Research on the Influence of Friction on the Determination of Rock Fracture Toughness

The accurate determination of fracture toughness ( K Ic ) in rock is of great significance to the study of rock fracture characteristics, the earthquake preparation process and the inversion of earthquake occurrence mechanism, especially for earthquakes induced by hydrocarbon extraction and shale gas mining. However, the effect of contact friction in the loading process on the test results of fracture toughness is rarely considered, and the tested K Ic in previous studies is generally higher than the inherent K Ic of the material. Based on the ABAQUS software, the influence of friction on the test results of K Ic was investigated under different material elastic moduli, loading conditions and specimen sizes by the finite element analysis in this study. The results show that for the specimen with the cracked straight through Brazilian disc (CSTBD) configuration, contact friction has little effect on the test results of fracture toughness. For the specimen with the notch semi-circular bend (NSCB) configuration, if the presence of friction is considered, the changes of load level, the span of roller support and the specimen size can significantly affect the test results of fracture toughness, except the elastic modulus of the material; if the influence of friction is not considered, there will be a large deviation in the research results of the size effect of fracture toughness in rock.