Dynamic crack characteristic and failure mechanism of fractured granite under the influence of fissure angle and impact velocity

Abstract

The energy-release dependent rock burst is crucial to the tunnel engineering for fractured granite rock. To study the influence of fissure angle and impact velocity on the mechanical properties and failure behavior of fractured granite, dynamic tensile tests were conducted by the Split Hopkinson Pressure Bar system, and dynamic fracture morphology and damage condition were monitored through the digital image correlation (DIC) method. The mechanical response and energy evolution of fractured granite under the varying impact velocities were analyzed, and the crack propagation mechanism was revealed by the Particle Flow Code method. The results show that the failure mode of fractured granite transits from tensile damage to tensile-shear mixed damage with the increasing impact velocity, and tensile damage, tensile-shear mixed damage, and tensile damage were successively observed with the increase of fissure angle. In addition, the failure morphology was gradually dominated by increasing impact velocity with the weakened influence of fissure angle, and the crack initiation gradually shifted from the fissure tip into the center of the fissure. Simultaneously, the dissipated energy density and energy dissipation rate exhibit a non-monotonic “increase-decrease-increase” evolution trend with increasing fissure angle, and present a decrease trend from 32.70 % to 11.64 % with the increasing impact velocity. The highest and lowest dissipation rates were presented at 45° and 0° fissure angle for 0.30 MPa loading stress. The minimal tensile stress occurred at 30°, and the highest shear stress was presented at 45° for the stress intensity factor. The finding provides insight into the theoretical analysis and numerical simulation of fractured rock burst in an extreme environment.