Reference‐free delamination detection using Lamb waves

SUMMARY This paper presents a new Lamb wave-based delamination detection technology that allows detection of delamination in a single wave propagation path without using prior baseline data or a predetermined decision boundary. This study shows that, if delamination exists along a wave propagation path, the first arrival antisymmetric (A0 )m ode is followed by other A0 modes reflected from the inside of the delamination. Unlike other conventional Lamb wave techniques, the proposed technique takes advantage of the first A0 mode reflected from the inside delamination to instantly identify the existence of delamination. First, the proposed study employs a dual piezoelectric transducer (PZT), which is composed of a concentric ring and disk PZT segments, for Lamb wave excitation and a circular PZT for sensing. By activating either the circular or ring PZT segment separately, two pitch-catch Lamb wave signals are obtained from the single wave propagation path. Then, a normalized A0 mode signal is decomposed from the measured Lamb wave signals using a previously developed mode decomposition technique, and the first A0 mode reflected from the delamination is further extracted by using a matching pursuit algorithm. Finally, a reference-free damage classifier is built on the extracted A0 mode reflection from the delamination. Because the proposed technique does not require baseline signals during the entire delamination detection process, robust delamination detection has been achieved even under varying temperature conditions. Copyright © 2013 John Wiley & Sons, Ltd.