PSI - Issue 33

A. Kansy et al. / Procedia Structural Integrity 33 (2021) 1173–1180 A. Kansy, M. Kaynak, C. Bleicher, H. Kaufmann / Structural Integrity Procedia 00 (2019) 000–000

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Figure 6. HSV 90% diagram

In general, the fatigue strength decreases with increasing HSV 90% when looking at cast iron material. This was demonstrated in investigations of nodular cast iron grades by Bleicher [8]. For the transition from notched to unnotched specimens, slopes between ν = 0.04 and 0.10 were determined, depending on the grade. With slopes of ν = 0.08 and 0.09 for EN-GJL-300, respectively, this is in good agreement. For the transition to larger unnotched specimens, a saturation in the decrease in fatigue strength was observed and the value of the slope was ν = 0.01 to 0.03. For EN-GJL-300, negative slopes were calculated, since fatigue strength increases with increasing HSV 90% . This observation is contrary to the concept of statistical size effect. In the evaluation of Buthmann [4] according to the three-parameter Weibull distribution, this effect could also be observed. However, it was not explicitly considered, since the differences in the fatigue strength were within the scatter band of 15 %. 4. Conclusion The cast iron grade EN-GJL-300 was investigated in terms of microstructure and fatigue strength on the basis of cast samples and a component. The microstructure of both castings is characterized by the graphite arrangement A graphite. Despite minor differences in the graphite content and the lamellar structure, the material can be compared well. The fatigue strength was determined with three specimen geometries of different notch factors and highly stressed volumes. Notched specimens with a very small highly stressed volume have a higher maximum stress amplitude due to the good micro-support effect. In addition, notched specimens show a higher scatter band. Large specimens compared to small specimens have an increased fatigue strength of 14 % (component) and 17 % (cast sample). This effect is contrary to the concept of statistical size effect, which describes a reduction in fatigue strength for larger highly stressed volumes. Further investigations are necessary to determine other variables in addition to the HSV 90% for describing the statistical size effect on the fatigue strength of grey cast iron. Acknowledgements The results presented in this paper were derived during the research project “Optiguss”. For the funding of this project, sincere thanks are given to the German Federal Ministry of Economic Affairs and Energy (BMWi). Special thanks are given to SEW-Eurodrive GmbH & Co KG for providing the gearbox housing. Furthermore, all project partners are thanked for their participation and support to complete this project successfully.