Performance Characteristics of the Fluorescence Optrode Cure Sensor

The autoclave curing of carbon-epoxy laminates is the most critical and costly stage in the fabrication of composites. A reliable, low-cost cure sensor suitable for use in manufacturing is needed to implement realtime control of the process. A second-generation FOCS which measures fluorescence intensity and wavelength with a fiber-optic spectrofluorometer and a tool-mounted optrode were used to monitor the curing of Hercules 3501-6 laminates. Changes of fluorescence intensity during cure follow changes in resin viscosity up to the gel-point, after which it increases in proportion to the degree of cure (DOC). The fluorescence wavelength as a function of cure-time produces a highly characteristic signal profile which is reproducible and independent of fluctuations in fluorescence intensity. Both FOCS signals detect changes in DOC during late stages of cure. Factors affecting the performance of the second-generation FOCS are discussed.