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Hultqvist, T., Vrček, A., Marklund, P., Prakash, B. & Larsson, R. (2020). Transient analysis of surface roughness features in thermal elastohydrodynamic contacts. Tribology International, 141, Article ID 105915.
Open this publication in new window or tab >>Transient analysis of surface roughness features in thermal elastohydrodynamic contacts
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2020 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 141, article id 105915Article in journal (Refereed) Published
Abstract [en]

Understanding the influence of surface roughness in elastohydrodynamically lubricated (EHL) contacts is essential to improve durability and friction performance of machine elements employing non-conformal contacting surfaces. In this work, the transient event of a surface feature passing through a thermal EHL line contact operating under different sliding conditions is investigated with the purpose of providing a deeper understanding of surface roughness influence. This is achieved by solving the EHL problem in space and time. It was seen that sliding influences the temperature rise in the contact significantly, especially in the vicinity of the asperity. However, due to the characteristic behaviour of EHL contacts, the local temperature rise mainly influence the film thickness during exiting of inlet perturbations and the asperity.

Place, publisher, year, edition, pages
Elsevier, 2020
Keywords
Thermal elastohydrodynamic lubrication, Transient conditions, Surface features, Numerical modelling
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-75817 (URN)10.1016/j.triboint.2019.105915 (DOI)2-s2.0-85071778495 (Scopus ID)
Funder
Swedish Energy Agency, 41215-1
Note

Validerad;2019;Nivå 2;2019-09-10 (johcin)

Available from: 2019-09-03 Created: 2019-09-03 Last updated: 2019-09-20Bibliographically approved
Martin del Campo Barraza, S., Schnabel, S., Sandin, F. & Marklund, P. (2019). Detection of particle contaminants in rolling element bearings with unsupervised acoustic emission feature learning. Tribology International, 132, 30-38
Open this publication in new window or tab >>Detection of particle contaminants in rolling element bearings with unsupervised acoustic emission feature learning
2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 132, p. 30-38Article in journal (Refereed) Published
Abstract [en]

The detection of contaminants in the lubricant of rolling element bearings using acoustic emission signals is a challenging problem, in particular at high rotational speeds. This problem calls for new analysis methods beyond the conventional amplitude- and frequency-based methods. Feature learning is successfully used in the machine learning field to characterize complex signals. Here we use an unsupervised feature learning approach to distinguish acoustic emission signals. We investigate the repetition rates of features identified with shift-invariant dictionary learning and find that the signature of contaminated lubricant is significantly stronger than the effect on conventional condition indicators like the RMS and the enveloped RMS at rotational speeds above 300 rpm and up to 3000 rpm.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Acoustic emission, Contamination, Dictionary learning, Unsupervised feature learning
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear) Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Machine Elements; Industrial Electronics
Identifiers
urn:nbn:se:ltu:diva-63112 (URN)10.1016/j.triboint.2018.12.007 (DOI)000456758700004 ()2-s2.0-85058395512 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-01-03 (svasva)

Available from: 2017-04-21 Created: 2017-04-21 Last updated: 2019-05-14Bibliographically approved
Björling, M., Habchi, W., Bair, S., Larsson, R. & Marklund, P. (2019). Erratum: Towards the true prediction of EHL friction (ed.). Tribology International, 133, 297-297
Open this publication in new window or tab >>Erratum: Towards the true prediction of EHL friction
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2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 133, p. 297-297Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-73121 (URN)10.1016/j.triboint.2018.10.018 (DOI)
Note

Erratum in: Tribology International, vol. 66, p.19-26, DOI:10.1016/j.triboint.2013.04.008

Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2019-03-06Bibliographically approved
Hultqvist, T., Vrček, A., Prakash, B., Marklund, P. & Larsson, R. (2019). Influence of lubricant pressure response on sub-surface stress in elastohydrodynamically lubricated finite line contacts. Journal of tribology, 141(3), Article ID 031502.
Open this publication in new window or tab >>Influence of lubricant pressure response on sub-surface stress in elastohydrodynamically lubricated finite line contacts
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2019 (English)In: Journal of tribology, ISSN 0742-4787, E-ISSN 1528-8897, Vol. 141, no 3, article id 031502Article in journal (Refereed) Published
Abstract [en]

In order to adapt to increasingly stringent CO2 regulations, the automotive industry must develop and evaluate low cost, low emission solutions in the powertrain technology. This often implies increased power density and the use of low viscosity oils, leading to additional challenges related to the durability of various machine elements. Therefore, an increased understanding of lubricated contacts becomes important where oil viscosity-pressure and compressibility-pressure behaviour have been shown to influence the film thickness and pressure distribution in EHL contacts, further influencing the durability. In this work, a finite line EHL contact is analysed with focus on the oil compressibility- and viscositypressure response, comparing two oils with relatively different behaviour and its influence on subsurface stress concentrations in the contacting bodies. Results indicate that increased pressure gradients and pressure spikes, and therefore increased localized stress concentrations, can be expected for stiffer, less compressible oils, which under transient loading conditions not only affect the outlet but also the edges of the roller

