Fourier Transform Infrared (FTIR) Fiber Optic Monitoring Of Composites During Cure In An Autoclave

Abstract

Real time in situ monitoring of the chemical states of epoxy resins were investigated during cure in an autoclave using infrared evanescent spectroscopy. Fiber evanescent sensors were developed which may be sandwiched between the plies of the prepreg sample. In this work a short length of sapphire fiber as the sensor cell portion of the fiber probe was utilized. Heavy metal fluoride glass (HMFG) optical fiber cables were designed for connecting the FTIR spectrometer to the sensor fiber within the autoclave. The sapphire fibers have outstanding mechanical properties (Young's Modulus 65 = Mpsi) and outstanding thermal properties (T. = 2000°C) which should permit their use as an embedded link in all thermoset composites. The system is capable of operation at a temperature of 250°C (482 °F) for periods up to 8 hours without major changes to the fiber transmission. A discussion of the selection of suitable sensor fibers, the construction of a fiber optic interface, and the interpretation of in situ infrared spectra of the curing process is pre-sented.