A common cause for premature bearing failures in wind turbine gearboxes are the so-called White Etching Cracks (WEC). These undirected, three-dimensional cracks are bordered by regions of altered microstructure and ultimately lead to a cracking or spalling of the raceway. An accelerated WEC test was carried out on a FE8 test rig using cylindrical roller thrust bearings made of martensitic 100Cr6 steel. The resulting WECs were investigated with several characterisation techniques. Ultrasonic measurements showed the WEC were mainly located in the region of the overrolled surface in which negative slip occurs, which agrees with hypotheses based on an energetic approach for a prognosis. SEM orientation contrast imaging of the area around WEC revealed an inhomogeneous structure with varied grain sizes and a large amount of defects. Microstructure characterization around the WEA using EBSD showed significant grain refinement. Atom probe tomography showed the microstructure in the undamaged zone has a plate-like martensitic structure with carbides, while no carbides were detected in the WEA where the microstructure consisted of equiaxed 10 nm grains. A three dimensional characterisation of WEC network was successfully demonstrated with X-ray computerized tomography, showing crack interaction with unidentified inclusion-like particles.@en

WEC is an aggressive and unpredictable failure mode affecting bearings in particular in the wind energy sector. This paper focuses on the most common used method for WEC laboratory accelerated testing, the FE8 type test rigs using martensitic through hardened 100Cr6 cylindrical roller thrust bearings, analyzing the load conditions, test results and damage quantification. The surface and sub-surface stress conditions as well as the surface frictional loading were analyzed using a half-space model. Simulations and experiments were conducted under different load conditions, including tests with different number of rollers and tests using dynamic load and speed. Tests under constant loads show a low load influence and prove that a WEC failure can occur both prematurely and after exceeding the rated lifetime. Dynamic conditions did not accelerate WEC failure, and only rollers (not washers) were affected by WEC under dynamic loading conditions. Damage characterization was performed using optical microscopy and ultrasound scanning. Advanced image analysis based on characterization of defect regions in the ultrasound scans was used for quantifying the subsurface damage. Tests showed WEC failure could be achieved consistently, however there were seemingly large random variations in the observed damage.@en