Dynamic Damage Constitutive Model and Fracture Evolution Law of Coal and Rock Masses Under Different Confining Pressures and Impact Velocities

ABSTRACT During high‐voltage electric pulse hydraulic fracturing, coal‐rock masses suffer combined static confining pressure and dynamic impact, causing damage accumulation and crack propagation. A dynamic damage constitutive model based on Weibull distribution is established. Hopkinson bar impact tests and LS‐DYNA numerical simulations are performed at five confining pressures (1, 3, 5, 7, 9 MPa) and four impact velocities (3.0, 6.1, 8.9, and 12.1 m/s), with SEM for microscopic observation. The results show that the proposed model precisely characterizes the coupled effects of confining pressure and impact velocity and accurately reproduces the damage evolution of coal and rock masses. The model accurately describes coupled loading effects and damage evolution. At fixed impact velocity, damage decreases by 9% per 2‐MPa pressure rise, and cracks transform from tensile to tensile‐shear types. Under constant confining pressure, higher impact velocity raises damage by over 30% and forms interconnected crack networks.