Modelling Forming of Multi-Ply Preforms

The aim of this study was to evaluate existing numerical methods for predicting the drape behaviour of composite reinforcements, and adopt them to investigate the forming behaviour of thick multi-ply fibre preforms. A particular area of interest was to understand the opportunities offered by locally stitching multiple plies together, to reduce in mould assembly times and to aid robotic preform placement.

The main objective of this work was to benchmark a user-defined material model implemented in Abaqus/Explicit against the commercial forming code PAM-FORM. Whilst previous research typically predicts the forming behaviour for individual thin plies, or multiple plies of the same orientation, the novelty of this work was in studying heterogeneous multi-layer performs with potentially different material behaviour in each ply.

The presence of stitch-bonds significantly affects the forming forces and the shear angle distribution across all plies of the preform, rather than having just a localised effect. Stitches can be used to effectively control local yarn angles to transfer shear forces into un-sheared regions during forming. It is therefore possible to use stitches to redistribute strains within the fabric to avoid wrinkling. It was concluded that stitches are an effective way of joining multi-ply stacks of fabric together, but an optimisation algorithm is required to select stitch locations and patterns, in order to minimise their influence on forming behaviour . This will be developed as part of a follow-on project funded by the TSB (TS/M001237/1) in collaboration with an automotive OEM and a non-crimp fabric manufacturer.