Modeling the Effect of Fiber Diameter and Fiber Bundle Count on Tow Impregnation during Liquid Molding Processes

Abstract

This paper explores the effect of fiber diameter and fiber bundle count on tow impregnation during liquid molding processes. Resin and fiber wetting properties play an important role on the resin infiltration behavior within a single fiber tow. Dynamic and equilibrium microflow models, based on Darcy’s Law and force equilibrium at the resin flow front, assume that the infiltration of the resin is driven through capillary pressure and hindered by the entrapped gas within the tow. The results of the dynamic model show that the fiber tow count and the fiber diameter have a significant effect on the tow infiltration time. The infiltration time is 10 times longer for a 60 K carbon fiber tow than for a 6 K one. The infiltration time is also inversely proportional to the fiber diameter. As the fiber diameter is decreased 100 times, from 3.5 mm to 35 nm, the infiltration time increases 100 times for the same diameter tow. It also shows that fiber volume fraction also has a significant effect on the tow infiltration time and any fiber volume variations along the fiber tow could lead to dry spots in the composite due to the large differences in infiltration rates. The model indicates that the entrapment of a critical amount of air within a tow will lead to higher than acceptable void contents.