Experimental Study of Sandstone Deformation and Acoustic Emission under Cyclic Loading at Different Frequencies

Considering that the frequency of cyclic loading is not constant in practical rock engineering, uniaxial compression experiments with sinusoidal cyclic loading with a fixed amplitude at different frequencies were designed to investigate the effect of loading frequency on axial deformation and circumferential deformation of sandstone, and to explore the damage mechanism of sandstone by combining with the acoustic emission and the energy evolution law. The experimental results show that the loading frequency affects the deformation process, damage pattern and acoustic emission characteristics of sandstone. Under cyclic loading, the cyclic deformation of sandstone not only forms hysteresis loop, but also undergoes the same deformation process as axial deformation. At 0. 1 Hz, sandstone deformation undergoes the initial stage, isochronous stage and accelerated stage, whereas only the initial stage and isochronous stage are found at 0. 02 Hz and 0. 2 Hz. In the initial stage, the sandstone has acoustic emission signals; in the isokinetic stage of deformation, the acoustic emission signals are weakened; when the deformation enters the acceleration stage, the external work promotes the further expansion of micro cracks in the sandstone, and the acoustic emission signal gradually increases. A large number of micro cracks penetrate into macroscopic cracks, ultimately forming a multi crack splitting failure mode.