Study of energy evolution and acoustic emission characteristics of red sandstone under multi-stage amplitude-increasing cyclic loading

This research aims to examine the damage and failure behaviour of red sandstone under multistage-stage amplitude increasing cyclic (MS-AIC) loading, with three different increasing stress amplitudes (ISA). By combining macroscopic mechanical testing and acoustic emission (AE) monitoring techniques, the impacts exerted by three distinct ISA schemes are comprehensively analysed. The investigation focuses on the stress–strain behaviour, energy evolution, AE activity, and damage development in red sandstone. The results demonstrate that (1) Under MS-AIC loading, both the axial strain and damage accumulated progressively with cycle number. According to the irreversible axial strain produced during cyclic loading, a model which can describe the process damage of red sandstone was proposed. (2) The energy evolution analysis showed that under the effect of different ISA, the input energy accumulated, and the dissipated energy exhibited an initial decrease followed by an increase. (3) The cumulative AE counts rose steadily with cycles; AE counts and energy release rate increase sharply when the stress increases. As ISA increased, the tensile cracks ecrease gradually, with the growth in the shear cracks. The final failure mode was a composite tensile-shear fracture. The results support further understanding of the stability of rock mass under MS-AIC loading.