Research On Guided Wave Tomography Of Metal Plate Defects Based On Secondary Development Of Finite Element

Due to the characteristics of high strength and easy machining,sheet metal is widely used in various complex engineering fields.Due to its own structural characteristics,plate structure often has defects in the process of production,processing and transportation,which has an impact on material properties.Therefore,it is necessary to detect the health status of thin plates.The ultrasonic sensor array used in Lamb wave tomography can accurately obtain the position,size,shape and other defects in the thin plate,and detect the defects on the surface and inside of the thin plate clearly.This theses is mainly based on the finite element method to study the technical theory of Lamb wave tomography for defect reconstruction imaging of metal plates.The main research contents are as follows:Taking aluminum plate as the research object,the frequency equation of Lamb wave propagation in aluminum plate is derived.The frequency equation of Lamb wave is calculated by numerical method and the dispersion curve is drawn.This paper analyzes the related theories of computer tomography,including the principle of analytical reconstruction algorithm and iterative reconstruction algorithm,which provides theoretical basis for the selection of Lamb wave excitation signal and aluminum plate defect reconstruction in finite element simulation.In order to verify whether the imaging technology can reconstruct the defects in aluminum plate,the scattering field data of Lamb wave are solved by finite element method to judge the accuracy of defect reconstruction technology.Due to the large amount of scattered field data needed in the reconstruction process,manual data acquisition is a huge workload and easy to introduce artificial errors.Through the secondary development of finite element software ABAQUS,the automatic simulation of aluminum plate model and batch acquisition of scattered field data are realized,so as to realize fast imaging.Firstly,the theory of secondary development of finite element software ABAQUS is introduced,and the development process of GUI plug-in in ABAQUS software is familiar.The RSG dialog box builder in ABAQUS is selected as the development tool of GUI plug-in.After determining the specific development process of GUI plug-in,taking aluminum sheet as simulation object,loading tone burst signal modulated by Hanning window to excite Lamb wave in aluminum plate,using RSG dialog box builder to create GUI plug-in independently developed,and input relevant parameters of aluminum plate model in the modeling interface of plug-in to realize automatic simulation of the model.Through the GUI plug-in,the automatic simulation of defect free model,center defect model and skew defect model is completed,which greatly improves the work efficiency.Finally,on the basis of automatic simulation and data acquisition,the scattering field data of Lamb wave in the simulation results of the three models are analyzed and processed respectively,and the projection data for defect reconstruction are calculated.According to the projection data,two-dimensional curve and two-dimensional plan are drawn to preliminarily judge the defect information of aluminum plate.The direct back-projection algorithm,fan beam filtering back-projection algorithm and algebraic reconstruction algorithm are used to reconstruct the aluminum plate defects,and the image reconstruction results of the three methods are compared.Among them,the algebraic reconstruction algorithm has the best effect and the defect profile in the plate is clearly visible.The defect image is segmented by global threshold segmentation and adaptive threshold segmentation based on OTSU algorithm,and the segmentation results of the two methods are compared and analyzed.Among them,the adaptive segmentation method based on OTSU algorithm has a better effect and can directly judge the size,shape and location of the defect.