<title>In situ cure monitoring of advanced fiber reinforced composites</title>

Abstract

of Manufacturing and Engineering Systems, Department of Chemistry.#To whom correspondence should be addressed.ABSTRACTThis paper describes a comparative study of in-situ cure monitoring and cure modelling by three methods; (a) evanescentwave spectroscopy, (b) refractive index change, (c) near-infrared spectroscopy.Optical fibres were embedded into aerospace epoxy resins during the manufacturing process of the composite. The curecharacteristics were then tracked in real-time during the processing of the material via evanescent wave interaction. Thistechnique is based upon monitoring of characteristic infrared absorption bands of the resin system to find the concentrationof the epoxy and amine hardener as a function of cure time. Hence this technique is suitable for on-line process monitoringand optimisation.Results obtained from the optical fibre sensors were used to model the curing behaviour of the resin system. The results werecompared with near-infrared spectroscopy and differential scanning calorimetry experiments carried out under similarconditions. The feasibility of utilising refractive index changes to monitor the extent of cure has also been demonstrated.Keywords: optical fiber sensors, cure monitoring, epoxy resins, evanescent wave, near-infrared spectroscopy1. INTRODUCTIONThe matrix dominated properties of advanced fibre reinforced composites (AFRC) can be influenced by the initial chemicalcomposition of the resin system. Subsequent processing, i.e. the cure schedule used, can also play an important role indetermining the final properties of the resin. There is therefore demand for a sensor which can determine the state of cureof a composite in-situ and at points remote from the surface, without affecting the integrity of the finished component.Traditionally, methods as diverse as electrical resistance and dielectric analysis', ultrasonic wave propagation2' ,