Ultrasonic guided wave monitoring of resin flow in vacuum assisted resin injection processes

Newly developed out-of-autoclave (OoA) methods for resin transfer moulding (RTM) in heated moulds could potentially represent a cost-effective method of manufacturing aerospace composite panels by replacing the need for large autoclaves and their energy-consuming nature. However, due to the lack of the autoclave’s higher pressures, the lower fibre volume fraction and increased porosity of the resulting parts hinder the industry implementation of this environmentally-conscious approach. Real-time resin flow monitoring is, thus, imperative to ensure suitable impregnation of the reinforcements. This research aims to apply a distributed ultrasonic sensor network to monitor the resin flow, utilising guided waves generated by ultrasonic transducers in a pitch-catch configuration. A COMSOL model featuring two 500 kHz piezoelectric probes was developed, and the response of the fundamental out-of-plane propagating mode (A0) to liquid loading is analysed and employed to facilitate accurate detection and mapping of the resin front. In parallel, an experimental setup mimicking RTM conditions was constructed, and time-stamped resin images were captured to validate the sensor readings. The system effectively tracked the liquid front within a 0.5 cm margin, with excellent agreement between the simulation and the experimental findings, offering a holistic approach to the optimisation of OoA composite manufacturing processes.