Lubricants

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3 pages, 167 KiB

Open AccessEditorial

Rolling Contact Fatigue and White Etching Cracks of Bearings

by Walter Martin Holweger and Jürgen Gegner

Lubricants 2023, 11(6), 247; https://doi.org/10.3390/lubricants11060247 - 4 Jun 2023

Viewed by 1542

Abstract

Lubricants have taken a leading role as drive- train system components in recent years, mainly attributed to their viscosity as a quality criterion [...] Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

Research

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28 pages, 9242 KiB

Open AccessArticle

A Study on the Influence of Electrical Discharges on the Formation of White Etching Cracks in Oil-Lubricated Rolling Contacts and Their Detection Using Electrostatic Sensing Technique

by Kamran Esmaeili, Ling Wang, Terry J. Harvey, Neil M. White and Walter Holweger

Lubricants 2023, 11(4), 164; https://doi.org/10.3390/lubricants11040164 - 3 Apr 2023

Cited by 4 | Viewed by 2263

Abstract

In bearing applications, the presence of stray and parasitic currents in combination with lubricants has been studied for almost a century and has been found to cause fluting and corrugation damages under high current densities. However, recent research has suggested that at low [...] Read more.

In bearing applications, the presence of stray and parasitic currents in combination with lubricants has been studied for almost a century and has been found to cause fluting and corrugation damages under high current densities. However, recent research has suggested that at low current densities (<1 mA/mm²) under specific operating conditions, electrical discharges can substantially reduce bearing life due to the formation of white etching cracks (WECs). To date, limited studies have investigated the critical operating and electrical conditions for WEC formation and demonstrated effective fault detection techniques. This study uses a novel monitoring technique known as the electrostatic sensing technique to detect, monitor and characterise electrical discharges in an oil-lubricated steel–steel rolling contact on a TE74 twin-roller machine. The findings demonstrate that WECs can be formed under the influence of electrical discharges in less than 50 h, and the electrostatic sensors are effective for the early detection of critical electrical discharges related to WEC-induced failures. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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20 pages, 4270 KiB

Open AccessArticle

A Validated Computational Study of Lubricants under White Etching Crack Conditions Exposed to Electrical Fields

by Walter Holweger, Luigi Bobbio, Zhuoqiong Mo, Joerg Fliege, Bernd Goerlach and Barbara Simon

Lubricants 2023, 11(2), 45; https://doi.org/10.3390/lubricants11020045 - 28 Jan 2023

Cited by 7 | Viewed by 1990

Abstract

The problem of White Etching Cracks (WEC) leading to failures in the life cycle of industrial and automotive drive trains has existed for more than 30 years. Many parameters leading to WEC, such as the presence of electricity, unfavorable lubricants, and other factors, [...] Read more.

The problem of White Etching Cracks (WEC) leading to failures in the life cycle of industrial and automotive drive trains has existed for more than 30 years. Many parameters leading to WEC, such as the presence of electricity, unfavorable lubricants, and other factors, have been identified by the use of test rigs. However, since (a) within lifecycle operation these impacts appear incidentally, and (b) the identified impacts stimulate each other as stated in WEC research, the appearance of WEC in a drive train is impossible to predict for any given application. This difficulty causes WEC to be a serious problem. Obtaining reliable failure prediction rates using construction guidelines is still impossible, resulting in warranty claims. The aim of this paper is, first, to establish a routine to determine if and how lubricants could be described numerically with respect to their susceptibility toward electrical fields and to see how this factor could be added in a later stage to construction guidelines. Second, this paper aims to give advice to the applicant in terms of countermeasures. Currently, as predictors are missing, extensive and time-consuming testing is required. Contradictory test results in the field of application, indicate the need for fundamental parameters to determine in which circumstances the application is exposed to WEC risk and to suggest countermeasures. The current study presents a simulation method based solely on the chemical structure of lubricant components, investigating the appearance of WEC and their response to increasing electrical fields. The results show a clear pattern in WEC criticality with respect to lubricants: if two or more components present in the lubricant create clusters through their dipolar interaction, an apparent WEC risk could be accurately predicted apart from test rig results. These clusters are charged like one big particle in an early stage of electrical field exposure. As a result, the surface area increases, facilitating a higher uptake of charge. The incidental breakdown of this charge is assumed. As the charge of a cluster is higher than that of single molecules, WEC critical lubricants are subjected to this pattern. The study validates these results by comparing them using lubricants known to be critical with respect to WEC, suggesting further tests in the near future. Despite the fact that some lubricants seem more critical than others related to WEC, each lubricant clearly might lead to WEC under given conditions. Thus, constructing guidelines for a prediction routine is essential. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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15 pages, 11155 KiB

