Energy characteristics and damage deformation of rock subjected to cyclic loading

According to the damage deformation and energy characteristics of rock element under different confining pressures, a series of tests on rock subjected to cyclic loading and unloading are carried out. Based on the current rationale of damage, the damage variable is revised. On this basis, the relationship among the dissipated energy, damage variable, plastic strain and cycle index under different stress levels is explored, and likewise the energy transformation rule of rock in the process of fatigue damage is obtained. Meanwhile, the threshold value of fatigue damage is analyzed quantitatively. The results indicate that the hysteresis loop area and dissipated energy will enlarge if the stress level rises, and the same happens on the condition that the damage variable and plastic strain rise. Above and below the threshold value, it is shown that the variation trends of the dissipated energy, damage variable and plastic strain are markedly different along with the increase of cycle index, and they exhibit the sparse-dense-sparse development process. The fatigue damage states are different under different confining pressures, however, there is a significant linear correlation between the dissipated energy and damage variable before destruction. An equation for energy is proposed based on the analysis of the dissipated energy and damage variable.