Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

On fatigue strength of large-size bolt-assemblies in steel constructions under consideration ofmanufacturing and surface condition related impacts
Ralf Glienke a, Mathias Schwarz b, Frithjof Marten c, Rasmus Eichstädt d, Daniela Schwerdt a, Melanie Meyer a, Maik Dörre ba
Department of Mechanical Engineering, University of Applied Sciences Technology, Wismar, Germanyb Fraunhofer-Institute for Large Structures in Production Engineering IGP, Rostock, Germanyc Department of Mechanical Engineering, Process Engineering and Maritime Technologies, Hochschule Flensburg, GermanydTÜV SÜD Industry Service GmbH, Munich, Germany

and more ring-flange connections are dimensioned for service loading(Wegener, et al., 2020). The lower flanges, where large bolt diameters
are used, are particularly affected by this. Since the ring-flange
connection represents a neuralgic point in the tubular tower design not
only from the dimensioning point of view but also from the cost point ofview, the fatigue strength of connections with large-size bolting
assemblies has meanwhile become a decisive factor for cost-effectivetowers. The fact that the fatigue strength of bolts in general is becoming
increasingly important is also shown by the growing number of papers
on this topic in recent times (Bartsch, et al., 2021), (Feldmann, et al.,2020), (Maljaars, et al., 2021).

ABSTRACTThe fatigue strength of structural steel bolts is significantly affected bymanufacturing impacts. These impact factors are taken into account very
inconsistently in the design rules, depending on the set of rules used ineach case. In particular for large-diameter bolts, such as those used inlarge numbers in wind energy plants, an experimental basis forevaluating various impacts was only available to a very limited extent in
the past. This paper evaluates the results on three different high-strengthbolt-systems with varying manufacturing conditions. The test
background covers a diameter range between M12 and M64 and focuseson tests with high, representative mean stress levels. In addition to theresults of fatigue strength tests, fractographic investigations of fracture
pattern growth are also used.

KEY WORDS:
high-strength bolt assemblies, size-effect, manufacturing impact,
surface-layer, ring-flange connections, wind turbines, fatigue tests

INTRODUCTION
In the last few years, the reduction of electricity generation costs Levelized Cost Of Energy (LCOE) - has gained massive importance inwind energy. Effects of LCOE optimization include both significantly
faster increases in rotor diameters and turbine ratings, as well as pressure
to generate ever more cost-effective plants. The tower has always played
an important role in the total cost of a plant, which is about 20-30%.
Accordingly, optimized and lightweight tower structures are important(Schaumann, et al., 2021; Lange, et al., 2017).

Fig. 1: Investigated HV bolt assemblies, IHF-Stretch-Systems acc. toabZ-14.4-800 (2021) and mechanical engineering assemblies (nominaldiameter M12, M20, M27, M36 and M48)

Tubular steel towers are still the dominant tower concept. In the courseof increasing hub heights, in order to make even low wind sites usable
for wind energy, a soft-soft design for cost-effective tubular towers witha hub height of more than 120 m is now state of the art. This trend, as
well as the fact that wind farm project developers are increasingly
demanding lifetimes of more than 20 years, means that fatigue strength
is becoming more and more important for tower dimensioning. This isalso evident in the ring-flange dimensioning. Whereas a few years ago
the extreme loads were usually decisive for the flanges, nowadays more

FATIGUE STRENGTH OF DIFFERENT STANDARDSThe verification against fatigue failure according to DIN EN 1993-1-9(2010) is usually performed with the nominal stress concept. On theresistance side, the detail category 50 (Constructional detail 14, Tab. 8.1(DIN EN 1993-1-9, 2010)) is to be applied for bolts under axial load,3271