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Noncontact Evaluation of Defects in Thin Plate With Multimodes Lamb’s Waves and Wavelet Transform

[+] Author Affiliations
Morimasa Murase, Koichiro Kawashima

Nagoya Institute of Technology, Aichi, Japan

Paper No. IMECE2002-33456, pp. 27-30; 4 pages
doi:10.1115/IMECE2002-33456
From:
  • ASME 2002 International Mechanical Engineering Congress and Exposition
  • Nondestructive Evaluation
  • New Orleans, Louisiana, USA, November 17–22, 2002
  • Conference Sponsors: Nondestructive Evaluation Division
  • ISBN: 0-7918-3649-5 | eISBN: 0-7918-1691-5, 0-7918-1692-3, 0-7918-1693-1
  • Copyright © 2002 by ASME

abstract

Multimode’s Lamb waves in aluminum plates with various defects were excited by a Q-switched Nd:YAG laser. The Lamb waves past through the defects were received a laser interferometer. The received signals of the Lamb waves are processed by the wavelet transformation. The wavelet transformation is generally shown on the time-frequency domain. By dividing a propagation distance by the time, the group velocities are identified. In this way, group velocity dispersion maps of multimode’s Lamb waves are constructed with the received temporal signals. By changing the shape of the mother wavelet, Gabor function, we can identify the dispersion curves of the higher mode Lamb waves. The group velocity dispersion maps of a intact specimen agree well on theoretical dispersion curves of S0 , A0 , S1 , A1 , S2 , A2 , and A3 modes. The difference between the dispersion maps of the intact specimen and that with defects clearly visualizes the existence of defects. This non-contact method is effective for inspecting various defects in thin plate structures.

Copyright © 2002 by ASME

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