A study of fracture toughness of granite under impact load using three-dimensional reconstruction and high-speed photography techniques

Abstract

To study the dynamic fracture toughness of granite under impact load, the dynamic stress intensity factor of I-type cracks was calculated based on a bending test for straight cut grooves in semi-circular discs. With the help of high-speed photography, the process of dynamic fracture failure was studied, and it was found that the cracks propagated rapidly in the dynamic fracture toughness test; initiation of cracks occurred at the crystal boundaries; then, the cracks propagated rapidly, accompanied by intracrystalline and cleavage cracks, followed by convergence, penetration, and ultimately failure. By performing surface three-dimensional reconstruction of sample cross-sections using the LM740 laser confocal microscope, the surface coarseness and surface three-dimensional reconstruction of the granite were determined, and relationships between the surface coarseness and crack propagation velocity and between the dynamic propagation toughness and crack propagation velocity were determined. The research results show that the average value of dynamic fracture toughness of the granite was 4.12 MPa m1/2, the crack propagation velocity during dynamic loading was 400–600 m/s, the maximum dynamic propagation toughness was 14.88 MPa m1/2, and the crack surface coarseness and crack dynamic propagation toughness exhibited exponential increasing trends with the increase in crack propagation velocity.