Monitoring microwave curing of composites using FBG sensors

Composites with good material properties and light weight have been extensively applied to high speed rail systems to improve operation speeds and energy efficiency. Recently, composites became cost-competitive owing to their mass production and short manufacturing time facilitated by new methods like microwave curing. Cure monitoring needs to be optimized in terms of the cure cycle considering materials characteristics in order to manufacture high quality composites using microwave curing. Thermocouples made of metal are generally used for conventional cure monitoring; however, it is not suitable to be used for microwave curing. Therefore, in this study, cure monitoring of CFRP fabric is performed using FBG sensors with EMI immunity for microwave curing. Two types of FBG sensors (strain/temperature) were embedded in the specimens and they measured the strains and temperatures during the curing process in real time. The test results showed that the tensile strain was generated by the reduced viscosity of resin during both increasing and maintaining temperature and compressive strain of 85 to 490 με occurred during the cooling process. Consequently, it was confirmed that FBG sensors could be applied to cure monitoring of composites using microwave. Further, the data collected in this study can be used as preliminary data for optimizing the cure cycle of microwave curing in the future