Abstract
The permeability of the preform materials used in liquid molding processes such as resin transfer molding and structural reaction injection molding is a complex func tion of weave pattern, packing characteristics, tow structure, and intra-tow properties. The development of tools for predicting permeability as a function of these parameters is of great practical importance because such capability would speed process design and op timization and provide a step towards establishing processing-performance relations. In this study, microscale flow in unidirectional-fiber porous media has been investigated. The effect of tow shape, packing, and intra-tow permeability on the overall bed permeability has been modeled by the simulation of axial flow through rectangular arrays of porous elliptical cylinders. The Brinkman equation was used to model flow inside the porous structures, and the Stokes equation was used to model flow in the open media between the structures. The calculations show that the influence of the intra-tow permeability on the overall bed permeability increases with inter-tow packing and increasing degree of tow ellipticity. Experiments on a commercially available unidirectional material (Knytex D155) have also been carried out and compared with the numerical calculations. The data show that reducing the number of warp threads holding the tows in place has a substantial effect on the permeability (removal increases it by as much as a factor of 6). Good agreement is obtained between modeling and experiment when the warp threads are almost com pletely eliminated, thus indicating the need to extend the numerical model to account for such subtle features.