Multi-resolution non-contact laser-sensing damage detection technique for composite laminates

Numerous ultrasonic (UT) modalities have been developed to perform inspections of engineered structures. However, increased precision often comes at the cost of longer inspection times. As an example, guided waves propagating in plate-like structures allow 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. Here, we discuss a two-step laser-interferometer-based non-contact approach for the inspection of carbon-fiber-reinforced structures. First, a full-field screening using guided waves is performed to determine the possible damage locations. The identified hot spots are further evaluated in the second step with a high-frequency bulk wave system. 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.