Diagnosing Bearing Fatigue for Better Wind Turbine Operability
Wind turbine gearbox bearings are consequential components made primarily of high-strength martensitic steel, due to the exceptional durability required for continuous high-contact pressure applied to the rolling elements and raceway components.
In spite of being excellent engineered solutions, rolling contact fatigue (RCF) — characterized by the formation of surface or subsurface cracks — accounted for more than 75% of premature wind turbine gearbox bearing failure. The transformed regions within the steel microstructure — “white etching matter” (WEM) as they’re known in metallurgy for their white appearance under optical microscopy — usually precede unexpected flaking and spalling of raceways.
This is a significant issue in tribology, generally — and in wind energy, specifically. Because massive turbines that stand hundreds of feet above ground or float miles offshore to generate enormous amounts of power should perform optimally with minimal maintenance, it’s imperative to be able to predict WEM formation — to diagnose symptoms of fatigue and reduce their potential to lead to operational problems.
That’s precisely what our latest paper is about. We sought to better understand the mechanisms for WEM formation and clarify the role of frictional energy dissipation.
In our study, we hypothesize that a combination of multiaxial loading and subsurface frictional energy changes could be drivers for WEM formation.
To test that, we employed a novel parametric analysis that assesses damage at the junction of contacting surfaces under oscillating forces and used a computational model to consider orientation, size, and local friction of a subsurface crack.
The simulation results not only support our hypothesis and experimental observations; they demonstrate the fretting damage parameter we introduce as a useful predictor of WEM and a consistent, replicable framework for evaluating energy dissipation.
Our results are guiding future studies, and we are developing new models that build on this work, all of which are aimed at improving gear drive bearing reliability for better wind turbine operability.