Polymer reinforced by flax fibres as a viscoelastoplastic material

International audience; Flax fibre reinforced polymers are at the heart of current scientific and societal concerns. However their mechanical behaviour is still poorly known despite significant scientific efforts, in particular the non-linear behaviour observed under tensile tests. In this paper, results of hardening, creep and repeated progressive tests under uniaxial loading performed on various quasi-unidirectional flax fibre reinforced composites are analysed in terms of the volume fraction of fibre, the titration of yarn reinforcement and temperature testing. To identify the respective parts of pure elastic, viscoelastic and viscoplastic components in the global mechanical response, a phenomenological model is built based on eight independentparameters. The parameter identification based on experimental data and checked by a sensitivity analysis shows that the viscoelastic effects are non-significant at room temperature. The non-linear behaviour can mainly be attributed to viscoplastic effects. Viscoplastic modelling is based on a combination of two hardenings; the first classical (linear) one describes the translation of the elastic domain ; the second (non-linear) one describes a translation coupled with a contraction of the elastic domain during loading that improves the unloading behaviour during repeated progressive loading tests.