Study On Acoustic Emission Nonlinear Dynamic Characteristics Of Pre-cracked Coal And Rock Samples In Deformation And Failure

Coal and rock dynamic disasters,such as rock burst,coal and gas outburst,roof caving,threaten the safety production of mine seriously,and it’s becoming more and more serious with the increase of mining depth.The coal and rock dynamic disaster is mainly caused by the unstable fracture of coal and rock,and it’s the defect of the coal and rock samples,the initiation,development and coalescence of cracks,that lead to the failure of coal and rock samples.Thus,The paper conducts a systematic study on the pre experiment of different angle crack of coal rock samples under uniaxial compression deformation and failure of the acoustic emission signal,analysis of samples with different crack inclination of coal rock acoustic emission signal and its characteristic form,influence of different angle crack on coal rock damage.On the basis of fractal theory,the dynamic nonlinear analysis of acoustic emission signals of coal and rock failure process was carried out by MATLAB programming.The results showed as follows:The pre-crack significantly decreased the strength of coal and rock samples,and affected its failure mode,the pre-cracked coal or rock samples with different inclination angles had different failure mode:The samples without crackle showed shear tensile failure;those with 30 degree crack showed shear failure,those with 45 degree crack showed tensile and shear failure and those with 60 degree crack showed tensile failure.The AE characteristics of the samples with different inclination angles crack were different at different stages.The AE signal of the samples with cracks had a sudden increase before fracture,while those without cracks showed a gradual increase.The AE signals in the process of coal and rock samples failure have good fractal and multifractal characteristics.The correlation dimension Dm and multifractal spectrum parameters △α and △f of AE sequence had different dynamic changes.Dm showed the phenomenon of increase-wave-dump-wave during rupture process.The multifractal spectrum width Aa increased volatility before the main rupture,decreased after rupture.△freflected the damage of the samples,the smaller the value was,the greater the proportion of large signal was,and the more serious the samples failure.According to the variation of the correlation dimension Dm and multifractal parameters △α and △f,the occurrence of the main fracture can be predicted.The research results provide a basic understanding of the damage of coal and rock samples,and have important theoretical significance and engineering application value for early warning of coal and rock dynamic disasters.