Effect of water ageing on the load-unload cyclic behaviour of flax fibre-reinforced thermoplastic and thermosetting composites

In the present work, twill flax fabrics-reinforced thermoplastic and thermosetting composites were subjected to water ageing in order to study its effect on their mechanical properties. Water ageing was conducted by immersing composite specimens into tap water at room temperature until saturation. To assess their mechanical behaviour, the aged composites were subjected to monotonic and load-unload tensile tests completed by Acoustic Emission (AE) recording. The AE records were analysed by the k-means unsupervised pattern recognition algorithm associated with the Principal Components Analysis (PCA) and the Silhouette index. In particular, the load-unload tensile tests highlighted a decrease of about 10% of the aged composites stiffness with respect to unaged ones at high loads. Besides, three classes of damage events were identified and assigned to the damage mechanisms. Finally, the mechanical behaviour of the aged composites is found to exhibit a significant Felicity effect synonymous of a substantial damage induced by water ageing.