Research On Granite Cracks And Energy Changes Under Cyclic Loading

A large number of engineering practice shows that the rock mass is not in a stable stress environment but in a state of repeated loading and unloading.In order to understand the mechanical behavior of rock mass(granite)under cyclic load,this paper has carried out loading and unloading tests with different cyclic upper limit and numerical simulation tests of particle flow The mechanical properties,micro crack development and energy change are studied.The main research results are as follows:(1)Macro mechanical part: the hysteresis loop of granite formed in the process of uniaxial cyclic loading and unloading shows the characteristics of "sparse dense sparse";in the cyclic stage,the deformation modulus decreases with the increase of the number of cycles;in the early stage of the cyclic stage,there will be particle ejection phenomenon,and after the high number of cycles,there will be local longitudinal tensile crack and even block peeling at the end of the specimen;test After the failure,the fracture morphology is mainly in the form of steps,and it can be well seen that the cuttings are filled in the pores.In addition,with the increase of the number of cycles,the rougher the fracture surface is,the more cuttings are peeled off,and the lower the uniaxial compressive strength is.(2)Micro crack part: the development of crack number is bounded by the peak point,which shows "overlapping and jumping" development before the peak due to different test plans.The main stage of crack development is after the peak,and the number of cracks accounts for 83% ? 88% of the total crack number.In addition,the evolution equation of crack number with axial strain is established;the crack distribution and growth shows that the initial stage is the most at the end of the test piece In the later stage,the tension crack and shear crack run through in the middle of the specimen to form the macro diagonal shear failure and the end tensile failure;the shear crack angle is mainly distributed in the loading direction,while the tension crack angle is mostly in the horizontal direction.(3)Energy part: before the peak,there is mainly a large amount of elastic energy accumulation and slow release of dissipated energy.The above two kinds of energy increase in a "downward convex shape",and after the peak,there is a sharp release of elastic energy.During the cycle loading and unloading stage,the dissipative energy unloading ring overlaps with the increase of cycle times and increases at a certain inclination angle.The curve of dissipative energy and elastic energy proportion intersects into an "X" shape,And its width becomes wider with the increase of the number of cycles;after the end of the low cycle,the curve of the proportion of the dissipative energy is the same as the development trend before the cycle because of the "memory" of the rock;after the high cycle,the curve of the proportion of the dissipative energy shows the development phenomenon of cumulative increase in advance;the value of the dissipative energy mainly shows three development stages with the increase of the number of cycles,namely the initial drop stage Based on the elastic energy,the damage variable and the loss criterion of rock strength are defined,and the principle of critical slowing down is introduced.The results show that the corresponding early warning information appears 20?105 seconds before the failure of rock.The above study not only helps to deepen people's understanding of the macro and micro mechanical behavior of granite under cyclic loading,but also provides a reference for the research based on energy monitoring and early warning.