Influence of axial prestress and loading rate on dynamic fracture of pre-faulted granite

Understanding the interplay between axial prestress and dynamic loading rate is critical for elucidating dynamic rupture mechanisms in pre-faulted rock masses, with direct implications for earthquake nucleation and underground engineering stability. This study investigates the dynamic fracture responses of granite specimens containing pre-existing faults with joint angles of 20° and 25°, subjected to axial prestress ranging from 0 to 6 MPa and loading rates between 195 and 1437 GPa/s. An improved split Hopkinson pressure bar (SHPB) system integrated with ultrahigh-speed camera and digital image correlation (DIC) technique was employed to capture real-time fracture evolution, energy dissipation, and slip dynamics. The results reveal that both axial prestress and loading rate substantially regulate dynamic strength, rupture mode, and energy absorption. Notably, peak energy absorption occurs at an intermediate prestress level (4 MPa), while elevated prestress (6 MPa) suppresses slip rate and enhances rupture stability. With increasing loading rate, fracture transitions from tensile-dominated to mixed shear-tensile failure. The findings highlight the nonlinear coupling effects of prestress and strain rate on rupture dynamics, offering new insights into fault activation mechanisms under combined static-dynamic loading conditions.