Advances in Boundary Lubrication

A special issue of Lubricants (ISSN 2075-4442).

Deadline for manuscript submissions: closed (15 February 2024) | Viewed by 12548

Special Issue Editor


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Guest Editor
Automotive Development Centre (ADC), Institute for Vehicle System & Engineering (IVeSE), Universiti Teknologi Malaysia, Skudai 81310, Johor, Malaysia
Interests: automotive tribology; biolubrication; lubrication science; waste valorisation; mathematical modelling

Special Issue Information

Dear Colleagues,

In machine elements, rough surface contacts are often not dry and are lubricated by thin boundary films. The surface roughness effect could be significantly reduced with advanced precision engineering. Hence, thin boundary lubricant films remain the last barrier preventing direct metal-to-metal interaction. Such interactions could lead to an undesirable drop in machine element efficiencies. In preventing this, the boundary lubrication performance can be enhanced by introducing suitable additives that could adsorb (either physically or chemically) onto the surface to form thin protective films. The additives often involve molecules with active boundary elements or nanoparticles that could impart solid lubrication at a molecular level. More importantly, the additives must be relevant to the application, which might require sulfur- or phosphorous-free lubrication. Thus, it is essential to elucidate the effect of boundary lubricant additivation and the mechanisms that give rise to boundary lubrication.

This Special Issue intends to share advances in the design/synthesis of additives, characterization, optimization, and other novel aspects in boundary lubrication. It covers studies involving the adoption of advanced and green materials and elucidating their boundary lubrication mechanisms. Both theoretical and experimental investigations are highly welcome.

Dr. William W. F. Chong
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Lubricants is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • boundary friction
  • anti-wear
  • thin film
  • additives
  • nanoparticles
  • advanced materials
  • green lubricant
  • adsorption
  • modelling
  • nanotribology

Published Papers (8 papers)