Place, publisher, year, edition, pages
ASME Press, 2019
Keywords
Elastohydrodynamic lubrication, Finite line contacts, Sub-surface stress, Transient loading
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-71551 (URN)10.1115/1.4041733 (DOI)000457029800007 ()2-s2.0-85057759100 (Scopus ID)
Funder
Swedish Energy Agency, 41215-1
Note

Validerad;2018;Nivå 2;2018-12-07 (johcin)

Available from: 2018-11-12 Created: 2018-11-12 Last updated: 2019-09-13Bibliographically approved
Vrček, A., Hultqvist, T., Baubet, Y., Björling, M., Marklund, P. & Larsson, R. (2019). Micro-pitting and wear assessment of engine oils operating under boundary lubrication conditions. Tribology International, 129, 338-346
Open this publication in new window or tab >>Micro-pitting and wear assessment of engine oils operating under boundary lubrication conditions
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2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 129, p. 338-346Article in journal (Refereed) Published
Abstract [en]

Current state-of-the-art engine oils tend to enhance micro-pitting damage in rolling contacts under certain operating conditions. ZDDP anti-wear additive was shown to promote such behavior. However, in order to optimize an engine oil formulation for rolling contacts, further studies are needed to assess engine oils in terms of micro-pitting and wear damage. This investigation studies the micro-pitting and wear performance of a number of engine oils for rolling contacts in a ball-on-disc configuration under conditions prevalent in crankshaft roller bearing applications. Based on the results it was concluded that an engine oil containing higher blend of PAO base oil compared to the oil mixture of Group III and PAO has a lower tendency towards micro-pitting and wear.

Place, publisher, year, edition, pages
Elsevier, 2019
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-70731 (URN)10.1016/j.triboint.2018.08.032 (DOI)000447575600028 ()2-s2.0-85052642062 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-09-24 (inah)

Available from: 2018-09-03 Created: 2018-09-03 Last updated: 2018-11-01Bibliographically approved
Vrček, A., Hultqvist, T., Baubet, Y., Björling, M., Marklund, P. & Larsson, R. (2019). Micro-Pitting and Wear Assessment of PAO vs Mineral-Based Engine Oil Operating under Mixed Lubrication Conditions: Effects of Lambda, Roughness Lay and Sliding Direction. Lubricants, 7(5), Article ID 42.
Open this publication in new window or tab >>Micro-Pitting and Wear Assessment of PAO vs Mineral-Based Engine Oil Operating under Mixed Lubrication Conditions: Effects of Lambda, Roughness Lay and Sliding Direction
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2019 (English)In: Lubricants, E-ISSN 2075-4442, Vol. 7, no 5, article id 42Article in journal (Refereed) Published
Abstract [en]

Under certain operating conditions, rolling contacts have been shown to experience some challenges when lubricated with engine oils containing zinc dialkyldithophosphate (ZDDP) anti-wear additive. In order to better understand the main damage mechanisms during various operating conditions, further studies are needed. This article studies micro-pitting and wear damages of bearing steel surfaces under mixed lubrication conditions in a ball-on-disc setup, lubricated with different engine oils. Based on the results, micro-pitting and wear damage is shown to be highly case-dependent. In general, PAO-based engine oil tends to eliminate micro-pitting damage compared to mineral-based engine oil at less severe lubricating conditions. Moreover, a critical lambda was found for both oils, where the highest micro-pitting damage was observed. 

Place, publisher, year, edition, pages
MDPI, 2019
Keywords
micro-pitting, ZDDP, mild wear, surface-initiated fatigue
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-75059 (URN)10.3390/lubricants7050042 (DOI)000470959700003 ()2-s2.0-85066431252 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-06-27 (johcin)

Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-06-27Bibliographically approved
Vrček, A., Hultqvist, T., Baubet, Y., Marklund, P. & Larsson, R. (2019). Micro-pitting Damage of Bearing Steel Surfaces under Mixed Lubrication Conditions: Effects of Roughness, Hardness and ZDDP Additive. Tribology International, 138, 239-249
Open this publication in new window or tab >>Micro-pitting Damage of Bearing Steel Surfaces under Mixed Lubrication Conditions: Effects of Roughness, Hardness and ZDDP Additive
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2019 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 138, p. 239-249Article in journal (Refereed) Published
Abstract [en]

Micro-pitting presents a failure of the rolling/sliding contact metal asperities operating under boundary/mixed lubrication conditions. The studies have shown that micro-pitting failure competes with mild wear and that lubricant additives can have either detrimental or beneficial effects on micro-pitting evolution. This article describes a methodology to investigate micro-pitting damage on bearing steels using a twin-disc machine to better represent mechanical components, i.e. bearings, crankshafts, etc. In addition, effects of roughness, hardness and the ZDDP additive are presented and discussed. A sufficient hardness difference can completely eliminate micro-pitting damage mode. Furthermore, the presence of ZDDP anti-wear additive in fully formulated engine oil was shown to protect rougher surfaces and promote wear on smoother surfaces, thus completely eliminating the micro-pitting damage mode.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Micro-pitting, Mild wear, Hardness, ZDDP
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-75061 (URN)10.1016/j.triboint.2019.05.038 (DOI)000484647200024 ()2-s2.0-85066476632 (Scopus ID)
Note

