Application of Ultrasonic C-Scan Techniques for Tracing Defects in Laminated Composite Materials

In this paper practical ultrasonic C-scan techniques for NDT of laminated composite materials are developed and applied, aiming at tracing specific artificial defects. Two types of materials are examined, namely an advanced carbon/epoxy system with unidirectional fibers and a typical marine type glass/polyester system with woven roving reinforcement. Both materials were used in association with two manufacturing methods, namely the simple Hand Lay-Up method and the more advanced Vacuum Infusion one. Several artificial defects made of Upilex polyamide material were embedded into the test plates. These defects have varying shape and magnitude, as well as varying through thickness position, overlapping between each other in one case. A typical layer wrinkle was also manufactured at mid-thickness in each test plate. Test plates were C-scanned using an UltraPack II ultrasonic system in association with UltraWin software. The determination and characterization of defects was attempted by applying typical examination techniques, such as layer to layer examination, full width examination, etc. However, software tuning procedures and appropriate examination strategies were applied, in order to further develop and optimize the scanning procedure. These efforts resulted in effective C-scan images, allowing the determination of the position and, in some cases, of the size of the defects. Finally, precise determination of specimens'thickness was also achieved.