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

Deadline for manuscript submissions: 30 November 2025 | Viewed by 8432

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Dr. Marcus Björling

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Guest Editor

Division of Machine Elements, Department of Engineering Sciences and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden
Interests: contact mechanics; tribology; elastohydrodynamic lubrication
Special Issues, Collections and Topics in MDPI journals

Dr. Deepak K. Prajapati

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Guest Editor

Division of Machine Elements, Department of Engineering Sciences and Mathematics, Luleå University of Technology, 97187 Luleå, Sweden
Interests: machine learning in tribology; numerical modeling of wear; rolling contact fatigue

Special Issue Information

Dear Colleagues,

In the 21st century, applications of tribology can be observed in many fields, such as automotives, biomechanics, manufacturing, renewable energy, aviation, healthcare, transportation, and many more in daily human activities. In general, two types of lubricated tribological contacts are found: conformal and counterformal (non-conformal or concentrated) in various machine elements, for instance, gears, seals, hip and knee joints, bearings (rolling element bearings and journal bearings), cam/followers, piston/ring liner conjunctions, etc. Primarily, these machine components are lubricated using solid or liquid lubricants to reduce friction and wear and, consequently, increase energy efficiency and the service life of machine components. Due to the large progress in modern computer efficiency, tribological contacts nowadays can be successfully analyzed by performing macro-to-atomic-level simulations. Recent advances in the analysis of aforementioned tribological contacts include, but are not limited to: (a) the use of AI/ML for the analysis of lubricated tribological contacts; (b) the development of novel coatings, textures, and heat treatment methods; (c) the analysis of lubricated tribological contacts under the influence of electric current or electrical discharge; and (d) the development of sustainable liquid lubricants to enhance the efficiency of tribological contacts.

This Special Issue deals with recent advances in lubricated tribological contacts and papers dealing with the aforementioned topics or related topics that can increase the knowledge of lubricated tribological mechanisms. Contributions from both academic and industrial research are welcome.

We are looking forward to receiving your submissions.

Dr. Marcus Björling
Dr. Deepak K. Prajapati
Guest Editors

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

lubricated tribological contacts
rough contact mechanics
coatings
tribology
lubrication

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Published Papers (11 papers)

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Research

14 pages, 10258 KiB

Open AccessArticle

Atomic Simulation of Wear and Slip Behavior Between Monocrystalline Silicon and 6H-SiC Friction Pair

by Jiansheng Pan, Jianwei Wu, Daiyi Lei, Huan Liu, Pengyue Zhao, Bo Zhao, Jiang Liu and Qingshan Yang

Lubricants 2025, 13(4), 147; https://doi.org/10.3390/lubricants13040147 - 27 Mar 2025

Viewed by 150

Abstract

The slip mechanism between the chunk and wafer during high-speed dynamic scanning of the extreme ultraviolet lithography (EUV) motion stage remains unclear. Considering real-machined roughness, molecular dynamics (MD) simulations were performed to investigate the nanotribological behavior of 6H-SiC sliders on single-crystal silicon substrates. The effects of sinusoidal asperity parameters and normal loads on wear and slip were systematically analyzed. Results indicate that, for friction between sinusoidal asperities and ideal flat surfaces, the amplitude of surface parameters exhibits negligible influence on friction. In contrast, reduced normal loads and lower periods significantly increase both friction force and coefficient of friction (COF). Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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13 pages, 2323 KiB

Open AccessArticle

Effects of Gait Patterns on the Viscoelastic Squeeze-Film Lubrication of Hip Replacements

by Xianjiu Lu, Manyu Liang, Qingen Meng and Zhongmin Jin

Lubricants 2025, 13(3), 131; https://doi.org/10.3390/lubricants13030131 - 18 Mar 2025

