Mode I fracture behavior of heterogeneous granite: Insights from grain-based FDEM modelling

•A breakable grain-based model based on FDEM is established for brittle heterogeneous rock.•Simulating the meso-scale mode I fracture characteristics of Beishan granite via SCB specimens.•Taking into account the length of the fracture process zone (FPZ) to investigate mode I fracture toughness. The failure of brittle rock has a significant influence on engineering stability. The purpose of this study is to understand the progressive fracture mechanism of heterogeneous granite from a mesoscopic perspective. In the present work, the fracture process zone (FPZ) model is used to characterize the constitutive relationship of rock cracking in the combined finite-discrete element method (FDEM). Moreover, the breakable grain-based model (bGBM) is established to study the fracture behavior of granite via the semi-circular bending (SCB) tests. To rebuild the meso-structure of granite specimens, an algorithm that considers the mesoscopic grain geometry characteristics and grain contact mechanical properties is utilized. Then, three classic examples, namely, a uniaxial compressive test, a Brazilian splitting test and a semi-circular bending test, are investigated with the numerical model. A good agreement of the load–displacement curves and crack propagation paths can be found between the simulation and laboratory tests. The meso-heterogeneity of granite cause the macroscopic fracture surface of the slit tip to be nearly upright, with local roughness and zigzag. The slit length has a significant effect on the damage distribution range of the SCB specimen, and the peak load and mode I fracture toughness decreases with increasing slit length and supporting span. The accurate measurement of the mode I fracture toughness of SCB specimens needs to consider the FPZ, and the average increment is 39% and 41% under different slit length and supporting span conditions, respectively.