Study on fatigue characteristics and thermal damage mechanism of red sandstone under high temperature-cyclic load coupling

•The red sandstone was tested under high temperature-cyclic load coupling.•The factors of limiting energy storage and dissipation were defined.•Coupling damage was determined based on Lemaitre strain equivalence hypothesis.•The thermal damage mechanism was revealed by XRD and TG-DSC techniques. In this paper, the fatigue characteristics of red sandstone after heat treatment were analyzed from the aspects of stress-strain curve, deformation, energy and damage. Furthermore, the thermal damage mechanism was discussed by X-ray diffraction and thermogravimetric-differential scanning calorimetry synchronous analysis tests. The results showed that 400 °C was the threshold temperature. Below this temperature, the brittleness, failure stress and stiffness of the specimen were enhanced. Otherwise, they were weakened. Mineral decomposition, dehydration and crystal expansion occurred during the heat treatment process. The thermal damage mechanism of red sandstone can be clarified by a competitive mechanism of strengthening and weakening effects.