Material and structural testing to improve composite tidal turbine blade reliability

Most tidal turbine blades are currentlymade from glass or carbon fibre reinforced epoxycomposites. These represent a significantpart of theturbine cost, but few data are available either tovalidate current safety factors or to proposealternative more environmentally-friendly materials. This study, performed within the EU H2020 RealTideproject, aimed to provide these data. First, a detailedinvestigation of the staticand fatigue behavior wasperformed at the coupon scale, including not onlythose materials currently used, but also alternative recyclable thermoplastic matrix composites andnatural fibre reinforced materials. Tests wereperformed before and after seawater saturation, inorder to quantify the change in design properties withwater uptake. Then a first full scale 5 meter longcomposite blade was designed and tested to failure. Aspecific test frame was built, allowing loads up to 75tons to be applied and simulating theappliedmoments corresponding to service loads. Static andcyclic loads were applied and extensiveinstrumentation was used to detect changes inbehavior, inluding optical fibres implanted duringmanufacture, acoustic emission recording,andspecificinstrumentation developed within the project.The results have enabled numerical simulations to beverified,and this has provided confidence in themodelling tools. These were then employed in orderto propose an improveddesign of a lower cost blade.