Study of rock dynamic fracture toughness by using VB-SCSC specimens under medium-low speed impacts

Abstract

Dynamic fracture toughness, including initiation toughness, propagation toughness and arrest toughness, are important parameters for describing fracture behavior of rock materials. In order to study these parameters, a new V-shaped bottom single cleavage semi circle (VB-SCSC) specimen which has the arrest function for propagating cracks was proposed in this paper. The arrest function of this specimen is produced by the compressive waves set off from the two inclined bottoms, and the horizontal components of these compressive waves have the confining action on the propagating cracks. The experiments were performed by using a low & medium speed impact test system, and the crack propagation time and propagation speed were measured by using crack propagation gauges (CPG). The angle of the two inclined bottoms of the VB-SCSC specimens was designed as 120° or 150°, and both types of specimens have the arrest function on the propagating cracks. The finite difference code AUTODYN was applied in the simulation of crack propagation path, and the finite element code ABAQUS was applied in the calculation of stress intensity factors. Finally the dynamic fracture toughness was determined by using experimental-numerical method. The results show that the VB-SCSC specimen can be used to measure not only the initiation and propagation toughness, but also the arrest toughness. In the process of crack propagation, the crack may arrest for a period, and the arrest toughness is higher than both the initiation toughness and propagation toughness.