Modelling and monitoring of out-time and moisture absorption effects on cure kinetics and viscosity for an out-of-autoclave (OoA) prepreg

Out-time and moisture absorption during out-of-autoclave (OoA) prepreg preparation are generally unavoidable. The resulting cross-linking and increase in resin viscosity can prevent sufficient flow into the fiber tows during processing and cause porosity. In this study, efficient modelling and in situ methods to monitor cure kinetics and viscosity were developed to account for the effects of out-time and absorbed moisture. First, a commercial OoA prepreg was conditioned to specific levels of out-time and relative humidity (RH). Property data were obtained from differential scanning calorimetry (DSC) and rheometry and used to develop cure kinetics and viscosity models for a wide range of process conditions, initial out-times, and humidity conditions. The dielectric signals were correlated to the measured data and used to demonstrate real-time monitoring of resin state during cure. The predictive models were then used to understand the influence of out-time and absorbed moisture on resin viscosity during consolidation of OoA prepreg.