Effect of water absorption on Mode I interlaminar fracture toughness of flax/basalt reinforced vinyl ester hybrid composites

In this study, the influence of water absorption on the Mode I interlaminar fracture toughness of flax and basalt fibre reinforced vinyl ester hybrid composites is presented. Three types of composite laminates namely, flax fibre reinforced vinyl ester (FVE), flax fibre hybridised basalt unstitched (FBVEu) and flax hybridised basalt stitched (FBVEs), fabricated by vacuum infusion technique are investigated. Double cantilever beam (DCB) tests were performed to evaluate the Mode I critical energy release rate (GIC) and the crack length (R-curve) by using three different data reduction methods. It was found from the experimental results that the Mode I fracture toughness initiation and propagation of water immersed FVE composites were decreased by an average of 27% and 10% respectively, compared to the dry specimens, whereas the fracture toughness propagation of water immersed FBVEu and FBVEs composites were improved by approximately 15% and 17% compared to dry specimens. The fractured surface and delamination of different composites were evaluated by using scanning electron microscopy (SEM) and X-ray computed micro-tomography (µCT). The results showed that basalt fibre hybridisation has positive effects on durability and the moisture resistance of natural fibre composites.