PSI - Issue 19

Jennifer Hrabowski et al. / Procedia Structural Integrity 19 (2019) 259–266 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

266

8

The calculated stress intensity factors K t are also strongly correlated with the angular misalignment  of the samples (Hrabowski, 2019). If the influence of  is calculated taking into account the additional bending stresses, this results in average stress intensity factors of K t,corr = 2.2 for butt welds and K t,corr 2.6 for welded transverse stiffeners. The demarcation for the fatigue strength analysis based on effective notch stresses can be determined on the basis of the number of cycles N LCF,k as a function of the deformation limit R e * using the stress intensity factors K t in equation (4). , = { (225 (( ∙ ∗ ⁄ ) ∙ 2.000.000 1.000 (4) 5. Conclusions Very and ultra-high strength structural steels are often assumed to lack ductility. This is refuted in the investigations shown. Even at high stress amplitudes up to the yield strength, after initial plastification the samples provide sufficient resistance to cyclic loading, followed by a pronounced crack propagation behavior. With a limitation of the angle misalignment to a maximum of 2 ° (evaluation group C63 according to ISO 5817 (2006)), both, the butt welded samples and the samples with welded transverse stiffeners meet the FAT class 80 for nominal stresses. This corresponds to the classification according to EN 1993-1-9 (2010) for steels with nominal yield strengths up to 700 N/mm². For evaluation according to the effective notch stress approach, the FAT 225 becomes decisive, which is met by all investigated specimens. The linear-elastic design and the application of the nominal stress and effective notch stress approach prove to be valid and applicable in the examined range of 1,000 to 2 million load cycles. In the static design, the exploitation of plastic load reserves is a common procedure. The investigations show that components can utilize plastic reserves and to reload stresses even under cyclic loading.

Acknowledgements

The authors would like to thank the Forschungsvereinigung Stahlanwendung e.V. for funding the examinations within the research project FOSTA P900 (Melz et al, 2015), the project-accompanying working group and the stuff of the LBF Darmstadt for the good cooperation. Special thanks go to Prof. Alain Nussbaumer for taking over the correferation of the doctoral thesis, which is the basis for the presented research results.

References

EN 1993 - 1 - 9, 2010. Eurocode 3: Design of steel structures - Part 1 - 9: Fatigue; German version EN 1993 - 1 - 9:2005 + AC:2009 EN 10025 - 6, 2009. Hot rolled products of structural steels - Part 6: Technical delivery conditions for flat products of high yield strength structural steels in the quenched and tempered condition; German version EN 10025 - 6:2004+A1:2009 Gudehus, H., Zenner, H., 2000. Leitfaden für eine Betriebsfestigkeitsrechnung: Empfehlung zur Lebensdauerabschätzung von Maschinenbauteilen, Verein zur Förderung der Forschung und Anwendung von Betriebsfestigkeits - Kenntnissen in der Eisenhüttenindustrie (VBFEh) im Verein Deutscher Eisenhüttenleute (VDEh), Düsseldorf, Germany Hobbacher, A.F., 2016. Recommendations for Fatigue Design of Welded Joints and Components, Second Edition, IIW - Doc. IIW - 2259 - 15 ex XIII - 2460 - 13/XV - 1440 - 13, International Institute of Welding (1996) and Springer International Publishing Switzerland Hrabowski, J., 2019. Ermüdungsverhalten von Schweißverbindungen aus höchstfestem Stahl im Kurzzeitfestigkeitsbereich, doctoral thesis KIT Stahl - und Leichtbau ISO 5817, 2006. Welding – Fusion - welded joints in steel, nickel, titanium and their alloys (Beam welded excluded) – Quality levels for imperfections. German version EN ISO 5817:2003 + AC 2006 Melz. T. et al, 2015. Erweiterung des örtlichen Konzeptes zur Bemessung von LCF - beanspruchten geschweißten Kranstrukturen aus hochfesten Stählen, Final report FOSTA P900, Forschungsvereinigung Stahlanwendung e.V., Düsseldort, Germany Radaj, D. Sonsino, C.M., Fricke, W., 2009. Recent Developments in local concepts of fatigue assessment of welded joints. Int. Journal of Fatigue 31, 2 - 11