Monitoring of the resin flow front within a resin transfer moulding during fabrication using fibre Bragg gratings

Composite structures are becoming significantly larger. Discarding these large structures due to manufacturing defects is unacceptable due to cost, time, and environmental concerns. To mitigate the risk of defects, real-time monitoring of resin flow during infusion is needed to ensure complete wetting of glass mats. However, current studies lack real-time flow-front monitoring, relying instead on manual post-production checks, and may result in costly repairs or disposal of defective parts. Fibre Bragg grating sensors have been shown to spectrally respond to resin during infusion, but the physical mechanism behind this response—crucial for interpreting flow front location and direction—has not been investigated. For the first time we report an in-depth study of fibre Bragg grating sensors for real-time monitoring of the flow front of liquids in the resin transfer moulding (RTM) infusion process and the mechanisms that produce the spectral response based upon the viscous force generated by the liquid and its flow-front. We present experimental wavelength shift data of the fibre Bragg grating sensors during infusion to show that viscous force is the dominant mechanism. Furthermore, we created a model that shows good agreement with experimental data, the model predicts wavelength shifts of the sensors at different locations to the approaching flow-front. Current model can aid numerical simulations of the infusion process to ensure complete impregnation of glass reinforcement mats.