An experimental study of micropitting, using a new miniature test-rig

Benyajati, C; Olver, A.D.; Hamer, Clive

doi:10.1016/s0167-8922(03)80088-3

Cited by 28 publications

(24 citation statements)

References 7 publications

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“…The triple contact disc tester fully described in Benyajati, et al (8) and also used for previous experiments with additives (Olver,et al (13)) was used. The arrangement is shown in Fig.…”

Section: Micropitting (Mpr) Testsmentioning

confidence: 99%

The Effect of a Friction Modifier Additive on Micropitting

Lainé

Olver

Lekstrom

et al. 2009

Tribology Transactions

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Previous studies have shown that many anti-wear additives have a tendency to aggravate micropitting damage in hard steels subjected to rolling sliding contact at low lambda values. This is apparently because anti-wear additives suppress the gradual smoothing of the rough surfaces that takes place when a pure base stock is used under mild conditions. However, in practice, it is common to combine anti-wear and friction modifier additives in formulated oils, a combination that leads to reduced boundary friction. In the work described in this article, we added a common friction modifier agent, a molybdenum bis-diethylhexyl dithio-carbamate (MoDTC), to an oil containing an anti-wear additive, a secondary zinc dialkyldithio-phosphate (ZDDP) in a mineral base-stock. We examined micropitting behavior using a disc tester. The oil with both MoDTC and ZDDP showed initial micropitting that gradually disappeared with continued running, whereas ZDDP alone led to continuing severe damage. Analysis of the counter-discs after the test showed the presence of MoS 2 deposits on the asperity crests. Reduced boundary friction was confirmed using a tribometer test. It is speculated that the improved micropitting behavior resulted from the effect of a reduction in local tensile stress due to reduced asperity friction. This may have reduced the opening of the surface cracks and inhibited their extension.

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“…The triple contact disc tester fully described in Benyajati, et al (8) and also used for previous experiments with additives (Olver,et al (13)) was used. The arrangement is shown in Fig.…”

Section: Micropitting (Mpr) Testsmentioning

confidence: 99%

The Effect of a Friction Modifier Additive on Micropitting

Lainé

Olver

Lekstrom

et al. 2009

Tribology Transactions

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“…In his studies on the influence of surface roughness on pitting behaviour, Dawson [2,3] defined a parameter 'D' as a ratio of surface roughness to film thickness, equal to the reciprocal of what is now known as the specific film thickness or Λ ratio. It is now well established that micropitting only occurs if the specific film thickness is low enough to facilitate severe asperity-to-asperity contact [4,5]. Other factors, including the magnitude and direction of sliding, level of Hertz contact pressure, material and running-in, have also been shown to have a significant influence on micropitting by several authors [6][7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

“…In a series of studies, Olver and co-workers [4,5,16] showed that lubricant additives can affect the extent of micropitting by suppressing the wearing-in process, which in turn leads to an increased number of asperity stress cycles [5], and by changing the level of contact friction, which modifies tensile stresses and hence affects crack initiation and propagation [16]. These studies clearly indicated that the onset and progression of micropitting is highly dependent on the outcome of the continuous competition between surface fatigue and mild surface wear.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Slide–Roll Ratio on the Extent of Micropitting Damage in Rolling–Sliding Contacts Pertinent to Gear Applications

