This is an excerpt from the Second Quarter 2013 edition of the Wind Program R&D Newsletter.

Researchers at Argonne National Laboratory (ANL) are investigating a leading cause of premature bearing failures in wind turbine gearboxes that can occur within the first 2 years of a gearbox's intended design life (20 years). The bearing failures, typically referred to as white-etching cracks, first appear as cracks or pits on the bearing's surface and are associated with irregular alteration to the steel microstructure that occurs during the operation of the bearing. The root cause of white-etching cracks is still a mystery and effective methods to mitigate the failure are under debate.

The Tribology Section at ANL is working in collaboration with the National Renewable Energy Laboratory's Gearbox Reliability Collaborative to help shine a light on white-etching-crack failures and to identify and develop effective mitigation methods to improve reliability. Working closely with industry, the ANL team has examined numerous failed bearings from the field to characterize the white-etching-crack failures. Early observations conclude that these premature bearing failures (surface cracks and/or pits) are directly associated with subsurface alteration to the steel microstructure (white-etched areas), and the altered microstructure resulted in a localized increase of hardness, which was more prone to the formation of micro-cracks.

Although no single root cause could be identified at this point, the formation of the altered microstructure is thought to be a result of localized plastic deformation of the bearing, possibly linked to unsteady operation of the wind turbine drivetrain. Early results of this investigation were recently published in the peer-reviewed journal Wear, titled "Material Wear and Fatigue in Wind Turbine Systems" and presented at the corresponding Wear of Material Conference.

Bench-top test methods are currently under development to mimic white-etching-crack failures under controlled conditions; the tests will be used to validate potential mitigation techniques.

Argonne National Laboratory in Argonne, Illinois, is also developing improved methodologies for wind power forecasting and working to increase the deployment of advanced wind forecasting techniques that will optimize overall grid reliability and systems operations. In addition, work at ANL is underway to assess and mitigate the environmental impacts of wind power plants.