The Influence of Mechanical Heterogeneity of Grain Boundary on Mechanical and Microcracking Behavior of Granite Under Mode I Loading Using a Grain-Based Model

Granite is a heterogeneous material characterized by a significant population of mechanically distinct grain boundaries, which exert a substantial influence on crack propagation. An extended grain-based model was developed by integrating the geometric heterogeneity, represented by Voronoi tessellations, and the mechanical heterogeneity of grain boundary, as described by Weibull distribution. This study numerically investigates the influence of mechanical heterogeneity in grain boundary on the mechanical properties and microcracking behavior of semi-circular bend granite samples under mode I loading. The mechanical heterogeneity of grain boundary was assessed by independently varying the heterogeneity index, defined by the shape parameter m in the Weibull distribution. The findings indicate that the force–displacement curve and fracture toughness are primarily influenced by the parallel bond tensile strength and cohesion of grain boundary contacts. When the value of m in Weibull distribution is between 1.5 and 2, a compromise between failure patterns and diverse grain boundaries characterization can be reached. Considering the heterogeneous mechanical properties of grain boundary numerically is able to simulate the local stress concentration of the real rocks, thus accelerating the generation of microcracks and reflecting the brittleness of rock failure. Otherwise, the fracture toughness of the rock will may be overestimated. Generally speaking, models that consider grain boundary heterogeneity will produce larger fracture process zone and microscopically complex crack propagation patterns during loading, and these phenomena are more consistent with experimental observations than those models in which grain boundaries are homogeneous.