Determination of dynamic rock Mode-I fracture parameters using cracked chevron notched semi-circular bend specimen

Rock dynamic fractures are common in many geophysical processes and engineering applications. Characterization of rock dynamic fracture properties such as the initiation fracture toughness, the fracture energy, and the fracture velocity, is thus of great importance in rock mechanics. A novel method is proposed in this work to measure dynamic Mode-I rock fracture parameters using a cracked chevron notched semi-circular bend (CCNSCB) specimen loaded by a split Hopkinson pressure bar (SHPB) apparatus. A strain gauge is mounted on the sample surface near the chevron notch to detect the fracture onset, and a laser gap gauge (LGG) is used to monitor the crack surface opening distance (CSOD) during the dynamic 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 calculated from the dynamic peak load. The average dynamic fracture energy as well as the fracture propagation toughness are calculated based on the first law of thermodynamics. The measured dynamic fracture properties of Laurentian granite using CCNSCB method are consistent with those reported in the literature using other methods.

► A cracked chevron notched semi-circular bend (CCNSCB) specimen was adopted to measure the dynamic fracture properties of fine-grained rocks.
► We used a modified split Hopkinson pressure bar (SHPB) to exert controlled dynamic load to the rock.
► We proposed a method to quantify the dynamic fracture initiation toughness of the rock sample using finite element analysis.
► We proposed methods to quantify the dynamic fracture energy and fracture velocity of the rock sample.
► The fracture transition from stable growth to unstable growth of the specimen is demonstrated.