Fatigue properties and damage constitutive model of salt rock based on CT scanning

To investigate the macroscopic fatigue properties and the mesoscopic pore evolution characteristics of salt rock under cyclic loading, fatigue tests under different upper-limit stresses were carried out on salt rock, and the mesoscopic pore structures of salt rock before and after fatigue tests and under different cycle numbers were measured using CT scanning instrument. Based on the test results, the effects of the cycle number and the upper-limit stress on the evolution of cracks, pore morphology, pore number, pore volume, pore size, plane porosity, and volume porosity of salt rock were analyzed. The failure path of salt rock specimens under cyclic loading was analyzed using the distribution law of plane porosity. The damage variable of salt rock under cyclic loading was defined on basis of the variation of volume porosity with cycle number. In order to describe the fatigue deformation behavior of salt rock under cyclic loading, the nonlinear Burgers damage constitutive model was further established. The results show that the model established can better reflect the whole development process of fatigue deformation of salt rock under cyclic loading.