Lubricants

21 pages, 5688 KB

Open AccessArticle

Investigation of the Mechanical Characteristics of Linear Rolling Guides Considering Multiple Errors

by Cheng Huang, Wentao Zhou, Wanli Liu, Yupeng Yi, Lei Shi, Rulin Xiong, Xiaobing Li and Xing Du

Lubricants 2026, 14(1), 46; https://doi.org/10.3390/lubricants14010046 - 22 Jan 2026

Viewed by 541

Abstract

Existing research on the linear rolling guide has predominantly focused on performance under ideal conditions or isolated error types, while systematic studies concerning multi-error coupling mechanisms and their impact on internal contact parameters remain limited. To address this, a comprehensive static model based [...] Read more.

Existing research on the linear rolling guide has predominantly focused on performance under ideal conditions or isolated error types, while systematic studies concerning multi-error coupling mechanisms and their impact on internal contact parameters remain limited. To address this, a comprehensive static model based on Hertz contact theory is proposed that simultaneously incorporates ball diameter, raceway radius, and raceway curvature center distance errors. This model is validated using finite element analysis (FEA) in ABAQUS, and the numerical results verify the feasibility and effectiveness of the proposed analytical model. Analysis of single, combined, and random errors indicates that geometric errors significantly influence vertical stiffness, load distribution, and critical load-carrying capacity. For example, as the ball diameter error varies from −2.5 to 2.5 μm, the vertical stiffness increases by a factor of 3.8, while a representative negative error combination reduces the critical load by nearly 40%. Additionally, random error analysis reveals that larger manufacturing tolerance ranges lead to increased fluctuation in ball contact forces, raising performance uncertainty. These findings establish the proposed model as a theoretical foundation for the precision design and load-bearing assessment of linear rolling guides under static conditions. Full article

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29 pages, 5712 KB

Open AccessArticle

Load Characteristics and Friction Torque Analysis of Triple-Row Wheel Hub Bearings

by Wei Xiong, Guilai Zheng, Haibo Zhang, Min Yu and Xiaomeng Wang

Lubricants 2026, 14(1), 45; https://doi.org/10.3390/lubricants14010045 - 20 Jan 2026

Cited by 1 | Viewed by 723

Abstract

Aiming at analyzing the load characteristics and friction torque of triple-row hub bearings for new energy vehicles, this work established a comprehensive theoretical and experimental methodology for predicting the internal load distribution and friction torque. Firstly, considering the preload effect via an initial [...] Read more.

Aiming at analyzing the load characteristics and friction torque of triple-row hub bearings for new energy vehicles, this work established a comprehensive theoretical and experimental methodology for predicting the internal load distribution and friction torque. Firstly, considering the preload effect via an initial negative clearance, deformation coordination and force balance equations for the triple-row bearing under axial load were formulated, to analyze the external loads under various driving conditions. Based on contact deformation theory, a quasi-static model was developed to combine radial, axial, and moment loads. The Newton–Raphson iterative algorithm was employed to solve the ball load distribution equations, and the correctness was verified by using the finite element method. Furthermore, accounting for the elastic hysteresis, differential sliding, and spin sliding, the theoretical models for friction torque components were established, to investigate the influence of structural parameters and the total friction torque under different driving conditions. Finally, to confirm the effectiveness and the precision of the model, a finite element simulation and experimental measurements of friction torque were conducted, respectively, which showed good agreement with theoretical calculations. The main innovations include proposing a mechanical modeling method for triple-row hub bearings that accounts for preload effects, and establishing an integrated friction torque analysis model applicable to multiple driving conditions. This work provides theoretical support and a methodological foundation for the design of next-generation hub bearings for new energy vehicles. Full article

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18 pages, 8088 KB

Open AccessArticle

A Potentially Repairable Composite Coating for Significantly Enhancing Wear and Corrosion Resistance of Magnesium Alloy

by Yueyu Huang, Ruilin Zeng, Shequan Wang, Ninghua Long, Yingpeng Zhang, Qun Wang and Chidambaram Seshadri Ramachandran

Lubricants 2026, 14(1), 44; https://doi.org/10.3390/lubricants14010044 - 20 Jan 2026

Viewed by 739

Abstract

The AZ31 magnesium alloy is an attractive lightweight metallic material, but its low corrosion resistance and wear resistance significantly limit its widespread application in fields such as aerospace, the automotive industry, and mechanical engineering. Moreover, most coating systems currently cannot restore their original [...] Read more.

