Visualization of hidden delamination and debonding in composites through noncontact laser ultrasonic scanning

This study proposes a complete noncontact laser ultrasonic wavefield imaging technique to automatically detect and visualize hidden delamination and debonding in composite structures. First, ultrasonic wavefield is obtained from a target structure by scanning a Nd:YAG pulse laser beam for ultrasonic wave generation and measuring the corresponding ultrasonic responses using a laser Doppler vibrometer. Then, hidden damages are identified and visualized through adoption of a standing wave filter, which can isolate damage-induced standing waves from the obtained wavefield. The proposed technique has following advantages over the existing techniques: (1) it does not require any sensor installation; (2) it is noninvasive, rapidly deployable and applicable to harsh environments; and (3) it can visualize damage with high spatial resolution without any baseline data, which enables automated and intuitive damage diagnosis. The feasibility of the proposed technique is demonstrated by visualizing a debonding in a carbon fiber reinforced plastic aircraft wing and a delamination in a glass fiber reinforced plastic wind turbine blade. Furthermore, the effects of temperature and static loading variations on the proposed technique are also examined.