Damage evolution and failure characteristics of red sandstone with prefabricated crack under coupled dry–wet cycle-fatigue loading

•The red sandstone is tested under coupled dry–wet cycle-fatigue loading tests.•Coupling damage is determined based on Lemaitre strain equivalence hypothesis.•The damage characteristics are discussed with the help of DIC technology. Dry-wet cycle and fatigue loading both severely affect the stability of hydraulic engineering. In this paper, the deterioration process of red sandstone under coupled dry–wet cycle-fatigue loading was investigated from three aspects of deformation, energy, and damage. And the variation law of crack propagation mode of the samples was revealed. The results showed that the elastic modulus and the deformation modulus had a negative correlation with the number of dry–wet cycles, while the maximum strain and the residual strain were the opposite. Coupled damage variable was defined based on porosity and dissipated energy density, and a damage evolution model was established. With the increase of dry–wet cycles, the failure characteristics of the samples evolved from predominantly wing cracks to anti-wing cracks.