Influence of Mineral Grain Size on Crack Propagation in Crystalline Rocks: A Numerical Study Based on Phase‐Field Model

ABSTRACT Regarding the influence of mineral grain size on fracture behavior in crystalline rocks, this paper establishes a heterogeneous unified phase‐field model by integrating the unified phase‐field model, heterogeneous geometric model, and interface phase‐field model, and verifies its capability to simulate crack propagation in heterogeneous materials. Based on this model, numerical simulations of semi‐circular bend (SCB) tests are conducted on crystalline rock specimens with six grain sizes to investigate the influence mechanism of grain size on crack propagation in crystalline rock. The results indicate that as the grain size decreases, the crack propagation path exhibits increased local tortuosity but globally more regular linearity. Under identical failure modes, crack paths in specimens with different grain sizes show significant clustering phenomena. The Load‐CMOD (Crack Mouth Opening Displacement) curve and Length‐CMOD curve correspond to each other, reflecting the crack propagation process and demonstrating that crack propagation is driven by the release of accumulated energy within the specimen. Finally, a hypothesis regarding the influence mechanism of mineral grains on crack propagation paths is proposed based on the principle of minimum energy. Crack propagation is governed by the competition between strain energy and surface energy. When the strain energy increment under non‐propagating conditions exceeds the minimum surface energy increment across all potential propagation paths, the crack advances along the path exhibiting the lowest surface energy requirement.