The AZ31 magnesium alloy is an attractive lightweight metallic material, but its low corrosion resistance and wear resistance significantly limit its widespread application in fields such as aerospace, the automotive industry, and mechanical engineering. Moreover, most coating systems currently cannot restore their original functions and dimensions after localized damage. Based on this, this study combined cold spray (CS), micro-arc oxidation (MAO), and magnetron sputtering (MS) to develop a high-performance and repairable composite modification strategy. First, a 5056 aluminum alloy coating was prepared on AZ31 via CS, followed by the growth of a hard alumina (Al₂O₃) coating via MAO and a diamond-like carbon (DLC) coating via MS on the 5056 aluminum alloy surface. The microstructure, phase composition, hardness, tribological properties, and electrochemical corrosion behavior of the coatings were evaluated using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), X-ray diffraction (XRD), Vickers hardness testing, ball-on-disk dry sliding wear testing, and potentiodynamic polarization testing in a 3.5% sodium chloride solution. The CS 5056 aluminum alloy coating reduced the corrosion current density of AZ31 from 4.098 × 10⁻⁵ A/cm² to 2.714 × 10⁻⁶ A/cm². The MAO alumina coating increased the hardness of AZ31 from 68.60 HV_0.05 to 1614.00 HV_0.05 and decreased the wear rate from 1.703 × 10⁶ μm³/(N·m) to 2.038 × 10³ μm³/(N·m). The DLC coating further reduced the average coefficient of friction of the alumina coating from 0.48 to 0.27, decreased the wear rate to 6.979 × 10² μm³/(N·m), and lowered the corrosion current density from 3.020 × 10⁻⁶ A/cm² to 8.860 × 10⁻⁹ A/cm². This indicates that the three-phase composite coating achieves synergistic improvements in the corrosion and wear resistance of AZ31 through complementary advantages. Additionally, the thick CS aluminum alloy underlayer provides potential repairability, enabling the restoration of function and dimensions after damage without compromising the magnesium substrate. Overall, the proposed 5056Al/Al₂O₃/DLC composite coating strategy offers a reliable protective approach for AZ31 components and is expected to further expand their application fields. Full article

(This article belongs to the Special Issue Advanced Surface Treatments and Coatings for Friction and Wear Reduction)

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16 pages, 4497 KB

Open AccessArticle

Research on the Metal Sealing Performance of a Casing Head Hanger Under High-Pressure Conditions

by Zhenyu Jia, Pengcheng Wang, Junhui Wei, Guanggui Zou, Jinli Zhu, Jianfei Wang and Cong Guo

Lubricants 2026, 14(1), 43; https://doi.org/10.3390/lubricants14010043 - 16 Jan 2026

Cited by 1 | Viewed by 712

Abstract

With the deepening of oil and gas exploration and development into ultra-deep and ultra-high pressure environments, the pressure of wellhead equipment is becoming higher and higher. The sealing performance of the casing head hanger is directly related to the safety and reliability of [...] Read more.

With the deepening of oil and gas exploration and development into ultra-deep and ultra-high pressure environments, the pressure of wellhead equipment is becoming higher and higher. The sealing performance of the casing head hanger is directly related to the safety and reliability of the whole wellhead equipment. Firstly, based on the numerical simulation method, the sealing performance of three different metal seal rings—H-type, X-type, and U-type—under 175 MPa working conditions is compared and analyzed. The simulation results show that the sealing performance of the H-type metal sealing ring is better than that of the X-type and U-type. The parametric analysis method is further used to study the influence of the structural parameters of the convex radius and the bottom angle of the H-ring on its sealing performance. The results show that when the convex radius is designed to be 3 mm, and the bottom angle is 90°, the effective contact width reaches 5.91 mm, and the contact uniformity is the best. Finally, based on the H-type metal sealing ring sample trial-produced with optimized parameters, a 175 MPa nitrogen medium sealing pressure test was completed on an 8 1/8” all-metal sealed mandrel casing hanger. The test results show that the system pressure drop is 0.7 MPa during the 5-min pressure stabilization process, which has good sealing reliability. Full article

(This article belongs to the Special Issue Advances in Mechanical Seals)

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31 pages, 4459 KB

Open AccessReview

Prospects and Challenges for Achieving Superlubricity in Porous Framework Materials (MOFs/POFs): A Review

by Ruishen Wang, Xunyi Liu, Sifan Huo, Mingming Liu, Jiasen Zhang, Yuhong Liu, Yanhong Cheng and Caixia Zhang

Lubricants 2026, 14(1), 42; https://doi.org/10.3390/lubricants14010042 - 15 Jan 2026

Viewed by 870

Abstract

Metal–organic frameworks (MOFs) and porous organic frameworks (POFs) have been extensively explored in recent years as lubricant additives for various systems due to their structural designability, pore storage capacity, and tunable surface chemistry. These materials are utilized to construct low-friction, low-wear interfaces and [...] Read more.

