Creep behaviour of single hemp fibres. Part II: Influence of loading level, moisture content and moisture variation

This work investigates the tensile creep behaviour of single hemp fibres under constant and cyclic loading coupled to constant or variable moisture content environment. Results show that the primary creep strain rate of such fibres decreases with the increasing stress, while the secondary creep strain rate increases. Load cycling at an average load higher than constant creep load produces a large additional extra creep strain and an increase of the creep rate. Both primary and secondary creep strain rates increase with the increasing moisture content. More creep is also observed in cyclic humidity conditions than in a constant environment at the high-humidity. In agreement with some observations on synthetic fibres, we showed that this accelerated creep is only observed for high moisture cycling rates. This mechanosorptive effect is consistent with sorption-induced stress-gradient explanations proposed in literature.