Mechanical Response and Energy Dissipation Mechanism of Sandstone under Cyclic Dynamic Loading Using Particle Flow Code Simulations

The mechanical response and damage mechanism of rocks under cyclic dynamic loading are important factors that affect the stability of geotechnical engineering. However, only a few studies have tracked and described accurately the whole process of internal cracks and energy dissipation during fatigue damage. To study the dynamic response characteristics of sandstone under cyclic dynamic loading, this work conducted a cyclic dynamic loading test on sandstone using the improved MTS973 fatigue test system under indoor cyclic dynamic loading. The fatigue stress-strain curve of sandstone under cyclic dynamic loading was also analyzed. On the basis of correctly calibrated parameters, the numerical simulation method for particle flow code was employed to restore the indoor cyclic dynamic loading test accurately. The micro-damage law of sandstone under different frequencies and stress levels was discussed. Finally, the whole process and mechanism of energy dissipation were recorded and studied. Results show the following. (1) The energy absorbed during cyclic loading is stored in the form of sliding friction and elastic strain energy, and the energy dissipation presents a good correlation with the meso-damage evolution of rock mass. (2) At the same frequency, a large tress amplitude equates to a high primary cyclic energy consumption when the upper stress limit is fixed; moreover, the fatigue level of sandstone increases as the stress amplitude rises. (3) Under the same stress amplitude, a high frequency equates to a large number of cycles and cracks in each cycle stage and to a large total number of cracks. In conclusion, this study deepens the understanding of the damage evolution and mechanism of rock materials from the point of view of meso-damage and energy dissipation.