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

Out-of-autoclave (OoA) processes, particularly resin transfer moulding (RTM), could significantly reduce the costs for composite panel manufacturing in the aerospace sector, superseding the voluminous, energy-intensive autoclaves. However, the concern surrounding this method is the lower fibre volume fraction and higher porosity of components in the absence of the autoclave’s higher pressures. Therefore, to ensure the imposed mechanical properties, there is an immediate demand for in situ monitoring of the resin flow to ensure adequate permeation of the plies. This research aims to employ a distributed ultrasonic sensor network to monitor the resin front, which utilises guided waves generated by directly coupled transducers in pitch-catch configuration. A COMSOL model of two 500 kHz piezoelectric probes monitoring a column of resin was developed, and the response of the fundamental out-of-plane propagating mode (A0) to liquid loading is analysed and applied to detect and map the liquid front. Concurrently, an experimental arrangement replicating the conditions in RTM setups was built, and time-stamped recorded images of the resin were used to validate the collected measurements. The system accurately discerned the progression of the liquid front within an approximate margin of 0.5 cm, and excellent agreement was found between the simulation and the experimental study.