Air-coupled ultrasonic testing to estimate internal defects in composite panels used for boats and luxury yachts

In constructions of boats and luxury yachts, Glass Fiber Reinforced Polymer (GFRP) composite materials are widely employed owing to their high mechanical performance, light weight and flexibility in manufacturing complex shapes. However, GFRP composite materials can be affected by several intrinsic defects (e.g. inclusion, delamination, resin excess or lack), because of both wrong production process and post-production handling. Although conventional ultrasonic testing is the most applied method to enhance the structural safety and quality, it presents a strong limitation in achieving an efficient contact between the transducers and the testing surfaces. Air-coupled ultrasonic testing can be used as a valid alternative, overcoming the previous disadvantage. Aim of this study is to demonstrate the ability of air-coupled ultrasonic testing (ACUT) for qualitatively and quantitatively evaluation of internal defects in GFRP composite panels as those typically used for boats and luxury yachts construction. Simulated delaminations of different sizes have been analysed as well as excess and lack of resin. Results highlighted that a good signal-to-noise ratio can be achieved for delamination greater than 15 mm with correct defect shape recovering, hence making ACUT an appropriate choice for the interactive engineering design and manufacturing of boats.