The Influence of Sliding and Contact Severity on the Generation of White Etching Cracks

Gould, Benjamin; Greco, Aaron

doi:10.1007/s11249-015-0602-6

Cited by 83 publications

(79 citation statements)

References 46 publications

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“…Limitations, however, do exist as this criterion does not take into account the lubricant formulation. Evidence for the degree of boundary lubrication (the range of λ) controlling the propensity for WEC formation is also suggested, more WECs forming for more severe boundary regimes (λ in the range of 0.06-0.7) [56]. No WECs were found in the raceway washers, with no evidence of WEC formations being observed in the zones corresponding to high slip energy dissipation or asperity friction accumulation.…”

Section: Wec Initiation and Evolutionmentioning

confidence: 97%

“…11, 12, 13 and Video 2). Slip has been shown to influence the formation of WECs in both FAG-FE8 and three ring roller micropitting rig (MPR) tests using the same 'special' oil known used in this study [29,55,56], where evidence for the influence of negative slip being more dominant in WSF over positive slip is provided [56]. More recently the influence of slip on WEC formations has also been shown in a two-disc test rig set-up, where again negative slip showed dominance in WEC production in contrast to positive [57].…”

Section: Wec Initiation and Evolutionmentioning

confidence: 99%

“…This dominance has been attributed to higher material stressing, lowered fracture mechanic properties under alternating load and preferential surface crack propagation due to the traction force and surface motion vectors pointing in the same direction in negative slip as opposed to positive [57]. It is proposed that negative slip results in the compressive closure of cracks enhancing the crack rubbing mechanism for WEA formation [56]. The localisation of the WECs recorded across 4-18 h is more densely populated in the 2-3 mm (outer) and 8-9 mm (inner) zones across the roller (see Fig.…”

Section: Wec Initiation and Evolutionmentioning

confidence: 99%

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

et al. 2017

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The formation of white etching cracks (WECs) in steel rolling element bearings can lead to the premature rolling contact fatigue (RCF) failure mode called white structure flaking. Driving mechanisms are still debated but are proposed to be combinations of mechanical, tribochemical and electrical effects. A number of studies have been conducted to record and map WECs in RCF-tested samples and bearings failed from the field. For the first time, this study uses serial sectioning metallography techniques on non-hydrogen charged test samples over a range of test durations to capture the evolution of WEC formation from their initiation to final flaking. Clear evidence for subsurface initiation at non-metallic inclusions was observed at the early stages of WEC formation, and with increasing test duration the propagation of these cracks from the subsurface region to the contact surface eventually causing flaking. In addition, an increase in the amount of associated microstructural changes adjacent to the cracks is observed, this being indicative of the crack being a prerequisite of the microstructural alteration.

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Section: Wec Initiation and Evolutionmentioning

confidence: 97%

Section: Wec Initiation and Evolutionmentioning

confidence: 99%

Section: Wec Initiation and Evolutionmentioning

confidence: 99%

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

et al. 2017

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“…Therefore, this inconsistency could be due to differences in the cleanliness of the materials used between studies, where there is a lack of inclusion sites readily available to trap hydrogen. Evidence for the degree of boundary lubrication (the range of λ) controlling the propensity for WEC formation is also suggested, more WECs forming for more severe boundary regimes (λ in the range of 0.06-0.7) [61]. It could be reasoned that a more severe contact condition results in additional asperity contact and Fig.…”

Section: Rcf Testingmentioning

confidence: 99%

“…A number of additives found in lubricants have been shown to promote WSF occurrence, these include; extreme pressure (EP) and anti-wear (AW) additives consisting of sulphur and phosphorus compounds [66,67], where sulphur aids in hydrogen diffusion by preventing atomic hydrogen recombination [68] and formulations of AW zinc dithiophosphates (ZDDP/ZnDTP/ZnDDP) with detergent/rust preventative calcium sulphonate additives [6,61,[69][70][71][72][73][74].…”

