Damage evolution of coal under SHPB impact and multi-scale simulation

Abstract

As energy exploitation advances, operations are increasingly moving into deep coal seam regions. Understanding the dynamic mechanical properties of coal seams under complex stress conditions in such deep-seated environments has become a key focus in mining engineering. In this study, an improved Split Hopkinson Pressure Bar (SHPB) test system was used to perform impact loading tests on coal samples under varying pre-stress conditions. Furthermore, triaxial SHPB impact loading experiments were simulated and analyzed using coupled numerical methods: the Finite Element Method (FEM) and the Finite Difference Method–Discrete Element Method (FDM-DEM). A detailed comparison of the two simulation methods was conducted. The research comprehensively investigated the dynamic mechanical properties and damage characteristics of deep coal seams, revealing how peak strength varies under different pre-stress conditions. Merged with previous sentence to reduce repetition: see combined version below. The results showed that coal sample strength gradually decreased with increasing axial pressure. Additionally, confining pressure significantly affected strength, and this effect intensified at higher confining pressures. Under varying axial pressure conditions, the damage mode of coal samples was identified as X- and Y-type shear damage, accompanied by a progressive increase in fractal dimension. In contrast, under varying confining pressure conditions, the fractal dimension gradually decreased. In contrast, under varying confining pressure conditions, the fractal dimension gradually decreased. Additionly, FDM-DEM generally outperforms FEM in simulating dynamic mechanical responses and progressive damage, with smaller average errors, despite occasional larger deviations under extreme prestress. This method enabled a more intuitive representation of the mechanical properties of coal samples and a quantitative characterization of the damage degree. As such, it provides a reliable numerical approach for investigating the damage process and dynamic mechanical properties of coal, offering valuable insights for the safe and efficient exploitation of deep - seated coal resources.