That's how the preform crumples: Wrinkle creation during forming of thick binder-stabilised stacks of non-crimp fabrics

The simultaneous forming of multiple layers of fabric is being used in industry to increase the throughput of composite parts. A polymeric binder may be used to stabilise the fabric layers to make it easier to handle, however, the binder may also restrict relative fibre movement, which may lead to wrinkles during forming. Despite the increasing interest in using binder-stabilised preforms in the wind industry, defects arising during forming have scarcely been investigated. This study investigates fibre wrinkling in binder-stabilised preforms (layers of dry non-crimp fabric stabilised with an interply polymeric binder) during forming. The results from an experimental campaign are presented, in which full-thickness pre-consolidated preform specimens are being formed over two different ramp geometries. Wrinkles are observed at the transition edges during forming. To aid the discussion on wrinkle mechanisms, a numerical model is presented that uses continuum shell elements for modelling the NCFs and a cohesive law for modelling the interface. This model is capable of predicting the wrinkle onset and wrinkle location and may be used to study the formability of the preform.