Viewed by 186

Abstract

The present study investigated the influence of various gait patterns on the viscoelastic squeeze-film lubrication characteristics of UHMWPE-based artificial hip replacements. Different gait loads (slow walking, normal walking, slow running) measured by Bergmann et al. were adopted in the present lubrication simulation. A comprehensive squeeze-film lubrication model for UHMWPE hip replacement was developed and numerically solved to determine the spatial distributions of film thickness and pressure profiles. The results showed that physiological loads had a negligible impact on the minimum film thicknesses during the stand phases. However, they significantly enhanced the minimum film thicknesses in both the elastic (1.16–1.31 times) and viscoelastic models (1.43–2.85 times) during the swing phases when compared to constant loads. This improvement was notably more pronounced in the viscoelastic model than in the elastic model. The slow-running gait, characterized by its higher frequency, demonstrated a more pronounced enhancement in squeeze-film lubrication of UHMWPE artificial hip joints compared to both normal-walking and slow-walking gaits. Specifically, the minimum film thicknesses during slow running were found to be 1.15 to 1.35 times greater than those observed during normal walking and 1.33 to 1.66 times greater than those during slow walking, highlighting the superior lubrication performance in the slow running case. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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16 pages, 6195 KiB

Open AccessArticle

A Mechanics Model for Contact with Rough Surface Considering the Interaction of Micro-Asperity Bodies

by Yazhou Mao, Qingxin Hu, Yingying Yu, Shaolin Shi, Jiaming Pei, Zichen Li and Linyuan Wang

Lubricants 2025, 13(3), 96; https://doi.org/10.3390/lubricants13030096 - 20 Feb 2025

Viewed by 354

Abstract

In order to evaluate contact characteristics, a modified contact model was proposed considering the deformation characteristics of asperity bodies, and the variation rules of wear rate with fractal dimension, material property constant and debris probability were established. The results show that the actual contact area increases with an increase in load when the surface topography is constant, whereas the contact area decreases with an increase in characteristic scale coefficient if the fractal dimension or load is constant. For running-in wear, the wear rate increases with an increase in surface profile parameters under the same contact area. In addition, the wear rate increases with an increase in actual contact area when the surface profile parameter is constant. Regarding abrasive wear, the wear rate is the smallest when the fractal dimension is 1.6. The wear rate increases with an increase in contact area under the same characteristic scale coefficient, but decreases with an increase in the characteristic scale coefficient under the same contact area, and the smaller the material constant and the larger the probability constant, the higher the wear rate. The establishment of this model provides a basis for further study of the tribological properties of the contact surface. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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17 pages, 15072 KiB

Open AccessArticle

Effect of Pipe Wall Wear Defects on the Flow Characteristics of Slurry Shield Discharge Pipe

by Yingran Fang, Xinggao Li, Xingchun Li, Yidong Guo and Hongzhi Liu

Lubricants 2025, 13(2), 68; https://doi.org/10.3390/lubricants13020068 - 4 Feb 2025

Viewed by 618

Abstract

During slurry shield tunneling in hard rock or cobble strata, the discharge pipes suffer serve wear and damage. However, the effect mechanism of pipe wall wear defects on the flow characteristics of two-phase flow is unclear. In this study, a three-dimensional slurry particle model of pipeline transport was established using the coupled computational fluid dynamics–discrete element method (CFD-DEM) considering the pipe wall wear defect, and the typical pipeline forms of straight pipe and 90° elbow pipe were selected as the research targets. The results indicated that the localized wear defect of pipes can lead to increased inhomogeneity in the velocity distribution, generating localized low-flow zones and resulting in a reduced flow rate or stagnancy in parts of the pipe. Meanwhile, the wear defect of the pipe results in local shape changes, so that the fluid flow path through the pipe is no longer smooth, causing more vortex/turbulence and secondary flow, where an increased vortex promotes localized kinetic energy reduction and creates larger pressure losses at the elbow. In addition, for the elbow pipe without wear defect, the pressure drop of the elbow increases quadratically from an increase of 6.5% to an increase of 16.9%, with the maximum wear depth increasing from 4 mm to 19 mm. For the straight pipe without wear defect, the pressure drop of the elbow increases linearly, from an increase of 2.2% to an increase of 10.2% with the maximum wear depth increasing from 4 mm to 19 mm. The paper investigates the potential mechanism of pipe flow characteristics influenced by wear defect and provides practical guidelines for the efficient operation of a slurry shield circulating system. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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17 pages, 5487 KiB

