Non-contact detection of interlaminar defects in titanium-graphite FMLs using laser ultrasonics and thermography

The use of fully non-contact Laser Ultrasonic Testing (LUT) for the inspection of advanced hybrid composites, such as Fiber Metal Laminates (FMLs), offers significant advantages for industrial applications. The LUT setup provides high flexibility, enabling the generation of multiple ultrasonic wave modes and access to difficult-to-reach areas without the need for surface preparation. However, the inherent heterogeneity of FMLs, characterized by multiple interfaces and contrasting material properties, presents challenges in wave propagation and signal interpretation, particularly due to the presence of Lamb waves. In this study, a LUT pitch-catch ultrasonic configuration was developed to inspect a 10-layers Ti-Gr laminate containing artificial defects. The system successfully identified flaws up to the fourth interface and enabled partial shape characterization up to the third. Rapid scanning via B-scan mapping and targeted high-resolution C-scans allowed efficient localization and detailed evaluation of defects. Results were validated through complementary pulsed thermography, confirming the reliability and robustness of the proposed inspection method.