Keywords

Rolling Contact Fatigue, White Etching Cracks, Tribochemical Hydrogen Enhanced Cracking, Twin-Discs Test Rig

Understanding White Etching Cracks in Rolling Element Bearings - Reproduction and Influent Tribochemical Drivers 

Among tribological failures in wind turbine rolling element bearings, an unusual and premature rolling/sliding contact fatigue mode has been defined as White Etching Cracks (WEC) being wide subsurface 3D branching crack networks bordered by nano-grained ferritic white etching microstructure. As WEC occurrences present no common denominator and are delicate to reproduce and observe, no consensus on the formation mechanisms has been verified yet. Analysis of a standard bearing test rig reproducing WEC repeatedly, without artificial hydrogen charging, suggest that WEC initiate through incipient axial surface microcracks and propagate by hydrogen enhanced cracking due to lubricant decomposition. Initiation and propagation require a subtle equilibrium between contact kinematics and stresses, material parameters and lubrication aspects as additives and water ingress. Contact conditions are transposed on a twin disc machine to simulate WEC and qualify the influence of different drivers.

Authors and Company/Institution

A. Ruellan, F. Ville and J. Cavoret, LaMCoS-INSA Lyon, Université de Lyon, Villeurbanne Cedex, France
X. Kleber, MATEIS – INSA Lyon, Université de Lyon, Villeurbanne, France
C. Burnet and D. Girodin, NTN-SNR Research Center, Annecy, France