Deformation Characteristics and Energy Evolution Rules of Siltstone under Stepwise Cyclic Loading and Unloading

Uniaxial step cyclic loading and unloading tests on siltstone were conducted to investigate the mechanisms and evolution characteristics of rock deformation, including elastic, viscoelastic, and plastic aspects. This study proposes a method for separating dissipated energy into damage energy, which is used for particle slippage and structural fractures, and plastic energy, which remains in cracks that do not open after unloading. Additionally, elastic energy is divided into particle elastic energy, released by particle rebound, and crack elastic energy, released by the reopening of compacted cracks. The results indicate that as the stress amplitude increases, the damage energy consumption, plastic energy consumption, particle elastic energy, and crack elastic energy increase. At peak stress, significant expansion and penetration of cracks within the rock sample occur, leading to a sharp increase in damage energy consumption and a dramatic decrease in the rock sample’s mechanical properties, with the particle elastic energy dropping quickly. Plastic energy dissipation relates solely to cracks that do not reopen during unloading, with minimal change after reaching peak stress. The calculated damage variables, based on damage energy consumption, align with the deformation and energy characteristics of the rock, providing a reasonable description of the damage development process of the rock under cyclic loading and unloading.