FEM Simulation And Experimental Study For Lamb Wave Evaluate The Defects Of Plates

Ultrasonic Lamb wave detection technology is a kind of relatively advanced nondestructive testing technology in thin plates structure detection, in the petrochemical industry, aviation, electric power, nuclear energy and other fields has significant advantages and function, and created great social benefit and economic benefit. But due to the dispersion characteristics of Lamb wave, limit its application to the actual industrial production, in order to determine the parameters and modal analysis, this thesis study on the propagation characteristic the transmission characteristics of dispersion curves and defect detection of Lamb waves in plates, and compared with the experimental results, specific work is as follows:First of all,this thesis made an exposition of the current situation at home and abroad of Lamb wave detection, introduced the theory of Lamb wave, mainly from the wave equation of Lamb wave, the define and relation of the phase velocity and group velocity, and draw the phase velocity and group velocity dispersion curves. Through research Rayleigh-Lamb equation,use the MATLAB to make numerical simulation of frequency equation, the visual observation of Lamb wave propagation in the plate change with the product of Frequency and the thickness, and observe the dispersion phenomenon of group velocity and phase velocity.Secondly,the basic process of the board of Lamb wave propagation use ABAQUS numerical simulation explained in this paper, and gave the flow chart of finite element analysis, in view of finite element simulation of the board of Lamb wave propagation, made the simple elaboration of the content of each step, especially incentive selection problem,we choose Harming window signals can effectively improve the degree of identification of the simulation results and prepare for the behind numerical simulation results.Then, this thesis made the detailed elaboration of the concrete parameters by two-dimensional finite element modeling and numerical simulation of Lamb wave propagation in the board, mainly including meshing time step length and determine, etc. We analyse the Lamb wave dispersion phenomenon and the product of Frequency and the thickness range ofl MHZ-mm simulation results, and analyze the results of finite element simulation of AO mode and SO mode through the calculation of the size of the group velocity and phase velocity and comparing with the results of the MATLAB numerical simulation, verifying the accuracy of the finite element simulation. Then, we carry on the finite element simulation for defective board structure, respectively for comparing models with defects and without defects, and analyze the influence of Lamb wave propagation in the plate suffer from the defect. Using of Lamb wave propagation in the board met defect echo to determine the defect position, and the finite element simulation results of different depth of the defect of aluminum plate were compared.Finally, this thesis introduce the experiments of Lamb wave propagation in plates,respectively for boards with defects and without defects for Lamb wave damage detection experiment, analyzed the different modal analysis of experimental results and compared with the finite element simulation results.Confirming the guiding role of finite element simulation to determine the result of the experiment.