The effect of reinforcement architecture on the long-range flow in fibrous reinforcements

Abstract

The resin transfer moulding process involves the long-range flow of resin into a closed mould which is filled with dry fibre reinforcement. The rate of resin flow can be calculated using the Darcy and Kozeny-Carman equations. The flow rate is thus a function of the pressure drop across the fibre bed, the resin viscosity and the permeability of the fibre bed. The permeability constant is dependent on the fibre radius and the porosity of the bed. A number of reinforcement fabrics are now available commercially which promote faster resin flow than that in equivalent fabrics of the same areal weight at the same fibre volume fraction. The KozenyCarman equation includes a parameter known as the mean hydraulic radius. If this parameter is varied by calculating specific hydraulic radii, then the flow enhancement may be modelled. Calculations for model materials have been published and demonstrate that this approach predicts that significant changes in flow rate are possible. The commercial fabrics do not have model structures, but feature variations in the mesoscale architecture of the reinforcement: fibres clustered into tows and uneven distribution of pore space. The paper will report on the correlation of quantitative image analysis of optical micrographs with the flow rates in a range of reinforcement fabrics.