Nondestructive Evaluation of Holed CFRP Laminates by a New Technique to Visualize Propagation of Ultrasonic Waves

This study investigated damage detection in holed CFRP laminates by using a newly developed technique for visualizing ultrasonic waves. This technique provided a moving diagram of propagating waves with non-contact scanning by a pulsed laser. Its measurement scheme overcame the difficulties of sensitivity in conventional methods and enabled us to observe ultrasonic waves on CFRP laminates. We observed two types of ultrasonic waves propagating on the CFRP laminate in the measured snapshots. These waves were identified as the <i>S</i>₀ and the <i>A</i>₀ Lamb modes by the dispersion curves, confirming the validity of the visualization technique for composite laminates. Furthermore, ply cracks and delamination, as well as the damage during manufacturing, were observed near the hole in the loaded specimens, and we successfully visualized the Lamb waves scattered by the delamination. The region of wave scattering agreed with the damage observed by soft X-ray radiography. These inspection results demonstrated the usefulness of the visualization technique in inspecting composite laminates.