Open AccessArticle

Alkylated Polyphenyl Ethers as High-Performance Synthetic Lubricants

by Renguo Lu, Hiroshi Tani, Shinji Koganezawa and Masayuki Hata

Lubricants 2022, 10(10), 275; https://doi.org/10.3390/lubricants10100275 - 21 Oct 2022

Cited by 4 | Viewed by 2906

Abstract

Lubricants exhibiting both thermal and chemical stability that consequently generate less hydrogen during friction are required to avoid the hydrogen embrittlement of moving mechanical components. The present work studied the effects of the length and number of alkyl chains on the tribological properties [...] Read more.

Lubricants exhibiting both thermal and chemical stability that consequently generate less hydrogen during friction are required to avoid the hydrogen embrittlement of moving mechanical components. The present work studied the effects of the length and number of alkyl chains on the tribological properties of polyphenyl ethers (PPEs), which feature good thermal and radiation resistance. PPEs were found to have much lower friction coefficients compared with a poly-alpha-olefin and alkyldiphenyl ether, and the effect of the running-in process on friction appeared to be negligible. The formation of polymers on the friction track evidently decreased the friction coefficients of the lubricants and the wear rates were almost zero for all the PPEs, indicating excellent anti-wear properties. Analyses with a quadrupole mass spectrometer connected to a friction tester under vacuum indicated negligible hydrogen generation from 4P2E, which had no alkyl chains, after the running-in. R1-4P2E, having a C₁₆H₃₃ chain, showed hydrogen desorption similar to that of the alkyldiphenyl ether, which had a C₁₈H₃₇ alkyl chain. R2-4P2E, with two C₁₆H₃₃ chains, produced significant hydrogen, but with a long induction period; thus, it provided good wear protection. Although alkyl chains increased the risk of hydrogen generation, PPEs with such chains may have applications as standard lubricants. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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26 pages, 13002 KiB

Open AccessArticle

Nano- and Micro-Tribological Investigations of Boundary Layers on Axial Bearing Washers Tested under WEC Critical Conditions

by Florian Pape

Lubricants 2022, 10(8), 198; https://doi.org/10.3390/lubricants10080198 - 22 Aug 2022

Cited by 4 | Viewed by 3053

Abstract

The formation of boundary layers on bearing surfaces due to the operational conditions has a significant influence on bearing lifetimes and frictional properties. Zinc dialkyldithiophosphate is an anti-wear additive widely used in oil and grease formulations that forms beneficial surface boundary layers. Under [...] Read more.

The formation of boundary layers on bearing surfaces due to the operational conditions has a significant influence on bearing lifetimes and frictional properties. Zinc dialkyldithiophosphate is an anti-wear additive widely used in oil and grease formulations that forms beneficial surface boundary layers. Under certain circumstances, this additive can cause early bearing failure due to white etching cracks (WEC) formation. By influencing chemical reactions and diffusion processes, the boundary films are suspected to be a reason for the emergence of WECs. The properties of these layers under WEC critical and uncritical conditions are of interest. To gain knowledge of these layers, nano- and micro-tribological tests were performed. One possibility is to measure the hardness by nanoindentation and scratching on and into the layers by nano scratch tests. Another way is to perform local resolved micro-pin-on-disk tests. Additionally, ToF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) was performed on the bearing surfaces to conclude the chemical compositions of the boundary layers. In the focus was, if the measured properties of the layers can be correlated to the bearing’s early failures due to WEC, frictional properties of the whole system, and the wear on the surfaces. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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12 pages, 5522 KiB