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Research

19 pages, 15266 KiB  
Article
Coarse-Grained Molecular Dynamics Simulations of Organic Friction Modifier Adsorption on Rough Surfaces under Shear
by Jiahao Tang, William Woei Fong Chong and Hedong Zhang
Lubricants 2024, 12(2), 30; https://doi.org/10.3390/lubricants12020030 - 24 Jan 2024
Viewed by 1196
Abstract
Reducing friction energy losses is crucial in mechanical systems, often achieved through lubrication strategies employing friction modifiers. These additives adsorb onto surfaces, forming boundary film to prevent solid–solid contacts. However, atomistic simulation techniques used to study these additives often ignore surface roughness due [...] Read more.
Reducing friction energy losses is crucial in mechanical systems, often achieved through lubrication strategies employing friction modifiers. These additives adsorb onto surfaces, forming boundary film to prevent solid–solid contacts. However, atomistic simulation techniques used to study these additives often ignore surface roughness due to high computational cost. This study addresses this gap by employing Coarse-Grained Molecular Dynamics (CG MD) to investigate the impact of surface roughness on the adsorption of Organic Friction Modifiers (OFMs) under shear. Traditional self-diffusion methods prove inadequate for determining the damping coefficients in CG models because of strong OFM adsorption effects. Therefore, shear-induced motion is introduced for the coefficient determination. The simulation reveals that a symmetrical model (identical opposing surfaces) shows OFM slip, desorption, and re-adsorption trends on rough surfaces, while an asymmetrical model (smooth cylinder on a flat surface) demonstrates increased adsorption on rough flat surfaces (up to 60.9%) compared to smooth flat surfaces under similar shearing conditions. However, rough flat surfaces with a smaller wavelength (6 nm) exhibit faster OFM desorption along the asperity region, up to four times more than a 24 nm wavelength surface. This research emphasizes the importance of considering surface roughness in simulating OFM behavior for lubrication applications. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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20 pages, 10260 KiB  
Article
Predicting Wear under Boundary Lubrication: A Decisive Statistical Study
by Bernd Goerlach, Walter Holweger, Lalita Kitirach and Joerg Fliege
Lubricants 2023, 11(12), 514; https://doi.org/10.3390/lubricants11120514 - 4 Dec 2023
Viewed by 1602
Abstract
The forthcoming revolution in mobility and the use of lubricants to ensure ecological friendliness intensifies the pressure on tribology for predictors in new life cycles, mainly addressing wear. The current paper aims to obtain such predictors by studying how the wear processes that [...] Read more.
The forthcoming revolution in mobility and the use of lubricants to ensure ecological friendliness intensifies the pressure on tribology for predictors in new life cycles, mainly addressing wear. The current paper aims to obtain such predictors by studying how the wear processes that occur in a standard FE8 bearing test rig under thin film lubrication are conducted by the properties of the lubricant rather than simple viscosity parameters. Assuming that the activity of a lubricant with respect to the temperature, surface, and chemicals is a matter of its chemical potential, the results show that the nature of the base oil is a key parameter, apart from the chemical structure of the additives. Moreover, it becomes clear that chemical predictors are changing by altering the conditions they are exposed to. As an important result, the lubricant is effective in the prevention of wear if it has the capacity to uptake and transmit electrical charges due to its polarisability during a wear process. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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15 pages, 1670 KiB  
Article
A Methodological Approach to Assessing the Tribological Properties of Lubricants Using a Four-Ball Tribometer
by Tareq M. A. Al-Quraan, Fadi Alfaqs, Jamil Haddad, Viktor Vojtov, Anton Voitov, Andrey Kravtsov, Oleksandr Miroshnyk and Andrii Kondratiev
Lubricants 2023, 11(11), 457; https://doi.org/10.3390/lubricants11110457 - 25 Oct 2023
Cited by 1 | Viewed by 1346
Abstract
Based on the analysis of standards for the testing of lubricants, both liquid and plastic, on a four-ball tribometer, and the analysis of the parameters by which lubricants are evaluated, this paper proposes a methodology and an integral parameter for the estimation of [...] Read more.
Based on the analysis of standards for the testing of lubricants, both liquid and plastic, on a four-ball tribometer, and the analysis of the parameters by which lubricants are evaluated, this paper proposes a methodology and an integral parameter for the estimation of tribological properties. The methodological approach proposed in this paper allows for the integration of a variety of parameters provided in the standards for the testing of lubricants into one indicator. Herein, we show that the developed technique is based on the energy approach and takes into account the specific wear work of the test material (steel balls) in the lubricating medium to be investigated. The results of laboratory tests of a wide range of lubricants are presented: hydraulic fluids, motor and transmission oils of various purposes and classifications. It is shown that the magnitude of the integral parameter can be used to assess the effectiveness of anti-wear and anti-scuff additives in base lubricants, as well as the ranges of their applications. This allows for differentiation and quantitative evaluation of the effectiveness of such additives. The obtained results allow us to state that all tests according to the developed method are reproducible and homogeneous, which is confirmed using the Cochran criterion. The coefficient of variation during testing does not exceed 18%. We show that the presented methodology and the integral parameter can be used in the first stage of the laboratory selection tests of new lubricants and additives of various origins, reducing the costs of their development and implementation. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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19 pages, 4844 KiB  
