Hydrothermal ageing of glass/epoxy composites for wind turbine blades

Abstract

In this work, a glass/epoxy material system commonly applied in wind turbine design was used to evaluate damage processes brought by water ingression during service life. Composite short-beams and neat epoxy beams and dog-bones were conditioned by water immersion at 50º until saturation and tested both statically and in fatigue. By comparing results from mechanical tests with those from reference specimens, significant fibre-matrix interface damage was identified, with reductions of up to 34% on the static strength and fatigue life reduction of up to three orders of magnitude. On the other hand, neat epoxy specimens showed a lower degree of damage, with up to 20% lower moduli and strength properties. Microscopic observations of conditioned specimens point out to extensive debonding on composite specimens after immersion, while neat epoxy specimens show signs of colour changes possibly due to hydrolytic attack. Lastly, changes in the glass transition temperature of the resin due to water ingression are assessed through the DMA technique. From the results, apart from a Tg reduction brought by material degradation, additional relaxation peaks brought by phase changes in the absorbed water molecules were identified.