Influence of hydrothermal fatigue on mechanical properties and damage mechanisms of hemp-reinforced biocomposites and comparison with glass-reinforced composites

The aim of this work was to evaluate the tensile properties and the damage mechanisms of hemp and glass-reinforced composites when they were subjected to hydrothermal fatigue. Each wet/dry cycle consisted in immersing samples in water at 60°C during 12 days and drying them in an oven at 40°C during 2 days. Three different matrices (Epolam, Greenpoxy and Elium) were studied with two reinforcement orientations (±45° and 0°/90°). Gravimetric measurements were performed during 30 wet/dry cycles to determine the evolution of the parameters of the Fick diffusion model. Repeated progressive tensile loading tests instrumented with an acoustic emission setup were also carried out. Damage was investigated by means of SEM and micro-CT. Results showed that hydrothermal fatigue affects significantly the tensile properties of all the composites studied. Hemp/Greenpoxy appears to better resist to hydrothermal fatigue while the hemp/Elium behavior is more impacted. Moreover, contrary to what might be expected, glass/Epolam samples are not the least sensitive to hydrothermal fatigue.