Metal–organic frameworks (MOFs) and porous organic frameworks (POFs) have been extensively explored in recent years as lubricant additives for various systems due to their structural designability, pore storage capacity, and tunable surface chemistry. These materials are utilized to construct low-friction, low-wear interfaces and investigate the potential for superlubricity. This paper systematically reviews the tribological behavior and key mechanisms of MOFs/POFs in oil-based, water-based, and solid coating systems. In oil-based systems, MOFs/POFs primarily achieve friction reduction and wear resistance through third-body particles, layer slip, and synergistic friction-induced chemical/physical transfer films. However, limitations in achieving superlubricity stem from the multi-component heterogeneity of boundary films and the dynamic evolution of shear planes. In water-based systems, MOFs/POFs leverage hydrophilic functional groups to induce hydration layers, promote polymer thickening, and soften gels through interfacial anchoring. Under specific conditions, a few cases exhibit superlubricity with coefficients of friction entering the 10⁻³ range. In solid coating systems, two-dimensional MOFs/COFs with controllable orientation leverage interlayer weak interactions and incommensurate interfaces to reduce potential barriers, achieving structural superlubricity at the 10⁻³–10⁻⁴ level on the micro- and nano-scales. However, at the engineering scale, factors such as roughness, contamination, and discontinuities in the lubricating film still constrain performance, leading to amplified energy dissipation and degradation. Finally, this paper discusses key challenges in achieving superlubricity with MOFs/POFs and proposes future research directions, including the design of shear-plane structures. Full article

(This article belongs to the Special Issue Superlubricity Mechanisms and Applications)

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20 pages, 5426 KB

Open AccessReview

Morphological Diversity and Interparticle Interactions of Lubricating Grease Thickeners: Current Insights and Research Approaches

by Maciej Paszkowski, Ewa Kadela and Agnieszka Skibińska

Lubricants 2026, 14(1), 41; https://doi.org/10.3390/lubricants14010041 - 15 Jan 2026

Viewed by 936

Abstract

The study systematizes the current state of knowledge on the morphological diversity of dispersed-phase particles in the most widely used lubricating greases, encompassing their shape, size, surface structure, and overall geometry. The extensive discussion of the diversity of grease thickener particles is supplemented [...] Read more.

The study systematizes the current state of knowledge on the morphological diversity of dispersed-phase particles in the most widely used lubricating greases, encompassing their shape, size, surface structure, and overall geometry. The extensive discussion of the diversity of grease thickener particles is supplemented with their microscopic images. Particular emphasis is placed on the influence of thickener particle morphology, the degree of their aggregation, and interparticle interactions on the rheological, mechanical, and tribological properties of grease formulations. The paper reviews recent advances in investigations of grease microstructure, with special emphasis on imaging techniques—ranging from dark-field imaging, through scanning electron microscopy, to atomic force microscopy—together with a discussion of their advantages and limitations in the assessment of particle morphology. A significant part of the work is devoted to rheological studies, which enable an indirect evaluation of the structural state of grease by analyzing its response to shear and deformation, thereby allowing inferences to be drawn about the micro- and mesostructure of lubricating greases. The historical development of rheological research on lubricating greases is also presented—from simple flow models, through the introduction of the concepts of viscoelasticity and structural rheology, to modern experimental and modeling approaches—highlighting the close relationships between rheological properties and thickener structure, manufacturing processes, composition, and in-service behavior of lubricating greases, particularly in tribological applications. It is indicated that contemporary studies confirm the feasibility of tailoring the microstructure of grease thickeners to specific lubrication conditions, as their characteristics fundamentally determine the rheological and tribological properties of the entire system. Full article

(This article belongs to the Special Issue Rheology of Lubricants in Lubrication Engineering)

