Study on the mechanical response mechanism and constitutive model of black sandstone under uniaxial cyclic loading–unloading with medium–high temperature cycles

During deep roadway blasting excavation, surrounding rock experiences transient thermal impacts from explosive detonation characterized by short duration (< 8 h intervals) and moderate peak temperatures (100–200 °C). To investigate sandstone mechanical behavior under such conditions, black sandstone specimens were subjected to medium–high temperature cycles (100–200 °C, 4–8 cycles, with a single cycle consisting of 2 h of isothermal heating and 6 h of natural cooling) in a constant-temperature chamber, followed by uniaxial cyclic loading–unloading tests with gradient loading rates (0.3–1.0 MPa/s) using a servo-controlled testing machine until specimen failure, with stress–strain evolution and energy dissipation characteristics systematically analyzed. Experimental results show that temperature elevation and cycle accumulation synergistically reduce rock strength, with temperature effects dominating over cycle count, while elastic modulus exhibits distinct behavior by increasing with loading rate and demonstrating progressive enhancement through cyclic loading. Post-thermal treatment energy evolution reveals critical dependence on final-cycle input energy, and a novel damage constitutive model incorporating temperature-mechanical coupling effects was developed to improve prediction accuracy for sandstone strength degradation under cyclic blasting conditions. This work establishes quantitative relationships between thermal damage accumulation, loading rate sensitivity, and energy dissipation mechanisms, providing computational foundations for deep roadway stability evaluation and blasting parameter optimization.