Experimental Study On Acoustic Emission Characteristics Of Rock Materials With Different Particle Sizes Under Cyclic Loading And Unloading Conditions

In order to study the relationship between particle size of rock-like materials and their mechanical properties and acoustic emission characteristics.Three rock-like materials with different particle sizes(0.13-0.16 mm,0.61-0.73 mm,1.21-1.75 mm)were prepared using quartz sand as aggregate.Acoustic emission tests of rock-like materials were carried out respectively under uniaxial compression and uniaxial cyclic loading-unloading.The characteristics of mechanical properties,energy and AE in rock-like materials were studied under cyclic loading and unloading.The main conclusions are as follows:(1)Under uniaxial compression,rock-like materials generally exhibit ductile failure.With the increase of particle size,the uniaxial compressive strength of rock-like materials increases,and gradually changes to brittle failure.Cyclic loading and unloading has strengthening effect for the strength of rock-like materials,and the smaller the particle size,the more obvious the strengthening effect of samples.(2)With the increase of cyclic loading and unloading times,the total strain and elastic strain of rock-like materials increase linearly,while the plastic strain first decreases,and then the change trend of increase.When the first loading reaching the relative stress level of 20%,With the increase of particle size,the plastic strain increases,the elastic strain energy still shows an increasing trend because of the more obvious increase of the total strain.(3)In the cyclic loading and unloading test,When the first loading reaching the relative stress level of 20%,with the increase of particle size,the average ringing counting rates of group A(0.13-0.16 mm),group B(0.61-0.73 mm)and group C(1.21-1.75 mm)were 2032,2513 and 3048 respectively,and the acoustic emission energy rates showed the same law as the ringing counting rates.The ringing counting rate and acoustic emission energy rate increased with the increase of particle size.(4)Contrast the process of loading and unloading acoustic emission signals,the acoustic emission during loading process is more obvious in the cyclic loading and unloading test.When the last stage is loaded to the peak stress,the counting rate of acoustic emission ringing and the acoustic emission energy rate increase sharply before the peak stress.(5)In cyclic loading and unloading tests,the RA values(Ratio of rising time to magnitude)of three groups of specimens in each cycle are analyzed.The results show that the deformation and failure of rock-like materials present complicated failure modes of tension and shear fracture,and the value of RA increases suddenly before the peak value.With the increase of particle size,the change range of RA value is larger.(6)In cyclic loading and unloading tests,with the increase of particle size,the minimum value of loading and unloading response ratio which expressed by the cumulative acoustic emission ringing number.The corresponding axial relative stress levels of Group A,B and C were about 42%,67% and 70% respectively.(7)Three groups rock-like materials with different particle sizes have obvious irreversible characteristics of acoustic emission.The Kaiser effect of acoustic emission has different upper stress limits.The corresponding axial relative stress levels of group A,group B and group C are about 58%,65% and 70% respectively.