Open AccessArticle

Friction in Cylindrical Joints

by Andrei Marius Mihalache, Vasile Merticaru, Vasile Ermolai, Oana Dodun, Gheorghe Nagiț, Adelina Hrițuc, Marius Ionuț Rîpanu and Laurențiu Slătineanu

Lubricants 2025, 13(2), 66; https://doi.org/10.3390/lubricants13020066 - 4 Feb 2025

Viewed by 555

Abstract

Cylindrical clearance joints are commonly employed in mechanisms that involve the rotation of a shaft spindle within a cylindrical sliding bearing. The intensity of the friction process in such joints is governed by several factors, including the clearance size between components, the materials of the interacting surfaces, the properties and characteristics of the lubricant, the surface roughness (asperities), and the magnitude of the relative velocity between the joint’s components. To experimentally determine the friction coefficient in cylindrical clearance joints, a custom device was designed and implemented. This device is adaptable to a universal lathe and enables the measurement of the friction coefficient under varying normal forces and relative movement speeds between the joint components. The experimental data were subjected to mathematical analysis, leading to the development of an empirical model. This model effectively characterizes the direction and intensity of the influence of various factors on the friction coefficient, accounting for the use of different lubricants. The findings provide valuable insights into optimizing cylindrical clearance joints for improved performance in practical applications. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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28 pages, 9743 KiB

Open AccessArticle

Improved Calculation of Dynamic Load Capacity for Cylindrical Roller Thrust Bearings: Numerical Update of the Lifetime Reduction Factor η for Bearings with Small and Medium Spin-to-Roll Ratios

by Paul Sauvage, Torben Terwey, Benjamin Lehmann and Georg Jacobs

Lubricants 2025, 13(2), 65; https://doi.org/10.3390/lubricants13020065 - 3 Feb 2025

Viewed by 865

Abstract

The standard procedures for calculating the lifetime of rolling bearings, defined by DIN ISO 281 and ISO/TS 16281, have been revisited in this work with a specific focus on redefining the η factor for cylindrical roller thrust bearings (CRTBs). The new η factor proposed in this study accounts for the additional spinning motion of the rolling elements on the raceway, which affects the lifetime of thrust roller bearings. By considering different spin-to-roll ratios (SRRs), the revised η factor results in a smaller lifetime reduction, improving from a 42% reduction with η = 0.85 to a 27% reduction with η = 0.91. This modification opens industrial opportunities for bearings that can handle higher loads or feature fewer or smaller rolling elements while maintaining the same lifespan target as bearings sized with the original η factor. An analytical and numerical methodology was developed to calculate the η factor for various bearing configurations. Two bearing geometries were selected to assess the influence of the SRR on bearing life. The methodology integrates calculations of the total friction coefficient, 2D and 3D stress distributions, and lifetime predictions based on subsurface-initiated fatigue failure modes. The numerical results demonstrate the impact of contact stresses and bearing kinematics on η. Although this study was based on numerical simulations, it sets the groundwork for experimental validation. Future work includes experimental testing to validate these findings, with a focus on subscale CRTBs subjected to varying γ values. Accelerated testing strategies, including higher rotational speeds and optimized lubrication, are proposed to enhance the accuracy of the results. These experiments would provide further insights into the life expectancy differences between various configurations, contributing to more precise lifetime calculations for CRTBs. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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21 pages, 7358 KiB

Open AccessArticle

Dynamic Response Analysis of Ballastless Tracks Considering the Temperature-Dependent Viscoelasticity of Cement-Emulsified Asphalt Mortar Based on a Vehicle–Track–Subgrade Coupled Model

by Yunqing Chen, Bing Wu, Linquan Yao and Xianglong Su

Lubricants 2025, 13(2), 58; https://doi.org/10.3390/lubricants13020058 - 30 Jan 2025

