The compression behaviour of Wet Non-Crimp-Fabrics

Many industries, such as the automotive one are making great effort to reduce costs and increase the productivity of composites manufacturing processes. Even if all these technologies are still emerging, it appears that Liquid Composite Moulding (LCM) processes in which there is a compression phase, as the Wet Compression Moulding (WCM) or Compression Resin Transfer Moulding (CRTM), are the best positioned. In these cases, as the wet fibre preform is compressed during the process, it is essential to know the compression behaviour of these materials in order to select and optimise the manufacturing process by simulation tools. When dealing with the compression process, the preforms have usually been considered to exhibit an elastic linear behaviour. Nevertheless, the last publications have shown that this behaviour is mainly viscoelastic. In this work the relaxation of a wet 50k carbon fibre Non-Crimp Fabric (NCF) under compression has been characterised for 3 different velocities. To do so, the viscoelastic behaviour has been described by fractional models, which compared with classical exponential models, are able to correctly reproduce the relaxation of the material during the maximum compression stage.