Energy characteristics of rocks prior to macroscopic fracture under cyclic loading

To clarify the damage evolution of rock-like materials with defects under cyclic loading, gypsum specimens containing prefabricated nonpenetrating crack(s) are employed to undertake a quantitative study of the energy in the failure process of brittle materials under cyclic loading. The results show that under cyclic loading, the laws of energy accumulation, transformation, and release can effectively reflect the damage evolution process of rock-like materials. In the damage process of gypsum specimen, the number of nonpenetrating cracks can influence the elastic energy density, the total energy density, and dissipated energy density. The surface free energy of new cracks tends to increase to a certain extent as the number of cycles increases. Additionally, the expressions for the total energy, stored energy, dissipated energy, and damage of the gypsum specimen under cyclic loading are derived and tested through the experimental results. A quantitative analysis and calculation of the crack surface energy have also been conducted, along with an estimation and analysis of the microcrack surface free energy. These findings are of great significance for understanding the mechanisms of rock failure and rock engineering disasters in deep rock engineering, such as spalling, collapse, and rock burst, from the perspective of energy accumulation, transformation, and release.