Comparing Fatigue Strength From Full Scale Blade Tests With Coupon-Based Predictions

Abstract

In order to get a deeper understanding of the blade to blade variations and to determine the statistical distribution of the fatigue strength of rotor blades, 37 small rotor blades have been tested in static and fatigue loading. The blades are 3.4 m commercially available blades adapted to the needs of the project. Next to these blade tests, also coupons of identical material have been tested. The tests have encompassed static flapwise bending tests, flapwise fatigue tests at two different sections of the blade and edgewise fatigue tests. Since some blades could be re-used after a first test, a total number of 42 blade tests has been carried out in three different testing laboratories. The blades showed large deformation and development of creep. After correction for these phenomena, the fatigue strength of the blades seemed very good predictable with the classical Goodman relation using the well known slope parameter of 10.