Evolution of Mechanical Properties and Damage Mechanisms in White Sandstone Subjected to Freeze–Thaw Cycles

To explore the mechanical evolution and damage mechanisms of rock in cold regions under freeze–thaw cycles, this study selected white sandstone from mining areas in western China as the research object. Uniaxial compression tests were performed after different numbers of freeze–thaw cycles. Digital Image Correlation (DIC) was employed to analyze the deformation evolution and crack propagation characteristics, and the damage mechanisms were interpreted from the perspective of energy evolution. The results show that with an increasing number of freeze–thaw cycles, the peak stress and elastic modulus of the white sandstone decrease significantly, with the most substantial reduction occurring between the 15th and 30th cycles. The stress–strain curves exhibit a prolonged compaction stage and increased peak strain, indicating that freeze–thaw action exacerbates the accumulation of internal damage in the rock. DIC analysis reveals that freeze–thaw action causes rock deformation to concentrate at the specimen edges at an earlier stage, accelerates crack propagation, and leads to a gradual transition in failure mode from tensile failure to tensile-shear composite failure, with the degree of failure becoming more severe. Energy evolution analysis indicates that freeze–thaw cycles reduce the total input energy and the elastic strain energy at peak stress, while the proportion of dissipated energy increases, suggesting that freeze–thaw damage results in greater energy consumption through irreversible deformation. Finally, based on the Lemaitre strain equivalence hypothesis and the Weibull distribution, a damage constitutive model considering the coupled effects of freeze–thaw and mechanical loading was established by introducing correction factors, and its validity was verified.