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24 pages, 4253 KB

Open AccessArticle

Performance Evaluation of a Halbach Permanent Magnet Axial Protection Bearing Under Vertical Magnetic Levitation Flywheel Rotor Drop

by Dengke Li, Jun Ye, Gang Chen, Lai Hu, Zixi Wang, Taishun Qian, Jiahao Zhang, Mengchen Zi and Chao Liang

Lubricants 2026, 14(1), 40; https://doi.org/10.3390/lubricants14010040 - 15 Jan 2026

Cited by 1 | Viewed by 900

Abstract

This study addresses the issues with traditional rolling protection bearings in vertical magnetic levitation flywheel energy storage systems (FESSs), which are prone to impact, wear, and temperature rise under abnormal conditions, such as drops. It designed a permanent magnet axial protection bearing based [...] Read more.

This study addresses the issues with traditional rolling protection bearings in vertical magnetic levitation flywheel energy storage systems (FESSs), which are prone to impact, wear, and temperature rise under abnormal conditions, such as drops. It designed a permanent magnet axial protection bearing based on a Halbach array, utilizing N42SH permanent magnet material. The five-layer Halbach array achieved a maximum axial magnetic force of 86 KN and a maximum air gap magnetic flux density of 2.2 T, meeting the application requirements. Simulation results, combined with rotor drop dynamics and thermal analysis, show that under an 8000 rpm drop condition, the permanent magnet bearing reduces radial and axial contact forces by approximately 60% and 54%, respectively, and wear by around 70%. Additionally, the maximum system temperature decreases from 109 °C to 74 °C, with a 32% reduction in temperature rise. Friction experimental analysis indicates that low frequency, low load, and moderate temperatures improve friction stability and reduce wear. Overall, the permanent magnet axial protective bearing effectively mitigates drop impact, reduces friction heat and wear, and enhances the safety and reliability of the flywheel energy storage system under abnormal working conditions, providing valuable theoretical support and a design reference for engineering applications. Full article

(This article belongs to the Special Issue High Performance Machining and Surface Tribology)

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35 pages, 16491 KB

Open AccessArticle

Laser Surface Texturing of AA1050 Aluminum to Enhance the Tribological Properties of PTFE Coatings with a Taguchi-Based Analysis

by Timur Canel, Sinan Fidan, Mustafa Özgür Bora, Satılmış Ürgün, Demet Taşkan Ürgün and Mehmet İskender Özsoy

Lubricants 2026, 14(1), 39; https://doi.org/10.3390/lubricants14010039 - 15 Jan 2026

Viewed by 812

Abstract

Fiber laser surface texturing was applied to AA1050 aluminum to improve friction and wear performance of PTFE coatings. A Taguchi L16 design varied texture geometry (square, diamond, hexagon, circle), scanned area ratio (20% to 80%), and laser power (40 to 100 W) prior [...] Read more.

Fiber laser surface texturing was applied to AA1050 aluminum to improve friction and wear performance of PTFE coatings. A Taguchi L16 design varied texture geometry (square, diamond, hexagon, circle), scanned area ratio (20% to 80%), and laser power (40 to 100 W) prior to primer plus PTFE topcoat deposition (25 to 35 µm). Dry reciprocating sliding against a 6 mm 100Cr6 ball was conducted at 20 N, 1 Hz, and 50 m, and wear track geometry was measured by non-contact profilometry. The non-textured reference exhibited an average COF of 0.143, whereas the lowest mean COF was achieved with diamond 60% and 40 W (0.095) and the highest with hexagon 60% and 100 W (0.156); hexagon 20% and 60 W matched the reference. ANOVA indicated scanned area ratio as the dominant contributor to COF (39.72%), followed by geometry (35.07%) and power (25.21%). Profilometry confirmed reduced coating penetration for optimized textures: the reference wear track was approximately 1240 µm wide and 82 µm deep, compared with 930 µm and 34 µm for square 80% and 40 W, 997 µm and 39 µm for diamond 60% and 40 W, and 965 µm and 36 µm for hexagon 40% and 40 W. Full article

(This article belongs to the Special Issue Laser-Assisted Surface Modification to Enhance Tribological Performance Under Extreme Conditions)

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19 pages, 6121 KB

Open AccessArticle

Study on Particle Wear Mechanism of Slurry Pumps Based on Computational Fluid Dynamics-Discrete Element Method Coupling

by Meng Xue, Jianjun Peng, Xiangchen Ku and Guanhua Dong

Lubricants 2026, 14(1), 38; https://doi.org/10.3390/lubricants14010038 - 15 Jan 2026

Viewed by 635

Abstract

To investigate the influence of particle characteristics on wear in slurry pump flow-through components, this study established a computational fluid dynamics-discrete element method (CFD-DEM) coupled with the Archard wear model for numerical simulation of solid-liquid two-phase flow characteristics and wear mechanisms within the [...] Read more.

