PSI - Issue 42

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

1135

8

complicated stress superposition. For this reason, tests were conducted on compression joints under combined rotating bending and equal-frequency dynamic torsion at the same stress amplitude using notched specimens and contact specimens. A normalized C45+N steel and a quenched and tempered 42CrMo4+QT steel were investigated. The integral strength criterion according to Böhme was used for the stress evaluation, which was carried out below the shaft surface according to the theory of critical distance. The stress evaluation was performed numerically using the finite-element method and a programming routine that calculated the equivalent stress for the stress field near the hub edge. Since important material parameters for the determination of the critical distance in mixed-mode loading are not known, the evaluation location was determined for the shrink fit by inverse search. Compared with the literature, the critical distance of C45+N shafts is at a plausible level of approx. = 75 µm . Surprisingly, the interference fit of 42CrMo4+QT shows approximately the same FE fretting-fatigue strength in the experiment, despite the better material fatigue properties. The comparative experiment with notched shafts without contact confirms the better material fatigue limit. However, the subsequent attempt to determine the critical distance of 42CrMo4+QT shafts was therefore unsuccessful, since the basic strength at which the critical distance was determined far exceeded the local stress state. The result of these investigations suggests that the crack length of higher-strength steels, in particular quenched and tempered steels, is higher and thus a non-growing crack does not exist for this case. Thus, further crack investigations should confirm this thesis. Furthermore, friction-corrosion products occur in components with contacts, which on the one hand could fuel the crack formation, but on the other hand also enter the cracks and thus influence crack opening and closing processes. Based on the present study, the authors see limits to the application of the theory of critical distances on fretting fatigue. Further open questions concern the fatigue parameters of the criterion, which, like the fatigue parameters, is determined for free surfaces and not for contact surfaces. Further investigations address other amplitude and frequency ratios and different geometries of the interference fit. In multiaxial fatigue, other methods such as critical plane methods are in focus. Furthermore, the increase in the friction coefficient and wear at the contact joint should be a subject of investigation for future projects. Acknowledgements Authors acknowledge funding from Bundesministerium für Wirtschaft und Klimaschutz as well as

Arbeitsgemeinschaft industrieller Forschungsvereinigungen (AiF). Appendix A. Material parameters of used multiaxial criterion Material parameters for Eq.(3) according to[22]: 2 = 1/5(3 2 − 4)

(7)

2 = 1/5(6 − 2 2 )

(8)

2 + 84

2 − 2 − 1]

2 = − 5 1 8 0 ( 11 − 2 2 17−4 2 ) + √[ 5 1 8 0 ( 11 − 2 2 17−4 2 )]

02 (17 − 4 2 ) [( 2 −1 0 )

(9)

2 = ( −1 ) 2

(10)

References [1] Sunde SL, Berto F, Haugen B. Predicting fretting fatigue in engineering design. International Journal of Fatigue 2018;117:314 – 26. https://doi.org/10.1016/j.ijfatigue.2018.08.028. [2] Funk W. Der Einfluß der Reibkorrosion auf die Dauerhaltbarkeit zusammengesetzter Maschinenelemente. 1968. [3] NISHIOKA K, HIRAKAWA K. Fundamental Investigations of Fretting Fatigue : Part 1 -5. Bulletin of JSME 1969;12:692 – 7. https://doi.org/10.1299/jsme1958.12.692. [4] Fouvry S, Kapsa Ph, Vincent L, Dang Van K. Theoretical analysis of fatigue cracking under dry friction for