Viewed by 577

Abstract

This study aims to explore the dynamic response of ballastless tracks under various temperatures of the cement-emulsified asphalt (CA) mortar layer and other environmental factors. CA mortar is the key material in the ballastless track structure, exhibiting notably temperature-dependent viscoelastic properties. It can be damaged or even fail due to the continuous loads from trains. However, the dynamic behaviors of ballastless tracks considering the temperature-dependent viscoelasticity of CA mortar have been insufficiently studied. This paper captures the temperature-dependent viscoelastic characteristics of CA mortar by employing the fractional Maxwell model and applying it to finite element simulations through a Prony series. A vehicle–track–subgrade (VTS) coupled CRTS I ballastless track model, encompassing Hertz nonlinear contact and track irregularity, is established. The model is constrained symmetrically on both of the longitudinal sides, and the bottom is fixed on the infinite element boundary, which can reduce the effects of reflected waves. After the simulation outcomes in this study are validated, variations in the dynamic responses under different environmental factors are analyzed, offering a theoretical foundation for maintaining the ballastless tracks. The results show that the responses in the track subsystem will undergo significant changes as the temperature rises; a notable effect is caused by the increase in speed and fastener stiffness on the entire system; the CA mortar layer experiences the maximum stress at its edge, which makes it highly susceptible to damage in this area. The original contribution of this work is the establishment of a temperature-dependent vehicle–track–subgrade coupled model that incorporates the viscoelasticity of the CA mortar, enabling the investigation of dynamic responses in ballastless tracks. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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21 pages, 8951 KiB

Open AccessArticle

Analysis of Chaotic Features in Dry Gas Seal Friction State Using Acoustic Emission

by Shuai Zhang, Xuexing Ding, Jinlin Chen, Shipeng Wang and Lanxia Zhang

Lubricants 2025, 13(1), 40; https://doi.org/10.3390/lubricants13010040 - 20 Jan 2025

Viewed by 643

Abstract

In this study, a chaos theory-based characterization method is proposed to address the nonlinear behavior of acoustic emission (AE) signals during the startup and shutdown phases of dry gas seals. AE signals were collected through a controlled experiment at three distinct phases: startup, normal operation, and shutdown. Analysis of these signals identified a transition speed of 350 r/min between the mixed lubrication (ML) and hydrodynamic lubrication (HL) states. The maximum Lyapunov exponent, correlation dimension, K-entropy, and attractors of the AE signals throughout the operation of the dry gas seal are calculated and analyzed. The findings indicate that the chaotic features of these signals reflect the friction state of the seal system. Specifically, when the maximum Lyapunov exponent is greater than zero, the system exhibits chaotic behavior. The correlation dimension and K-entropy first increase and then decrease in boundary and hybrid lubrication states, while remaining stable in the hydrodynamic lubrication state. Attractors exhibit clustering in boundary lubrication and dispersion in mixed lubrication states. The proposed method achieves an accuracy of 98.6% in recognizing the friction states of dry gas seals. Therefore, the maximum Lyapunov exponent, correlation dimension, and K-entropy are reliable tools for characterizing friction states, while attractors serve as a complementary diagnostic feature. This approach provides a novel framework for utilizing AE signals to evaluate the friction states of dry gas seals. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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25 pages, 10155 KiB

Open AccessArticle

Effect of Surface Roughness on the Friction Moment in a Lubricated Deep Groove Ball Bearing

by Harsh Kumar, Vaibhav Gupta, Velamala Bharath, Mayank Tiwari, Surajit Kumar Paul, Lokesh Agrawal, Arendra Pal Singh and Ayush Jain

Lubricants 2024, 12(12), 443; https://doi.org/10.3390/lubricants12120443 - 11 Dec 2024

