FATIGUE PERFORMANCE OF NON-WOVEN FLAX/BIO-EPOXY COMPOSITES FOR SUSTAINABLE PEDESTRIAN BRIDGE DECKS

Natural fibre composites (NFCs) are increasingly recognised as sustainable alternatives to conventional materials like concrete and steel in pedestrian and cycle bridges. However, their long-term fatigue performance under cyclic loading remains underexplored, particularly for randomly oriented non-woven flax/bio-epoxy composites. This consideration is important for these structures, as their lighter weight makes them more susceptible to vibrations and repeated stress. This study investigates the fatigue behaviour of such composites manufactured via vacuum-assisted resin infusion.

Fatigue tests were conducted at a stress ratio of R = 0.1 across multiple stress levels of ultimate tensile strength (UTS). Three standard specimens were tested per level using a servo-hydraulic Instron machine. The results showed a higher average UTS. This surpassed the performance of non-woven hemp composites reported in a previous bio-composite pedestrian bridge study. The fatigue tests exhibited linear stress–strain behaviour up to approximately 40 MPa at 1.3–1.4% strain. Stress–Cycle (S–N) curves showed the expected inverse trend, with lower stress levels producing longer fatigue lives. Young’s modulus stayed stable at lower stress levels, indicating elastic behaviour. It decreased at higher stress levels because of damage and failure mechanisms seen under optical microscopy.

These findings align with known composite fatigue mechanisms but uniquely highlight the potential of low-cost, non-woven flax mats to sustain predictable performance under cyclic loading. The study provides new fatigue data on non-woven flax/bio-epoxy laminates, a rarely reported material system. The results highlight their potential for sustainable engineering applications. These findings will guide future design strategies for natural fibre composite pedestrian and cycle bridges.