Dynamic mechanical properties of rocks with initial defects under impact loading: A comprehensive review

With the continuous development of deep rock engineering, the crumbling and collapse of defect-containing rocks have become unavoidable challenges. Under impact loading, the defect-containing rocks exhibit complex dynamic mechanical responses, and their energy dissipation paths and crack extension mechanisms are significantly affected by the type of defects, loading mode, and endowment environment. This work centers on the Split Hopkinson Pressure Bar (SHPB) test and systematically reviews the current status and the latest progress. Firstly, the testing principles, analytical methods, and damage constitutive models of the SHPB experiment are summarized. Secondly, the effects of different defect types and multi-field coupling environments on the dynamic behavior of rocks are explored, and the means of characterizing the damage evolution by combining with Digital Image Correlation (DIC), 3D laser scanners, and other techniques are discussed. Finally, the research progress and applicability of continuous medium (FEM), discontinuous medium (DEM), and continuous-discontinuous medium methods (FDEM) based on the dynamic damage simulation of defect-containing rocks are analyzed. The results show that the presence of defects significantly alters the local stress distribution of rocks, leading to anisotropy in dynamic strength, fracture characteristics, and energy absorption. In addition, complex environments such as hydraulic action, temperature, and confining pressure further affect the dynamic response of defect-containing rocks. This work reveals the current challenges, including the accuracy of defect characterization, the inadequacy of the nonlinear damage constitutive model, and discrepancies between laboratory environments and in-situ conditions, which provide important references for future dynamic mechanical studies of defect-containing rocks.