Experimental Study on Mechanical and Energy Properties of Granite under Dynamic Triaxial Condition

This article experimentally investigates the mechanical and energy properties of granite under dynamic triaxial loading through improved split Hopkinson pressure bar tests. These tests are conducted under five confining pressures of 0, 2.5, 5, 10, and 20 MPa. The effects of impact velocity (or strain rate) and confining pressure on stress-strain curve, dynamic strength, plastic deformation, energy dissipation, and failure mode are explored. The test results show that the dynamic strength of the granite obviously increases with the increase of confining pressure and strain rate. The plastic deformation of the granite increases, and a plastic yield platform is detected in the stress-strain curve as the confining pressure rises. The influence of strain rate on the Mohr-Coulomb criterion is mainly embodied in the cohesion, and the three-parameter Bieniawski criterion is the best to fit these experimental data. The energy evolution course is divided into four stages according to the slope of stress-strain curve. The effects of energy dissipation density and strain rate on the granite strength are similar to each other. The strain rate and energy dissipation density have a good linear relationship with the incident energy under certain confining pressure. For the same incident energy, both strain rate and energy dissipation density decrease with the increase of confining pressure. However, no clear correlation between energy dissipation rate and incident energy is observed. When the confining pressure increases from 0 to 20 MPa, the dissipation rate of energy is decreased by 62.5 %. Besides, the crack propagation velocity and the damage degree of the granite increase with the energy dissipation density, and the failure modes of the specimens change from the axial splitting to the oblique shear as confining pressure increases.