Investigation into the tensile properties of ISO-401 double-thread chain-stitched glass-fibre composites

Interlaminar stitching has proven to be an effective through-thickness reinforcement technique for laminated composites but a major drawback is the negative effect it has on the in-plane tensile properties. This study aims to optimise stitching for composites to reduce the associated negative effects by introducing a new stitch type to composite laminates. The double-thread chain-stitch (ISO-401) has shown great utility in the textile industry but has not yet been applied as through-thickness reinforcement to composites. In this paper, tensile properties of glass fibre composite laminates stitched with ISO-401 double-thread chain stitch have been examined, as stitching reduces in-plane strength while improving damage tolerance. Three variations of the ISO-401 geometry were employed by varying the stitch junction position and each position was applied at two stitch densities by varying the stitch pitch at 3 mm and 4 mm. The composites were manufactured using E-glass 2 × 2 twill fabric and a Bisphenol-A type epoxy resin, stitching was performed with core-spun tex 24 polyester thread. The experimental data demonstrated the influence of ISO-401 junction position and stitch density on the composite tensile properties. Furthermore, adjustment of the junction position was found to affect the size of stitch-induced resin pockets and severity of in-plane fibre misalignment.