Transition from large-scale fibre bridging to short-scale via a thin plain weave interleaf

Hybridisation of fibre architectures in composite laminates offers a means to improve damage tolerance. This has been investigated in the area of Hybrid Unidirectional Woven Composite Laminates (HUWCL) under impact loading conditions. This study examines the Mode I delamination behaviour of hybrid unidirectional and woven interfaces in Carbon Fibre Reinforced Polymer (CFRP) composites by introducing a thin plain weave (PW) interleaf at the midplane of a unidirectional (UD) laminate. Double Cantilever Beam (DCB) testing was conducted to evaluate the effect of hybridisation on Mode I fracture toughness and fibre bridging laws for two different initial crack lengths. Results reveal that hybridisation with a thin (90 g/m²) PW interleaf significantly alters the delamination process by reducing large-scale fibre bridging and concentrating energy dissipation at the crack tip. This led to a substantial increase in initiation fracture toughness, with a 147 % improvement observed in PW/UD hybrid laminates compared to non-hybridised UD controls. The hybrid interfaces also exhibited a uniform R-curve. Additionally, bridging laws demonstrated that hybridisation shifts the fibre traction response, with PW interleafed laminates producing short-scale bridging rather than large-scale fibre bridging typically observed in UD laminates. While for the non-hybridised control laminates, initial crack length changes the bridging stress distribution, indicating that the bridging law is not a material property when considering initial crack length. These findings suggest that selective hybridisation with thin PW layers offers a promising strategy to enhance fracture toughness while mitigating the stochastic nature of large-scale fibre bridging generation and its impact on propagation fracture toughness.