Fatigue Damage Mechanics of Potassic Granite Under Constant Amplitude Cyclic Loading

Abstract:

To investigate the effects of the upper limit stress ratio on the fatigue damage mechanics of potassic granite， uniaxial compression tests and constant amplitude cyclic loading tests with four upper limit stress ratios （0.75， 0.80， 0.85， 0.90） were conducted. Based on the experimental data， the stress-strain curves， fatigue life， fatigue limit strain ratio， as well as the macroscopic and microscopic evolution pattern of granite failure characteristics were summarized and analyzed. Based on the hysteresis curves during cyclic loading， key parameters such as dynamic modulus， damping ratio， dynamic Poisson’s ratio， and cumulative residual strain were calculated. Additionally， a damage value computation method based on average residual strain was proposed to describe the deformation and failure process of the rock sample. The results indicate the presence of a dilatancy stress ratio. When the upper limit stress ratio exceeds this threshold， the samples undergo fatigue failure， and the fatigue life decreases as the upper limit stress ratio increases. The axial deformation during fatigue failure is governed by the evolution of the uniaxial static stress-strain curve. Macroscopically， the extent of damage in the samples increases with the upper limit stress ratio， while microscopically， the complexity of fracture morphology also intensifies. The dynamic elastic modulus and Poisson’s ratio during fatigue failure exhibit a two-stage variation trend， while the damping ratio and residual strain show a three-stage varying feature. The fatigue damage values， calculated using the average residual strain method， exhibit a three-stage “inverse ‘S-shaped’” evolution pattern as the number of cycles increases. Finally， a low-cycle fatigue damage model was introduced to describe the fatigue damage pattern， whose predictive performance was satisfactory according to the comparison with experimental data.