Tunneling cracks are observed in the adhesive of the trailing edge bond line of wind turbine rotor blades subjected to high-cycle fatigue. To identify the root causes of these cracks, their initiation was calculated using a stress-based approach. The mechanical stresses caused by aerodynamic and gravity loads which arise when operating in the field were considered on the one hand, and the residual stresses caused by thermal material shrinkage during manufacture on the other. This work investigates the impact of each mechanical stress and thermal residual stress component on the fatigue stress exposure along the blade span. It was found that the thermal residual stresses make a significant contribution to the bond line fatigue. Besides the dominating longitudinal stress, peel and shear stress also contribute to the fatigue.

We acknowledge the support within the Future Concept Fatigue Strength of Rotor Blades project granted by the German Federal Ministry for Economic Affairs and Energy (BMWi) (0325939) and the Senator for Health, Environment and Consumer Protection of the Free Hanseatic City of Bremen within the ERDF programme Bremen 2014-2020 (201/PF_IWES_Zukunftskonzept_Betriebsfestigkeit_Rotorblätter_Phase I). Moreover, we would like to thank SSP Technology A/S for providing the wind turbine blade model for this research.