Effective average permeability of multi-layer preforms in resin transfer molding

Abstract

Resin transfer molding is a process in which two or more layers of fiber mats are stacked on one another, placed in a closed mold, and infiltrated with a thermoset resin to form a composite part. As the thickness of the part is many orders of magnitude less than the in-plane directions, the flow of resin through the preforms is described using Darcy's law in the in-plane direction by averaging the permeability of the preform through the thickness. If the transverse permeability is very small as compared with the in-plane permeability of the fiber mats, there will be a significant transverse flow between the layers. Hence any averaging scheme for effective permeability across the thickness should take this into consideration. A new scheme for average effective permeability is proposed that does account for the transverse flow between the adjacent layers. This effective permeability is a function of the in-plane and transverse permeabilities, the thickness of each layer, as well as the total length of the mold. Results are presented for two- and three-layer cases and the influence of transverse permeability on the inlet pressures and the flow front differences between the layers is explored. To do this, a two-dimensional flow, based on a finite-element/ control-volume approach, and one-dimensional flow, based on the arithmetic and the transverse flow averaging schemes are used. Since the experimental measurement of the transverse permeability is very difficult, an additional outstanding advantage of the new approach is that it allows us to characterize this property between two adjacent layers.