Fibre Bragg gratings: monitoring of infusion process in liquid composite molding manufacturing

The authors report the use of FBGs to monitor the infusion process of the Resin Transfer Molding (RTM). Composite structure can be very large, ensuring that the resin has reached every part of the mold during the infusion process becomes a critical step to ensure the structural integrity and minimize failure. During the infusion stage of the process, the FBG undergoes a blue wavelength to red wavelength shift. The magnitude of wavelength shifts depends upon the location and depth of the sensors along with the viscosity of resin (we used a resin-like material with similar viscous properties) being used for the infusion. The observed wavelength shifts varied from ~10pm to ~400pm, which is small but still significant and readily measurable also showing reasonable repeatability for all experiments conducted with the same conditions. Evidence will be presented to show that viscous force is a major factor in explaining the observed FBG wavelength shifts. Due to the small wavelength shifts of the FBG sensors, this allows the opportunity to embed a dense population of sensors within a single structure, hence ensuring a satisfactory spatial resolution to monitor the resin flow front to ensure complete impregnation of the reinforcement.