Acoustic Emission and Failure Process of Rocks under Compression

Abstract

In this paper, the authors deal with the correlation between the stress-strain diagram and the rate of acoustic emission during the failure process of rocks under uniaxial compression.The rock specimens which contain a rectangular slit were loaded by a stiff testing machine (total stiffness=0.68×106kg/cm) in order to observe the process of fracture crack propagation from the corner of the rectangular slit and the rate of acoustic emission, which was detected with a piezoelectic type transducer (the inherent frequency of vibration=145kHz).The test results show that, if the abrupt and unstable propagation of a fracture crack takes place, the rate of acoustic emission increases abruptly and the applied load drops. On the other hand, the slow and stable propagation of a fracture crack takes place without accompanying any remarkable increase in the rate of acoustic emission.Based on the above test results, the fracture crack is classified into the stable or unstable type, according to the mode of propagation. It is clarified that the unstable propagation of a fracture crack is accompanied with stress drop and depends on the stiffness of the testing system, which suggests that the role of the stiff testing machine is to control the propagation of the unstable type of fracture cracks.