Mesoscopic crack evolution and damage constitutive modeling in double-fractured granite: Effects of rock bridge angle and energy dissipation mechanisms

To investigate the mesoscopic crack evolution characteristics and energy damage evolution laws of granite under different rock bridge inclinations, a discrete element mineral crystal model (GBM) was established based on laboratory tests and mineral composition analysis of granite. Combined with uniaxial compression tests and numerical simulation experiments, the reliability of the GBM was verified, the mesoscopic crack evolution process and energy evolution laws were analyzed, and a damage constitutive equation was developed. The research results indicate that the peak stress of granite exhibits a U-shaped variation with respect to the inclination angle, with the lowest strain and most pronounced brittleness at 60° and the highest strain and ductility at 0°. The elastic modulus increases with the inclination angle, which is attributed to the enhanced stiffness resulting from the oriented arrangement of minerals at high inclinations. The greater the rock bridge inclination, the higher the compressive strength of granite and the greater the strain required for failure, while the elastic modulus is less affected by the inclination angle. Intergranular tensile cracks appear first and dominate, mainly distributed within quartz minerals. The total energy exhibits a semi-parabolic trend with strain, and the energy accumulation rate of specimens with a 90° inclination is significantly higher. The elastic energy shows a similar increasing trend before the peak and dissipates rapidly after the peak, reflecting the rapid release of elastic stored energy. The peak energy storage efficiency fluctuates within the range of 0.7–0.8, showing a “rise-fall-rise-fall” pattern with increasing inclination angle, but remains generally stable. Specimens with a rock bridge inclination of 60° are most prone to fracture. A damage constitutive model with three variable parameters was constructed, and verification results indicate that the model has high fitting accuracy, providing a theoretical basis for the stability assessment of rock engineering.