Study on acoustic emission and strain field evolution of red sandstone under different loading and unloading paths

In order to study the damage evolution law of red sandstone under different cyclic loading and unloading paths, the MTS815 rock mechanics test system was used to perform constant lower limit cyclic loading and unloading test and variable lower limit cyclic loading and unloading test on red sandstone. Meanwhile, acoustic emission(AE) and digital image correlation(DIC) monitoring technique were carried out to capture microfracture and strain evolution information during test. The results showed that compared with the uniaxial compression test, the average compressive strength of the rock under constant lower limit cyclic loading and unloading increased by 6.5%, while the increase under variable lower limit cyclic loading and unloading was not significant. The average ratio of Felicity decreased continuously with the increase of stress under constant lower limit cyclic loading and unloading, while the ratio of Felicity basically remained unchanged in the later period of variable lower limit cyclic loading and unloading. The evolution trend of the apparent strain field was consistent with the variation characteristics of acoustic emission. Under constant lower limit cyclic loading and unloading, the damage deformation of rock increased gradually before failure, showing the characteristics of continuous increase. However, under cyclic loading and unloading of the variable lower limit, the damage strain was relatively dispersed in the early stage of loading and unloading. It was not until the stress exceeds 66% of the peak strength that the large apparent strain points of the rock were dispersed and rapidly concentrated, and the local regional deformation increased sharply, showing the characteristics of abrupt change, and the samples showed severe brittle failure, which should be paid attention to in practical engineering. © 2022, Science Press. All right reserved.