Study On Mechanical Response Of Fractured Rock Materials Under Graded Cyclic Loading

In order to explore the strength law,damage characteristics and energy evolution mechanism of fractured rock mass under the combined effects of opening,fracture inclination and cyclic loading and unloading of different stress levels,single fracture rock materials with different opening and inclination were prepared with cement mortar,and cyclic loading and unloading of single fracture rock materials with three different stress levels were carried out based on RMT –150B rock mechanics testing machine The characteristics of stress-strain curve,hysteresis loop area,dynamic elastic modulus and damage characteristics of rock like materials with cracks are studied.The experimental results show that:(1)Under the same loading condition,the peak strength and initiation strength of rock like materials decrease with the increase of fracture opening,while the peak strength and initiation strength first decrease and then increase with the increase of fracture inclination angle,and reach the minimum at 45 °,that is,the sensitive angle of fracture body is 45 °,and when the fracture inclination angle is 45 °.(2)With the increase of cyclic stress level,the hysteresis loop changes from "dense" to "sparse" at the beginning,and the peak strength of rock like material decreases,and the strength weakens.The crack opening and dip angle have little effect on the overall change of axial stress-strain curve of rock like material,and the uniaxial loading and cyclic loading and unloading of rock like material After reaching the peak strength,the stress decreases rapidly,and the rock like material loses its bearing capacity in a short time,which is consistent with the characteristics of brittle rock failure.(3)Under the same cyclic stress level and cycle times,the dynamic elastic modulus of rock like material decreases with the increase of opening degree,and decreases first and then increases with the increase of fracture angle,and reaches the minimum at 45 ℃.(4)In the same stress cycle loading,the hysteresis area of different opening and different inclination decreases sharply with the increase of cycle times and then tends to be flat.However,the decrease range of hysteresis loop area at different opening degrees and different dip angles is obviously different with the increase of the number of cycles.The larger the fracture opening degree is,the greater the decrease range of hysteresis loop area is With the increase of the angle,the decrease of the hysteresis loop area is the largest at 45 ° and the decrease of the complete specimen is the smallest.(5)With the increase of cyclic stress level,the absolute damage variable of rock like materials with different opening degrees first decreases approximately linearly,then increases slowly and then increases sharply;with the increase of cyclic stress level,the absolute damage variable of rock like materials with different crack dip angles increases rapidly In low stress cyclic loading,it decreases approximately linearly.In medium stress and high stress cyclic loading,it increases,while in high stress cyclic loading,it increases greatly.(6)The failure mode of rock like materials changes from tensile failure to shear failure with the increase of fracture angle.With the increase of fracture opening,the probability of tensile crack initiation increases greatly.And the crack evolution of rock like materials is different in different cyclic stress levels.