Observation of forming process of voids in CFRP prepregs by optical fiber sensors

Abstract

Although a Fresnel’s fiber optic sensor is very useful to monitor cure process of CFRP in real time, some voids remain in resin rich region around the sensor tip and reflected lights from them may affect measurement accuracy. The effect of lights from the voids on the accuracy could be reduced by appropriate filtering method, however the lights provide information of voids forming during molding. In the present study, we observed reflected light spectrum obtained by the Fresnel’s sensor embedded in CFRP prepreg during hot-press molding. The results showed that the voids disappeared when resin melted but formed again when the degree-of-cure became about 0.6 because the increased viscosity of resin resulted in the voids trapping on the boundary between fibers and resin.