Dynamic mechanical degradation of thermally treated sandstone under impact loading: A 3D numerical analysis with experimental validation

To investigate the mechanical responses of sandstone subjected to dynamic impact loading after exposure to high temperatures, this study adopted a collaborative analysis approach that integrates experiments, numerical simulations, and theoretical models. It systematically examined the dynamic response and damage evolution of sandstone in coal fire regions during the SHPB (split Hopkinson pressure bar) dynamic impact tests. The primary objective was to elucidate the rate-temperature effect characteristics of sandstone under the combined influence of varying impact loads (impact air pressure) and temperatures. A three-dimensional numerical model was developed using the ANSYS/LS-DYNA software in combination with the HJC (Holmquist-Johnson-Cook) constitutive model. The findings showed that: The stress-strain curves derived from the numerical simulations are basically consistent with those obtained from the experiments. The peak strength of sandstone diminished significantly with increasing temperature, whereas it exhibited strengthening characteristics with rising impact velocity; An analysis of the failure mode revealed that sandstone subjected to impact loading at high temperatures (200-1000℃) generally exhibits a double-cone or inverted cone failure morphology. Moreover, sandstone specimens at high temperatures failed earlier than those at room temperature, which indirectly suggested that high temperature induces certain damage to the sandstone, resulting in premature failure; A modified constitutive equation considering the strain-rate effect was developed based on the Z-W-T (Zhang-Wang-Tang) constitutive model. The curves fitted by this equation exhibited a strong correlation with the experimental data. The research results elucidated the dynamic mechanical degradation mechanism of sandstone under the coupled conditions of high temperature and impact loading. This study provides a theoretical foundation for evaluating stability and implementing disaster prevention and control measures for rock masses affected by blasting in coal fire environments.