Sub-Component versus full wind turbine blade structure: Influence of manufacture-induced thermal residual stresses on tunneling crack initiation in adhesive joints

This work investigates the root causes for tunneling crack initiations in the trailingedge adhesive joint that were observed on the fleet of more than 100 rotor blades of a single type for 2 MW wind turbines during manufacture and in the field. The highest crack frequency was observed at around 50% blade length. To identify the root causes, a trailing-edge subcomponent of the blade was manufactured from the main mold under process conditions comparable to those used in the manufacture of the full blade. Contrary to the observations made for the full blade, no cracks were initiated during the sub-component manufacture. A linear thermal stress analysis by means of a comparable FE blade model revealed that the full blade was subjected to a higher residual stress level than the sub-component, which was in line with observations. This research shows that sub-components do not necessarily represent all aspects of the structural behavior of a full blade. Therefore, caution must be exercised when designing sub-components for design model validation.