

Reference-Free Structural Health Monitoring for Detecting Delamination in Composite Plates
Abstract
This paper presents a new methodology 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 anti-symmetric mode (A0) is followed by another A0 mode reflected off from the “inside†delamination. Unlike other conventional techniques, the proposed technique takes advantage of this A0 mode reflected off from the inside delamination to instantly detect the existence of delamination. First, Lamb wave signals are measured in a pitch-catch mode using a dual PZT composed of concentric ring and disk PZTs for excitation and two circular PZTs for sensing. Here, the dual PZT actuator is used to extract only the A0 mode at any desired driving frequency. Then, the response time signals are measured by the two circular PZTs, and the damage sensitive feature, which is the A0 mode reflected off from the delamination, is extracted. Because the proposed technique does not require baseline signals during the entire delamination detection process, it has been demonstrated that robust delamination detection can be achieved even under varying temperature conditions.