Investigation of dynamic fracture in VASCT samples under the effect of different loading modes

In order to clearly reveal the dynamic failure mechanism of cracked rock mass with mixed-mode I/II cracks under impact loads, a variable angle single cleavage triangle (VASCT) sample was proposed. A series of impact tests were implemented using a drop weight impact (DWI) apparatus, dynamic crack initiation time and crack speeds were measured using two strain gauges in the experimental process. AUTODYN code was applied to simulate crack propagation trajectories, and the simulation results of sample failure pattern and crack initiation time were in good agreement with experimental results. The maximum tangential stress around the crack tip was calculated and crack fracture mechanism was also discussed in numerical simulation. Dynamic initiation toughness of mixed-mode I/II crack was calculated using the experimental-numerical method. The results of this study revealed that dynamic crack initiation time becomes earlier with the increase of crack inclination angle alpha, but the crack speeds decrease with the crack inclination angle alpha; When crack inclination angle alpha changes from 0 degrees to 10 degrees, i.e., the failure modes of the pre-crack change from pure mode I fracture to mixed-mode I/II fracture, and the maximum tangential stress, crack initiation time and dynamic fracture toughness change sharply; With the increasing of crack inclination angle alpha, the variation of mode II dynamic fracture toughness is little, and the crack gradually transforms from opening to closing mode.