A Dynamic CCNBD Method for Measuring Dynamic Fracture Parameters

摘要

The cracked chevron notch Brazilian disc (CCNBD) method is widely used in characterizing static rock fracture toughness. We explore here the possibility of extending the CCNBD method to characterizing the dynamic fracture parameters of rocks. The relevant fracture parameters are the initiation fracture toughness, fracture energy, propagation toughness, and fracture velocity. The dynamic load is applied with a split Hopkinson pressure bar (SHPB) apparatus. A strain gauge is mounted on the sample surface near the notch tip to detect the fracture-induced strain release on the sample surface, and a laser gap gauge (LGG) is used to monitor the crack surface opening distance (CSOD) during the test. With dynamic force balance achieved in the tests, the stable-unstable transition of the crack propagation crack is observed and the initiation fracture toughness is obtained from the peak load. The dynamic fracture initiation toughness values obtained for the chosen rock (Laurentian granite) using this method are consistent with those reported in the literature. The fracture energy, propagation toughness and the fracture velocity are deduced using an approach based on energy conservation.