Investigation of the Structural Response of Large Wind Turbine Blades Under Bending‐Torsion Coupled Loading

ABSTRACT Fatigue testing of wind turbine blades is currently conducted primarily under bending loading. However, with the continuous increase in blade size, torsional effects become increasingly significant. In additional, the complex materials properties and structural configurations of wind turbine blades pose considerable challenges to the realization of combined bending–torsion testing. In this study, the static structural response of a blade under combined bending and torsional loading is investigated to clarify the underlying bending–torsion coupling mechanism. A coupled bending–torsion model is established, and the IEA 15 MW reference blade is taken as a case study to analyze its sectional stiffness characteristics, coupling behavior, and structural responses under various loading conditions. The results indicate that under bending loads, the blade exhibits a pronounced bending–torsion coupling behavior, where the torsional response arises from the combined effects of material anisotropy and structural asymmetry. Under combined bending–torsion loading, the blade's structural response is predominantly governed by the bending‐to‐torsion load ratio. Furthermore, analysis of the stress response of the blade's main spar under different loading conditions reveals that significant stress concentrations occur in the mid‐to‐aft span region during coupled loading. These findings provide valuable insights for the design and implementation of bending–torsion coupled static and fatigue tests of large composite wind turbine blades.