Study on Granite Damage and Fracture Behavior and Theoretical Model Based on Pre-Peak Constant Amplitude Cyclic Loading Test Combined with Acoustic Emission Technology

Rocks may be continually unloaded and loaded until they break in subsurface engineering tasks such as tunnel excavation. To investigate the effect of pre-peak constant amplitude cyclic loading (PPCACL) on fatigue damage and rock fracture features, three-point bending (TPB) experiments were performed on granite samples of varying amplitudes subjected to pre-peak constant amplitude cyclic loading (PPCACL). The calculation technique of fracture toughness formula is innovated and changed in conjunction with theoretical analysis, based on experiments and original standards, and AE events in the fracturing process are monitored by AE technology. The results demonstrate that in the instance of PPCACL, the first cycle of PPCACL causes the most damage to the rock. When the test results are compared, the damage to the rock specimen increases as the amplitude increases. After PPCACL, the sample was monotone loaded by manipulating crack mouth opening displacement (CMOD) until it was destroyed. With increasing PPCACL amplitude, the fracture energy, tensile strength, fracture toughness, and monotone loading peak of granite samples all decreased. Meanwhile, increasing the PPCACL amplitude increased the brittleness of rock samples and flattened the fracture surface.