Validerad;2019;Nivå 2;2019-06-27 (johcin)

Available from: 2019-06-27 Created: 2019-06-27 Last updated: 2019-09-27Bibliographically approved
Strömbergsson, D., Marklund, P., Berglund, K., Saari, J. & Thomson, A. (2019). Mother wavelet selection in the discrete wavelet transform for condition monitoring of wind turbine drivetrain bearings. Wind Energy, 22(11), 1581-1592
Open this publication in new window or tab >>Mother wavelet selection in the discrete wavelet transform for condition monitoring of wind turbine drivetrain bearings
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2019 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 11, p. 1581-1592Article in journal (Refereed) Published
Abstract [en]

Although the discrete wavelet transform has been used for diagnosing bearing faults for two decades, most work in this field has been done with test rig data. Since field data starts to be made more available, there is a need to shift into application studies.

The choice of mother wavelet, ie, the predefined shape used to analyse the signal, has previously been investigated with simulated and test rig data without consensus of optimal choice in literature. Common between these investigations is the use of the wavelet coefficients' Shannon entropy to find which mother wavelet can yield the most useful features for condition monitoring.

This study attempts to find the optimal mother wavelet selection using the discrete wavelet transform. Datasets from wind turbine gearbox accelerometers, consisting of enveloped vibration measurements monitoring both healthy and faulty bearings, have been analysed. The bearing fault frequencies' excitation level has been analysed with 130 different mother wavelets, yielding a definitive measure on their performance. Also, the applicability of Shannon entropy as a ranking method of mother wavelets has been investigated.

The results show the discrete wavelet transforms ability to identify faults regardless of mother wavelet used, with the excitation level varying no more than 4%. By analysing the Shannon entropy, broad predictions to the excitation level could be drawn within the mother wavelet families but no direct correlation to the main results. Also, the high computational effort of high order Symlet wavelets, without increased performance, makes them unsuitable.

Place, publisher, year, edition, pages
John Wiley & Sons, 2019
Keywords
bearing failure, condition monitoring, discrete wavelet transform, mother wavelet selection, wind turbine field measurements
National Category
Other Civil Engineering Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements; Operation and Maintenance
Identifiers
urn:nbn:se:ltu:diva-75777 (URN)10.1002/we.2390 (DOI)000480192400001 ()
Note

Validerad;2019;Nivå 2;2019-12-06 (johcin)

Available from: 2019-08-30 Created: 2019-08-30 Last updated: 2019-12-06Bibliographically approved
Björling, M., Habchi, W., Bair, S., Larsson, R. & Marklund, P. (2018). Correction to: Friction reduction in elastohydrodynamic contacts by thin-layer thermal insulation (ed.) [Letter to the editor]. Tribology letters, 66(4), 1-1
Open this publication in new window or tab >>Correction to: Friction reduction in elastohydrodynamic contacts by thin-layer thermal insulation
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2018 (English)In: Tribology letters, ISSN 1023-8883, E-ISSN 1573-2711, Vol. 66, no 4, p. 1-1Article in journal, Letter (Refereed) Published
Abstract [en]

The original version of this article unfortunately contained a mistake. The correct information is given below. [ABSTRACT FROM AUTHOR]  Copyright of Tribology Letters is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-71140 (URN)10.1007/s11249-018-1079-x (DOI)
Available from: 2018-10-08 Created: 2018-10-08 Last updated: 2018-10-08Bibliographically approved
Dittes, N., Pettersson, A., Marklund, P., Lang, D. & Lugt, P. M. (2018). Dielectric Thermoscopy Characterization of Water Contaminated Grease. Tribology Transactions, 74(3), 60-73
Open this publication in new window or tab >>Dielectric Thermoscopy Characterization of Water Contaminated Grease
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2018 (English)In: Tribology Transactions, ISSN 1040-2004, E-ISSN 1547-397X, Vol. 74, no 3, p. 60-73Article in journal (Refereed) Published
Abstract [en]

The temperature dependence on the dielectric properties of water-contaminated grease is investigated in this article. The purpose of this investigation was to identify the dielectric properties that could be measured to differentiate varying levels of water contamination in calcium sulfonate complex (CaS-X) grease with three different test cells with the purpose of eventually developing a grease condition sensor. Measuring the change in dielectric constant over a small temperature change yielded useful estimations of water content and amount of grease where the added water content ranged from 0.22% to about 5.5%. Additionally, other parameters such as incomplete fill/coverage of the sensors were investigated as a prestudy. The results from this set of experiments show that the measurement has potential to be developed into a condition monitoring sensor in the future.

Place, publisher, year, edition, pages
Taylor & Francis, 2018
National Category
Tribology (Interacting Surfaces including Friction, Lubrication and Wear)
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-65054 (URN)10.1080/10402004.2017.1333664 (DOI)000444573200001 ()2-s2.0-85045005667 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-04-16 (andbra)

Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2019-09-14Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-3157-4632

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