Fracture toughness and impact damage resistance of sustainable composites

The increasing demand for sustainable composites stems from the critical need to mitigate environmental impacts and ensure a more sustainable future. Traditional fibre-reinforced composites, such as carbon/epoxy and glass/epoxy systems, exhibit excellent strength and stiffness but are associated with energy-intensive manufacturing processes and complex recycling and energy recovery methods, which result in low efficiency and raise significant environmental concerns. Sustainable composites, including bio-based materials derived from renewable sources and recyclable systems employing thermoplastic and vitrimer matrices, present environmentally favourable alternatives. These materials are integral to achieving net-zero carbon objectives and addressing the ecological challenges posed by conventional composites. However, the adoption of these sustainable composites in structural applications requires a thorough understanding of their mechanical behaviour, particularly their damage resistance under impact loading. For non-penetrative impacts, damage is predominantly characterized by interlaminar fracture, specifically delamination, which compromises structural integrity by reducing strength and stiffness, potentially leading to catastrophic failure. Enhancing interlaminar fracture toughness, especially in Mode II (shear mode), is critical for extending the operational durability of sustainable composites under low- and high-velocity impacts. This enhancement is essential to position these materials as viable substitutes for traditional composites in demanding applications, such as marine and automotive industries.

This research focuses on evaluating the Mode II interlaminar fracture toughness of sustainable composites, emphasizing strain rate effects through end-notched flexure (ENF) testing under both quasistatic and high strain rate conditions. A detailed fractographic analysis of fracture surfaces will be conducted to elucidate the failure mechanisms, complemented by the development and evaluation of a toughening strategy to improve fracture toughness. The results will be integrated into a finite element model to predict delamination behaviour under impact loading and assess its impact on the structural performance of sustainable composites.