Preliminary multi-axial strain analysis in wind turbine blades under fatigue test loads

A preliminary experimental characterization of the longitudinal, transverse, and shear strains in wind turbine blades under fatigue loading is presented in this study. For that, strains at different cross-section regions of a 14.3 m blade under different uni-axial and biaxial fatigue tests are recorded and analyzed.

The results from this analysis provide initial indications on how current testing methods used to certify and characterize the fatigue response of wind turbine blade materials can be improved to better represent what the blades experience during testing. It is shown, for example, how some of the blade regions can experience high biaxiality strain ratios, and how some of these regions can also experience broad internal loading conditions, in terms of strain levels and load orientation (i.e., compression, tension-compression, and tension), depending on the test type.