Influence of drapability by using stitching technology to reduce fabric deformation and shear during thermoforming

Forming of woven fabric into a complex shape involves shear deformation of the fabric elements (warp and weft). Various researchers investigated the shear deformation during the manufacturing of thermoplastic composites (TPC) based on the hemispherical geometry, where the highly deformed edges and corners are considered as a waste. In many applications the complete formed geometry including areas around the curvature has to be used. A new idea to influence the deformation behavior of woven fabric by incorporated seams at localized sections is presented in this paper. The study is based on the photographic analysis of dry sewn preforms and thermoplastic matrix (PA12) impregnated laminates, before and after the deformation. The seams applied at the highly deformable and predefined zones help to reduce fabric shearing or to transfer the shear forces into the unsheared areas during the thermoforming process. The intensity of reduction in the fabric shear depends on the type of the sewn geometry. The results obtained can be applied in the part design, the preform engineering, and the positioning of stitches.