LENAH: Lifespan extension and lightweight construction optimisation thanks to nanomodified and hybrid material systems in rotor blades

The rotor blades of modern wind turbines can reach lengths of 85 metres and more. At the same time, they are one of the components of a wind turbine for which very particular requirements are specified: They have to be as light as possible yet also rigid and sturdy in order to be able to withstand the loads in the field. They must endure more than 100 million load cycles, this naturally causes the lightweight material to suffer from extreme fatigue.

Unlike aircraft wings which, as components kept as light as possible, also have to stand up to strong loads, wind turbine rotor blades are not made of carbon fibre reinforced plastics (CRP) but mostly of glass reinforced plastics (GRP) which, because of their lower price, are more closely aligned to the cost structure in the wind energy sector. At 60 per cent, the material costs already make up the largest share of production costs – substitution to use more expensive CRP materials is not a simple option.

As part of the LENAH project, two approaches are being examined:

- New nanoparticle-modified plastics are being developed in order to improve further the robustness of rotor blades. The plastic resins are reinforced with nanoparticles, i.e., metal oxide particles. Together with the plastic molecules, they form so-called “boundaries” with properties which neither the particles nor the plastic modules previously possessed. The result is a new and particularly resilient material, which, in turn, increases the fatigue strength of the rotor blades. The second area in which nanoparticles can improve material properties is with respect to the adhesive used to fuse the two rotor blade half shells. Its cohesion properties are improved considerably so that it doesn't tear when subjected to loading.

- Hybrid laminates are being tested for their suitability for rotor blades. They comprise numerous very thin layers which are connected to each other and arranged in such a way that the fibres run in different directions. The project is focused on examining how these hybrid laminates can be used in areas subject to very heavy loads in order to improve performance. For example, carbon fibres could be used in the belt area and metals could help to raise bearing stress strength at points where bolts are necessary for securing the blades to the hub.

The project comprises numeric simulation with multi-scale methods and the development of the materials through to the construction and testing of components, e.g., at Fraunhofer IWES' test stands in Bremerhaven.

Fraunhofer IWES is responsible for all technologies behind the development of suitable experimental validation methods for material and structure modelling. Furthermore, Fraunhofer IWES is in charge of the development of CRP and GRP hybrid materials and nanoreinforced adhesives. Consultation services on development work from the perspective of the user and the evaluation of technology development round off the activities at IWES.