The dynamic asymmetric fracture test and determination of the dynamic fracture toughness of large-diameter cracked rock specimens

Abstract

We propose large-diameter (160 mm) pre-cracked chevron notched Brazilian disc (P-CCNBD) specimens were used to study the asymmetric fracture law and determine the dynamic fracture toughness of rock. Specimens were diametrically impacted by a split Hopkinson pressure bar. The dynamic fracture failure process of each specimen was monitored by crack propagation gauges and strain gauges. Each of the large-diameter P-CCNBD specimens was found to exhibit prominent asymmetric fracture under impact load. The stress equilibrium condition cannot be satisfied. The dynamic fracture toughness values of the rocks were measured using the experimental-numerical method rather than the quasi-static method. The calculation results showed that the dynamic fracture toughness of rocks increases with the dynamic loading rate. In addition, at the 3-D crack front, the dynamic stress intensity factor was found be substantially different at each point. These data suggest that the dynamic fracture toughness of P-CCNBD specimens should be calculated by removing the value affected by an edge arc crack and taking the average value of the remaining points.