Experimental and numerical investigations on the fracture surface roughness of crack branching of granite

Dynamic fracture events occur when the input energy is enough to cause breaks along defects, typically resulting in crack branching. In this study, the branching and fracture surface roughness of granite are comprehensively examined. The fracture surface roughness is described in terms of the joint roughness coefficients (JRCs), which are calculated using the dimensionless parameter Z2. The data processing results reveal that Z2 is sensitive to both sampling interval and the size of the Gaussian filter. Through comparative analysis, the optimal filter size and sampling interval for calculating JRCs are determined to be 0.8 mm and 0.01 mm, respectively. The relationship between dissipated energy and JRCs is established using non-symmetrical branch fractures with various roughness values. The findings indicate that an increase in the system's total dissipated energy causes a decrease in the mean roughness of the crack branching surface, leading to an increasingly smoother fracture surface. Finally, a numerical simulation model is developed for the split Hopkinson pressure bar (SHPB) test by employing a discrete-continuous coupled approach of Particle Flow Code (PFC) and Fast Lagrangian Analysis of Continua (FLAC). This hybrid approach facilitates an in-depth investigation of the mesoscopic fracture properties of granite using the grain-based discrete element method (GB-DEM).