Multi-resolution non-contact damage detection in complex-shaped composite laminates using ultrasound

Numerous nondestructive testing (NDT) methods have been developed to perform inspections of engineered structures. Frequently, increased precision of a given method is associated with longer inspection time. The trade-off between precision and inspection time is especially apparent in ultrasonic testing (UT). The imaging resolution is directly related to the applied frequency of the ultrasound. As an example, guided waves propagating in plate-like structures, provide the means for fast inspection of large areas due to their long propagation distances. Damage characterization accuracy is, however, limited in this case due to relatively large wavelengths. On the other hand, local inspection with high-frequency bulk waves provides much more accurate damage characterization thanks to shorter wavelengths. The drawback of local inspection is the long scanning time necessary for large components. In order to optimize the inspection time and accuracy, we propose a two-step damage evaluation framework. In the first step, a global full-field screening with the use of guided waves is performed to determine the possible damage locations. In the second step, the identified hot spots are further evaluated with a high-frequency bulk wave system. Both testing modalities are implemented using non-contact laser vibration sensors. A piezoceramic exciter is used for the guided wave setup, while a pulsed laser excitation source is used in the bulk wave setup. The proposed approach minimizes sample preparation time and is completely non-intrusive. The feasibility of the proposed framework is demonstrated in a complex shape, thin-walled composite structure with multiple defects.