Sustainability-oriented design optimisation of flax/glass hybrid composites using integrated FEA, surrogate modelling and life cycle assessment

Natural fibre-reinforced composites offer significant sustainability advantages but are often limited by relatively low mechanical performance in structural applications. Hybridisation with synthetic fibres provides a promising approach for balancing structural efficiency and environmental performance. This study develops a sustainability-oriented optimisation framework for flax/glass fibre-reinforced hybrid composites subjected to flexural loading. The framework integrates finite element analysis, regression-based surrogate modelling, multi-objective optimisation, and screening-level environmental indicators to evaluate trade-offs between flexural strength, cost, density, embodied energy, and global warming potential (GWP). A validated finite element model based on layered shell elements and homogenised lamina properties was used to predict flexural behaviour, with predicted strengths agreeing within 10% of experimental data. Regression-based surrogate models enabled efficient exploration of feasible laminate configurations under different flexural strength requirements. The results demonstrate that laminate architecture strongly influences flexural performance, with glass plies positioned on the tensile surface significantly enhancing strength. As the required flexural strength increases, the feasible design space progressively shifts toward glass-dominated laminates, resulting in increased economic and environmental indicators. Strong correlations were observed between cost, embodied energy, and GWP, indicating that these metrics are primarily governed by material composition. The results further show that the epoxy matrix contributes significantly to environmental impact, limiting the sustainability gains achievable through fibre hybridisation alone. The proposed framework provides a computationally efficient decision-support methodology for early-stage sustainability-informed hybrid composite design.