To investigate the influence of particle characteristics on wear in slurry pump flow-through components, this study established a computational fluid dynamics-discrete element method (CFD-DEM) coupled with the Archard wear model for numerical simulation of solid-liquid two-phase flow characteristics and wear mechanisms within the pump. Focusing on the correlation between wear contour distribution and particle collision frequency, the study systematically analyzed the influence mechanisms of particle concentration, size distribution, and shape on wear patterns within the pump. The reliability of the coupled model was validated through external characteristic tests. Results indicate that wear severity on both the impeller and volute increases significantly with rising particle concentration, while wall particle collision frequency exhibits a positive correlation with concentration. Particles of 1.5 mm diameter cause the most severe localized wear on the impeller, whereas the presence of mixed particles partially mitigates the wear effect of larger particles. Both total and localized wear on the volute peak at a particle diameter of 1 mm. Low-sphericity particles intensified overall wear on both the impeller and volute; while high-sphericity particles reduced overall wear, they induced more severe localized wear on the impeller. Volute localized wear was most pronounced at a sphericity of 0.84. This study elucidates the mechanism by which particle characteristics influence wear on slurry pump flow-through components, providing a theoretical basis for optimizing slurry pump design. Full article

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19 pages, 6631 KB

Open AccessArticle

Research on the Influence of Ore Particle Shape on the Load Behavior of Charge and Wear of Ball Mill Liners Based on Rocky-DEM

by Zixin Yin and Xiangyi Pan

Lubricants 2026, 14(1), 37; https://doi.org/10.3390/lubricants14010037 - 15 Jan 2026

Viewed by 522

Abstract

This study investigates the influence of ore particle shape on the wear behavior of ball mill liners using the Rocky-DEM software. A simulation model of a laboratory-scale ball mill was established to analyze the wear patterns of liners under three different ore particle [...] Read more.

This study investigates the influence of ore particle shape on the wear behavior of ball mill liners using the Rocky-DEM software. A simulation model of a laboratory-scale ball mill was established to analyze the wear patterns of liners under three different ore particle shapes: polyhedron, ellipsoid, and sphere. The results indicate that while the overall motion patterns of the charge showed minor differences across particle shapes, significant variations were observed in flowability, with the polyhedral system exhibiting the lowest fluidity. Particle shape had a negligible impact on translational velocity but a substantial effect on rotational velocity. Regarding liner wear, the polyhedral system generated significantly higher wear compared to the spherical and ellipsoidal systems. The polyhedral system also exhibited the highest shear stress, identifying shear stress as the core factor dominating liner wear. The wear-time curves for individual liners in both radial and axial directions displayed a stepwise increase, suggesting that wear is primarily concentrated in the toe region. Full article

(This article belongs to the Special Issue Tribology in Ball Milling: Theory and Applications)

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25 pages, 4121 KB

Open AccessReview

Advances in the Tribological Research of Ceramic-on-Ceramic Artificial Joints

by Menglin Zhou, Zihan Lin, Xiaolu Jiang, Jianhua Jin, Qi Wan, Li Zhang and Zhaoxian Zheng

Lubricants 2026, 14(1), 36; https://doi.org/10.3390/lubricants14010036 - 14 Jan 2026

Viewed by 571

Abstract

Ceramic-on-ceramic (CoC) bearings are widely used in total hip arthroplasty due to their extremely low wear rate, excellent chemical stability, and good biocompatibility. They are considered one of the most reliable long-term friction bearing systems. Although frictional instability, lubrication regime transitions, and microstructural [...] Read more.

