A Damage Localization Method With Multimodal Lamb Wave Based on Adaptive Polynomial Chirplet Transform

Ultrasonic Lamb wave testing allows health monitoring for plate structures and has been extensively applied in the modern industry. To obtain the location and further form the damage imaging, the time of flight (TOF) is a pivotal parameter. However, the dispersive and multimodal nature of the Lamb wave obstructs the accurate measurement of TOF. The objective of this article is to develop efficient techniques to separate multimodal Lamb wave signals and accomplish accurate damage localization. The narrowband Lamb wave is generated by the excitation signal with a center frequency of 150 kHz. The fundamental symmetric and antisymmetric modes are exploited. The adaptive polynomial chirplet transform (CT) is proposed to decompose the Lamb wave signals and identify the modes. Then, the instantaneous frequency characteristics are utilized to extract time information. Thus, the TOF is obtained and damage location can be calculated. The reconstruction error is defined to quantitate the difference between the reconstructed signal and the received signal. The obtained reconstruction errors from the simulation and experiment are 0.1631 and 0.2875, respectively. The varied defect location is adopted to obtain the TOF estimation. The results show that the proposed method outperforms the CT and cross correlation, especially for the longer propagation distances where the dispersion effect is distinct. For experiments considering the defect and boundary reflection, the localization errors of the collinear defect are 2.51% and 3.04% for the two Lamb wave modes. In comparison with smoothed-pseudo-Wigner-Ville distribution and CT, the proposed method owns superior performance on mode identification and location accuracy.