Influence of moisture uptake on the static, cyclic and dynamic behaviour of unidirectional flax fibre-reinforced epoxy laminates

This papers aims to characterize the influence of moisture uptake on the mechanical behaviour of unidirectional flax fibre-reinforced epoxy laminates. Monotonic and cyclic tensile tests and free vibration characterization are carried out. Results show that LID flax-epoxy composites, when exposed to hygrothermal conditioning at 70 degrees C and 85% RH, exhibit a diffusion kinetic which follows a one dimensional Fickian behaviour. The mass uptake at equilibrium is approximately 3.3% and the diffusion coefficient 6.5 x 10(-6) m(2) s(-1). Water vapour sorption is shown to induce a significant change in the shape of the tensile stress-strain curve, a decrease in the dynamic elastic modulus of about 20% and a 50% increase in the damping ratio. Contrary to all expectations, water saturation does not degrade the monotonic tensile strength of such a flax-epoxy composites and leads to an increase in the fatigue strength for a high number of cycles. (C) 2016 Elsevier Ltd. All rights reserved.