Structural health monitoring using fiber optic distributed sensors for vacuum-assisted resintransfer molding

Abstract

In this study we implemented manufacturing process and strain monitoring of a compositestructure by optical fiber sensors for vacuum-assisted resin transfer molding (VaRTM).Optical fibers with fiber Bragg gratings were embedded into a glass fiber reinforced plasticspecimen made by VaRTM and the applicability of structural health monitoring with fiberBragg grating (FBG) sensors based on optical frequency domain reflectometry(OFDR) was investigated. In this study, long-gage FBGs which are 10 timeslonger than ordinary FBGs (which are about 10 mm long) were employed fordistributed sensing. We can easily map the strain or temperature profile alonggratings by OFDR and the spatial resolution of this sensing technique is about1 mm. The resin flow process in VaRTM could be monitored by measuring thedifference in temperature between the resin and preform. Then, the shrinkageof resin could be also monitored during the curing process. The specimen wasthen subjected to a bending load in a three-point bending test and the straindistributions along the FBGs were measured. From these results we could show theapplicability of distributed sensors to quality assurance of a composite structure madeby VaRTM and assessment of the structural integrity of in-service compositestructures.