Issue 38

S. Averbeck et alii, Frattura ed Integrità Strutturale, 38 (2016) 12-18; DOI: 10.3221/IGF-ESIS.38.02 17 torsional loading. It is also possible that the ratio between compressional and torsional load at the torsional maxima prevented microstructural change and even crack formation, as was the case in several specimens. S UMMARY olling contact fatigue conditions were simulated with in-phase and out-of-phase cyclic multiaxial loads. It was found that the material behaviour differed greatly between the two load patterns. While the out-of-phase load led to regular crack initiation and propagation, zones of altered microstructure were found adjacent to fatigue cracks in the in-phase specimens. Detailed investigations with SEM, FIB, nanoindentation and metallographic methods revealed that these zones resemble the microstructural change in the bearing damage phenomenon White Etching Cracks. A CKNOWLEDGEMENTS e would like to thank SKF GmbH, Schweinfurt, for supporting us with the heat treatment of the specimens. Further thanks go to Dr. Thomas Löber of the Nanostructuring Center (NSC) at the University of Kaiserslautern for his help with the FIB examinations. This study is part of a project funded by the Deutsche Forschungsgemeinschaft (DFG) under grant KE 1426/6-1. R EFERENCES [1] Evans, M.-H., White structure flaking (WSF) in wind turbine gearbox bearings: effects of ‘butterflies’ and white etching cracks (WECs), Tribol. Int., 28 (2012) 3–22. [2] Gegner, J., Tribological Aspects of Rolling Bearing Failures, in: Kuo, C.-H. (Ed.), Tribology - Lubricants and Lubrication, InTech, Rijeka, (2011) 33–93. [3] Stadler, K., Lai, J., Vegter, R.H., A Review: The Dilemma With Premature White Etching Crack (WEC) Bearing Failures, in: Beswick, J.M. (Ed.), Bearing Steel Technologies, ASTM International, West Conshohocken, (2014) 487– 508. [4] West, O., Diederichs, A.M., Alimadadi, H., Dahl, K.V., Somers, M., Application of Complementary Techniques for Advanced Characterization of White Etching Cracks, Pract. Metallogr., 50 (2013) 410–431. [5] Greco, A., Sheng, S., Keller, J., Erdemir, A., Material wear and fatigue in wind turbine Systems, Wear, 302, (2012) 1583–1591. [6] Harada, H., Mikami, T., Shibata, M., Sokai, D., Yamamoto, A., Tsubakino, H., Microstructural Changes and Crack Initiation with White Etching Area Formation under Rolling/Sliding Contact in Bearing Steel, ISIJ Int., 45 (2005) 1897–1902. [7] Evans, M.-H., Wang, L., Jones, H., Wood, R., White etching crack (WEC) investigation by serial sectioning, focused ion beam and 3-D crack modelling, Tribol. Int., 65 (2013) 146–160. [8] Ruellan Du Crehu, Arnaud, Tribological analysis of White Etching Crack (WEC) failures in Rolling Element Bearings, PhD thesis, INSA Lyon, (2014). [9] Evans, M.-H., Richardson, A.D., Wang, L., Wood, R.J.K., Anderson, W.B., Confirming subsurface initiation at non- metallic inclusions as one mechanism for white etching crack (WEC) formation, Tribol. Int., 75 (2014) 87–97. [10] Surborg, H., Einfluss von Grundölen und Additiven auf die Bildung von WEC in Wälzlagern, Shaker, Aachen, (2014). [11] Burkart, K., Bomas, H., Schroeder, R., Zoch, H.-W., Rolling Contact and Compression-Torsion Fatigue of 52100 Steel with Special Regard to Carbide Distribution, in: Beswick, J.M. (Ed.), Bearing Steel Technologies, ASTM International, West Conshohocken, (2012) 218–236. [12] Beretta, S., Foletti, S., Propagation of small cracks under RCF: a challenge to Multiaxial Fatigue Criteria, in: Carpinteri, A., Iacoviello, F., Pook, L.P., Susmel, L. (Eds.), Proceedings of the 4th International Conference on Crack Paths (CP 2012), Gruppo Italiano Frattura, Cassino, (2012) 15–28. [13] Fatemi, A., Shamsaei, N., Multiaxial fatigue: An overview and some approximation models for life estimation, Int. J. Fatigue, 33 (2011) 948–958. [14] Baumann, G., Fecht, H.J., Liebelt, S., Formation of white-etching layers on rail treads, Wear, 191, (1996) 133–140. R W