PSI - Issue 75

Florian Kalkowsky et al. / Procedia Structural Integrity 75 (2025) 581–592 Florian Kalkowsky et al. / Structural Integrity Procedia 00 (2019) 000 – 000 In the calculation the surface roughness was conservatively assumed to be z = 200 μm for mill scale. The synthetic S-N curves type I were calculated with the characteristic tensile strength k ( u,obs ) of the base material in order to obtain a fatigue resistance value with a survival probability of 95 % and a confidence level of 75 %, which can be compared with the value of the statistical evaluation according to Eurocode 3. The input parameter of the stress intensity factor t,zd (superimposition macro geometric effect and concentrated load effect) and the stress gradient σ were taken from 2D FE analysis with Ansys Workbench. Further information about the model can be found in Kalkowsky (2024). In contrast to the general FKM approach, the value of the component fatigue endurance limit for certain mean stresses was converted from Dσ = 1 ∙ 10 6 to C =2 ∙ 10 6 number of cycles using the standardized slope parameter of = 5 . This allows a direct comparison of these results with the results from the fatigue tests. The graphical comparison of the test results with the synthetic S-N curves shows a very good predictive quality of the chosen approach. Only for the test series III with components made of the high-strength structural steel S700MC, which was already characterized by a lack of increase in fatigue resistance, was a data point found on the unsafe side. So, the synthetic S-N curves are mostly on the safe side of the test data points and thus confirm the possibility of a purely analytical assessment of fatigue strength of components in bearing type connections by this approach. However, the determination of the stress concentration factor (SCF) must be done by FEA. 4. Design proposal 4.1. Diagram for determination of SCF in bearing type connections In order to enable a purely analytical calculation for simple connection configurations, the diagrams shown below were derived by systematically varying the geometric parameters in the FEA. Based on these simulations, a correlation between the related geometric parameters ( 1 / 0 , 2 / 0 , 2 / 0 , 2 / 0 ) and the stress concentration factor t,zd could be found. This correlation can be described by a linear dependency of these values. In addition, hole clearance was identified as a further influencing factor. With an increasing hole clearance, the determined stress concentration factor t,zd increase. In order to have a conservative assumption when deriving these diagrams, the maximum ratio of / 0 for oversized round holes according to EN 1090-2 (2024) was used. 8

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Fig. 4. Stress concentrations factors for bearing type connections

These diagrams also represent a possible extension of the FKM-Guideline (2020) to include a further constructional detail with a superimposed notch effect like shaft-to-hub connection.