Computer modelling for the prediction of the in-plane permeability of non-crimp stitch bonded fabrics

The purpose of this paper is to present and validate a model for the prediction of in-plane permeability in non-crimp stitch bonded fabrics. The model is based on the combined flow through the multi-layer assembly in each non-crimp fabric. The permeability of each layer of the assembly is predicted on the basis of a meso-/micro-flow computer model. In this the meso-flow between fibre tows is considered as Stokes' flow and it generally progresses ahead of the micro-flow. Darcy's law is employed to model micro-flow through each fibre tow, taking into account injection and capillary pressures in both types of flow. Transverse mass transfer is considered from the advancing meso-flow to the micro-flow through the permeable boundaries of fibre tows. The model is tested in biaxial non-crimp stitch bonded fabrics with either chain or tricot stitch. Excellent agreement exists between predictions and experiment when the meso-channels are straight of homogeneous cross-section. The permeability predictions are very sensitive to the dimensions of the meso-channel cross-section and require input data from a detailed microstructural analysis for meso-channels with varying cross-section.