Multi‐Scale Fracture Behavior and Energy Evolution Characteristics of Heterogeneous Granite Under Impact Loading

ABSTRACT To investigate the influence of heterogeneity on the dynamic mechanical behavior of rocks, a series of impact tests was conducted on mica‐rich granite and vein‐type granite using a large‐diameter split Hopkinson pressure bar. These experimental studies were complemented by 3‐d grain‐based model (3‐d‐GBM) and Discrete Element Method‐Finite Difference Method (DEM‐FDM) coupled modeling. The results indicate that the large grain size of mineral particles in vein‐type granite leads to a pronounced reduction of homogeneity at the mineral scale. The dynamic mechanical behavior of these rocks is governed by the combination of the weakening effect of microcrack networks and the strengthening effect of high quartz and feldspar contents. These dual influences lead to highly heterogeneous and discrete sensitivities in dynamic strength, energy dissipation density, and fractal fragmentation characteristics relative to the strain rate. Under impact loading, intergranular damage predominates, and the strain rate is correlated with the evolution of microcracks. Tensile cracks consistently outnumber shear cracks, with a slightly higher proportion of intergranular over intragranular cracks. As the mica content grows, the sensitivity of both the dynamic strength and failure mode to the strain rate also significantly increases. Furthermore, the dynamic strength and failure strain exhibit a quasi‐linear negative correlation with both the mica content and the degree of heterogeneity. The greater the heterogeneity coefficient, the more sensitive the dynamic strength to the strain‐rate effect. Furthermore, a strain‐rate evolution model was developed to describe the dynamic strength under different mineral contents and heterogeneity conditions.