Optimization of the mechanical performance of UD flax/epoxy composites by selection of fibres along the stem

In this study, we measure and compare the mass distribution, morphology and tensile properties of elementary flax fibres (Eden variety) along the stem. A significant improvement is found in the tensile properties of elementary fibres from the base to the middle of the stem, with the Young's modulus and breaking stress being increased by 19.3% and 56.6%, respectively. UD thermoset composites were manufactured with fibres from the bottom, middle and top of the stem. The efficiency of the reinforcement is lowest with bottom fibres, which appear to be poorly individualized and have many cortical residues on their surface. Several scenarios are proposed to select the most suitable fibres according to the desired mechanical properties of the composite.