Post-testing measurement of freely movable and diffusible hydrogen in context of WEC formation at cylindrical roller thr
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ISSN 2223-7690 CN 10-1237/TH
RESEARCH ARTICLE
Post-testing measurement of freely movable and diffusible hydrogen in context of WEC formation at cylindrical roller thrust bearings from 100Cr6 Martin LINZMAYER1,*, Francisco Christopher SOUS1, Michael POHL2
GUTIÉRREZ
GUZMÁN1,
Gregor MANKE2,
Georg
JACOBS1,
1
Institute for Machine Elements and System Engineering, RWTH Aachen University, Schinkelstrasse 10, Aachen 52062, Germany
2
Institute for Materials, Material Testing, Ruhr University Bochum, Universitätsstr 150, Bochum 44801, Germany
Received: 17 January 2020 / Revised: 11 August 2020 / Accepted: 22 September 2020
© The author(s) 2020. Abstract: Sub‐surface crack networks in areas of altered microstructure are a common cause for bearing failures. Due to its appearance under light microscopy, the damage pattern is referred to as White Etching Cracks (WEC). The root causes leading to the formation of WEC are still under debate. Nevertheless, it has already been shown that atomic hydrogen can have an accelerating effect on the formation and propagation of WEC. In addition to hydrogen pre‐charging, hydrogen can be released and absorbed during rolling/sliding due to the decomposing of the lubricant and water. The current work focuses on the analysis of the hydrogen content of cylindrical roller thrust bearings after testing in a FE8 type test rig using two different lubricants. Within the framework of this work, two different hydrogen analysis methods were used and assessed regarding their applicability. The results show that the so‐called Hydrogen Collecting Analysis (HCA) is more suitable to investigate the correlation between lubricant chemistry and hydrogen content in the test bearings than the Local Hydrogen Analysis (LHA). The measurements with the HCA show a continuously increasing freely movable and diffusible hydrogen content under tribological conditions, which leads to the formation of WEC. Comparative tests with an oil without hydrogen showed that the tendency of the system to fail as a result of WEC can be reduced by using a lubricant without hydride compounds. Keywords: White Etching Crack (WEC); White Etching Areas (WEA); hydrogen content; Hydrogen Collecting Analysis (HCA); freely movable hydrogen; diffusible hydrogen; cylindrical roller thrust bearing; roller bearings; roller contact fatigue
1 Introduction The estimation of the service life of rolling bearings is usually carried out following DIN ISO 281 [1] and assumes a failure caused by subsurface initiated rolling contact fatigue (RCF). However, early failures due to cracks in regions of altered microstructures below the surface have occurred over the years in various applications, including
wind turbines [2–4], motor vehicles [2, 4–6], washing machines [2, 7], paper machines [2, 5, 6], a
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