A review of NDE methods for porosity measurement in fibre-reinforced polymer composites

Low porosity levels are essential for ensuring the performance of carbon fibre-reinforced composite structures. Despite many attempts to measure absolute porosity levels as a process-control tool, the currently accepted methods often rely on relative measurements in comparison with a reference standard. However, newer low-cost manufacturing methods such as resin-transfer moulding (RTM) and resin film infusion (RFI) would benefit from a reliable absolute ‘porosity meter.’ This paper reviews the literature documenting NDE methods for porosity measurement in fibre-reinforced polymer composites. The majority of the papers have concentrated on ultrasonic methods to determine porosity levels, mainly for quality control purposes. A few workers have reported on the application of other NDE methods. The review concentrates on methods that have potential for use during composite manufacture. To date, no one NDE method has been able to provide a porosity measurement independent of both the pore morphology and the fibre and resin matrix materials.