Effect of strain rate on the fracture behavior of granite under unconfined compression: A meso-scale energy evolution perspective

The macro mechanical behavior of rock material is attributed to the meso/mineral characteristics. To deeply reveal the mechanisms of strain rate effect on mechanical properties and crack propagation, a series of unconfined compression experiments and simulations for exploring the meso-scale characteristic were conducted at different strain rates. Based on the micro-loading equipment with microphotography capabilities and the numerical grain-based model (GBM) method, the meso-scale crack propagation and energy evolution characteristics of granite during the pre-peak loading process were analyzed. The results indicate that with the increase of strain rate, the crack distribution entropy value increases, which means that cracks are more evenly distributed among various minerals. The differences in stored elastic strain energy among different minerals decrease, resulting in more uniform energy release. In addition, cracks associated with biotite transits from intergranular to transgranular modes. Therefore, the increased strain rate can prompt more minerals to participate in deformation, thereby enhancing the mechanical properties. This study deeply reveals the mechanisms of strain rate on granite crack propagation at the meso-scale, offering valuable insights for the stability and safety of underground space engineering.