Quantitative reconstruction of debonding in ultra-thin honeycomb sandwich panel based on noncontact thermoelastic laser tapping

Aluminum skin honeycomb sandwich panels (HSPs) are commonly used in aerospace structures. Conventional contact-based detection methods may scratch the skin surface or result in couplant immersion, and thus a novel quantitative, baseline-free, and noncontact laser tapping (LT) algorithm is proposed to detect the debonding in the aerospace HSP with an ultra-thin 0.3 mm thick skin and a 0.04 mm thick honeycomb wall. The algorithm features an LT C-scan imaging with a baseline-free debonding index, followed by an image processing-based reference-reconstruction quantification algorithm. The numerical results validate the robustness of the proposed algorithm against strong noises with an average accuracy over 99 %. Experimentally, the proposed algorithm shows the detectability of a single debonding wall not fulfilled with the conventional contact ultrasound, and the accuracies of 90.80 % and 95.81 % experimentally in quantifying two types of debonding defects are achieved, spotlighting the application potential of the proposed technique to noncontact HSP debonding detection.