Rycerz

Kadiric

2019

Tribol Lett

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Micropitting is a type of surface damage that occurs in rolling-sliding contacts operating under thin oil film, mixed lubrication conditions, such as those formed between meshing gear teeth. Like the more widely studied pitting damage, micropitting is caused by the general mechanism of rolling contact fatigue but, in contrast to pitting, it manifests itself through the formation of micropits on the local, roughness asperity level. Despite the fact that micropitting is increasingly becoming a major mode of gear failure, the relevant mechanisms are poorly understood and there are currently no established design criteria to assess the risk of micropitting occurrence in gears or other applications. This paper provides new understanding of the tribological mechanisms that drive the occurrence of micropitting damage and serves to inform the ongoing discussions on suitable design criteria in relation to the influence of contact slide-roll ratio (SRR) on micropitting. A triple-disc rolling contact fatigue rig is used to experimentally study the influence of the magnitude and direction of SRR on the progression of micropitting damage in samples made of case-carburised gear steel. The test conditions are closely controlled to isolate the influence of the variable of interest. In particular, any variation in bulk heating at different SRRs is eliminated so that tests are conducted at the same film thickness for all SRRs. The results show that increasing the magnitude of SRR increases the level of micropitting damage and that negative SRRs (i.e. the component where damage is being accumulated is slower) produce more micropitting than the equivalent positive SRRs. Measurements of elastohydrodynamic film thickness show that in the absence of bulk heating, increasing SRR does not cause a reduction in EHL film thickness and therefore this cannot be the reason for the increased micropitting at higher SRRs. Instead, we show that the main mechanism by which increase in SRR promotes micropitting is by increasing the number of micro-contact stress cycles experienced by roughness asperities during their passage through the rolling-sliding contact. Therefore, the asperity stress history should form the basis of any potential design criterion against micropitting.

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“…A custom made oil consisting of PAO 5 base oil and ZDDP antiwear additive (0.1 wt% P) was used in all tests. The anti-wear additive was introduced in order to minimize wear of the MPR specimens which is known to have an effect on micropitting and pitting behaviour through its influence on wearing-in and hence asperity stresses [27,28]. Minimizing wear also means that the contact pressure remains constant throughout the test.…”

Section: Methodsmentioning

confidence: 99%

Assessing the effectiveness of data-driven time-domain condition indicators in predicting the progression of surface distress under rolling contact

Gouda

Rycerz

Kadiric

et al. 2019

Proceedings of the Institution of Mechanical Engineers, Part J:

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Condition monitoring of machine health via analysis of vibration, acoustic and other signals offers an important tool for reducing the machine downtime and maintenance costs. The key aspect in this process is the ability to relate features derived from the recorded sensor signals with the physical condition of the monitored asset in real time. This paper uses simple machine learning techniques to examine the ability of specific time-domain features obtained from vibration signals to predict the progression of surface distress in lubricated, rolling-sliding contacts, such as those found in rolling bearings and gears. Controlled experiments were performed on a triple-disc rolling contact fatigue rig using seeded-fault roller specimens where micropitting damage was generated and its progression directly observed over millions of contact cycles. Vibration signals were recorded throughout the experiments. Features known as condition indicators were then extracted from the recorded time-domain signals and their evolution related to the observed physical state of the associated specimens using simple machine learning techniques. Five time-domain condition indicators were examined, peak-to-peak, root-mean-square, kurtosis, crest factor and skewness, three of which were found not to be redundant. First, a classification model using KNN nearest neighbor was built with the three informative condition indicators as training data. The cross-validation results indicated that this classifier was able to predict the presence of micropitting damage with a relatively high precision and a low rate of false positives. Secondly, a k-means clustering analysis was performed to measure the significance of each condition indicator by leveraging patterns. The peak-to-peak condition indicator was found to be a good predictor for progression of micropitting damage. In addition, this indicator was able to distinguish between micropitting and pitting failure modes with a high success rate. Finally, the condition indicator response was correlated with the predicted damage state of the test specimen obtained through an existing physics-based surface distress model in order to illustrate the potential of hybrid models for improved prognostics of damage progression in rolling-sliding tribological contacts.

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An experimental study of micropitting, using a new miniature test-rig

Cited by 28 publications

References 7 publications

The Effect of a Friction Modifier Additive on Micropitting

The Effect of a Friction Modifier Additive on Micropitting

The Influence of Slide–Roll Ratio on the Extent of Micropitting Damage in Rolling–Sliding Contacts Pertinent to Gear Applications

Assessing the effectiveness of data-driven time-domain condition indicators in predicting the progression of surface distress under rolling contact

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