Ceramic-on-ceramic (CoC) bearings are widely used in total hip arthroplasty due to their extremely low wear rate, excellent chemical stability, and good biocompatibility. They are considered one of the most reliable long-term friction bearing systems. Although frictional instability, lubrication regime transitions, and microstructural damage mechanisms have been widely reported at the experimental and retrieval-analysis levels, current clinical evidence, limited by follow-up duration and event incidence, has not demonstrated a definitive negative impact on the clinical performance of fourth-generation ceramic components, including BIOLOX^® delta. Data from national arthroplasty registries consistently demonstrate excellent survivorship and low complication rates for 4th-generation ceramics in both hard-on-soft and hard-on-hard configurations. The most reported causes for revision, such as infection, dislocation, aseptic loosening, and periprosthetic fracture, are not primarily associated with ceramic-related complications, such as ceramic fracture, excessive wear, squeaking, and revision, related to bearing failure; however, these mechanisms remain highly relevant for the design and evaluation of emerging ceramic materials and next-generation implant systems, where inadequate control may potentially impact long-term clinical performance. This review summarizes recent advances in the tribological research of CoC artificial joints, focusing on clinical tribological challenges, material composition and surface characteristics, lubrication mechanisms, wear and microdamage evolution, and third-body effects. Recent progress in ceramic toughening strategies, surface engineering, biomimetic lubrication simulation, and structural optimization is also discussed. Finally, future research directions are outlined to support the performance optimization and long-term reliability assessment of CoC artificial joint systems. Full article

(This article belongs to the Special Issue Tribology of Medical Devices)

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20 pages, 5660 KB

Open AccessArticle

Synthesis and Tribological Properties of Multifunctional Nitrogen-Containing Heterocyclic Dialkyl Dithiocarbamate Derivatives

by Mengxuan Wang, Ting Li, Zhongxian Li, Wenjing Hu, Junwei Wang and Jiusheng Li

Lubricants 2026, 14(1), 35; https://doi.org/10.3390/lubricants14010035 - 14 Jan 2026

Viewed by 589

Abstract

Energy conservation and efficiency enhancement necessitate continuous advancement in the development and preparation of multifunctional, high-performance lubricant additives. This paper reports three novel ashless, phosphorus-free, multifunctional nitrogen-containing heterocyclic dialkyl dithiocarbamate derivative additives (Py-2-DBDTC, PDM-DBDTC, and BZT-DBDTC). Thermal stability, oxidation resistance, and tribological properties [...] Read more.

Energy conservation and efficiency enhancement necessitate continuous advancement in the development and preparation of multifunctional, high-performance lubricant additives. This paper reports three novel ashless, phosphorus-free, multifunctional nitrogen-containing heterocyclic dialkyl dithiocarbamate derivative additives (Py-2-DBDTC, PDM-DBDTC, and BZT-DBDTC). Thermal stability, oxidation resistance, and tribological properties were investigated for the synthesized additives. All three additives demonstrated excellent thermal stability and oxidation resistance. Furthermore, their extreme-pressure properties improved by 116.33% or more compared to the base oil, while wear reduction rates also exceeded 58.32%. Under both point-to-point and point-on-flat friction conditions, the friction-reducing performance of all three additives was equally outstanding. Across a broad temperature range (25 °C–150 °C), all additives maintained their friction-reducing properties. Analysis of the worn surface morphology reveals that all three additives undergo tribochemical reactions during the friction process, forming tribofilms containing sulfur elements. Research indicates that introducing different nitrogen-containing heterocyclic structures into dialkyl dithiocarbamates can effectively enhance the adsorption capacity of the additives on metal surfaces and promote the formation of tribofilms at the friction interface, thereby significantly improving tribological performance. These systematic investigations not only provide important guidance for the molecular design and industrial application of multifunctional lubricant additives but also further advance the development of sustainable lubrication technologies. Full article

(This article belongs to the Special Issue Sustainable and Advanced Lubrication Strategies for Industrial and Environmental Applications)

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19 pages, 3332 KB

Open AccessArticle

Effects of Rotor Centrifugal Expansion on the Static and Dynamic Characteristics of Porous Gas Journal Bearing

by Shengye Lin, Zhengru Wu, Haiqing Zhang and Xun Huang

Lubricants 2026, 14(1), 34; https://doi.org/10.3390/lubricants14010034 - 10 Jan 2026

Viewed by 436

Abstract

As the rotational speed increases, the centrifugal expansion of the rotor will significantly affect the performance of the porous gas bearing. However, this rotor’s centrifugal effect has not been studied thoroughly. In this paper, the rotor centrifugal expansion is simplified as a two-dimensional [...] Read more.

