Film stacking impregnation model for a novel net-shape thermoplastic composite preforming process

An impregnation model has been developed to evaluate the infiltration phenomena that occur during a novel near net shape preforming method. This process comprises automated deposition of thermoplastic resin and unidirectional (UD) carbon fibres to a pre-programmed stacking sequence, thereby forming tailored preforms for subsequent stamp-forming. Infiltration kinetics have been simulated to study the effect of different stacking scenarios, materials, and preconsolidation routes on the novel preforming process. Isothermal infiltration of a liquid thermoplastic polymer into a compressed UD fibre bed has been examined and the experimental results have been used to validate an infiltration model based on local fluid flow in compressible porous media. This enables simulation of infiltration in alternating matrix film and fibre layers, relating pressure, time, and temperature with the local fibre volume fraction, pressure, and liquid and solid velocities in the stacked material. For a given set of processing conditions, the model fibre volume fraction distribution prediction enables the optimum matrix stacking layer thicknesses to be determined. It was shown that infiltration is inhibited above a limiting pressure which leads to increased fibre bed compaction and hence decreased permeability.