Analysis of the hydro-mechanical behaviour of flax fibre-reinforced composites: Assessment of hygroscopic expansion and its impact on internal stress

Abstract The present work aims at modelling the hydro-elastic behaviour of twill flax fabric-reinforced epoxy composites. These latter were manufactured using the vacuum infusion technique and aged into tap water until saturation. Their heterogeneity is taken into consideration by modelling the twill weave fabrics with two geometric paths: [0/90] and elliptical undulation. Moreover, the water diffusion coefficient and the hygroscopic expansion parameter of the flax fibre are estimated by an inverse approach exploiting the experimental results. In particular, the finite element simulations reveal high mechanical stress concentrations especially at the fibre-matrix interface caused by the differential swelling between the flax fabrics and the epoxy resin. This water absorption-induced internal stress is the main cause of damage initiation in the flax-epoxy composites, which leads to high variations of their mechanical properties and reduces their long-term sustainability.