Mechanical strength enhancement of natural fibre composites via localized hybridization with stitch reinforcement

Abstract Stress concentration is an unavoidable phenomenon during the fabrication of composite structures. This research focuses on reducing stress concentration. Circular holes made on the composite structural member induce stress-concentrated regions. These stress-concentrated regions around the circular hole (considered as a weak section) were strengthened by adding synthetic fibre (local hybridization) in the form of fibre stitches (locked loop stitch). Through conducting a single fibre pull-out test, the present study analysed the impact of incorporating synthetic fibres in stitch form and the enhancement of Interfacial Shear Strength (IFSS). The load acting on the broken warp fibres is distributed to the broken weft fibres when the number of concentric stitches increases. The increment of concentric stitches resulted in the increase of IFSS due to localized hybridization. The tensile test results also show a significant improvement with 110 Nmm axial fastening force, from 6.749 MPa (for the natural fibre composite) to 76.91 MPa (for locally hybridized with eight concentric stitches). A simple bolted lap joint with local hybridization around the hole has been evaluated for different clamp-up forces. The best combinations of the clamp-up force and the extent of hybridization have been identified. SEM images illustrate the reduced voids and the reduced fibre pull-out due to the local hybridization around delamination-prone areas.