Influence of loading rate on macro and micro formation mechanism of acoustic emission events in sandstone and granite

The distribution characteristics of acoustic emission events of sandstone and granite at different loading rates are analyzed. Electron microscopy of rock fragments with and without acoustic emission events is performed. The effects of loading rate on the formation mechanism of acoustic emission events are analyzed from macroscopic and microscopic combined with acoustic emission signal characteristics. The results show that with the increase of loading rate, the characteristics of the mirror area are gradually weakened, that is, the slip between the corresponding particles and the micro-cracks in the rock become less, and the more likely the rock is brittle, the more the acoustic emission signals are mostly continuous (or quasi-continuous), which is not conducive to the formation of acoustic emission events, so the number of acoustic emission events is gradually reduced. For sandstone, micro-destruction and small macroscopic damage are the root causes of acoustic emission events. For granite, dislocations between particles are the source of acoustic emission events. The characteristics and range of granite mirror area are more obvious than that of sandstone, that is, the slip and micro-fracture interaction between particles is more obvious. At the same time, the fracture degree and scale of macroscopic sandstone are much smaller than that of granite, so the number of acoustic emission events of sandstone is much less than that of granite. The characteristics of the mirror area clearly indicate that the slip between particles and the micro-destruction inside the rock are the main failure components of the rock, so the granite has an acoustic emission event from the beginning of loading, but the sandstone does not. There are obvious differences in the formation mechanism of acoustic emission events between sandstone and granite.