Research on Fatigue Life Testing of Sandstone Based on Energy Evolution

Rock fatigue research is of crucial importance in a range of engineering disciplines, including deep resource development, underground engineering support, and slope stability. The present study proposes a fatigue life prediction method based on critical elastic properties, with a view to addressing the shortcomings of traditional methods. These include strong stress path dependency and unclear physical mechanisms. The present study utilised standard sandstone specimens as the test material, employing an MTS815 servo-rigid testing machine. Tests were conducted under varying confining pressures and stress amplitude conditions. The mechanical properties of the material were analysed, including hysteresis loop characteristics, residual strain evolution, dynamic elastic modulus, and damping ratio response. The law of elastic energy accumulation was summarised, and a critical elasticity criterion formula accounting for confining pressure effects was established. A quantitative relationship between energy evolution and fatigue damage was constructed. Results indicate that when the upper limit of cyclic stress exceeds yield stress, elastic energy exhibits concave function accumulation, and total energy evolution shows “step-like” growth characteristics.Within the 4–12 MPa confining pressure range, the fatigue life prediction model achieves a relative error of less than 10% between predicted and actual values.