PSI - Issue 37

Patrick Yadegari et al. / Procedia Structural Integrity 37 (2022) 500–507 P. Yadegari et al. / Structural Integrity Procedia 00 (2019) 000 – 000

507

8

4. Conclusion Ultra-high strength steels are increasingly used in mechanical engineering and automotive components as they provide several advantages, especially in terms of durability and sustainability. However, they are not as widely investigated and the procedure for dimensioning components is not yet defined in guidelines like low and medium strength steels. For this purpose, four high and ultra-high strength steels were investigated and experimentally tested to determine the static and cyclic material behaviour as well as the fatigue strength. These results serve as a data basis to extend existing estimation methods of the "FKM Guideline non-linear", which provides an estimation of the cyclic stress-strain curve, the mean stress sensitivity and the fatigue life curve. For these estimation methods, the ultimate tensile strength and material type (steel, cast iron and wrought aluminium alloys) is the only information needed. As the material group "Steel" is only approved up to a maximum tensile strength of 1250 MPa, a new material group for ultra-high strength steels was introduced. The calculation values required for this were determined empirically on the basis of the test results. Although the only experimental input value is the tensile strength, the new material group "Ultra-high-strength steel" enables appropriate estimations of the cyclic stress-strain-curve and the damage parameter life curves in combination with the existing methods of the "Guideline non-linear". This succeeded for all four examined materials, despite their major differences in the static and cyclic material behaviour. For the proof of structural durability based on the local strain approach, these estimation methods can be used to provide the characterization of the material behaviour for the dimensioning of components made of ultra-high strength steels without the need for time-consuming fatigue tests. By recalculating experimental tests with component-like specimens, it could be shown that an appropriate fatigue life prediction is possible for the materials and specimens investigated in this research. It can be expected that this estimation procedure is also applicable to other ultra-high strength steels, but due to the small amount of test data available, no guarantee can be given here. Acknowledgements The present paper is part of the IGF project No. 19667 BG of the Research Association “Forschungskuratorium Maschinenbau e.V.” (FKM), which was funded by the AiF as part of the programme for the support of joint industrial research (IGF) by the Federal Ministry for Economic Affairs and Energy on the basis of a resolution of the German Bergmann, J.W., 1983. Zur Betriebsfestigkeitsbemessung gekerbter Bauteile auf der Grundlage der örtlichen Beanspruchungen, Darmstadt. Fällgren, C., Beier, H. Th., Vormwald, M., Kleemann, A., Kleemann, S., Richter, T., Beinersdorf, H., 2021. Hochdruckbauteile aus höchstfesten Stählen, final report, FVV-No. 1289. (to be published) Fiedler, M., Vormwald, M., 2016. Considering fatigue load sequence effects by applying the Local Strain Approach and a fracture mechanics based damage parameter. Theoretical and Applied Fracture Mechanics 83, 31-41. Fiedler, M., Vormwald, M., 2016. Fatigue life calculation based on local strain approach. Materialwissenschaft & Werkstofftechnik 47, 887-896. Fiedler, M., Vormwald, M., 2018. Introduction to the new FKM guideline which considers nonlinear material behaviour. Fatigue 2018, France. Fiedler, M., Wächter, M., Varfolomeev, I., Vormwald, M., Esderts, A., 2019. Richtlinie nichtlinear, VDMA-Verlag, Frankfurt am Main. Fiedler, M., Vormwald, M., 2021. Correlations between crack initiation and crack propagation lives of notched specimens under constant and variable amplitude loading. Fatigue & Fracture of Engineering Materials & Structures 44 (10), 2871-2889. Ramberg, W., Osgood, W., 1943. Description of stress-strain curves by three parameters. Technical Report NACA TN 902. Roessle, M. L., Fatemi, A., 2000. Strain-controlled fatigue properties of steels and some simple approximations. Int J Fatigue 22, 495-511. Smith, K. N., Watson, P., Topper, T. H., 1970. A stress-strain function for the fatigue of metals. Journal of Materials, 5(4), 767-778. Straub, T., Varfolomeev, I., Luke, M., Kleemann, A., Kleemann, S., Richter, T., Beinersdorf, H., Yadegari, P., Beier, H. Th., Vormwald, M., 2021. Höchstfeste Stähle, final report, VDMA-Verlag, Frankfurt am Main. Vormwald, M., Seeger, T., 1991. The consequences of short crack closure on fatigue crack growth under variable amplitude loading. Fatigue & Fracture of Engineering Materials & Structures 14 (2-3), 205-225. Vormwald, M., Heuler, P., Seeger, T., 1992. A Fracture Mechanics Based Model for Cumulative Damage Assessment as Part of Fatigue Life Prediction. Advances in Fatigue Lifetime Predictive Techniques 1122, 28-43. Vormwald, M., Heuler, P., Krä, C., 1994. Spectrum Fatigue Life Assessment of Notched Specimens Using a Fracture Mechanics Based Approach. In: Amzallag, C. (Ed.), Automation in Fatigue and Fracture Testing and Analysis, 221-240. Bundestag. References