Design of Tailored Non-Crimp Fabrics Based on Stitching Geometry

Automation of the preforming process brings up two opposing requirements for the used engineering fabric. On the one hand, the fabric requires a sufficient drapeability, or low shear stiffness, for forming into double-curved geometries; but on the other hand, the fabric requires a high form stability, or high shear stiffness, for automated handling. To meet both requirements tailored non-crimp fabrics (TNCFs) are proposed. While the stitching has little structural influence on the final part, it virtually dictates the TNCFs local capability to shear and drape over a mold during preforming. The shear stiffness of TNCFs is designed by defining the local stitching geometry. NCFs with chain stitch have a comparatively high shear stiffness and NCFs with a stitch angle close to the symmetry stitch angle have a very low shear stiffness. A method to design the component specific local stitching parameters of TNCFs is discussed. For validation of the method, NCFs with designed tailored stitching parameters were manufactured and compared to benchmark NCFs with uniform stitching parameters. The designed TNCFs showed both, generally a high form stability and in locally required zones a good drapeability, in drape experiments over an elongated hemisphere.