Study On Failure Law Of Rock Uniaxial Compression Under Different Loading Rates Based On Fractal

Based on the National Natural Science Foundation project(No.51764013),this paper studies the damage law of rock under different loading rates from macroscopic and mesoscopic perspectives.From a macroscopic point of view,this paper analyzes the energy change and damage relationship in rock failure process through indoor uniaxial experiments at different loading rates,and calculates the fractal dimension of the block at different loading rates based on the broken rock fragments.Based on this,the traditional damage evolution equation is used to establish the constitutive equation of block fractal damage evolution,and verified by experimental data.From a microscopic point of view,this paper uses the electron microscopy and image processing techniques to analyze the mesomorphology of the fracture structure of the rock fracture and the fractal dimension calculation of the meso-structure.The threshold value and magnification of the image are discussed.The effects of the number,combined with the energy relationship and the fracture morphology,explore the failure modes,fractal characteristics and energy changes of rocks at different loading rates.This paper combines theory with experimentation and has achieved the following main results:(1)Under uniaxial compression,the strain energy,dissipative energy and elastic energy increase with the increase of loading rate,although the three energy changes are different at different loading rates,but The damage process is consistent,and the faster the loading rate,the more severe the damage to the rock.(2)The macroscopic fracture property of rock is transformed by tensile failure and shear failure with the increase of loading rate.The higher the loading rate,the smaller the block coefficient after rock fragmentation.However,the fractal dimension of the block increases with the increase of the loading rate,and the experimental verification that the block fractal has a high linear correlation with energy.(3)The parameter f=block degree fractal dimension/maximum block degree fractal dimension under the same scale is replaced by the fractal dimension,instead of the traditional damage coefficient,the new block degree fractal evolution constitutive equation = (1-1))is derived.this equation can better describe the stress-strain relationship of rock,but there is a certain error,which decreases with the increase of loading rate.(4)The meso-destructive mode of rock at 0.001mm/s loading rate is dominated by intergranular fracture.With the increase of loading rate,the failure mode gradually transforms from intergranular fracture to transgranular fracture.When the loading rate is At 0.05 mm/s,transgranular fracture is the main failure mode.(5)The threshold value and rock fracture magnification of SEM image processing will have a great influence on the calculation of fractal dimension of fracture microstructure,and the fractal dimension will increase first and then decrease with the increase of threshold value,and decrease as the magnification increases(6)As the loading rate increases,the fractal dimension of the rock fracture increases,and the larger the fractal dimension,the more energy the rock destroys.The fractal dimension of the microscopic structure of the rock fracture can reflect the macroscopic fracture.The larger the fractal dimension of the fracture mesostructure,the larger the fractal dimension of the rock mass,and the better the fracture effect,the more severe the damage.