FE-simulation of the diaphragm draping process for NCF on a macro-scale level

Preforming of dry Non-Crimp Fabric (NCF) enables a near-net-shape structure of CFRP-parts before resin injection. Besides the common punch forming or hood forming, the diaphragm draping process offers greater possibility for automatable forming of textile reinforcements for composites. But the highly extendable membrane used to drape the preform over the tool influences greatly the draping results and may even introduce specific defects. To investigate the process mechanics of the single diaphragm process a FE-based simulation has been performed. A macro-scale model was set up by using a biphase shell element to model the reinforcement material. As first application a single NCF ply draped over a mold for a generic helicopter frame structure has been studied. Experiments have been carried out in order to validate the simulation results and to investigate the capability of this approach to present different types of defects like e.g. wrinkling. Based on that work a detailed study has been done on drapeability of a specific tailored reinforcement (multiple plies of NCF locally stitched together) [6]. The stitching for instance could lead to a locking of the fabric mechanics, which in turn results in a limited formability and local defects in the stitching region.