Comparison of Strength and Load-Based Methods for Wind Turbine Blades

The purpose of this paper is to compare two methods of blade test loading and show how they are applied in an actual blade test. Strength and load-based methods were examined to determine the test load for an Atlantic Orient Corporation (AOC)15/50 wind turbine blade for fatigue and static testing. Fatigue load-based analysis was performed using measured field test loads extrapolated for extremerare events and scaled to thirty-year spectra. An accelerated constant amplitude fatigue test that gives equivalent damage at critical locations was developed using Miner's Rule and the material S-N curves. Test load factors were applied to adjust the test loads for uncertainties, and differences between the test and operating environment. Similar analyses were carried out for the strength-basedfatigue test using the strength of the blade and the material properties to determine the load level and number of constant amplitude cycles to failure. Static tests were also developed using load and strength criteria. The resulting test loads were compared and contrasted. The analysis shows that, for the AOC 15/50 blade, the strength-based test loads are higher than any of the staticload-based cases considered but were exceeded in the fatigue analysis for a severe hot/wet environment.