Damage characteristics and energy evolution mechanism of heterogeneous granite under true triaxial dynamic and static loading

To investigate the dynamic mechanical properties and energy evolution behavior of heterogeneous granite under triaxial stress condition, combined dynamic-static loading cyclic tests were conducted on muscovite and vein-type granites using a true triaxial Hopkinson apparatus. Using the couploed FLAC3D−PFC3D coupling modeling, the effects of triaxial stress constraints and high strain rates on the dynamic crack propagation and energy evolution mechanisms of heterogeneous granite were investigated. The results show that during the cyclic dynamic loading process, the connectivity of the internal crack network in granite gradually increases, ultimately forming a highly dense macroscopic shear fracture network parallel to the direction of the minimum principal stress, with the dike specimens showing significantly lower impact resistance. Increasing axial stress raises the proportion of intergranular tensile cracks. This in turn reduces the crack initiation stress ratio (σ_ci/σ_d) and the damage threshold stress ratio (σ_cd/σ_d), achieving crack initiation stress and damage stress threshold earlier, and significantly weakening the dynamic strength of the samples. Lateral stress confinement increases the dynamic damage stress threshold of the samples, delays the timing of its occurrence, suppresses the frictional sliding of particles, reduces the release of destructive kinetic energy, and shows a strengthening effect on the dynamic strength of the samples. Under the true triaxial stress confinement, the impact loading mainly contributes to the dissipation of sliding friction energy, while the kinetic energy remains at relatively low levels throughout the process.