Abstract: To study the energy characteristics of intact rock samples under cyclic loading and unloading conditions and continuous complex stress conditions, the axial cyclic loading and unloading tests on the red sandstone with small values of constant amplitude cycle + amplitude variation (similar to sine wave) was performed to explore the energy variation rule of intact rock samples before yielding under the cyclic loading and unloading. At the same time, the strain stage of the sample was characterized by the energy of cyclic loading and unloading with small value. The test results show that: (1) During the loading and unloading tests, the external input energy is mainly converted into elastic energy storage, and some energy is consumed, that is, the dissipated energy. (2) The change of the proportion of input energy, elastic energy and loss energy is consistent with the strain stage of the sample, and the deformation characteristics and stage of the sample under sustained load can be quantitatively characterized by the change of energy. (3) The energy in the constant amplitude cyclic stage decreases gradually with the increase of stress, and the damage and deformation stage of the specimen can be indirectly assessed by the energy change under the cyclic loading and unloading with a small amplitude. (4) The change of energy consumption ratio at peak stress in each cycle stage is an inflection point at 45 MPa stage, and the change of energy also has a certain “memory”.

Key words: Complex Stress Conditions, Energy Characteristics, Elastic Energy, Energy Dissipation, Energy Consumption Ratio