Strain performance and fracture response characteristics of hard rock under cyclic disturbance loading

Fracture characteristics and damage mechanism of rock mass under cyclic loading and unloading is one of the basic research topics of rock mechanics. To study the deformation and fracture response characteristics of brittle hard rock under cyclic disturbance loading, cyclic loading and unloading tests were carried out at different loading and unloading rates, and the stress-strain curve shapes, modulus elastic, critical damage value, fracture characteristics and fractal dimension laws were analyzed. The results show that the loading and unloading effect has significant influence on stress-strain curve shape and fatigue life. The hysteresis loop is overdistributed from sparse to dense with increasing loading and unloading rate and fatigue life is significantly reduced. The loading and unloading action has a phased control effect on peak strength with a first increases and then decreases. The rock has a stable rupture type with a brittle strength about 1.16~31.07% of peak strength, and brittle strength indicates a brittle fracture. With increasing cycle number, loading elastic modulus and unloading elastic modulus firstly increase sharply then increase linearly and finally decrease gradually. The critical damage factor has an approximately linear relationship with loading and unloading rates. The rock mainly occurs oblique shear through and tension through ruptures, and the failure types changes from shear failure to tension failure excessively with increasing loading and unloading rate. The increased loading and unloading rate weakens the end constraint effect, the greater the loading and unloading rate, the more obvious the fragmentation degree, and the more significant the fragments uniformity. The fractal dimension is logarithmic function related to loading and unloading rate.