Numerical investigation of the effect of grain size-to-particle size ratio on the dynamic fracture toughness of granite by using PFC3D-GBM

Based on the Particle Flow Code, a novel grain-based model based on the Particle Flow Code (PFC3D-GBM) is proposed, in which the mineral grains can be filled and grouped at the three-dimensional scale. We model the notched semi-circular bending (NSCB) numerical sample using the PFC3D-GBM, and then implement it to a dynamic fracture test conducted on the SHPB system to investigate the dynamic fracture toughness and micro-cracking characteristic of granite at the grain scale. The influence of grain size-to-particle size ratio (Sr) on the dynamic mechanical properties is discussed from the microscopic point of view. Our numerical results show that as Sr increases, the percentage of intra-granular contacts in the sample increases, leading to an increase in the number of intra-granular cracks generated under dynamic loading. Because the bonding strength of intra-granular contacts is higher than that of grain boundary contacts, the breakage of intra-granular contact requires a relatively larger stress magnitude. Therefore, the external force required for the macro-fracture of the sample increases with increasing grain size. As the particle size decreases, the force chain distribution in the sample becomes significantly denser, which means that more particles are involved in the deformation process, thus increasing the deformation resistance of the sample.