Experimental study of fatigue damage properties of sandstone samples under cyclic loading with low frequencies

The fatigue damage properties of intact sandstone samples subjected to axially cyclic loads with different frequencies at confining stress state were investigated, and influence of frequency on dynamic mechanical features of sandstone was studied. The apparatus employed was the MTS-815 rock and concrete test system, three levels of confining pressure(2, 10 and 40 MPa) and three sets of frequencies(0.1, 1.0 and 3.0 Hz) were applied. The dry sandstone samples were extracted from Wenchuan with average diameter of 48.9 mm and the ratio of height to diameter of 2:1. Results demonstrated that: (1) The frequency has a strong influence on residual deformation, fatigue stiffness and failure mode under the same confining pressure. The higher the frequency, the bigger the residual axial strain and the more number of cycles at failure, and the larger the initial stiffness. (2) The damage variable D proposed could describe the fatigue damage process of sandstone samples under dynamic cyclic loading.