Three-dimensional discrete element simulation of the triaxial cyclic loading of sandstone based on a nonlinear parallel-bonded stress corrosion model

To reproduce the nonlinear damage of sandstone under cyclic loading, a nonlinear parallel-bonded stress corrosion (N-PSC) model is developed based on the linear parallel bond (LPB) model in particle flow code (PFC). The damage caused by cyclic loading is simulated by nonlinearly changing the bond diameter according to the nonlinear changes in the axial plastic strain of sandstone. The results show that the N-PSC model can effectively reproduce the main mechanical characteristics observed in laboratory tests, including the stress-strain curve, peak strength, axial plastic deformation, elastic modulus, and energy evolution characteristics. The sandstone specimens are damaged slowly during the elastic cyclic loading stage and rapidly after the plastic stage. In the first stage of post-peak cycling, the number of cracks inside the specimen increases dramatically as microcracks expand, coalesce, and form macroscopic fracture zones, resulting in a sharp release of energy. The specimens exhibit shear fracture under triaxial cyclic loading. However, in addition to the main shear fracture, tensile cracks are visible at the top and bottom of the specimen, which are caused by stress concentration extrusion. The N-PSC model is a powerful tool for investigating the evolution of rock damage under cyclic loading.