As the rotational speed increases, the centrifugal expansion of the rotor will significantly affect the performance of the porous gas bearing. However, this rotor’s centrifugal effect has not been studied thoroughly. In this paper, the rotor centrifugal expansion is simplified as a two-dimensional plane stress problem. The gas flow in the porous bushing and the gas film is governed by Darcy’s law and the modified Reynolds equation, respectively. The perturbation method and the finite difference method are adopted to calculate the bearing load and dynamic coefficients for a high-speed porous gas bearing. Comparisons between the simulated results and the available experimental and theoretical data are carried out to validate the proposed model. On this basis, the influence of rotor centrifugal expansion on the performance and the operational conditions of the high-speed porous gas bearing is studied systematically. The results indicate that rotor centrifugal expansion greatly improves the bearing load and dynamic coefficients of the high-speed porous gas bearing with a large rotor diameter and small bearing clearance, but reduces the allowable eccentricity ratio and titling angle. Full article

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21 pages, 6702 KB

Open AccessArticle

Modeling of Oil-Film Traction Behavior and Lubricant Selection for Aeroengine Mainshaft Ball Bearings

by Kaiwen Deng, Xinlin Qing, Florian Pape and Yishou Wang

Lubricants 2026, 14(1), 33; https://doi.org/10.3390/lubricants14010033 - 10 Jan 2026

Cited by 1 | Viewed by 694

Abstract

The traction behavior of lubricant films forms the foundation of dynamic modeling for aeroengine mainshaft ball bearings. Its accuracy directly determines the reliability of predicted dynamic responses and the available design safety margins. Existing traction models produce artificial friction in the zero slip [...] Read more.

The traction behavior of lubricant films forms the foundation of dynamic modeling for aeroengine mainshaft ball bearings. Its accuracy directly determines the reliability of predicted dynamic responses and the available design safety margins. Existing traction models produce artificial friction in the zero slip region and exhibit strong sensitivity to ball size effects, which leads to significant deviations from experimental observations. These limitations make them unsuitable for high-fidelity analyses of aeroengine mainshaft bearings. In this study, a self-developed high-speed traction test rig was used to systematically measure the traction–slip responses of three aviation lubricants, including the newly developed 4102 (7 cSt) and the inservice 4050 (5 cSt) and 4010 (3 cSt). The tests covered a wide range of operating conditions, including maximum Hertzian pressures of 1.0 to 1.5 GPa, oil supply temperatures of 25 to 120 °C, entrainment speeds of 25 to 40 m/s, and slide–roll ratios (SRR) of 0 to 0.3. The evolution of lubricant traction characteristics was examined in detail. Based on the experimental data, a four-parameter and three-coefficient traction model was proposed. This model eliminates the non-physical traction outputs at zero slip observed in previous formulations. When embedded into the bearing dynamic simulations, the maximum deviation between the predicted friction torque and the measured values is only 3.79%. On the basis of typical operating conditions of aeroengine bearings, lubricant selection guidelines were established. Under combined high-speed, light-load, and high-temperature conditions, the high-viscosity lubricant 4102 is preferred because it suppresses cage sliding and enhances film stiffness. When the cage slip ratio is below 15% and lubrication is sufficient, the low-viscosity lubricant 4010 is recommended, followed by 4050, in order to reduce frictional heating. This study provides a theoretical basis for high-accuracy dynamic design and lubricant selection for aeroengine ball bearings. Full article

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23 pages, 13374 KB

Open AccessArticle

Study on the Nonlinear Dynamic Behavior and Bifurcation of the Double-Rotor System Under the Coupling of Rubbing and Oil-Film Force

by Junjie Liu, Jingxin Wang, Lingyun Zhang, Tongrui Wang, Manchang Liu and Guorui Zhao

Lubricants 2026, 14(1), 32; https://doi.org/10.3390/lubricants14010032 - 10 Jan 2026

Viewed by 550

Abstract

Sliding bearings–rotor systems are widely present in rotating machinery structures. The dynamic behavior triggered by friction and rub-impact faults is a key factor restricting the safe and stable operation of a rotor system. Existing studies mainly focus on analyzing dynamic characteristics but rarely [...] Read more.

