Tunneling crack initiation in trailing-edge bond lines of wind-turbine blades

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.