Influence of hybridization on the pyrolysis and mechanical behaviour of carbon and flax fibres reinforced epoxy laminates under fire conditions

Overview & Synopsis

This study explores the impact of hybridization on the mechanical behaviour of carbon and flax fibrere inforced epoxy laminates exposed to fire, aiming to enhance sustainability in aerospace applications while addressing flammability challenges. Hybridization combines flax's environmental benefits and ductility with carbon's strength and thermal stability. Objectives include evaluating pyrolysis effects from brief kerosene flame exposure (60 s under 116 kW/m², ~1100°C) on carbon/epoxy (C/E), flax/epoxy (F/E), and hybrid carbon/flax/epoxy (C/F/E) laminates, and assessing residual flexural properties. Laminates were fabricated via compression moulding with Araldite LY 156 epoxy, 240 g/m² flax fabric, and 189 g/m² carbon twill, in six lay-ups and material configurations: [0 8C ], [45 8C ], [0 8F ], [45 8F ], [0 4C 0 4F ] and [45 4C 45 4F ]. Results indicate hybridization multiplies axial stiffness by ~6, optimized by outer carbon plies, reducing porosity and enhancing flexural strength, though carbon fractures first due to flax's higher elongation. Flame exposure caused mass loss of 8-15% (higher in hybrids and [45 8 ] layups), with greater matrix degradation, cracks, and delamination in flax-rich areas.Residual flexural strength decreased by 20-30% (e.g., hybrid [0 4C 0 4F ]: 250-300 MPa virgin to 200-250 MPa post-fire), but ductility increased (strain 3-4% to 5-6%), shifting failures from shear to brittle/delamination modes. Hybridization provides a balanced thermal barrier, preserving load-bearing capacity better than pure flax, suggesting potential for fire-resistant aeronautical composites.