For the last 20 years, plant fibres have emerged as an alternative to glass fibres in composites.However, a crucial issue with plant fibre composites is their durability, i.e. their long-term hygrothermal and fatigue performances. This study deals with the influence of different conditionings (Ambient, Wet and Wet/dry) on the fatigue behaviour of [(±45)] 7 hemp/epoxy composites. The induced damage mechanisms are investigated by acoustic emission and micro-CT. Results show that the Wet samples exhibit the lowest fatigue sensitivity despite their greatest damage quantity, whereas the Wet/dry specimens behave like pre-damaged Ambient ones.Micro-CT scans show that the same type of damage appears in all cases: cracks are made of a coalescence of partial debondings at hemp yarn/matrix interfaces, which can lead to macro-cracks crossing the sample thickness.Moreover it is demonstrated that, during fatigue tests, the evolution of cumulative AE energy and hysteresis loop energy, and the evolution of damage quantity measured by micro-CT and final hysteresis energy, are very similar whatever the conditioning.

Interface optimisation for continuous hemp reinforcements in epoxy resin is a current challenge for the development of biocomposites. A chemical treatment based on hydrogen peroxide and a physical one using a non-thermal plasma have been tested to optimise interface adhesion, by varying several parameters. FTIR analysis and FE-SEM observations have shown the effects of the treatments on chemical and morphological aspects of the treated yarns. Tensile tests on hemp yarns have allowed the selection of the treatment parameters leading to the best strength. Fragmentation tests results showed that the two treatments lead to a decrease in the fragment lengths and thus, an enhancement of the Interfacial Shear Strength (IFSS) values in comparison with the untreated yarn. This is confirmed by the micro-CT observations of the debonding lengths in the vicinity of each yarn fragment extremity. Finally, the plasma treated samples exhibit a better interface adhesion quality (IFSS = 44.7 ± 4 MPa) than the chemically treated ones (IFSS = 24.2 ± 4 MPa), which are better than the non-treated ones (IFSS = 13.5 ± 4 MPa).