Viewed by 1507

Abstract

Deep groove ball bearings (DGBBs) are extensively utilized in industrial machinery, mechanical systems, and household appliances due to their simple design, low maintenance, and ability to operate at high speeds. A critical issue in the performance of these bearings is the power loss by internal friction torque, which adversely affects system efficiency, longevity, and reliability, particularly in demanding applications such as aviation and marine systems. The friction torque in DGBBs is influenced by factors such as load, speed, surface roughness, and lubricant viscosity, making the precise understanding of these elements essential for optimizing system efficiency. Despite its significance, the effect of surface roughness on friction torque in DGBBs remains underexplored. This paper presents an analytical model to evaluate the frictional moments resulting from interactions between the ball–race and ball–cage in lubricated, low-speed DGBBs. This model employs a mixed elastohydrodynamic lubrication approach to determine the friction coefficient at the contact interfaces. This study explores how surface roughness and speed affect both ball–race and ball–cage friction torque, offering a comprehensive analysis of their influence on overall frictional torque. Additionally, the effect of surface roughness on ball–cage contact forces is investigated, enhancing the understanding of its contribution to friction torque. These insights aim to improve DGBB design and operation, maximizing performance and energy efficiency. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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10 pages, 2799 KiB

Open AccessArticle

The Temperature Dependence of Divergence Pressure

by Scott Bair

Lubricants 2024, 12(12), 434; https://doi.org/10.3390/lubricants12120434 - 6 Dec 2024

Cited by 1 | Viewed by 719

Abstract

The so-called controversy in elastohydrodynamic lubrication (EHL) regarding the nature of the shear dependence of viscosity, Eyring versus Carreau, is truly a controversy regarding the pressure and temperature dependence of low-shear viscosity. Roelands removed data that contradicted his claims of accuracy for his correlation. The Roelands hoax became acceptable in EHL because ignoring the universal previtreous piezoviscous response made the traction calculated with the Eyring assumption appear to be reasonable. Traction and minimum film thickness calculations sometimes require the description of viscosity at pressures up to the glass transition pressure. There have been few measurements of viscosity at pressures up to glass pressure. Therefore, a need exists for a piezoviscous model that extrapolates accurately, and the Hybrid model fills that need. Here, an improved relation for the temperature dependence of divergence pressure is offered and extrapolation is demonstrated for a polyalphaolefin and propylene carbonate. A linear dependence of divergence pressure with temperature is more useful than previous versions. An improvement in the capability of high-pressure viscometry is suggested based upon the fractional Stokes Einstein Debye relation and the relatively simple measurements of DC conductivity. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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21 pages, 7163 KiB

Open AccessArticle

Tribological Performance of Glycerol-Based Hydraulic Fluid Under Low-Temperature Conditions

by Paul Okhiria, Marcus Björling, Pontus Johansson, Mushfiq Hasan, Roland Larsson and Yijun Shi

Lubricants 2024, 12(12), 430; https://doi.org/10.3390/lubricants12120430 - 4 Dec 2024

Viewed by 852

Abstract

This study evaluated the tribological performance of a glycerol-based hydraulic fluid as a green alternative to conventional mineral-based hydraulic lubricants under low-temperature conditions, down to −20 °C. The performance of the glycerol hydraulic fluid (GHF) was compared against that of a mineral hydraulic fluid (MHF) using an SRV tribometer for steel-to-steel sliding contact under boundary lubrication conditions. Comparisons were also made at a moderate temperature to assess the fluids’ performance across different thermal conditions. The results show that the GHF demonstrated up to 55% lower friction coefficients under various test conditions than the MHF. With wear volumes up to 90% lower, the GHF produced thinner and less intense wear scars on the test discs compared to the deeper and more pronounced scars observed with the MHF. We conducted rheological tests which also revealed the green fluid’s stable viscosity transition with temperature changes and its Newtonian behaviour under the measured shear conditions, which may indicate its ability to maintain consistent lubrication. Full article

(This article belongs to the Special Issue Recent Advances in Lubricated Tribological Contacts)

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