Finite element forming simulation of locally stitched non-crimp fabrics

Locally stitched non-crimp fabric preforms are stacked fabric layers that are sewn together. Using a seam improves the manufacturing process by providing tailored and easy to handle preforms. On the other hand, local stitching modifies the forming behaviour of the layup. Single-lap shear tests and modified bias-extension tests are used to characterise and model the seam behaviour during forming. The modelling of such a stitching is performed using the commercially available finite element software PAM-Form® (ESI Group). The mechanical behaviour of the seam is modelled by a simple multi-linear approach. A comparison between experiment and simulation of the double diaphragm forming of a generic helicopter side frame with a locally stitched non-crimp fabric preform shows valuable benefits gained from such a model. After improvements, the finite element model can be used to determine the influence of the seam on the forming behaviour and thus optimise the arrangement of the stitches.