In-situ cure monitoring of an out-of-autoclave prepreg: Effects of out-time on viscosity, gelation and vitrification

The cutting, lay-up and bagging of out-of-autoclave (OOA) prepregs for composite part fabrication can take from several days to weeks, depending on the desired part size. This period of ambient temperature “out-time” induces resin polymerization/cross-linking, and affects critical physicochemical phenomena such as minimum viscosity, gelation, and vitrification. Therefore, the capability to monitor out-time at ambient conditions and to understand its influence on key resin properties is valuable to minimize waste and increase efficiency. In this study, the dielectric properties of out-of-autoclave (OOA) carbon/epoxy prepreg aged from 0 to 7 weeks are investigated. The measured dielectric data is used to develop an in-situ out-time monitoring method at ambient condition. Furthermore, the effects of out-time and out-life on critical physicochemical parameters are identified.