Damage behavior of sandstone under cyclic loading with different frequencies, amplitudes, and maximum strains

To investigate the effects of loading frequency, amplitude, and maximum strain on rock damage behavior under constant-amplitude cyclic loading, this study analyzed the peak stress, elastic modulus, energy evolution, and acoustic emission (AE) characteristics of rock samples under various loading parameters. The results show that, under otherwise identical conditions, a larger amplitude leads to greater damage per cycle, higher damage accumulation per unit time, and higher energy conversion efficiency related to damage. In contrast, a higher frequency results in less damage per cycle, greater damage per unit time, and lower energy conversion efficiency related to damage. A higher maximum strain also leads to greater damage per cycle, higher damage per unit time, and higher damage-related energy conversion efficiency. During energy conversion, most of the energy externally input to the rock sample is transformed into elastic energy, with a small portion converted into dissipated energy. The majority of the dissipated energy is converted into damping energy, while less than 0.1% is converted into damage energy. Regarding the elastic modulus, under otherwise identical conditions, an increase in frequency, a decrease in maximum strain, or an increase in amplitude all lead to a reduction in the elastic modulus. Similarly, the intensity of AE hits increases with larger amplitude, decreases with higher frequency, and increases with higher maximum strain.