Fraunhofer IWES presents its competencies in the field of wind forecast, grid integration and improved rotor blade testing at the European Wind Energy Conference and Exhibition 2010 (www.ewec2010.info).

The opening of the first German Offshore Wind farm alpha ventus fired the wind industry's imagination. Since the conditions are rough and the reachability is limited out at the sea, wind turbines that were designed for these dynamic loads can assure high availability and therefore profitability.

Fatigue is one of the key design drivers for the design of rotor blades of offshore wind turbines. For larger rotor blades, the swept area increases with the square of the rotor diameter. However, the weight of the blade increases to the third power. Therefore, in-depth knowledge about the failure mechanisms of materials is necessary.

Stefan Wessels, Project engineer at the competence center rotor blades of Fraunhofer IWES presents the results of a detailed fatigue analysis of rotor blades considering non-linear Goodman analysis combined with finite element analysis. "Considering the material properties more in depth and using their capacities, lead to a weight reduction without a reliability reduction", states Wessels.

Not only the material, also the assembly of rotor blades is a critical point that needs profound investigation to as-sure blade design optimization, especially for larger blade lengths. Since the composite parts of a rotor blade are bonded together, the adhesives play a key role in the structure. Stefan Wessels presents a beam scaled test for the evaluation of the structural adhesive bond between the web and spar cap of a MW scale wind turbine blade. In contrast to coupon size testing for the mechanical characterization of the bonding paste, this method takes into account the shape of the bonding line, material thickness variability and the stochastically distributed voids, and above all a more realistic stress distribution in the bond line.

(innovations report)

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