A permeability prediction for non-crimp fabrics

A model is proposed to analyse the variation in the permeability of Non–Crimp Fabrics, originating from variations in the internal structure of the material. A geometrical description of the fabric based on the distortion induced by the stitch threads piercing through the fabric is employed. The distortions form channels which are mutually connected. It is assumed that these channels dominate the permeability of the fabric. A network of flow channels is subsequently defined, in which the variations, measured in the dimensions of the distortions, is explicitly accounted for. The variations in the internal structure of the fabric affect the averaged permeability significantly. Moreover, a network rather that a single unit cell is required to predict the averaged permeability and its variation properly. Finally, the spatial distribution of the randomly generated channel dimensions affects the permeability significantly

Non-crimp fabric permeability modelling

A qualitative study to the in-plane permeability modelling of Non-Crimp\ud Fabrics has been carried out. A network flow model was developed to describe flow through\ud inter bundle channels (meso level). To improve this model, it was extended with details that\ud consider stitch yarn influenced regions. The model predicts a highly anisotropic permeability.\ud The predicted permeability in the machine direction of the fabric corresponds with the\ud experimental results. However, prediction of permeability perpendicular to the fabric’s\ud machine direction does not correspond with the experimental results. Possibly, flow through\ud fibre filaments (micro level) is significant and the network flow model has to be extended to\ud include this type of flow

A consolidation process model for film stacking glass/PPS laminates

The applied pressure, processing temperature and holding time influence the\ud consolidation of thermoplastic laminates. A model to optimise the processing\ud parameters is proposed. The influence of heating rate, processing temperature and pressure is investigated. Short textile impregnation times, in the order of seconds, are predicted. The model is validated in an experimental programme

A permeability prediction for (un)sheared non-crimp fabrics

A permeability prediction model for relaxed and sheared Non-Crimp Fabrics is proposed. The model is based on geometrical features of the fabric. The stitches penetrating the uni-directional plies of the NCF induce distortions of the fibres in the plane of the fabric. These Stitch Yarn induced fibre Distortions (SYD) form flow channels, which determine the permeability of the NCF. The channels are connected to each other in overlap regions, allowing the fluid to flow from one channel to another and finally to impregnate the entire preform. A network of SYD flow channels is created to account for the statistical variations in the dimensions of the SYDs. The system of flow resistances is solved analogously to the solution of the effective resistance of an electrical circuit with parallel and serial resistances. The flow in each of the SYD domains is calculated employing an energy minimisation method. Analysis of different networks, with varying spatial distribution of the dimensions of the flow channels, allows the prediction of the variation in the permeability of an NC

Braiding simulation for RTM preforms

Braiding is a manufacturing process that is increasingly being used to manufacture pre-forms for Resin Transfer Moulding. A fast simulation method is presented for the prediction of the fibre distribution on complex braided parts and complex kinetic situations (e.g. changes in velocity, orientation). The implementation is suited for triangular surface representations as generated by many CAD software packages in use. Experimental results are presented to validate the model predictions, showing an acceptable correlation with the data predicted by the simulation method. The guide ring dimensions and spacing appear to have a significant effect on the accuracy of the predicted fibre orientations