Analysis of Energy Characteristics and Failure Mode of Pegmatite Gabbro under Confining Pressure

To explore the relationship between energy release and failure mode of pegmatite gabbro under confining pressure, the dynamic mechanical properties under different confining pressures and different impact velocities were studied using split Hopkinson pressure bar and LS-DYNA simulation software, and the energy release characteristics and the failure laws under different confining pressures and strain rates were analyzed. The results show that there is no obvious plastic deformation stage under high confining pressure, and the confining pressure restrains the dynamic compressive strength under high strain rate, and the growth trend of the dynamic compressive strength slows down when the impact pressure is greater than 0.4 MPa in the specimen. The strain rate and the confining pressure have great significance for the energy and the failure mode of the specimen. With the increment of the confining pressure, the proportion of the reflected energy of the specimen gradually increases, while the proportion of the transmitted energy decreases. The energy consumption density increases with the increment of the strain rate, and there is an inflection point at the strain rate of 95 s^–1 (corresponding to 0.4 MPa of impact pressure). The energy consumption density under high confining pressure is greater than that under low confining pressure. The specimen under confining pressure usually has a certain angle on the failure section. LS-DYNA simulations showed the dynamic failure process of the specimen under confining pressure from microscopic point of view. The specimen is mostly shear failure under medium and low confining pressures, while under high confining pressure, the specimen has multiple shear cracks developed and penetrated, showing a composite failure mode.