Experimental Study On Failure Of Rock With Prefabricated Fractures Under Dynamic And Static Loading

In order to study the influence of fracture dip Angle on rock mechanical properties,energy evolution law,acousto-electric effect and fractal characteristics,RMT-150 C rock mechanics testing machine and SHPB dynamic test bed were used to carry out static and dynamic rock failure tests.At the same time,acoustic emission and electromagnetic radiation monitoring system were used to collect acousto-electric signals during rock failure process.Combined with the fractal geometry theory,the distribution characteristics of rock fragmentation are studied.The main research contents and conclusions of this paper are as follows:(1)Through static uniaxial compression tests,the stress-strain curves of fractured sandstone and intact sandstone have the same trend,which can be divided into four stages:compaction,elasticity,yield and post-failure.The compressive strength and elastic modulus of the specimen increase exponentially with the increase of crack inclination Angle,and the failure mode gradually changes from shear failure to tensile failure.(2)Through SHPB dynamic load test,the dynamic mechanical characteristics of the samples with different crack dip angles were obtained.The test results show that the failure process of the samples can be divided into three stages: elastic,plastic and post-peak.The dynamic elastic modulus increases with the increase of crack dip angles,the dynamic compressive strength increases exponentially,and the strain rate decreases exponentially.(3)By monitoring the acoustic emission and electromagnetic radiation signals during the failure process of the sample,it is obtained that the characteristic curves of acoustic emission and electromagnetic radiation of the sample under static load are in good agreement with the total stress-strain curve,and the acoustic and electric signals reach the maximum value at the stress peak point.With the increase of fracture dip Angle,the peak value of the cumulative acoustic emission characteristic value presents a "Z" type change,and the peak value of the cumulative electromagnetic radiation characteristic value presents an inverted "V" type change.The acoustic emission signal of the sample under dynamic load suddenly increases to the maximum value at the peak stress point,and the maximum value of the electromagnetic radiation signal appears before the peak stress point.The characteristic values of both acoustic emission and electromagnetic radiation signal increase linearly with the increase of the crack inclination.(4)Through theoretical analysis,the energy evolution of the specimen with prefabricated cracks during static uniaxial compression can be divided into four stages: compaction,elasticity,shaping and post-failure stage.The elastic strain energy at the peak stress point,the total strain energy at the peak stress point and the dissipated strain energy at the complete failure point increase exponentially with the increase of the crack inclination Angle.In the process of impact crushing,with the increase of crack inclination Angle,the reflected energy ratio decreases,the transmitted energy ratio increases,and the dissipated energy ratio changes little.(5)By using the mass fractal model of particle size distribution of rock fragments,the fractal dimension of the samples after crushing is calculated,and it is obtained that the fractal dimension of the samples under static and dynamic loading increases with the increase of fracture inclination Angle.Under static load,the elastic strain energy,total strain energy and dissipated strain energy at the stress peak point and the failure point all increase with the increase of fractal dimension.With the increase of fractal dimension,the strain rate of the specimen under dynamic load decreases,while the dynamic compressive strength and dissipated energy density increase.