Investigating the Process of White Etching Crack Initiation in Bearing Steel
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White etching cracks (WECs) have been identified as a dominant mode of premature failure within wind turbine gearbox bearings. Though WECs have been reported in the field for over a decade, the conditions leading to WECs and the process by which this failure culminates are both highly debated. In previously published work, the generation of WECs on a benchtop scale was linked to sliding at the surface of the test sample, and it was also postulated that the generation of WECs was dependent on the cumulative energy that had been applied to the sample over the entirety of the test. In this paper, a three-ring-on-roller benchtop test rig is used to systematically alter the cumulative energy that a sample experiences through changes in normal load, sliding, and run-time, in an attempt to correlate cumulative energy with the formation of WECs. It was determined that, in the current test setup, the presence of WECs can be predicted by this energy criterion. The authors then used this information to study the process by which WECs initiate. It was found that, under the current testing conditions, the formation of a dark etching microstructure precedes the formation of a crack, and a crack precedes the formation of white etching microstructure.
KeywordsWhite etching cracks Wind turbine gearbox bearings Microstructural alterations Bearing failures
This work is supported by the US Department of Energy Office of Energy Efficiency and Renewable Energy, Wind and Water Power Technology Office under Contract No. DE-AC02-06CH11357. The authors are grateful to DOE Project Managers Mr. Michael Derby and Mr. Nick Johnson for their support and encouragement. The authors would also like to acknowledge the assistance provided by our colleagues at Argonne National Laboratory’s Tribology Section, especially Dr. Maria De La Cinta Lorenzo Martin for her assistance with electron microscopy and Dr. Oyelayo Ajayi for his helpful discussion on metallurgy. As well as Dr. David L. Burris of the University of Delaware’s department of Mechanical Engineering for serving as an advisor over the course of this work. The authors would also like to thank Dr. Mihails Scepanskis for many useful conversations pertaining to WEC generation and PCS Instruments for providing samples for the MPR testing. Use of the Center for Nanoscale Materials an Office of Science user facility was supported by the US Department of Energy Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-06CH11357.
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