Article
Tribological, Oxidation and Thermal Analysis of Advanced Microwave–Hydrothermal Synthesised Ti3C2Tx MXene as Additives in Outboard Engine Oil
by Haizum Aimi Zaharin, Mariyam Jameelah Ghazali, Mohammad Khalid, Thachnatharen Nagarajan, Wong Weng Pin, Farah Ezzah, Ong Gerard, Rashmi Walvekar and Abdul Khaliq Rasheed
Lubricants 2023, 11(6), 264; https://doi.org/10.3390/lubricants11060264 - 16 Jun 2023
Cited by 1 | Viewed by 1518
Abstract
In today’s fast, globalised world, lubrication has become essential in enhancing engine efficiency, including in the marine sector. While the number of fishing vessels increased, so did the environmental pollution issues, due to inefficient engines. An outboard engine oil’s tribological, oxidation and thermal [...] Read more.
In today’s fast, globalised world, lubrication has become essential in enhancing engine efficiency, including in the marine sector. While the number of fishing vessels increased, so did the environmental pollution issues, due to inefficient engines. An outboard engine oil’s tribological, oxidation and thermal conductivity behaviour play a crucial role in improving the quality of an outboard engine’s life. In this research, Ti3C2Tx MXene nanoparticles with different interlayer spacing were synthesised via an advanced microwave–hydrothermal approach. Later, the nanoparticles were dispersed in TC-W outboard engine oil to formulate the Ti3C2Tx MXene nanolubricant with different concentrations. The results show that nanolubricant with a 0.01 wt.% Ti3C2Tx MXene concentration with higher interlayer spacing reduced the coefficient of friction, and the average wear scar diameter by 14.5% and 6.3%, respectively, compared to the base oil. Furthermore, the nanolubricant with a 0.01 wt.% concentration of the Ti3C2Tx MXene nanoparticle showed an improvement of 54.8% in oxidation induction time compared to the base oil. In addition, MXene nanolubricant established a more than 50% improvement in thermal conductivity compared to the base oil. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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19 pages, 4638 KiB  
Article
Different Behaviors of Friction in Open and Closed Forging Test Utilizing Palm Oil-Based Lubricants
by Aiman Yahaya, Syahrullail Samion, Ummikalsom Abidin and Mohd Kameil Abdul Hamid
Lubricants 2023, 11(3), 114; https://doi.org/10.3390/lubricants11030114 - 6 Mar 2023
Cited by 3 | Viewed by 1243
Abstract
Increasing demand for manufactured goods in industries such as automobiles, electronics, construction, and aerospace has motivated researchers to develop sustainable manufacturing processes. Most metal-forming lubricants are not eco-friendly; they may cause substantial chemical emissions and constitute a community threat. Bio-oil lubricants are seen [...] Read more.
Increasing demand for manufactured goods in industries such as automobiles, electronics, construction, and aerospace has motivated researchers to develop sustainable manufacturing processes. Most metal-forming lubricants are not eco-friendly; they may cause substantial chemical emissions and constitute a community threat. Bio-oil lubricants are seen as possible replacements for mineral oil-based lubricants. Computational modelling of the forging process uses the finite element method to accelerate and improve design. This research intends to act as a case study and demonstrate how friction behaves differently in open-closed forging tests of different palm oil derivatives. The relationship between the different types of friction was studied using a cold forging test in conjunction with the development of a Coulomb–Tresca friction model. From the results, it can be shown that the friction behavior for the closed forging test (CFT) and the ring compression test (RCT) differs; the CFT exhibits a diversified friction adaptation, while the RCT exhibits a single friction adaptation. From both tests, palm stearin (PS) shows the lowest friction behavior where at RCT the friction is estimated at m = 0.10/μ = 0.05 and the CFT has a varied friction and the average friction is estimated at m = 0.352/μ = 0.1626. On the other hand, commercial metal-forming oil (CMFO) shows the highest lubrication sample in friction, where the value of friction is similar to the no lubricant sample (NA-O), which is (m = 0.45/μ = 0.1875) on the RCT test and (m = 0.424/μ = 0.1681) on the CFT test. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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15 pages, 6645 KiB  
Article
Effect of Cu-Doped Carbon Quantum Dot Dispersion Liquid on the Lubrication Performance of Polyethylene Glycol
by Shusheng Liu, Xiuqian Yu, Enzhu Hu, Enhao Su, Yanjie Chen, Jianping Wang, Kunhong Hu, Yong Xu, Xianguo Hu and Hua Zhong
Lubricants 2023, 11(2), 86; https://doi.org/10.3390/lubricants11020086 - 16 Feb 2023
Cited by 3 | Viewed by 1541
Abstract
Energy saving and reduced consumption of key materials such as bearings in high-end equipment can be realized by synthesizing a new lubricating functional additive, copper-doped carbon quantum dot dispersion liquid (Cu-CQDs) via hydrothermal reaction with glycerol, cupric chloride dihydrate, and choline chloride as [...] Read more.
