Dynamic characteristics and damage constitutive model of high-temperature bedding sandstone under cyclic impact

To investigate the dynamic characteristics and dynamic damage constitutive model of high-temperature bedding sandstone under cyclic impact, the physical properties of bedding sandstone after exposure to 300−1100 ℃ were first examined, and the influence of temperature on the color, mineral composition, mass and wave velocity of the specimens was recorded. Second, the dynamic characteristics of high-temperature bedding sandstone under cyclic impact were studied with a split Hopkinson pressure bar (SHPB) apparatus, and the dynamic responses of bedding sandstone at different strain rates and impact numbers were analyzed. Finally, on the basis of the visco-elastic damage element model for bedding rock, a dynamic constitutive model that accounts for high-temperature-impact-load coupling damage was established and verified against experimental data. The results show that the crystallization temperature of the dominant mineral quartz lies between 500 ℃ and 700 ℃; the higher the temperature, the darker the apparent color of the rock and the lower its mass. With increasing temperature, the wave velocity and peak stress first decrease and then increase. Temperature inflicts greater damage on 0° and 45° bedding sandstone, and the damage is most pronounced at 900 ℃. Under an impact voltage of 1300 V, the peak stress of bedding sandstone increases and then decreases with increasing impact number. Impact loading renders 0° bedding sandstone more susceptible to failure after high-temperature exposure, whereas 45° and 60° bedding sandstone exhibit strong impact resistance. The difference between the predicted and experimental curves is small, indicating that the model satisfactorily describes the cyclic-impact mechanical behavior of high-temperature bedding sandstone. The findings provide a valuable theoretical reference for the prevention and control of rock dynamic disasters in complex deep geothermal engineering environments.