Anisotropic Elastic–Viscoplastic Modelling of a Quasi-unidirectional Flax Fibre-Reinforced Epoxy Subjected to Low-Velocity Impact

In the past decades, research was directed towards the use of plant fibres instead of synthetic fibres as reinforcement of composites. Due to their high specific mechanical properties coupled with low cost and their wide availability at the European scale, flax fibres could be considered as the most interesting plant fibres. Experimental tests carried out on flax fibre-reinforced composites have shown that these latter are characterized by a nonlinear viscoelastic–viscoplastic behaviour. In this paper, our work was focused on modelling the elastic–viscoplastic behaviour of a quasi-unidirectional flax fibre-reinforced composites. First of all, we developed a three-dimensional elastic–viscoplastic model taking into account the orthotropic elasticity and the anisotropic viscoplastic behaviour of quasi-unidirectional flax/epoxy composites. Then, based on tensile tests at different strain rates, we identified the isotropic hardening using an optimized exponential Johnson–Cook law. The model was validated against experimental data. Finally, we implemented the behaviour model in a UMAT procedure of the finite element code ABAQUS/Implicit and simulated low-velocity impact behaviour of a flax/epoxy circular plate. Simulation has shown that the impact velocity has a great influence on the behaviour of flax fibre-reinforced epoxy composite plate.