Novel stitching yarn for improved delamination performance of carbon fibre composites

Carbon fibre reinforced polymer composites are replacing metal where weight saving is required. Due to their laminate structure, one issue which is of concern is delamination. Sewing is seen as a simple method of improving the delamination performance, but as yet a suitable yarn does not seem to been identified. In this work, 4 thermoplastic yarns were created using polysulfone, polyethersulfone, polyphenylsulfone, polyetheretherketone and the mechanical properties (as a straight fibre, knotted fibre and looped fibres) compared to a commercial yarn from schappe. It was found that the commercial yarn had much better mechanical properties as a straight fibre compared to the thermoplastic yarns in both terms of stiffness and strength. It was found that the ultimate tensile strength of the commercial fibre was reduced by approximately 90% when knotted and by approximately 60% when looped compared to the straight fibre. The thermoplastic yarns did not show any significant change in performance. As a consequence, despite not having the same mechanical properties, the thermoplastic yarns may prove to be better suited to stitching.