Biaxial Dynamic Fatigue Tests of Wind Turbine Blades.

Testing rotor blades of wind turbines is essential to mitigate financial risks caused by serial damages. Present day uniaxial dynamic tests are time consuming and often inaccurate regarding the applied loading. This thesis proposes a faster fatigue test method by loading the two primary directions at the same time. In addition, a more realistic test, compared to uniaxial tests, is accomplished by loading larger areas of the blade cross-sections. To achieve this, an elliptical biaxial dynamic excitation is used. To fulfill the industry requirement for cost effective tests, a relatively simple test setup was developed, still achieving an elliptical dynamic excitation of the rotor blade. Two methods for an accurate determination of the applied loadings for dynamic fatigue tests are described. These calibration tests use easily measured values and simple analysis to achieve accurate test load measurements in a cost-effective way.