RESEARCH ON DYNAMIC FRACTURE BEHAVIORS OF STANSTEAD GRANITE

A recently proposed method is used to measure dynamic fracture parameters of Stanstead granite(SG), such as fracture initiation toughness,fracture energy,fracture propagation toughness,and fracture propagation velocity. With the method,a notched semicircular bend specimen is loaded by the split Hopkinson pressure bar(SHPB) system;and a laser gap gauge system is employed to monitor the crack surface opening displacement (CSOD) of the specimen. The dynamic initiation toughness is subsequently calculated by using a quasi-static formula,for the dynamic force balance is achieved in the test. Based on the CSOD data,residual kinetic energies of the two fragments are estimated. The average propagation fracture energy and thus the propagation toughness are calculated. The average fracture propagation velocity is estimated with a series of crack gauges glued on the specimen. It is shown from the results of the experiments that both the initiation and propagation toughnesses of this brittle solid are loadingdependent. The propagation toughness is larger than the initiation toughness. The propagation fracture toughness is shown to increase with the fracture propagation velocity. The fracture arrest toughness and the limiting fracture propagation velocity are obtained by a literature model of this relationship. The results of SG in this work are compared with the ones of Laurentian granite(LG). The grain size of SG is much larger than the one of LG,so that the fracture is easy to be generated and arrested but difficult to propagate. On the contract,the LG has smaller dynamic propagation toughness and the larger limit fracture propagation velocity.