Lamb wave-based Cure Monitoring of Carbon Fibre Reinforced Polymers for On-site Aircraft Repairs

The repair of carbon fibre reinforced polymer structures of aircraft is increasingly conducted on site. Monitoring the curing process of polymers has the potential to decrease repair costs by time optimisation and quality control. In this paper Lamb waves are utilised to determine the degree of cure. Waves are excited and recorded by two piezoelectric transducers, one serving as an actuator and the other as a sensor. The recorded signals are processed with a complex wavelet transform, which allows more accurate feature extraction than calculating features in time domain. Extracted features are the transmitted signal energy of the wave and the resonance frequency of the curing polymer. Waves are excited at different frequencies to identify the current resonance frequency. Excitation at or near the current resonant frequency ensures that curing is monitored with maximum sensitivity.