Understanding white etching cracks in rolling element bearings: State of art and multiple driver transposition on a twin-disc machine

Abstract

Among the prevalent tribological failures affecting rolling element bearings, an unconventional rolling contact fatigue mode has been identified as white etching cracks. Those correspond to three-dimensional branching crack networks partially bordered by white etching microstructure, eventually leading to premature and unpredictable failure. Recent work supports that this failure mode may be associated with various combinations of operating conditions depending on the application or test rig, but that all seem to converge towards similar tribological drivers related to surface-affected hydrogen evolution at asperity scales, which is known to embrittle the bearing steel. Nevertheless, as white etching cracks remain delicate to reproduce without artificial hydrogen charging, the underlying formation mechanisms remain unsettled. The present work aims to better understand how some of the main tribomechanical and tribochemical drivers may trigger white etching cracks and premature failures. In this study drivers such as sliding kinematics, water contamination, and electrical potential and lubricant additives are progressively transposed on a twin-disc machine that provides an enhanced control of contact parameters. Various attempts advocate that the tested drivers are not self-sufficient to reproduce the failure mode in such apparatus, but confirm that specific lubricant additives may reduce the fatigue life by promoting surface-initiated embrittled cracking similar to white etching cracks. A local criterion accounting for the local sliding frictional power dissipation and the lubrication regime is further proposed to assess the risk of white etching cracks based on the analysis of various reproduction and occurrences.

Tribochemical study of micropitting in tribocorrosive lubricated contacts: The influence of water and relative humidity

“…Meanwhile, water contamination can favour hydrogen generation and permeation into the steel under tribological contact [12,13] and accelerates rolling contact fatigue [14,15] although it may not be considered as a sufficient factor to induce white etching crack [16].…”

The Evolution of White Etching Cracks (WECs) in Rolling Contact Fatigue-Tested 100Cr6 Steel

“…10). Further progression of the slip energy criteria concept has been developed based upon information from different test rigs, using normal contact load and representing the slip energy criteria per film thickness sheared (N V/λ, N ms −1 ) to determine a threshold for WEC formation in most roller bearing configurations [21,61]. It is postulated that this threshold could exist due to the fact that sliding energy generates local flash temperatures influencing the tribochemical reactions taking place at nascent surfaces [62].…”

The influence of lubricant formulation on early thrust and radial bearing damage associated with white etching cracks

“…1,2,4 It is generally agreed that cracks precede the subsequent WEM, which is explained by intense microstructural alteration due to crack face rubbing during over-rolling. 1,3,4,6 Therefore, engineers should be concerned in general with the origins of early cracks in bearings, regardless whether or not they are decorated with WEM. Despite the WEC terminology, this study does not focus on the WEM but on the formation of extended cracks networks causing un-expected bearing failures.…”