The fatigue strength of structural steel bolts is significantly affected by variables introduced during manufacturing. These factors are generally inconsistent in the design codes, depending on the set of rules used. In particular for large-diameter bolts, such as those used in abundance in wind turbines, an experimental basis for evaluating various impacts was only available to a very limited extent in the past. This paper evaluates the results of three different high-strength bolt systems with varying manufacturing conditions. The test basis covers a diameter range between M12 and M72 and focuses on tests with high, representative mean stress levels. In addition to the results of fatigue tests, fractographic investigations of fracture pattern growth are included in this study.


In the last few years, reduction of electricity generation costs— i.e., Levelized Cost of Energy (LCoE)—has gained massive importance in wind energy. The effects of LCoE optimization include significantly faster increases in rotor diameter and turbine rating, as well as pressure to generate even more cost-effective plants. The tower has always played an important role in the total cost of a plant, approximately 20%–30% of the total. Therefore, optimized and lightweight tower structures are important (Lange and Elberg, 2017; Schaumann et al., 2021).

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