Abstract: To investigate the fracture mechanical behaviors and acoustic emission characteristics of of Beishan granites with different particle sizes, we used the MTS815 Flex Test GT rock mechanics testing system and acoustic emission three-dimensional positioning monitoring system to conduct three-point bending tests on the four different particle sizes of Beishan granites. The experimetal results show that under the condition of three-point bending test, there is still comparative large bearing area in the section of specimen after the peak. The bigger is the particle size , the lower is the peak load is, the lower is the yield load’s percentage of peak load, and the smaller is the fracture toughness value. But the bigger particle size allows larger total deformation, and the residual strength is also higher. For the fine-grained or medium-fine grained specimens with a relatively low strength, the acoustic emission events firstly appear near the tip of notch, where tensile stress is larger. In the coarse-grained or medium-coarse grained specimens, acoustic emission events initially emerge in the upper part in which point load is applied. Regardless of the fine-grained or coarse-grained granite, the acoustic emission events concentrated in the stable stage of crack extension which is the main stage of rock fracture. The statistical results indicate that the bigger the particle size of granite, the more the acoustic emission events is, and the broader the distribution of acoustic emission events is.

Key words: three-point bending, Beishan granite, acoustic emission, loading and unloading