Using self-designed tension shear auxiliary device

we carried out a tension shear test and a compression shear test under different normal stresses between ?0.28 MPa and 3.0 MPa. We applied acoustic emission to compare and analyze the mechanical properties and the damage failure mechanisms of the specimens for both tests. The main results are listed as below. The tension shear auxiliary device can help us carry out the tension-shear test well. The peak stress varies with the normal stress non-linearly and is more sensitive to the normal tensile stress. The Hoek-Brown strength criterion can generally characterize the strength of the full stress area. The post-peak stress of the specimen in tension shear test drops severely and separates into two parts rapidly

showing the failure characteristics with more brittleness than that of the compression shear test. The morphological characteristics of the fracture plane are closely related to the direction and magnitude of normal stress. For compression shear test

the damage degree represented by the acoustic emission parameters is greater

as well as the failure degree of the fracture plane

compared with those observed in tension shear test. The frictional area and the local spalling of the fracture plane are also more obvious for the specimens in compression shear test

compared with those in tension shear test. As the normal stress increases

the duration of the acoustic emission quiet period gets longer

and the start time of the unstable crack propagation gets later. Compared with the compression one

the tension shear test shows a shorter duration time for each stage of the failure process as well as a higher failure rate. The critical points ?cc

?ci and ?cd of the shear-stress plot and the acoustic emission parameters can represent

respectively

the macroscopic and microscopic failure process of the specimen. The critical point ?cd and the acoustic emission b value can be used as omens of rock failure.