Tensile properties of composite scarf joints reinforced by stitching fiber threads: An experimental and numerical study

This study investigates the tensile properties of composite scarf repairs reinforced by a stitching technique using a thick carbon fibre thread, through both experimental and numerical approaches. Stitched scarf joints were designed and manufactured using carbon fiber prepreg sheets and tapes. Tensile tests were subsequently conducted to evaluate the stiffness, strength characteristics, and failure mechanisms of the stitched repairs. The effects of scarf angle and stitching thread diameter on joint performance were also examined. In addition, finite element models of the stitched joints were developed to predict their mechanical responses under tension, and to investigate the corresponding damage mechanisms. The results demonstrate that the stitching technique significantly enhances both the load-carrying capacity and stiffness of the repairs, with the diameter of stitching thread playing a critical role in determining joint performance and failure modes. The numerical simulations show strong agreement with experimental measurements, offering deeper insight into failure mechanisms that are challenging to observe during testing. Thus, a thick thread stitching is an effective method for enhancing the performance of scarf repairs, though the stitching thread diameter must be carefully selected to optimize outcomes.