Determination of the Transverse Permeability of a Fiber Preform

Abstract

This paper addresses the flow properties of Resin Transfer Molding (RTM) with primary emphasis on transverse (z-direction) permeability. In the case of RTM, the permeability [K] matrix of the fabric preform is the quantity that governs the accuracy of any numerical flow simulation. Characterization of the in-plane permeabilities (Kxx, Kyy,) is done by simple radial flow experiments. However, the transverse permeability is difficult to measure accurately due to the inability to visualize the flow pattern through the thickness. Also, one dimensional flow experiments, which are ideal, encounter significant racetracking along the edges that inhibits proper monitoring of the true transverse flow. The need for accurate transverse permeabilities stems from use of three dimensional flow simulations to model the manufacture of thick section composite components fabricated by the vacuum assisted resin transfer molding genre of composite processes. The objective for this work is to develop an improved methodology to determine the transverse permeability of a fabric preform. This will include formation of the experimental apparatus, configuration of visualization tools, analytical solution for that geometry, creation of a numerical model, permeability predictions given flow front location with time, and finally plotting the series of permeabilities as a function of the percentage of fill. The experimental apparatus is based on a vacuum driven operation to simulate the process desired. A modified version of "SMARTweave," which is the enabling technology for insitu flow monitoring, is used for visualization of the fluid phase. Preliminary experimental data is reported and transverse permeabilities are calculated for several preforms. A comparison of the data to established methods is shown.