Damage tolerance of composite laminate toughened via yarn-level hybridisation and new fibre arcitecture

Recently, composite laminates are increasingly being used in different applications due to their higher specific strength and stiffness compared to metals. Their susceptibility to impact loading has also proven to be a critical factor. The aim of this project is focused on enhancing the impact damage tolerance of composite laminates by exploring yarn-level hybridisation and fibre architecture. Hybrid yarns, which consist of high-strength fibres (S-glass fibre) and high-toughness fibres (polypropylene (PP) fibres), are made by using commingling and core-wrapping processes respectively. Different types of preforms, such as non-crimp cross-ply, 5H satin, 2/2 twill, and 2/2 basket architectures, are manufactured from hybrid yarns. For comparison, the preforms made from twisted S-glass yarns (i.e. non crimp cross-ply and 2/2 twill) are also used, and subsequently, all composite laminates are manufactured via vacuum-assisted resin infusion. In addition, the impact resistance, residual compressive strength properties, and subsequent failure mechanism of all composite laminates were examined. It was found that the yarn-level hybridisation and fibre architecture had significantly influenced the energy-dissipation mechanisms and impact-damage tolerance of the hybrid laminates under low-velocity impact. The compressive strengths of undamaged 2D woven hybrid yarn composites were lower, but their residual compressive strength was found to be higher than that of non-crimp fabric composite laminate made with or without hybrid yarns. Although the yarn-level hybridisation and yarn architecture led to a reduction in the mechanical performance of composite laminates, the selective hybrisation, either at the yarn-level or at the lamina-level, can offer tailoring between impact-damage tolerance and the in-plane properties of hybrid composite laminates. It was found that the laminates made from unidirectional hybrid fabric exhibited higher in-plane properties (i.e. flexural, tensile, and compressive strengths) in comparison to laminates with yarn-level hybridization and yarn waviness. Additionally, the unidirectional hybrid fabric composite laminates appeared to have significantly improved compressive-strength retention than the non-crimp cross-ply glass yarn composites. It was also noticed that the woven 'non-crimp' cross ply hybrid layers composite laminates showed higher tensile strength and modulus compared to the hybrid fabric composites. Additionally, these hybrid layers composites exhibited higher impact damage tolerance than the non-crimp cross-ply glass composite up to certain level of impact energy. The FE simulations of the low-velocity impact response of hybrid composite laminates have been developed in this study. Its prediction for maximum impact force, maximum displacement, and impact energy were in reasonable agreement with the experimental results. However, the current simulations are reliable for predicting the level of damage failure available in composite laminates with glass fibre only. It seems that the level of accuracy decreases with an increasing number of interfaces of constituents inside the composite laminates (i.e. hybrid composite laminates).