PSI - Issue 13

Ann-Christin Hesse et al. / Procedia Structural Integrity 13 (2018) 2053–2058 Ann-Christin Hesse et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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5. Notch stress calculations

Additional notch stress calculations were carried out to create a larger data basis for a correlation between the weld imperfections and quality levels given in ISO 13919-1. The notch stress calculations were performed in two main steps: First, numerical models were built, which were based on the geometrical measurements of samples tested during the fatigue tests. After a validation of the numerical models, additional imperfections were taken into account to examine how the imperfections affected the fatigue strength. Detailed information on the notch stress calculations are given in Dilger et al. (2018). Using the fatigue tests and the notch stress calculations, correlations between the imperfections and the fatigue strength were found. The results are summed up in Table 5. Table 5: Suggestions for the matching of quality groups in ISO 13919-1 and fatigue classes FAT for beam welded butt joints Imperfection acc. to ISO 13919-1 Max. usable fatigue class FAT in assessment by nominal stress method for the different quality groups D C B B/2

Axial misalignment Excessive penetration Excessive weld metal Incomplete filled groove

FAT 45 FAT 71 FAT 71

FAT 56 FAT 71 FAT 71 FAT 56 FAT 56

FAT 71 FAT 71 FAT 71 FAT 71 FAT 71

FAT 80 FAT 80 FAT 80 FAT 80 FAT 80

Root concavity

Determined by fatigue tests

Determined with the help of notch stress calculations

6. Conclusions

In the presented work, the fatigue strength of welded joints with and without intended imperfections was tested. Suggestions for FAT classes depending on the quality levels in ISO 13919-1 were given. Aside from these suggestions, the following major findings were made: If laser welded joints are welded in a shop under controlled conditions, often a very high weld quality can be observed (quality level “B/2”). If such a quality level is reached, FAT 80 can be observed as a result of the fatigue tests, even if welding is only performed from one side. A conservative estimation of the fatigue strength of butt-welded joints can be made by using FAT 71, which is the FAT class that is also recommended for arc-welded joints. An axial misalignment of 15% of the sheet thickness (QL C according to ISO 13919-1) leads to a reduction of the fatigue strength. FAT 56 seems to be a conservative recommendation for beam welded butt joints with an axial misalignment of 0.15∙t. Acknowledgements The authors would like to thank the German Federation of Industrial Research Associations (AiF) for its financial support of the research project IGF-No. 18.174 B. This project was carried out under the auspices of AiF and financed within the budget of the German Federal Ministry of Economics and Technology (BMWi) through the program to promote joint industrial research and development (IGF). Special thanks is expressed to the Fraunhofer IWS for carrying out the welding work. References Dilger, K. et al.: Final report on the research project IGF-No. 18.174 B, “Untersuchungen zur Schwingfestigkeit strahlgeschweißter Verbindungen unter Berücksichtigung von Strahl- und Schweißnahtqualität und der resultierenden Nahteigenschaften “ , 2018. FKM Guideline: Guideline for analytical strength assessment of mechanical components made of steel, cast iron and aluminium materials, 4th edition. VDMA publishing house, Frankfurt/M., 2002. Fricke, W.: Guideline for the fatigue assessment by notch stress analysis for welded structures. International Institute of Welding, 2008. Haibach,E.: Betriebsfestigkeit - Verfahren und Daten zur Bauteilberechnung. 3. Auflage, Berlin: Springer Verlag, 2005. Hobbacher, A.: IIW recommendations for fatigue design of welded joints and components, WRC bulletin 520. TheWelding Research Council, New York Google Scholar, 2009. ISO 13919-1: Welding - Electrons and laser beam welded joints; guidance on quality levels for imperfections - Part 1: Steel (ISO 13919-1:1996)

Jonsson, B. et al.: IIW guidelines on weld quality in relationship to fatigue strength. Springer, 2016. Radaj, D.: Design and Analysis of Fatigue Resistant Welded Structures, Cambridge, Abington Publ, 1990.