Laser ultrasonic wave spatial gradient features for damage detection

Laser ultrasonic wave spatial gradient features for damage detection

Zihan Wu, Michael D. Todd

Abstract. This work presents a damage imaging method exploiting full-field guided ultrasonic waves excited by a thermoelastic-effect laser. From the high spatial resolution data produced, a spatial gradient–based image processing technique was developed using gradient vectors to extract features sensitive to defects. Localized mechanical impedance changes in the damaged area induce a local distortion of the waveform, which was quantified by the variation of the gradient vectors in the scanning area as time evolves. Such variation was accumulated over time with an analytically derived optimal statistical threshold filter to generate a gradient-orientation map for damage imaging. The proposed algorithm is shown to detect distinctive damage patterns when tested experimentally on a 3 mm aluminum plate with multiple simultaneous simulated defects. Compared to conventional techniques like local wavenumber estimation, the generation of the accumulated orientation map involves no filtering process in the frequency or wavenumber domain, but it comes at the expense of less accurate shaping of the defect. A spatial covariance analysis was adopted to locate damage from the results as well as to evaluate the correlation among different kinds of defects.

Keywords
Laser Ultrasonics, Spatial Gradient, Covariance, Ultrasonic Imaging

Published online 3/30/2023, 8 pages
Copyright © 2023 by the author(s)
Published under license by Materials Research Forum LLC., Millersville PA, USA

Citation: Zihan Wu, Michael D. Todd, Laser ultrasonic wave spatial gradient features for damage detection, Materials Research Proceedings, Vol. 27, pp 76-83, 2023

DOI: https://doi.org/10.21741/9781644902455-10

The article was published as article 10 of the book Structural Health Monitoring

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 license. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

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