Time-frequency damage index of Broadband Lamb wave for corrosion inspection

The method based on Lamb wave shows great potential for structural health monitoring (SHM) and nondestructive testing (NDT). Damage index (DI) is a series of features extracted from Lamb wave signal that can be linked with damage, which can serve as an indicator to depict the damage. Conventional DIs including time-of-flight, amplitude change and signal difference coefficient are extracted from narrowband Lamb wave. However, time-of-flight needs prior knowledge of accurate propagation distance, amplitude change and signal difference coefficient rely on the collection of reference signals in undamaged condition. To overcome these limitations, different DIs are established from time-frequency distribution of broadband Lamb wave, which contains rich interaction information between structural feature and various modes over a large frequency range. In particular, three DIs including ridge curvature, energy distribution ratio and image difference coefficient, are extracted from Lamb wave time-frequency images and employed in probability imaging algorithm for damage localization. An experiment is given to validate the effectiveness of established time-frequency DIs. (C) 2019 Elsevier Ltd. All rights reserved.