Normal and Parallel Permeability of Preform Composite Materials used in Liquid Molding Processes: Analytical Solution

The permeability of the preform composite materials used in liquid molding processes such as resin transfer molding and structural reaction injection molding is a complex function of weave pattern and packing characteristics. The development of tools for predicting permeability as a function of these parameters is of great industrial importance. Such capability would speed process design and optimization and provide a step towards establishing processing-performance relations. In this study, both normal and parallel permeability of fibrous media comprised of ordered arrays of elliptical cylinders is studied analytically. A novel scale analysis technique is employed for determining the normal permeability of arrays of elliptical fibers. In this technique, the permeability is related to the geometrical parameters such as porosity, elliptical fiber diameters, and the tortuosity of the medium. Following a unit cell approach, compact relationships are proposed for the first time for the normal permeability of the studied geometries. A comprehensive analysis is also performed to determine the permeability of ordered arrays of elliptical fibers over a wide range of porosity and fiber diameters. The developed compact relationship is successfully verified through comparison with the present results. As a result of assuming an elliptical cross section for the fibers in this analytical analysis, an extra parameter comes to play; therefore, the present analytical solution will be more complicated than those developed for circular fiber type in the literature.