PSI - Issue 42

1134 Lukáš Suchý et al. / Procedia Structural Integrity 42 (2022) 1128–1136 Author name / Structural Integrity Procedia 00 (2019) 000 – 000 7 two materials using the Böhme calculation method presented. Different evaluation paths (Fig. 4) were evaluated at the crack location = 0° . Due to the unknown parameter ℎ, for the present case of multiaxiality, the critical distance is unknown. For this reason, the authors follow the approach of the inverse search for the determination of the evaluation position analogous to Santus ℎ, . Because of the high accuracy, the determination of these results was pursued with the help of the criterion according to Böhme [1, 2]. The focus was not on investigating different strength criteria, but on comparing materials. For this purpose, four different paths of the equivalent stress were considered, starting from the shaft surface. According to Böhme ’ s criterion, the critical distance at which the equivalent stress corresponds to the material fatigue strength −1 is sought. Since the cracks in C45 start from the hub edge, the path at = 0 µm gives a critical distance of about = 75 µ . This finding fits well with the values obtained by Santus and Benedetti, where large critical distances (up to 250 µm ) were obtained for crack mode III and small critical distances (up to 45 µm ) for crack mode I (point method). In the preceding mixed-mode case, the determined value is thus within the plausible range. Compared to the normalized C45+N steel, a critical distance for the shaft made of the quenched and tempered 42CrMo4+QT steel could not be determined. The curve for the resulting equivalent stress is below the fatigue strength of this steel. One possible explanation is the excessive crack length, which results from tribological mechanisms such as the detachment of a local material weld. The initiated crack thus already has a length at which further crack growth has already started.

x=0 µm x=20 µm x=40 µm 45° diagonal

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Equivalent stress σ eq,BO (MPa)

Equivalent stress σ eq,BO (MPa)

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Fig. 4: Evaluation of different stress paths for shrink-fitted connections, determination of critical distance for the multiaxial mode

5. Summary and conclusions To date, multi-axial fatigue of press-fit connections has mainly been estimated using notch factors. A local strength verification would make it possible to calculate arbitrary geometries. However, the stress evaluation at the contact surface is not yet reliable and is strongly material dependent due to the different cracking mechanisms and the