Energy saving and reduced consumption of key materials such as bearings in high-end equipment can be realized by synthesizing a new lubricating functional additive, copper-doped carbon quantum dot dispersion liquid (Cu-CQDs) via hydrothermal reaction with glycerol, cupric chloride dihydrate, and choline chloride as raw materials. The influence of the dispersion liquid containing Cu-CQDs nanoparticles on the lubricating properties of polyethylene glycol (PEG200) was investigated on a four-ball friction tester. The wear scars of steel balls after friction were analyzed using a scanning electron microscope accompanied by energy dispersive spectroscopy (SEM/EDS), photoelectron microscopy, and Raman spectroscopy. The results revealed the friction and wear mechanism of Cu-CQDs. Cu-CQDs dispersion liquid can significantly enhance the lubrication performance of PEG. The average friction coefficient of PEG containing 2.0 wt% Cu-CQDs dispersion liquid was 40.99% lower than that of pure PEG. The friction and wear mechanism can be ascribed to friction, inducing Cu-CQDs to participate in the formation of boundary lubricating film, resulting in a low friction coefficient and wear scar diameter. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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16 pages, 1076 KiB  
Article
Methodological Approach in the Simulation of the Robustness Boundaries of Tribosystems under the Conditions of Boundary Lubrication
by Tareq M. A. Al-Quraan, Fadi Alfaqs, Ibrahim F. S. Alrefo, Viktor Vojtov, Anton Voitov, Andrey Kravtsov, Oleksandr Miroshnyk, Andrii Kondratiev, Pavel Kučera and Václav Píštěk
Lubricants 2023, 11(1), 17; https://doi.org/10.3390/lubricants11010017 - 4 Jan 2023
Cited by 1 | Viewed by 1464
Abstract
In the presented work, a methodical approach was developed for determining rational operation modes of tribosystems, taking into account their design. This approach makes it possible in the designing stage, according to the predicted operating modes, to calculate the limits and margins of [...] Read more.
In the presented work, a methodical approach was developed for determining rational operation modes of tribosystems, taking into account their design. This approach makes it possible in the designing stage, according to the predicted operating modes, to calculate the limits and margins of stable work in operation. The definition of the robustness of the tribosystem and the criteria for assessing the robustness are formulated based on the theory of stability of technical systems. It is shown that such a methodical approach allows for determining the modes of the rational operation of the designed structures without damaging the friction surfaces. Experimental studies have proven that not all designs of tribosystems lose stability due to the appearance of friction surface burrs. There are designs where the loss of stability occurs upon the appearance of accelerated wear. The developed criteria take into account two options for the loss of stability. An experimental verification of the modes of loss of stability of tribosystems was performed by the appearance of a burr or the beginning of accelerated wear with the calculated values of the robustness criteria. The obtained results allow us to conclude that the modeling error is within 8.3–18.7%, which is a satisfactory result in the study of friction and wear processes. Robustness criteria is based on the coefficient of friction RRf and wear rate RRI, and must be used when designing new constructions of tribosystems. Theoretical calculations of such criteria and the dependence of their change on changing the predicted operating modes will allow for justifying rational operating modes within their stability. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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23 pages, 1250 KiB  
Article
Boundary Lubricity of Vegetable-Oil-Derived Trimethylolpropane (TMP) Ester
by Chiew Tin Lee, Mei Bao Lee, William Woei Fong Chong, Jo-Han Ng, King Jye Wong and Cheng Tung Chong
Lubricants 2022, 10(12), 346; https://doi.org/10.3390/lubricants10120346 - 2 Dec 2022
Cited by 2 | Viewed by 1931
Abstract
Vegetable-oil-based biolubricants are an excellent alternative to conventional lubricants. Instead of focusing on novel feedstocks, these biolubricants should be further elucidated based on their fatty acid composition, which influences their tribological properties. Therefore, the study utilises gene expression programming (GEP) to derive a [...] Read more.
Vegetable-oil-based biolubricants are an excellent alternative to conventional lubricants. Instead of focusing on novel feedstocks, these biolubricants should be further elucidated based on their fatty acid composition, which influences their tribological properties. Therefore, the study utilises gene expression programming (GEP) to derive a boundary lubricity model for vegetable-oil-derived trimethylolpropane (TMP) esters, considering the fatty acid composition (saturation and monounsaturation levels), load and speed. Neat vegetable oil and blends from seven feedstocks are selected following a wide range of fatty acid profiles to synthesise TMP esters using a two-stage transesterification process. The TMP esters are spin-coated on wear discs that are subsequently rotated against a ball using a purpose-built tribometer. The frictional performance of the TMP esters with balanced saturation and monounsaturation levels of fatty acid are measured to improve it at higher speeds. The GEP model is statistically evaluated by adopting the friction data, a showing good generalisation and predictability capability. The model demonstrates that friction decreases with increasing saturation levels of the TMP ester. The GEP model for vegetable oil TMP esters allows for the tribological performance prediction of TMP esters following the fatty acid profile, providing a platform to optimise such biolubricant for desired applications. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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