Instantaneous delamination detection in a composite plate using a dual piezoelectric transducer network

This study proposes a new damage detection technique so that delamination in composite plates can be detected by comparing pitch-catch Lamb wave signals obtained from a piezoelectric transducer (PZT) network without using their own baseline signals obtained from the pristine condition. The proposed technique is based on the premise that the fundamental anti-symmetric (A0) mode slows down when it passes through a delamination area while the speed of the fundamental symmetric mode is little affected by delamination. First, the A0 mode in each path is isolated using a mode extraction technique. This mode extraction technique is able to isolate the A0 mode without frequency or transducer size tuning using dual PZTs composed of concentric ring and circular PZTs. Once the A0 modes are extracted from all paths in the transducer network, the relative time delay of the A0 mode in each path with respect to the other paths is defined as a delamination sensitive feature. Then, an instantaneous outlier analysis is developed and performed on the damage sensitive feature to identify the path(s) affected by the delaminated region(s). Because the relative time delays of the A0 modes are instantaneously compared, robust delamination detection is achieved even under varying temperature conditions.