Modelling the seam architectures for textile performing
Sewing of textile preforms offers a lot of opportunities for the future production of FRP parts. Although out of plane properties and damage tolerance abilities of the preform improve by stitching, stitching degrades the in plane properties of the preform. The choice of material and process parameters is crucial to realise the benefits of stitching. This demands modelling and simulation of stitched textile structures. Currently simple textile structures like multi layer woven fabrics and multi layer non-crimp fabrics can be modelled. This paper shows a concept for a mathematical modelling of stitching architectures including the generation of the thread surfaces. The model can help in realising two functions. On the one hand different material and process parameters can be taken into account and on the other hand the computed surface description including geometrical dependencies can be transferred into a structural mechanic model (e.g. WiseTex).
On Surface Fibre-Free Zones and Irregularity of Piercing Pattern in Structurally Stitched NCF Preforms
The paper addresses the surface imperfections (openings in fibrous plies) and irregularity of the piercing pattern in structurally stitched multilayer carbon-fibre preforms. Each layer is a multiaxial multiply non-crimp fabric (NCF) with a non-structural stitching. The term “structural” presumes here that the stitching yarn does not only consolidate the plies (as the non-structural one does) but forms also a through-the-thickness (3D) reinforcement. Four stitching methods are studied: ordinary CNC-sewing, tufting, dual-needle, and curved needle techniques with multifilament yarns: aramide (60 or 120 tex) or glass (204 tex). In total, 14 stitching cases are investigated experimentally. It is observed that a non-negligible variability exists in the meso-level geometry of the reinforcement. The geometrical characterization provides important input data for analysis of the permeability and mechanical properties of the preforms.
Effect of Stitching on the Mechanical and Impact Properties of Woven Laminate Composite
Mechanical and impact-resistant properties of stitched woven laminate composite have been studied. The S-2 Glass/Polyester, Kevlar/PVB-Phenol and Spectra/Vinylester composites were stitched at different stitch densities to improve its mechanical and impact properties of the composite. Both chain and plain stitches were used for reinforcing the laminate in the Z-axis of the composite. The mechanical properties of woven laminate composite were improved at the optimum stitch density compared to those of conventional unstitched one. Energy absorption capability of stitched composite was also higher than that of unstitched composite, and the stitched composite showed a significant increase in energy absorption capability under repeated impact. The damaged areas caused by the repeated impact or by the penetration of projectile were far smaller in the stitched composite than in the unstitched laminate one. The stitched composite showed about 10% improvement in ballistic efficiency over the conventional woven laminate composite at the optimum stitch design.