Propagation Characteristics And Application Of Ultrasound In Crack Extension Process Of Rock-Like Material

In this paper,based on the study of the national natural fund"Experimental Study on the mechanism of fracture evolution of surrounding rock of deep roadway based on ultrasonic phased array"(51404255),this paper aims to explore the acoustic parameters change rule of ultrasonic wave in the process of different types of crack propagation,and establish the research goal of fracture recognition and interpretation in large scale model experiment..With the combination of"uniaxial loading ultrasonic testing digital photography"combined with numerical simulation,four groups of rock material fissure models of single dip angle(QJ group),double parallel rock bridge(YQ group),double cross(JC group)and parallel multiple row(PS group)are designed,and RS-ST01C non-metallic ultrasound is used.The change law of wave velocity,amplitude and frequency of ultrasonic wave through these typical fracture models is tested and analyzed,and the attenuation law of the above ultrasonic parameters and energy(sound pressure intensity)is simulated.The main conclusions are as follows:(1)The wave velocity and amplitude of the specimen during the loading failure process can be roughly divided into three stages according to the complete stress-strain curve.The first stage is 0.65 Sigma c~0.9 sigma C at the beginning of loading to the peak,and the wave velocity and amplitude in this stage remain in a relatively stable state.The second stage is before the peak of 0.85 sigma C to the peak stress sigma C.The specimen begins to germinate and expands rapidly and increases the amount of deformation,leading to the rapid wave velocity and wave amplitude,and the complete test of no primary fissure.Because the crack growth rate is slow,the amplitude of wave amplitude drops obviously lag,the third stage is the residual strength stage,and the wave velocity and amplitude continue to decrease to the sudden change(can not be collected).(2)In the second stage of deformation damage accumulation in the model test,the internal crack development of the specimen is induced by early primary crack,and the crack initiation and the surface deformation amount have a significant influence on the wave velocity and amplitude change characteristics.But when the direction of crack development is consistent with the test direction(0~o),the crack initiation mode is conjugated tensile crack,and the symmetry of the crack leads to the peak stress reaching the peak stress.The wave velocity and amplitude reduction are close to the different test paths,so the ultrasonic testing technique is used to detect rock mass under the stress state.The internal fissures are easily missed.(3)The deformation and failure characteristics of typical fissure models with different fissure dip angles and rock bridge spacing are obtained and the corresponding ultrasonic propagation and attenuation characteristics are obtained.The linear or exponential relationship between wave velocity,wave amplitude and initial fracture parameters(inclination beta,rock bridge length B,cross angle gamma and fracture number s)is analyzed by regression analysis of zero stress conditions and loading peak two states.Through the pre and post acoustic characteristics of rock mass in the process of deformation and failure,a reverse interpretation method for ultrasonic parameters is obtained.(4)According to the acoustic parameters of the three stage of the full stress strain curve,combined with the analysis of the local deformation characteristics of the specimen obtained by the PhotoInfor digital photographic deformation measurement technique,the parameters setting range and the adjustment method of the existing NDT in the different stages of the model experiment are analyzed.(5)Using Comsol numerical simulation software,the correlation between acoustic parameters and fracture parameters is further analyzed and verified.Through regression analysis of the formula of ultrasonic wave amplitude transmission coefficient,energy transmission(acoustic pressure maximum)and different fracture parameters,combining the typical fracture propagation characteristics and the reverse interpretation method of model experiment,it lays a good foundation and important reference for the establishment of fracture recognition method in large scale model experiment.