Multi-scale computational fluid dynamics of impregnation die for thermoplastic carbon fiber prepreg production

A multi-scale computational fluid dynamics (CFD) model of a pultrusion process was proposed for unidirectional carbon fiber (UD-CF) prepreg production. Polyamide 6 (PA6) and polyacrylonitrile-based CF were used as the thermoplastic polymer matrix and reinforcement, respectively. The non-Newtonian viscosity of PA6 was expressed by Carreau's model. A micro-scale CFD model was constructed to obtain a proper resin permeability to CF filaments, while the tow domain was treated as sliding porous media in the macro-scale CFD. The resin velocity profile showed a similar shape to the relative resin amount experimentally measured in the UD-CF prepreg. The uniformity index of the resin velocity (UIv) on the outlet surface was calculated for 45 case studies with several tow speeds and resin flow rates. The tow speed showing a maximum UIv was remarkably well expressed as a linear function of the slip velocity, which is the difference between the tow speed and resin velocity.