A multi scale consolidation model for press moulding of hybrid textiles into complex geometries

Side-by-side hybrid textiles are an intermediate step for the production of fibre-reinforced thermoplastic composites. Press moulding these materials combining reinforcing fibre textiles and thermoplastic matrix textiles or flexible layers is a promising method to produce high-end fibre- reinforced thermoplastic composites parts with complex geometry at relatively short cycle times and lower costs. Since most of the established manufacturing methods for fibre-reinforced ther- moplastic composites can only produce parts with limited complexity, press moulding of hybrid textiles could broaden the manufacturing capabilities and offer a whole new set of possibilities. However, the current lack of three-dimensional consolidation model prevents the establishment of this technology, as appropriate design and process parameters cannot be determined and defect formation cannot be predicted. This thesis presents the development of a three-dimensional consolidation model for press moulding of hybrid textiles. First, a literature review is presented to identify the limits of models addressing effects relevant for consolidation. A model for the stress response of textile stacks, which is an effect taking place during consolidation, is validated and a numerical approach to characterize the model parameters is presented. Then, a novel consolidation model for hybrid textiles including air entrapment, dissolution and diffusion is developed and validated experimen- tally using glass reinforcements and polypropylene or polyethylene matrices. Direct measurement validates the model of Gebart for permeability, a key model parameter, at very high fibre vol- ume fractions and it is shown that entrapped air significantly influences impregnation. Finally, the model is extended in three-dimensions with some restrictions by considering a free-form plate with non-uniform thickness. By adopting a unit-cell approach with three-phase flow, it is possi- ble to take into account the volume change resulting from matrix flow and impregnation, and by adopting a homogenization method the computational challenges of a full-scale simulation can be bypassed. This novel consolidation model provides insights to explain the fiber movement in non-uniform thickness plates, enables part and process optimization, and paves the way for high-quality composite part production.