Effect of creep load on fatigue behavior and acoustic emission characteristics of sandstone containing pre-existing crack during fatigue loading

Abstract

To study the effects of creep loading on the fatigue behavior and acoustic emission characteristics of jointed rock masses during fatigue loading, a series of multilevel cyclic loading and unloading tests and fatigue-creep tests were carried out on jointed sandstone specimens. Experimental studies were carried out using acoustic emission (AE), digital image correlation (DIC), and scanning electron microscopy (SEM) techniques. Combined with the evolution trend of the b value and Felicity ratio, the acoustic emission characteristics of rock masses were studied. The damage evolution model of the specimens was established based on the load-unload response ratio (LURR) theory, and the fatigue behavior of the specimens was analyzed at a macro-meso multiscale. The results show that the application of a short-term, low-stress level of creep load during fatigue loading can reduce the increase in deformation parameters, slow down the attenuation of elastic parameters, and restrain the decline in response level. Effectively controlling the growth rate of damage, the phenomenon of early hardening occurs, thereby increasing the fatigue life of the rock mass. In terms of microstructure, under the influence of creep loading, most of the grains exhibit split failure, the area of folds caused by fatigue loading is reduced, the number of fatigue cracks is decreased, the roughness of the fracture is reduced, and the brittleness of the specimen increases when it fails. In addition, due to the application of creep loading, the Felicity effect appears later, and the Felicity ratio decays more slowly, leading to interlocking of particles within the rock mass and inhibiting the crack propagation process, which causes the b value to rise.