Random discontinuous carbon fibre preforms: Permeability modelling and resin injection simulation

The distribution of fibre bundles in chopped carbon fibre preforms was described using a stochastic model, as a function of geometrical and preform processing parameters. Local permeability distributions were generated from this, based on Gebart’s model for the permeability of aligned fibres. Resin injection simulations were evaluated statistically based on these permeability distributions. Results indicate that, as expected, the macroscopic preform permeability decreases with increasing superficial density (i.e. the average fibre volume fraction). It is independent of the tow filament count and the fibre length within the ranges investigated. The observed coefficient of variation of the permeability increases with increasing filament count, fibre bundle length and superficial density. At constant preform superficial density, variation of the preform processing parameters (fibre spray path offset, spray tool elevation, and spray path pattern) affects the fibre bundle distribution and thus the flow front patterns. Different combinations of the processing parameters have different effects on the mould fill times.