Study On The Characteristics Of Ultrasnic Propagation In Concrete Under Loading By The Numerical Simulation

Concrete is the main material of the existing majority of hydraulic buildings.In these hydraulic buildings,most of them have serviced for many years.In order to estimate their status,it’s necessary to detect the actual working stress accurately.In these methods of detecting stress,ultrasonic detection is one of the most accurate and convenient way.Currently,the research on the stress and acoustic parameters of concrete is mostly carried out by means of experimental methods.In the process of measurement,there are some external factors having a certain impact on the propagation of ultrasound,the law between the corresponding parameters and stress will have some differences.In view of this,this paper has carried out research on the ultrasonic propagation characteristics of concrete under loading.The main contents and achievements are as follows:(1).In the study,according to the manufacture requirements of laboratory concrete and the Test code for hydraulic concrete,based on the random aggregate model,a two-dimensional mesoscopic model of laboratory concrete is established.The coordinates of model are built in MATLAB,and introduced into the finite element software ABAQUS by AUTO-CAD.In ABAQUS,the model is divided into three parts:Mortar(sj),aggregate(gl),interface(jm).(2).Based on the mechanism of concrete damage and the mechanical properties(mainly for compression),the plastic damage model deduced based on standard is used as the constitutive relation of each component of the model.The damage analysis of concrete under uniaxial compression is by means of the implicit finite element method,and the ultrasonic propagation in mesoscopic concreteis by means of the explicit finite element method,.(3).Based on the ABAQUS,a new analysis method coupling for stress field and acoustic field.The specific process is as follows: Based on the plastic damage model,the relationship between the damage factor and the elastic modulus can be established,the value of poisson can be get by the formula gived by Guo Zhenhai,at the same time,the coordinates of each unit after deformation can be extracted,after that,the model will be reconstructed,that means a state of the force field has been saved.At last,simulating the ultrasonic propagation in "concrete 2D " mesoscopical model.(4).Time domain waveform can be obtained by the simulation of ultrasonicpropagation in concrete under loading conditions,and can be analysised by time-domain analysis and frequency-domain analysis by means of FFT and wavelet,after that,the available acoustic basic parameters(acoustic velocity,wave amplitude,maximum amplitude,frequency,amplitude of the main frequency,the spectrum area,the weighted spectral area)can be obtained.Through the analysis,of all parameters,the weighted spectral area,the first wave amplitude and acoustic velocity are the most sensitive,then fitting them with stress by ORIGIN,and the relations between stress and acoustic sensitivity parameters can be established.