Influence of Grain‐Scale Heterogeneity on Crack Propagation in Crystalline Rocks Based on Phase‐Field Modeling

The mesoscopic heterogeneity of crystalline rocks, primarily manifested in mineral distribution and content, critically controls crack path selection and macroscopic strength. However, a mechanistic and quantitative understanding of these grain‐scale controls remains limited. To bridge this gap, we conduct mixed‐mode Semi‐Circular Bend (SCB) numerical experiments using the heterogeneous unified phase‐field model developed in our previous work, which can effectively capture crack propagation and the associated mechanical response in heterogeneous rocks, to elucidate the distinct roles of mineral distribution and mineral content. The results demonstrate that mineral distribution primarily controls the crack trajectory by fixing soft‐hard phase positioning and interface topology: cracks preferentially circumvent high strength minerals and propagate along weak interfaces, consistent with the minimum potential energy principle. Meanwhile, mineral content dominantly regulates macroscopic mechanical properties, as the global load‐bearing capacity increases markedly with a higher proportion of hard minerals. Moreover, variations in mineral content inevitably induce different mineral distributions, which fundamentally reshape crack paths. From an energetic perspective, the peak load exhibits a clear positive correlation with the peak effective strain energy; when crack initiation occurs within weak mineral phases, effective strain energy is released prematurely at lower levels, constraining global energy accumulation and consequently reducing macroscopic strength. This work provides a quantitative basis for fracture prediction and stability assessment of heterogeneous rock masses, and promotes the understanding of the fracture mechanism of crystalline rocks.