Visualization and quantification of forced in-plane flow through deformed porous media

Fluid flow in liquid molding processes and in other applications involving porous media is often characterized with a permeability tensor and modeled by d'Arcy's law. The permeability is a sensitive function of pore structure, which, in deformable materials, is influenced by compression and extension. The majority of previous permeability measurements on composite reinforcement fabrics did not account for deformations imposed on them by corners and curves in the mold. In the present study, transparent molds were designed with a single 90 degrees bend in which the gap between plates was held constant throughout the flow path. Thus, the effects of fabric curvature on permeability were investigated independently of the effects of fabric compression in the thickness direction, A new experimental system was developed to visualize and quantify fluid flow in fabrics mounted in transparent molds. The reported measurements were conducted with fluid flowing through a (vertical) flat region of fabric, around the 90 degrees curve, and then along a second (horizontal) flat region. Permeability was found to be reduced by the imposed curvature for a nonwoven polyester and three-dimensional woven glass fabric. We were able to quantify the effect of curvature on permeability for the former, but not for the latter because of an enduring, dominant nonlinear entrance resistance. For the glass, comparison of two now rates indicates that the faster flow is characterized by a two stage filling process, whereas, at the slower rate, the liquid front fills all pores at the same time.