Damage Imaging in Composite Laminates Using Broadband Multipath Lamb Waves

This article presents a broadband multipath Lamb wave imaging method, which separates, interprets, and exploits echoes and reverberations in Lamb wave response for damage detection and localization in composite structures. In that method, a typical chirp excitation is first applied to collect structural information over a wide frequency range, providing a large number of candidates for efficient parameter optimization. Then, the short-time chirp-Fourier transform (STCFT) is introduced to map and separate echoes in the time-frequency domain. On this basis, a frequency slice of the spectrogram is taken, where multiple echoes could be separately identified in the time domain. Third, a modified elliptical method is proposed to accommodate those echoes for damage imaging. Finally, the effectiveness of the proposed method is illustrated by experimental examples conducted on carbon fiber-reinforced polymer (CFRP) laminates. Furthermore, the influence of the redundant sensing paths and the undesirable waves on the imaging results is also investigated.