Air-coupled ultrasound inspection of complex aluminium-CFRP components

Composite Overwrapped Pressure Vessels (COPVs) are widely used to contain high-pressure fluids. COPVs consist of a thin metallic liner covered with a composite material based on structural fibres. The main function of the liner is to avoid direct contact between composite and chemical agents which can degrade the resin matrix. In the filament winding process for COPV production, a metallic core is wrapped with impregnated carbon filaments. After that, the matrix can be cured at ambient temperature without use of an autoclave. The COPV's structural integrity can be assured using suitable designs, controlled manufacturing processes and effective Non Destructive Evaluation (NDE) methods. However, the ultrasound inspection of these components is challenging by several factors. Because no vacuum compaction process is applied, the sound attenuation in the laminate is high. Moreover, the strong reflection at the liner-fibre interface avoids inspecting from the metallic-side using conventional techniques. This work explores the possibility of inspecting COPVs by air-coupled ultrasound after the manufacture process.