Experimental and Numerical Simulation Study on Cross Interface Propagation Behavior and Main Control Mechanism of Tensile Cracks in Bi‐Granite

ABSTRACT This study investigated cross‐interface crack propagation mechanisms under tensile loading through integrated laboratory experiments and numerical simulations. Mineral compositions and grain characteristics of bi‐material granite (bi‐granite) were analyzed using X‐ray diffraction (XRD) and polarized light microscopy. Interface parameters were calibrated via Brazilian splitting tests, with a heterogeneous grain‐based model (GBM) developed through mineral‐boundary‐interface hierarchical calibration. Particle Flow Code (PFC) simulations systematically explored interface cementation strength ( N = 0.6–2) and inclination angle ( θ = 0°–90°) interactions. Results indicate tensile strength follows non‐monotonic angular dependence peaking at θ = 30°. Interface‐aligned propagation dominates under N ≤ 0.8 or θ ≤ 30°, transitioning to through‐interface penetration at N ≥ 1.4 or θ ≥ 60°. Crack evolution demonstrates strength‐energy dual control, where inclination angles regulate tensile‐shear conversion via stress field restructuring, accompanied by nonlinear critical threshold evolution. Concurrently, increased mica content significantly reduces tensile strength, while the inherent brittleness of quartz and feldspar intensifies stress concentration effects. These mechanistic insights advance the optimization of hydraulic fracturing strategies in deep geothermal reservoirs.