Modelling crack behavior of granite using multiscale grain-based model

Understanding the macroscopic and microscopic failure process of brittle rocks is helpful to predict the strength and deformation characteristics. However, the brittle rock is a typical heterogeneous material, and it is difficult to study the evolution mechanism of microcracks at the grain scale through laboratory tests. In this study, we propose a multiscale grain-based model based on FDEM, which can consider the actual grain size and the inter-grain and intra-grain contacts of diverse minerals. Most importantly, it can explicitly characterize local polycrystal inclusions and internal cleavage of some mineral grains. Based on the laboratory test data, a series of simulated tests were conducted, including uniaxial tensile tests, uniaxial compression tests, and conventional triaxial compression tests. The results reveal the importance of transgranular fracture capacity in the simulation of mesoscopic fracture. The failure mechanism of rock samples is controlled by the difference between inter-grain and intra-grain tensile strength under uniaxial compression condition. As the confining pressure increases, the tension failure mechanism is transformed into the shear failure mechanism, indicating a gradual change in rock properties from brittleness to ductility. The ability of mineral to absorb elastic strain energy will significantly affect the microcrack path. Under uniaxial tensile condition, the macroscopic failure results from multiple microcracks, and the intergranular tensile cracks are dominated. In addition, the cleavage planes will provide optimal paths for the propagation of microcracks. The results can help us to understand the mechanism of microcrack evolution in heterogeneous rock, and provide a method for comprehensive analysis of crack propagation and energy evolution.

Automated summary

Understanding the failure process of brittle rocks at both macroscopic and microscopic levels is important for predicting their strength and deformation characteristics. However, studying the evolution of microcracks in these rocks is challenging due to their heterogeneity. In this study, a multiscale grain-based model was developed based on FDEM to simulate the behavior of brittle rocks at the grain scale. The model considered the actual grain size, inter-grain and intra-grain contacts, as well as local polycrystal inclusions and internal cleavage. Simulated tests, including uniaxial tensile and compression tests, were conducted based on laboratory data. The results showed that the transgranular fracture capacity played a crucial role in mesoscopic fracture simulation, and the difference in inter-grain and intra-grain tensile strength controlled the failure mechanism of rock samples under uniaxial compression. The ability of minerals to absorb elastic strain energy significantly influenced the path of microcracks and the transition from tension to shear failure mechanisms. The findings of this study provide insights into the microcrack evolution mechanism in heterogeneous rocks and a method for comprehensive analysis of crack propagation and energy evolution.