Three-dimensional Numerical Simulation Of Ultrasonic Propagation Characteristics Of Concrete Under Low Stress

Concrete is the most commonly used material in various hydraulic structures.In actual engineering,the non-destructive testing method is commonly used to judge the stress state of the concrete structure and the mesoscopic changes generated internally to estimate how long the concrete structure can be serviced.Since the non-destructive testing experiment after loading is limited by various external conditions,the measured results have certain errors,and the experimental data needs to be supplemented and demonstrated by numerical simulation.Therefore,this paper carries out three-dimensional numerical simulation study on the ultrasonic propagation characteristics of concrete under low stress conditions.The results obtained are as follows:(1)Assume that concrete is a two-phase non-uniform composite composed of aggregate and mortar.In order to simplify the calculation,the aggregate is assumed to be a spherical structure.According to the concrete Fuller grading theory,reasonable aggregate gradation and aggregate are determined.Particle size,using Python program,based on the space sphere random generation algorithm and the mutual intrusion determination algorithm between aggregates,Monte Carlo method is used to realize the randomness of unit aggregate distribution,and three-dimensional random aggregates can be established for ultrasonic simulation and stress loading.Concrete model.(2)Based on the damage mechanism of concrete damage,and from the analysis of its stress characteristics(mainly compression and tension),the plastic damage model is used as the constitutive relation of each component in the three-dimensional mesoscopic model of concrete,which is implicitly limited.The element method is used to solve the uniaxial compression damage analysis of the concrete mesoscopic model,and the explicit finite element method is used to realize the propagation of ultrasonic waves in the concrete mesoscopic model.(3)Based on Abaqus software,an analytical method for establishing the coupling of stress field and sound field is proposed.In Abaqus,the damage factor and equivalent strain of concrete mortar unit under certain stress state are extracted.The Poisson's ratio calculation formula and the concrete damage plastic constitutive relation formula of the Zhenhai Sea are used to calculate the mooring of the concrete mortar after loading.The pine ratio and the elastic modulus are assigned to each unit under the specific values of the stress,the damage concrete model is established,and finally the ultrasonic simulation is performed.(4)After obtaining the corresponding waveform diagram,it performs time domain and frequency domain analysis by Fourier transform and wavelet analysis to obtain basic acoustic parameters of concrete under different stress states such as: wave speed,first wave amplitude,maximum amplitude,main Frequency,main frequency amplitude,spectral area,weighted spectral area,etc.,analyze the statistical relationship between acoustic parameters and stress.