Scaling analysis and a critical thickness criterion for thermosetting composites

In composites processing, the combination of thickness, mold temperature, and resin kinetics can lead to temperature overshoot within a part during cure. In this paper, the interplay between these variables was considered to establish a critical thickness separating parts having large overshoots from parts having small overshoots. The one-dimensional heat equation with an autocatalytic relation for curing was used to model the process. The equations were placed in dimensionless form using a scaling analysis. Five dimensionless groups were identified. Two of these groups were found to affect the overshoot of the temperature: the modified Damköhler number Da*, which distinguishes thin and thick composites and the dimensionless temperature ramp rate t̄_rise, which depends on the boundary condition and heat transfer characteristics of the composite. To validate the scaling analysis, a finite difference model was created to calculate part temperatures during cure. The numerical analysis confirms that thin and thick parts, as defined by the relative temperature overshoot, can be predicted by Da* and t̄_rise.