Experimental study on the dynamic coalescence of two-crack granite specimens under high loading rate

In this study, the dynamic fracture coalescence of Fangshan granite specimens was studied using the Split Hopkinson Pressure Bar system. Two prefabricated surface cracks with varying inclination angles and inner tip distances were applied to the granite specimens. Two high-speed cameras were set up on two sides of the specimens, one for the side with speckles and the other for crack propagation. According to the crack coalescence mode, the experimental outcome was classified into three types, namely Tensile crack coalescence, Tensile crack and second tension crack coalescence and Tensile crack and second shear crack coalescence. The coalescence mode is mainly a tensile failure, and the change in the inner tip distance of the prefabricated cracks had little effect on the coalescence mode. Digital Image Correlation (DIC) measurement results showed that there were obvious strain concentration areas instead of strain concentration bands in the crack coalescence area. This phenomenon is considerably different from the Brazilian disc tests. The alteration of the inclination angle was expected to have an impact on the coalescence area, thereby leading the coalescence area to change continuously. There was an elliptical enveloping area for crack coalescence. After dynamic equilibrium, the specimen was in a compressed state. The size of the enveloping area was significantly affected by the inclination of the prefabricated cracks.