Study On The Tomographic Method Of Aluminum Plate Defects Based On Electromagnetic Ultrasonic Guided Wave

All kinds of equipment made of metal sheet materials are widely used in military and civil fields.However,due to the structural characteristics of sheet metal,defects may occur in manufacturing and mechanical processing.In order to ensure the stability of the product in the special working environment,it is very important to study the nondestructive testing technology for the plate.Ultrasonic guided wave tomographic imaging detection technology provides a solution for the high-precision detection of plates.It can be used for the largescale detection of industrial metal plates.The image reconstruction results can not only identify the defects easily,but also quantify and classify the defects according to the category and size of the defects.The main research contents of this paper are as follows:The propagation of ultrasonic Lamb wave in the plate was studied deeply by consulting the domestic and foreign literatures,the Lamb wave characteristic equation was derived,and the dispersion curve was plotted by programming.This paper introduces the related theories of Lamb wave tomography and provides theoretical basis for Lamb wave tomography.The mechanism and structure of electromagnetic ultrasonic transducer(EMAT)are deeply studied,and a mathematical model including electricity,magnetism and force is established according to the working process of EMAT.The EMAT simulation model was established in the finite element simulation software Comsol,and the physical mechanism involved in the EMAT energy conversion process was analyzed and understood in depth.On this basis,the EMAT capable of excitation of omnidirectional Lamb wave was produced,which laid a foundation for the follow-up experiments of Lamb wave tomographic imaging.The filtering backprojection(FBP)imaging algorithm is improved,and a graphical user interface was designed for ultrasonic guided wave tomography for defect detection of aluminum plate.To test and verify the accuracy and feasibility of the imaging algorithm,using Abaqus finite element simulation software of three-dimensional Lamb wave and defects in aluminum plate after the scattering field of the simulation experiment,to obtain image reconstruction needed for projection data,then the projection data import of graphical user interface implementation of defect image,the resulting defects reconstruction results consistent with the model set up by the defects in basic,regardless of shape or position is clearly visible in the image.The experimental platform of ultrasonic guided wave tomography system was built.Firstly,it was verified that the electromagnetic ultrasonic transducer could excite pure A0 mode Lamb wave in the aluminum plate,and then the omnidirectional and frequency characteristics of EMAT were verified.Finally,the designed EMAT was used to form an array to detect the aluminum plate with defects.After processing the data detected in the experiment,the projected data were obtained and imported into the graphical user interface to reconstruct the defects.The reconstruction results verify that the designed tomography software can accurately identify the relevant information of the defect.This study provides a reference for the visual detection of aluminum plate defects,and verifies the feasibility of using electromagnetic ultrasound guided wave tomography to reconstruct the thinning defects in the plate structure.