Pressure distribution in resin transfer molding with a non-rigid fiber preform

Abstract

In mold filling processes of composite material manufacturing such as resin transfer molding (RTM), a polymer resin impregnates the fiber mat placed in a mold under a pressure gradient generated by pressure at gates or vacuum at outlets, or both. The flow characteristics in the fiber mat during the impregnation play a critical role in determining the mechanical properties of the final parts, as well as the cost effectiveness of the process. In this work, resin impregnation through a compressible fiber preform is modelled analytically using Darcy's law in an expanding flow domain of a rectangular shape with a uniform velocity profile at the injection gate. The model proposed in this work accomodates the effect of both the compressibility and relaxation of the fiber mat on the volume fraction of the resin. The compressible region of the fiber mat is confined phenomenologically to the front region of the resin impregnation where the impact of the resin on the fiber causes a higher volume fraction of the resin. A relaxation length is introduced in the resin front region to characterize the relaxation of the fiber mat under the impact of the resin. To analyse the pressure distribution, the Kozeny-Carman relationship is used for integration of Darcy's law. The influences of the compressibility and relaxation of the preform on the pressure distribution are analysed, the result showing that the pressure level is lower when preform compressibility and relaxation are considered in the modelling. This conclusion is in a good qualitative agreement with existing experimental data.