Understanding and prediction of fibre waviness defect generation

Fibre waviness is one of the most significant defects that occurs in composites, due to the severe knockdown in mechanical properties that it causes. This paper summarises a substantial research programme that has been undertaken at the University of Bristol to investigate the generation of fibre waviness defects during prepreg composites processing and develop predictive numerical models. Generation of fibre waviness can come from a number of sources, here the focus has been on thick sections, where consolidation of the ply stack leads to out of plane ply movement. This out of plane movement can directly lead to waviness generation or it can indirectly create the excess length in a ply that in turn leads to the formation of waviness. Initial experimental results on compaction of simplified specimens led to the development of a model that was embedded in the finite element software Abaqus as a user material. A number of case studies were then investigated using this model to show how the formation of wrinkle defects in typical component features can be predicted. Experimental testing has been undertaken to validate the model results.