Study On AE Testing Method Of Microscopic Mechanism Of Rock Failure Based On Moment Tensor

Rock is a typical anisotropic brittle material.With the increase of the external load,the internal micro-crack initiate,evolute,propagate and coalesce until the macroscopic fracture plane formate on therock surface.AE can be used to retrieve and predict the generation and propagation of micro-cracks in rock material in real time.At present,acoustic emission has a good application in the analysis of acoustic emission parameters,the interpretation of frequency spectrum,and the three-dimensional positioning of space.However,to research on the mechanism of rock burst,only obtaining micro-crack evolution process in time and space is insufficient,also need to classify the micro fracture of tensile and shear slip from mechanics angle,finallyget in-depth understanding of the micro crack interaction and the propagation and coalescence mechanism.Lay the foundation for study of the genetic mechanism for the mine microseismic monitoring,tunnel stability and deformation of the deep fracture,also for the hard brittle rock failure provides the basis for forecasting.Therefore,in this paper,the experiments of uniaxial compression(Brazil splitting,uniaxial compression test,“Z” shear test,compression test with prefabricated cracks)and synchronous acoustic emission were designed.Crack types and slip direction are solved based on Moment tensor,combined stress strain curve and acoustic emission parameters to divide rock failure stage,then,analysd the rock fracture characteristics and energy evolution mechanics under different damage stages.finally,explained the evolution process of rock fracture from microcosmic angle.Got the following conclusions:(1)Based on AR-AIC and simplex method(Simplex),compose the program to solve AE events point positioning the positioning error is less than 10 mm in tensor arry,and is about 15 mm out the tensor array,With break-pencil test?(2)The amplitude of AE(AMP)and combined with the spatial location,distribution map drawn AMP grade,can see main rupture surface and concentrated,can effectively discharge the invalid interference of acoustic emission point(low energy,low amplitude,discrete AE events).(3)Based on Matlab,Combinated the principle of elastic wave dynamics,to implement the program of moment tensor.In the uniaxial compression test of "Z" type specimens,JQ2 was compressed and stretched at the notch,and the shear rupture occurred in the middle beam of G2.The results of moment tensor show that the ratio of tension and shear cracks in JQ2 is 51%,,G2 is 77%,19%.Which is consistent with the macroscopic rupture,and proves the accuracy and applicability of the moment tensor program in the analysis of rock fracture micro-mechanism.(4)With Brazil experiment,the average ratio of tensile crack,shear crack and mixed crack is 59%,30%,and 11%.In general,the tensile cracks play a leading role in the Brazil splitting test,and the shear cracks play an important role in accelerating and promoting the fracture.So,Brazil proved splitting test and tension test of the stress distribution of different initiation point is different,but the focal mechanism(tension plays a dominant role),so it is reasonable to test the tensile strength of the specimen.(5)The ratio of tensile energy,shear energy and mixing energy in the process of rock fracture is close to that of tensile crack.The tensile strength of the rock is generally higher than that of the tensile fracture,whereas the shear energy is higher in the shear specimen.In the process of stress loading,the fracture energy is mainly concentrated in the time when the crack is dense or when it is large(large event),which is mainly concentrated in the 80-10% stress stage,and there is a sharp increase of energy in the later period.