Section: Influence Of Oilmentioning

confidence: 99%

Thermal Desorption Analysis of Hydrogen in Non-hydrogen-Charged Rolling Contact Fatigue-Tested 100Cr6 Steel

et al. 2017

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Hydrogen diffusion during rolling contact fatigue (RCF) is considered a potential root cause or accelerator of white etching cracks (WECs) in wind turbine gearbox bearing steels. Hydrogen entry into the bearing steel during operation is thought to occur either through the contact surface itself or through cracks that breach the contact surface, in both cases by the decomposition of lubricant through catalytic reactions and/or tribochemical reactions of water. Thermal desorption analysis (TDA) using two experimental set-ups has been used to measure the hydrogen concentration in non-hydrogen-charged bearings over increasing RCF test durations for the first time. TDA on both instruments revealed that hydrogen diffused into the rolling elements, increasing concentrations being measured for longer test durations, with numerous WECs having formed. On the other hand, across all test durations, negligible concentrations of hydrogen were measured in the raceways, and correspondingly no WECs formed. Evidence for a relationship between hydrogen concentration and either the formation or the acceleration of WECs is shown in the rollers, as WECs increased in number and severity with increasing test duration. It is assumed that hydrogen diffusion occurred at wear-induced nascent surfaces or areas of heterogeneous/patchy tribofilm, since most WECs did not breach the contact surface, and those that did only had very small crack volumes for entry of lubricant to have occurred.

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Investigation of high‐speed shaft bearing loads in wind turbine gearboxes through dynamometer testing

Guo

Keller

2017

Wind Energy

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Many wind turbine gearboxes require repair or replacement well before reaching the end of their design life. The most common failure is bearing axial cracks, commonly called white etching cracks (WECs), which typically occur in the inner raceways of the high-speed parallel-stage rolling element bearings. Although the root causes of WECs are debated, one theory is that they are related to routine dynamic operating conditions and occasional transient events prevalent in wind turbines that can result in high bearing stress and sliding of the rolling elements. This paper examined wind turbine gearbox high-speed shaft bearing loads and stresses through modeling and full-scale dynamometer testing. Bearing outer race loads were directly measured and predicted using a variety of modeling tools in normal operations, misaligned conditions, and transient events particularly prone to bearing sliding. Test data and models of bearing loads were well correlated. Neither operational misalignment due to rotor moments nor static generator misalignment affected the bearing loads when compared with pure-torque conditions. Thus, it is not likely that generator misalignment is a causal factor of WECs. In contrast, during transient events, the bearings experienced alternating periods of high stress, torque reversals, and loads under the minimum requisite at high rotating speeds while showing indications of sliding, all of which could be related to the formation of WECs. KEYWORDS axial crack, bearing load, gearbox, reliability, white etching crack 1 | INTRODUCTIONThe cost of energy from wind has declined tremendously over the past 2 decades 1 owing to a combination of lower capital costs, higher availability and production, and more efficient operation 2,3 ; however, wind power plant operation and maintenance costs are frequently higher than anticipated, 4 and a significant portion of these costs is related to drivetrain reliability. 5 In 2007, the US Department of Energy established the Gearbox Reliability Collaborative (GRC) with the goal of understanding the root causes of premature gearbox failures and improving gearbox reliability. 6 To date, the GRC has focused on testing and modeling a 750-kW drivetrain, including the dedicated design and testing of 2 gearboxes. The GRC has led to major insights relating to the detrimental effect of rotor moments on planetary load sharing, the predicted fatigue life in high-torque conditions, and the risk of planetary bearing sliding in low-torque conditions. 7Although planetary gear and bearing failures attract much attention because of their high repair costs, the most commonly damaged components in wind turbine gearboxes are the rolling element bearings in the high-speed parallel stages. 8 The damage is dominated by axial cracks, also commonly called white etching cracks (WECs), rather than classic rolling contact fatigue. 9 The term white etching refers to the appearance of the steel microstructure when the bearing cross sections are polished, etched with chemicals, and examined under reflect...

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The Influence of Sliding and Contact Severity on the Generation of White Etching Cracks

Cited by 83 publications

References 46 publications

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

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

Thermal Desorption Analysis of Hydrogen in Non-hydrogen-Charged Rolling Contact Fatigue-Tested 100Cr6 Steel

Investigation of high‐speed shaft bearing loads in wind turbine gearboxes through dynamometer testing

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