Experimental Study on Fracture Patterns and Crack Propagation of Sandstone Based on Acoustic Emission

To investigate the fracture pattern and crack propagation of rock under different stresses, Brazilian split tests, preset angle tests, and uniaxial compression acoustic emission (AE) tests were carried out on sandstone to obtain the mechanical parameters and AE signals of the whole test process. Based on the analysis of the distribution of the characteristic AE indicators rise time/amplitude (RA) and average frequency (AF) combined with the core definition of areal density, the test results showed the following. In Brazilian split tests and preset angle tests, shear fractures and tensile fractures accompanied the whole process of rock damage and failure, and the crack type reflected by the RA-AF distribution was consistent with the theoretical analysis and actual failure results. The fracture pattern of sandstone under uniaxial compression was dominated by shear fracture, and tensile and shear cracks had the same evolutionary trend. In uniaxial compression, the development of cracks was complicated from the stage of steady development of microcracks, and the crack development was different in different specimens, which eventually leads to different failure modes. That is, the failure mode of sandstone could provide positive feedback to the RA-AF distribution. Under different stresses, the characteristics of the cumulative event rate of tensile or shear fractures varied significantly among stages, which corresponded to the various stages of rock damage and deformation.

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