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Study on Imaging Test Method for Thin Metal Sheet Using Lamb Wave

Author: WeiYunFei
Tutor: LuChao
School: Nanchang University of Aeronautics and
Course: Measuring Technology and Instruments
Keywords: Sheet Ultrasonic Lamb wave Imaging Detection Finite Element Simultaneous iterative reconstruction algorithm
CLC: TG115.28
Type: Master's thesis
Year: 2010
Downloads: 148
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Abstract

The sheet has a wide range of applications in the field of aerospace, automobile manufacturing, and pressure vessel industry. Ultrasonic Lamb wave method is an effective means for detecting a sheet defect. Lamb wave detection has an incentive to spread the advantages of a large area, compared with the traditional point-to-point application of ultrasonic body waves (longitudinal and transverse waves) detection method, efficient detection. Lamb wave imaging detection method is to increase the effective technology for Lamb wave detection and location of quantitative accuracy, about imaging algorithms and techniques has become in this field focus. This paper studies the thin pieces of Lamb wave imaging detection method. Lamb wave detection plate, the mode selection is critical, the application of ultrasonic Lamb wave detection sheet, should first analyze the mode of transmission of Lamb waves in the sheet, and thus motivate appropriate mode. The oblique incidence generated Lamb wave distribution the laid and angle of rotation of the probe have high demands in the application of the cross-hole Scan. Therefore, this project proposes a straight probe longitudinal wave vertical excitation of Lamb waves. In order to a clear understanding of Lamb wave propagation characteristics, the subject of the two-dimensional Fourier method to be a mode of transmission sheet ultrasonic pattern recognition. Combined with the finite element method, given the wavefield snapshot view of Lamb wave propagation in sheet, in order to better understand the Lamb wave propagation characteristics of by solving Lamb wave frequency equation plotted dispersion curves, comprehensive theory The calculation and analysis, pattern recognition opted A0 mode Lamb wave detection sheet. Based on Lamb waves between wave velocity and plate thickness dependence of the cross-hole scanning technology into the Lamb wave scanning imaging plate structure. According to the principle of acoustic tomography detection area meshing, solving grid acoustic ray path, and the relationship between it and the corresponding slowness (the reciprocal of the group velocity), the establishment of the mathematical model of the sheet Lamb wave imaging. Imaging algorithm, by analyzing the deficiencies of the Algebraic Reconstruction Technique (ART), which introduced a joint seismic tomography technology iterative reconstruction algorithm (SIRT) completion of the Lamb wave imaging detection. Lamb wave excitation and propagation in the surface of the sheet, the use of finite element simulation, imaging detection technology, imaging detection of single-layer aluminum sheet and layered board. Imaging test method to analyze the impact of different factors on Lamb wave imaging results. Finite element simulation study to verify the feasibility of the Lamb wave imaging detection method, the probe selected for the experiment, the probe layout, data processing and imaging detection provides a useful reference. In the experiment, the low-frequency longitudinal wave direct probe of the vertical excitation of Lamb wave imaging detection of thin aluminum, analysis of longitudinal wave probe's performance, Hilbert - Huang Transform and low-pass filtering the signal processing methods to extract the A0 mode Lamb waves go based imaging detection method, the formation of defect images. Lack of straight probe, from real-time Lamb wave detection technology and structural health monitoring technology development considerations, further use of the paste piezoelectric element excited Lamb waves extracted be two groups of low-frequency signals on the sheet imaging detection, imaging results with numerical simulation. The use of the piezoelectric element Lamb wave imaging detection of subsequent layers of plywood. Lamb wave imaging detection technology is not mature, the research for this article provide a reference sheet of Lamb wave imaging detection.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metallurgy ( Physical Metallurgy ) > Analytical tests of the metal (Metal Testing and Materials ) > Physical test method > NDT
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