Development and testing of extruded aluminium rotor blades under consideration of economic series production and fatigue behavior

: Andreä, A.; Schöpfel, A.

Abstract
The rotor blades of a wind converter offer a large potential for cost reduction. They are typically manufactured of composite materials and require mostly manual and thus cost intensive processes. Rotor blades made of extruded aluminium profiles appear much more appropriate for series production. They are technically feasible up to a category of 250 kW. A thorough economic analysis confirms that the production cost for extruded blades depends substantially from the wind turbine size. In the 30-kW category the costs of these blades is 50 % lower than for conventional blades. In the 100-kW range the design concepts are equivalent in terms of economy. Extruded aluminium rotor blades were tested in a pitch-controlled wind turbine with nominal power of 30 kW. The certification authorities request for components which face predominantly dynamic loads a proof of the fatigue strength that considers all relevant load cases. Constant and variable amplitude fatigue tests with aluminium blades wer e carried out (standardized load sequence WISPER). Based on the test results and load data from service measurements of the aluminium blades a fatigue life assessment for the real components could be performed using the Relative Miner rule.