Energy evolution characteristics and mechanical properties of freeze-thawed red sandstone under repeat impact loading

To investigate the mechanical properties and energy evolution characteristics of freeze-thawed (F-T) red sandstone subjected to repeated impact loads, a series of repeated impacts were conducted on F-T red sandstone specimens using a split Hopkinson pressure bar (SHPB) device. The results demonstrate that with an increase in F-T cycle numbers, there is a continuous decrease in P-wave velocity accompanied by an increase in porosity and the number of cracks, leading to significant alterations in the microstructure. Both peak stress and modulus of elasticity show negative correlations with both the repeated impact times and F-T cycle numbers, whereas the peak strain and average strain rate exhibit positive correlations with these parameters. Moreover, the absorption energy per unit volume increases with both impact times and F-T cycle numbers, whereas the cumulative absorption energy per unit volume follows a linear increment trend. The established dynamic constitutive model can accurately describe the dynamic stress–strain characteristics of specimens under the repeated impact, demonstrating its high precision in forecasting. Furthermore, the observed failure mode of the specimen was characterized by tensile behavior, with a transition from intergranular fractures to transgranular fractures evident in the microcracks.