Mechanical properties and fatigue damage evolution of granite under cyclic loading and unloading conditions

To analyze the evolution law of mechanical properties and energy during the cyclic loading and unloading process,five kinds of granite triaxial cyclic loading and unloading experiments have been performed. Based on the experimental results,the evolution characteristics and their interrelationship of total absorption energy,elastic strain energy and dissipated energy under different confining pressure have been analyzed in detail,and the coupling evolution equation of rock damage dissipated energy changes with cycles loading and unloading times and confining pressure are established. The results show that:① When the load is less than the peak stress,the elastic modulus in the loading stage is smaller than that in the unloading stage;② Before the peak stress,the energy generated by the load is mainly shown as elastic strain energy,while after the peak stress,the energy generated by the load is mainly expressed as dissipated energy;③ As the confining pressure increases,rock elastic strain energy and dissipated energy increases;④ Under cyclic loading-unloading,the dissipated energy of the rock has a significant correlation with the confining pressure and the cycle loading and unloading times. Non-linear curved surfaces can be used for fitting the relationship. This finding can provide a basis for quantitative analysis of rock damage during cyclic loading and unloading.