Air-coupled ultrasonic testing with Lamb waves for straight and curved GFRP plates

The use of composite materials has been steadily growing during the last decades, as well as their requirements. Some processes, like the 3D UV pultrusion process, manufacture long and thin parts, whilst having a varying curvature radius along the same part. Studying their mechanical properties along the main fiber direction, which is of foremost interest, is not an easy task nor efficient with nondestructive methods. The use of air-coupled ultrasonics to evaluate the properties of composite materials has been widely proved by several authors, mainly using guided waves that provide information on the orthotropic properties of this kind of materials. Most of this work has focused on analyzing straight plate-like geometries, due to the simplicity to generate desired Lamb modes in the plate and analyze the behavior of guided waves. In our contribution, the differences in the propagation of Lamb waves for straight and curved geometry glass fiber reinforced polymers (GFRP) have been analyzed. A GFRP test sample cured with UV light with one straight and one curved area has been evaluated. The responses of generated Lamb wave modes for straight and curved geometries have been compared, accounting for variations in the transducer characteristics, e.g. resonance behavior and focusing.