Fatigue damage and fracture evolution characteristics of sandstone under multistage intermittent cyclic loading

Abstract

To explore the damage evolution and fracture law of rock under intermittent fatigue disturbance, multistage intermittent cyclic loading experiments were performed on red sandstone with prefabricated cracks at different angles. The fatigue damage and fracture evolution characteristics of rock samples were analyzed by combining acoustic emission (AE) technology and digital image correlation (DIC) method. The results showed that deformation parameters increased first and then stabilized gradually at the initial stage of loading. When rock samples were close to failure, the plastic strain accumulated rapidly, and the elastic modulus and deformation modulus decreased rapidly. The fatigue damage was characterized by first deceleration accumulation, then steady increase and finally accelerated development. A fatigue damage evolution model considering the initial damage was established based on the axial strain. The AE evolution could be divided into four stages: initial (SI), quiet (SII), stable increase (SIII) and rapid increase (SIV). Only after the Kaiser effect disappeared, the samples had significant AE in the load holding stage. The macroscopic crack initiation stress and angle of samples were proportional to prefabricated crack angle. The crack propagation was dominated by tensile cracks during loading, and crack propagation scale in the load holding stage was smaller than that in the cyclic loading stage. The effect of prefabricated crack angle on fracture characteristics was the difference in the proportion of shear fractures.