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Researchers at the U.S Department of Energy’s (DOE’s) Argonne National Laboratory (ANL) are investigating the root cause of failures to wind turbine drivetrain components, such as bearings and gears. One of the leading causes of drivetrain reliability issues is a complicated mode of bearing failure known as white-etching cracks (WECs). This failure is characterized by the formation of altered material microstructure near the contacting surface of the bearing raceway that results in cracks and pits that end the useful life of the bearing. Currently, there is no consensus on the cause of WECs and appropriate mitigation methods are still under debate.

ANL researchers are working to “shine some light” on this issue. In fact, they are using one of the brightest light sources in the world to do so. ANL’s Advanced Photon Source (APS) is the brightest synchrotron x-ray source in the western hemisphere, and is ANL’s largest and most heavily used scientific user facility supported by DOE’s Office of Science. Of the many measurement techniques available at the APS, x-ray micro-tomography can be used to image internal defects in a part, similar to how a CT scan is used to examine a human body in a doctor’s office. However, the APS source is powerful enough to look through hard bearing steel.

Using this micro-tomography capability, ANL researchers have examined several failed bearing pieces provided by their industrial collaborator, the SKF Group, a leading bearing manufacturer. Currently, they have successfully mapped entire subsurface crack networks in three dimensions, which previously could only be done through a destructive two-dimensional serial cross-sectioning technique. The information gained through this examination will provide insights into how the WECs are generated and the cause of their formation. In collaboration with their industrial partners, ANL scientists will apply these results toward identifying and developing appropriate mitigation methods to prevent WEC-related bearing failures.

A magnified photo of a single slice of the crack network found in a bearing.

The results of this work will be presented at the DOE-sponsored Wind Turbine Tribology Seminar, hosted by Argonne National Laboratory and co-organized by the National Renewable Energy Laboratory’s Gearbox Reliability Collaborative, October 29–31, 2014.

For more information and registration see Wind Turbine Tribology Seminar, 2014.