ACOUSTIC EMISSION CHARACTERISTICS AND FRACTURE MECHANISM OF GRANITE UNDER THREE-POINT BENDING TEST

Due to the influence of various factors such as mineral composition and crystal size, the failure and fracture evolution of granite under three-point bending tests have not been fully determined. In this study, active/passive AE tests are conducted on a cuboid granite specimen at a constant loading rate under a three-point bending test. Acoustic emission monitoring and DIC (Digital Image Correlation) technology are used to investigate the fracture mode and evolution during the fracture process of the specimen. Through analyzing the moment tensor inversion, RA (rise time/amplitude), AF (average frequency) and surface strain field variation characteristics, the fracture characteristics of the specimen is determined. The results show that the fracture of the specimen failure occurs instantaneously. In the early loading stage of the specimen, the main frequency and amplitude of the AE signals are low. However, a large number of high, medium and low frequency AE signals are observed when there is a fracture, which can serve as a precursor to determine the specimen fracture. The fracture type of the specimen is primarily linear tension fracture, with a small proportion of shear fracture, double force couple fracture, and mixed fracture sources. The strain on the surface of the granite specimen is mainly in the X -direction, with a significant increase of proportion in the early stage of fracture. Prior to fracture, the main fracture rapidly propagates from the bottom to the middle of the specimen, leading to the final specimen failure, where it breaks into two distinct blocks along the observable main fracture.