Effect of manufacturing defects on fatigue life of high strength steel bolts for wind turbines

Iman Shakeri*, Hilmar K. Danielsen, Adrien Tribhou, Søren Fæster, Oleg V. Mishin, Martin A. Eder

*Corresponding author for this work

Research output: Contribution to journalJournal articleResearchpeer-review

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This work investigates the effect of manufacturing defects induced by thread rolling on the high-cycle fatigue life of M30 class 10.9 stud bolts. High-cycle fatigue tests of two batches of nominally identical bolts show significant differences in fatigue performance between the batches. Scanning electron microscopy characterisation of defects in the form of rolling-induced microcracks in the thread root reveals a clear correlation between the defect size and the fatigue life of the investigated bolts. It is demonstrated that initial cracks present in the stud threads have a considerable effect on the slope of S-N curves. Numerical fatigue analysis shows good agreement with the experimental data. Electron backscatter diffraction is used to establish a characteristic length of microstructurally short defects in the tempered martensite microstructure. The obtained results shed light on the definition of critical manufacturing defect sizes in bolts as an essential parameter for quality control in manufacturing process.
Original languageEnglish
Article number106630
JournalEngineering Failure Analysis
Number of pages18
Publication statusPublished - 2022


  • Fatigue life
  • Manufacturing defects
  • Wind turbine bolts
  • Fatigue failure
  • Fatigue crack growth


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