohesive finite element method (CFEM) based model accounts for anisotropic grain constitutive and fracture behaviors and misorientation angle-dependent grain boundary fracture behavior, enabling the explicit resolution of complex crack paths and patterns. The material considered is Silicon Carbide (SiC), for which the model is calibrated using experimental and molecular dynamics data. Simulations under impact loading reveal dependencies of spall strength on grain size and grain shape. Specifically, the spall strength increases with grain size. 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 up to two-fold increases in the spall strength over aspect ratios in the range of 0.2–10. Analyses reveal that the interplay between intergranular fracture and transgranular fracture is responsible for the observed trends. The promotion of transgranular fracture, particularly in grain fracture sites with high orientation-dependent fracture energies, is essential for the strength enhancement. The findings can be used to identify microstructural configurations that maximize the spall strength under specific conditions. The model presented can also be used to explore microstructure design of other ceramics and ceramic composites.