The Influence of Cyclic Load Amplitude on Mechanical Response and Acoustic Emission Characteristics of Granite

Cyclic loading and unloading tests with varying stress amplitudes were carried out to study the evolution trends of the elastic modulus, plastic strain, dissipated energy density, and acoustic emission events for granite under cyclic loading with accidental extreme stress. The results were as follows: (1) The loading deformation modulus before and after extreme stress is different. In addition, at extreme stress levels, the loading deformation modulus of granite specimens decreases by approximately 5 similar to 13%, but the unloading deformation modulus does not change significantly. (2) When extreme stress causes rock damage, most of the plastic deformation potential of the rock at this stress level is released in advance. The stress constantly varies in the subsequent low-amplitude cycle, and the plastic strain caused by the extreme stress is partly recovered. (3) As the extreme stress increases, the cumulative dissipated energy density of granite increases significantly. Compared with the control group without a stress extremum, the cumulative dissipated energy density of samples in two groups with stress extrema of 20 kN and 40 kN increased by 48% and 153%, respectively. (4) A significant acoustic emission event occurs only when the rock is subjected to a load exceeding the maximum historical stress for the first time, and the acoustic emission intensity is positively correlated with the difference between this stress and the historical maximum value. (5) Extreme stress values below the crack damage threshold reduce the crack growth potential of the rock in advance, and extreme stress above the crack damage threshold aggravates rock damage.

Automated summary

Cyclic loading and unloading tests were conducted on granite with varying stress amplitudes to investigate the evolution trends of its elastic modulus, plastic strain, dissipated energy density, and acoustic emission events under extreme stress. The results showed that the loading deformation modulus of granite decreased by approximately 5-13% at extreme stress levels, while the unloading deformation modulus remained relatively unchanged. The cumulative dissipated energy density of granite significantly increased with the increase of extreme stress. Acoustic emission events occurred only when the rock was subjected to a load exceeding the maximum historical stress, and the intensity of acoustic emission was positively correlated with the difference between this stress and the historical maximum value. Extreme stress below the crack damage threshold reduced the crack growth potential of the rock, while extreme stress above the threshold aggravated rock damage.