Permeability of stitched preform packages

摘要

To obtain useful flow simulations to support mould design, it is necessary to use accurate permeability values. In the work described here, the permeability of carbon fibre preforms with and without stitches was measured. A preform is a multilayer package of material ready to be impregnated using liquid transfer moulding technology. The main parameters which vary in the preforms are the stitching pattern, meaning the distance between the stitch rows through the preform, the stitching thread tension and the stacking sequence of the layers. The permeability measurements were carried out using a continuous, two-dimensional radial-flow measurement technique. The measuring device consists of an aluminium mould with integrated dielectric sensors (surface treated to prevent short circuit). The sensor system relies on the change in the dielectric properties of the material as saturation takes place. The results showed that stitching has a positive influence on the permeability. The stacking sequence was found to be the most effective way to influence permeability.