PSI - Issue 42

Lukáš Suchý et al. / Procedia Structural Integrity 42 (2022) 1128–1136 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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the stresses underneath the shaft surface are evaluated according to the critical distance (Fig. 1). This theory states that a non-propagating crack length (structural length) is tolerable. When the stress state at a certain distance does not exceed a fatigue limit, the initiated crack will not lead to the global failure of the component. For crack mode I, according to El Haddad [23], the so-called “ structural length ” 0 can be calculated using the fatigue strength and the threshold (Eq. Fehler! Verweisquelle konnte nicht gefunden werden.Fehler! Verweisquelle konnte nicht gefunden werden. ). It corresponds to the maximum non-growing crack length of a structure. The evaluation point for the equivalent stress then corresponds exactly to half the structural length at (Eq. Fehler! Verweisquelle konnte nicht gefunden werden. ). Since the present case concerns a mixed mode with superimposed-crack-orthogonal variable contact stresses, the determination of a threshold value for the structural length is not possible (Eq. Fehler! Verweisquelle konnte nicht gefunden werden. ). For this reason, the reverse search is used to determine a crack length at which a strength assessment must be performed. 0, = 1/ ∙ (Δ ℎ, /Δ 0, ) 2 (4) = 0, /2 (5) 0, = 1/ ∙ (Δ ℎ, /Δ 0, ) 2 Δ ℎ, = ? = ? (6)

Stress evaluation

hub shaft

Fig. 1: FE model, meshing at hub edge, critical distance of shrink fits

4. Results The experimental results show the material comparison between the tribologically induced crack sensitivity and the crack sensitivity of the notched component. In Fig.2, the greater strength of the quenched and tempered steel can be observed as expected. The fatigue strength is evaluated according to Hück [17] at = = 88.8 MPa , which is an approximately 36% increase compared to a shaft made of C45+N with = = 65 MPa . On the other hand, the results of the shrink fits show the higher-strength 42CrMo4+QT steel to have an even lower strength of = = 66 MPa compared to the C45+N with = = 71.3 MPa . The result is essentially in agreement with the Hauschild’s results in [6]. He demonstrated an increased tribological notch sensitivity of higher strength steels in the uniaxial friction pad test. However, this has not yet been transferred to components subject to multiaxial loading.