Lubricants

Research

19 pages, 15266 KiB

Open AccessArticle

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 1735

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

Open AccessArticle

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 2363

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

Open AccessArticle

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 1936

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

Open AccessArticle

Tribological, Oxidation and Thermal Analysis of Advanced Microwave–Hydrothermal Synthesised Ti₃C₂T_x 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 3 | Viewed by 2168

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, Ti₃C₂T_x 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 Ti₃C₂T_x MXene nanolubricant with different concentrations. The results show that nanolubricant with a 0.01 wt.% Ti₃C₂T_x 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 Ti₃C₂T_x 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

Open AccessArticle

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 5 | Viewed by 1603

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

Open AccessArticle

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 4 | Viewed by 2011

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

Open AccessArticle

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 1831

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 RR_f and wear rate RR_I, 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

Open AccessArticle

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 4 | Viewed by 2489

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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