Open AccessArticle

An Analysis of Reaction Forces in Crankshaft Support Systems

by Krzysztof Nozdrzykowski, Zenon Grządziel, Rafał Grzejda, Mariusz Warzecha and Mateusz Stępień

Lubricants 2022, 10(7), 151; https://doi.org/10.3390/lubricants10070151 - 11 Jul 2022

Cited by 14 | Viewed by 2980

Abstract

During measurements, the crankshafts of marine engines are usually supported on a set of rigid prisms. Such prisms maintain a constant height position, cause different values of reaction forces and, consequently, may cause elastic deformations of the crankshafts. Thus, the measurements of the [...] Read more.

During measurements, the crankshafts of marine engines are usually supported on a set of rigid prisms. Such prisms maintain a constant height position, cause different values of reaction forces and, consequently, may cause elastic deformations of the crankshafts. Thus, the measurements of the dimensions and geometry of the crankshaft may be distorted. This article proposes a measuring system developed to support the crankshaft with a set of flexible supports. These supports implemented the given reaction forces, which ensured the elimination of the crankshaft deformations, regardless of the possible deviations, i.e., in the coaxiality of the main crankshaft journals. The values of these forces were calculated using the finite element method (FEM). These calculations showed that in order to eliminate the crankshaft deformations, the values of the reaction forces must change not only on individual supports, but also with the change of the shaft rotation angle during the measurement. The numerical experiments showed that the application of flexible supports results in uniform contact reaction forces on adjacent main journal supports. This uniformity occurs regardless of the quality of the crankshaft geometry. Thus, the necessity to use a set of flexible supports for measuring marine engine crankshafts was confirmed. The research also showed that the values of the reaction forces ensuring the elimination of shaft deflections under the assumption of nodal support can be treated as corresponding to the resultant reaction forces realized by the prismatic heads. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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17 pages, 7317 KiB

Open AccessArticle

A Study on Decisive Early Stages in White Etching Crack Formation Induced by Lubrication

by Jürgen Wranik, Walter Holweger, Tarek Lutz, Philipp Albrecht, Benedikt Reichel and Ling Wang

Lubricants 2022, 10(5), 96; https://doi.org/10.3390/lubricants10050096 - 12 May 2022

Cited by 13 | Viewed by 3204

Abstract

The reliability of rolling bearings is affected by white etching crack (WEC) or white structure flaking (WSF) failures, causing tremendous commercial burdens for bearing manufacturers and operators. The research for the underlying failure mechanism has attracted interest from a large scientific community over [...] Read more.

The reliability of rolling bearings is affected by white etching crack (WEC) or white structure flaking (WSF) failures, causing tremendous commercial burdens for bearing manufacturers and operators. The research for the underlying failure mechanism has attracted interest from a large scientific community over decades. Despite the significant amount of efforts, a root cause of white etching cracking is still missing. Amongst other factors, lubricant chemistry is considered to be essential in WEC formation. The authors aim to elucidate this key parameter by provoking white etching crack formation on a FE8 bearing test rig using a well-described set of chemicals in high- and low-reference lubricants. Scanning electron microscopy and energy dispersive X-ray analysis prove the presence of a patchy tribofilm on the surface of bearing washers, leading most likely to a higher frictional torque at the early stages of operation when the low reference oil is used. Secondary neutral mass spectrometry (SNMS) shows a hydrogen containing tribofilm in the shallow subsurface of about 30 nm depth, suggesting that hydrogen proliferating into bearing material may subsequently facilitate crack propagation via dislocation pileups, leading to premature bearing failure. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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14 pages, 6277 KiB

