Thermal-mechanical coupling induced strain rate sensitivity mechanism of coal-measure sandstone and its dynamic damage constitutive model

Abstract

Effective stability management of surrounding rock is critical to ensuring the safety and efficiency of underground coal gasification operations. This study investigates the strain rate sensitivity and damage evolution of coal-measure sandstone under coupled high-temperature and high-strain-rate conditions. Using a custom-built near-uniform high-temperature dynamic loading system, the dynamic mechanical properties, energy dissipation behavior, and fractal features of the rock were examined. Experimental results reveal that at elevated temperatures, coal-measure sandstone exhibits a clear strain rate effect. As the strain rate increases, the dynamic elastic modulus, compressive strength, and energy dissipation density increase by 50.31%, 50.16%, and 495.91%, respectively, while the peak strain decreases by 15.83%. The failure mode shifts from tensile to tensile-shear composite failure, the fractal dimension increases by 17.21%, and the energy dissipation rate declines by 49.82%. A temperature influence coefficient is defined based on energy dissipation density. By integrating this with micro-element strength theory, a damage evolution constitutive model is proposed and verified using MATLAB. This model provides a theoretical basis for evaluating rock stability and developing disaster prevention strategies under high-temperature dynamic loading conditions in similar geological engineering applications.

Keywords

coal-rock medium / strain rate effect / dynamic constitutive equation / near-uniform high-temperature condition

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