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Appl. Sci. 2018, 8(9), 1600; https://doi.org/10.3390/app8091600

Lamb Wave Local Wavenumber Approach for Characterizing Flat Bottom Defects in an Isotropic Thin Plate

1
School of Communication and Information Engineering, Shanghai University, Shanghai 200444, China
2
School of Urban Railway Transportation, Shanghai University of Engineering Science, Shanghai 201620, China
*
Author to whom correspondence should be addressed.
Received: 28 June 2018 / Revised: 18 July 2018 / Accepted: 24 July 2018 / Published: 10 September 2018
(This article belongs to the Special Issue Ultrasonic Guided Waves)
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Abstract

This paper aims to use the Lamb wave local wavenumber approach to characterize flat bottom defects (including circular flat bottom holes and a rectangular groove) in an isotropic thin plate. An air-coupled transducer (ACT) with a special incidence angle is used to actuate the fundamental anti-symmetric mode (A0). A laser Doppler vibrometer (LDV) is employed to measure the out-of-plane velocity over a target area. These signals are processed by the wavenumber domain filtering technique in order to remove any modes other than the A0 mode. The filtered signals are transformed back into the time-space domain. The space-frequency-wavenumber spectrum is then obtained by using three-dimensional fast Fourier transform (3D FFT) and a short space transform, which can retain the spatial information and reduce the magnitude of side lobes in the wavenumber domain. The average wavenumber is calculated, as a real signal usually contains a certain bandwidth instead of the singular frequency component. Both simulation results and experimental results demonstrate that the average wavenumber can be used not only to identify shape, location, and size of the damage, but also quantify the depth of the damage. In addition, the direction of an inclined rectangular groove is obtained by calculating the image moments under grayscale. This hybrid and non-contact system based on the local wavenumber approach can be provided with a high resolution. View Full-Text
Keywords: Lamb wave; local wavenumber; air-coupled transducer; wavenumber domain filtering; hybrid and non-contact system Lamb wave; local wavenumber; air-coupled transducer; wavenumber domain filtering; hybrid and non-contact system
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Fan, G.; Zhang, H.; Zhang, H.; Zhu, W.; Chai, X. Lamb Wave Local Wavenumber Approach for Characterizing Flat Bottom Defects in an Isotropic Thin Plate. Appl. Sci. 2018, 8, 1600.

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