Optical Transparency Change Method for Cure Monitoring of GFRPs

Abstract

The resin transfer moulding (RTM) process is becoming popular for low-cost fabrication of complicated commercial products made from glass-fibre-reinforced plastics (GFRPs). As regards the RTM process for complicated components, the optimal fabrication process is found by repeated trial and error. This process is time consuming and one of the reasons for the high cost of composite products. To overcome this problem, it is useful to monitor the degree of cure of target GFRP products. In this study, the luminance change method is used for cure monitoring of polyester-based composites. Polyester resin is normally used as the matrix resin for low-cost GFRP products. Polyester resin usually changes its optical transparency during the curing process. This enables us to monitor the degree of cure by measuring the luminance change of light or reflected light. In this study, we present a system that measures reflected light. The sensing system employs an LED as the light source and a photodiode as a light power sensor. This low-cost cure monitoring system is applied to the monitoring of the degree of cure in GFRPs and is achieved using commercially available dielectric sensors. Results are compared with the results of luminance change. The effectiveness of this method has been confirmed experimentally.