Open AccessArticle

Simulation of the Fatigue Crack Initiation in SAE 52100 Martensitic Hardened Bearing Steel during Rolling Contact

by Kiarash Jamali Dogahe, Vinzenz Guski, Marijo Mlikota, Siegfried Schmauder, Walter Holweger, Joshua Spille, Joachim Mayer, Alexander Schwedt, Bernd Görlach and Jürgen Wranik

Lubricants 2022, 10(4), 62; https://doi.org/10.3390/lubricants10040062 - 7 Apr 2022

Cited by 13 | Viewed by 3531

Abstract

An investigation on the White Etching Crack (WEC) phenomenon as a severe damage mode in bearing applications led to the observation that in a latent pre-damage state period, visible alterations appear on the surface of the raceway. A detailed inspection of the microstructure [...] Read more.

An investigation on the White Etching Crack (WEC) phenomenon as a severe damage mode in bearing applications led to the observation that in a latent pre-damage state period, visible alterations appear on the surface of the raceway. A detailed inspection of the microstructure underneath the alterations reveals the existence of plenty of nano-sized pores in a depth range of 80 µm to 200 µm. The depth of the maximum Hertzian stress is calculated to be at 127 µm subsurface. The present study investigates the effect of these nanopores on the fatigue crack initiation in SAE 52100 martensitic hardened bearing steel. In this sense, two micro-models by means of the Finite Element Method (FEM) are developed for both a sample with and a sample without pores. The number of cycles required for the crack initiation for both samples is calculated, using the physical-based Tanaka–Mura model. It is shown that pores reduce the number of cycles in bearing application to come to an earlier transition from microstructural short cracks (MSC) to long crack (LC) propagation significantly. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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12 pages, 40798 KiB

Open AccessArticle

A Study on Early Stages of White Etching Crack Formation under Full Lubrication Conditions

by Walter Holweger, Alexander Schwedt, Viktorija Rumpf, Joachim Mayer, Christof Bohnert, Jürgen Wranik, Joshua Spille and Ling Wang

Lubricants 2022, 10(2), 24; https://doi.org/10.3390/lubricants10020024 - 9 Feb 2022

Cited by 13 | Viewed by 3185

Abstract

The appearance of White Etching Cracks (WEC), not covered by the ISO 281 modified failure rate calculation, leads to difficulties in predicting bearing reliability. This uncertainty in bearing applications leads to a worldwide activity in order to understand and prevent this situation since [...] Read more.

The appearance of White Etching Cracks (WEC), not covered by the ISO 281 modified failure rate calculation, leads to difficulties in predicting bearing reliability. This uncertainty in bearing applications leads to a worldwide activity in order to understand and prevent this situation since the WEC failure mode deviates from the traditional Rolling Contact Fatigue (RCF) mode. Plenty of factors have been found to influence this phenomenon over the years, however the precise initiation of the WEC is still under debate. In order to understand the initiation and analyze the temporal evolution, interrupted tests on the same material were performed under conditions that were known to lead to WEC formation and RCF. To avoid the added complexity of boundary lubrication, a Deep Groove Ball Bearing (DGBB) test rig under full lubrication (Elastohydrodynamic Lubrication, EHL) was chosen. Within a standard operating mode, named Mode 1 (RCF), the bearings are solely subjected to a radial load. By suspending the tests at different time steps, a continuous progress of changes in the subsurface material structure seen as equiaxed grains with low dislocation densities, identified as ferrite, is observed. The bearings did not fail up to load cycles of 10⁹. In contrast, a Mode 2 Electrical Charged Contact Fatigue (ECCF) test provoked the early formation of cracks and crack networks, first without WEA, then later with WEA. It became obvious when comparing Mode 1 (RCF) with Mode 2 (ECCF) that Mode 2 (ECCF) achieves far fewer load cycles until failure occurs. Full article

(This article belongs to the Special Issue Rolling Contact Fatigue and White Etching Cracks of Bearings)

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