Sliding bearings–rotor systems are widely present in rotating machinery structures. The dynamic behavior triggered by friction and rub-impact faults is a key factor restricting the safe and stable operation of a rotor system. Existing studies mainly focus on analyzing dynamic characteristics but rarely explore the degree of friction and rub-impact in the system. This paper takes the sliding bearing–double-disk rotor system with friction and rub-impact as the research model, and defines the concept of the rubbing ratio. It analyzes the influence of relevant structural parameters on the system. The results reveal that the system exhibits rich nonlinear dynamics. Specifically, increasing either the rotor–stator clearance or the lubricant viscosity can drive the system into a broader regime of chaotic motion, while simultaneously reducing the extent of the rub-impact contact region. As the stator stiffness increases from 10⁷ N/m to 9 × 10⁷ N/m, the number of chaotic windows in the bifurcation diagram increases from one to three, while the maximum rubbing force rises by approximately 58% and the rubbing ratio increases from 50% to 56%. The phenomenon of coexisting attractors in the system is also revealed and analyzed. The above research results help to reveal the motion laws of this type of rotor system and have certain guiding significance for parameter matching and optimization design of the system dynamics. Full article

(This article belongs to the Special Issue Nonlinear Dynamics of Frictional Systems)

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18 pages, 5526 KB

Open AccessArticle

Dry-Sliding Behavior and Surface Evolution of SLS-Manufactured Glass Bead-Filled Polyamide 12 Bearings

by Ivan Simonović, Dragan Milković, Žarko Mišković and Aleksandar Marinković

Lubricants 2026, 14(1), 31; https://doi.org/10.3390/lubricants14010031 - 9 Jan 2026

Viewed by 712

Abstract

This study investigates the tribological behavior of selective laser-sintered (SLS) sliding bearings under dry-sliding operating conditions. These polyamide-12 bearings reinforced with glass beads (PA 3200 GF) were tested against a stainless-steel sleeve in three different pressure–velocity (PV) regimes that represent real operating conditions. [...] Read more.

This study investigates the tribological behavior of selective laser-sintered (SLS) sliding bearings under dry-sliding operating conditions. These polyamide-12 bearings reinforced with glass beads (PA 3200 GF) were tested against a stainless-steel sleeve in three different pressure–velocity (PV) regimes that represent real operating conditions. The coefficient of friction (COF) and contact temperatures were monitored throughout the experiment, while the specific wear rate was quantified based on mass loss measurements. The evolution of surface topography was analyzed using roughness parameters of the Abbott-Firestone family. Scanning electron microscopy (SEM) analysis was performed to identify the dominant wear mechanism. The results show a pronounced running-in phase, after which a stable thermomechanical equilibrium occurs in all regimes. Heavy-loaded regimes increase temperature but accelerate surface adaptation and lower stable coefficients of friction. Lower load regimes have the lowest thermal load but higher friction due to lower real contact. The medium PV regime has a low COF and moderate temperature rise, while peak and core roughness metrics increase more significantly. These results provide an experimentally based insight into the influence of the load regime on the tribological behavior and topography of the SLS-made polymer sliding bearings, thus contributing to a deeper understanding of their operation in real dry-sliding conditions. Full article

(This article belongs to the Special Issue Machine Design and Tribology)

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15 pages, 10135 KB

Open AccessArticle

Cooling and Lubrication Performance Analysis in Ultrasonic Vibration-Assisted Grinding by Heat Pipe Grinding Wheel

by Shuai Wang, Yongchen Xie, Bo Pan, Ning Qian, Sławomir Pietrowicz, Wenfeng Ding and Yucan Fu

Lubricants 2026, 14(1), 30; https://doi.org/10.3390/lubricants14010030 - 9 Jan 2026

Viewed by 730

Abstract

Due to low thermal conductivity and high specific strength, nickel-based superalloys are prone to service performance degradation caused by thermal damage during traditional high-efficiency grinding processes. Although the heat pipe grinding wheel with minimum quantity lubrication (HPGW-MQL) technology can reduce the probability of [...] Read more.

Due to low thermal conductivity and high specific strength, nickel-based superalloys are prone to service performance degradation caused by thermal damage during traditional high-efficiency grinding processes. Although the heat pipe grinding wheel with minimum quantity lubrication (HPGW-MQL) technology can reduce the probability of thermal damage to a certain extent, further breakthroughs are still needed. Therefore, this study proposes a new integrated process of ultrasonic vibration-assisted grinding by heat pipe grinding wheel with minimum quantity lubrication (UVAG-HPGW-MQL), aiming to balance the requirements of green grinding and the optimization of grinding performance for nickel-based superalloys. However, the mechanism of action of ultrasonic vibration on the cooling and lubrication performance of the proposed process remains unclear. Given that, comparative experiments between UVAG-HPGW-MQL and HPGW-MQL were conducted, focusing on exploring the influence of ultrasonic vibration on their cooling and lubrication performance. The experimental results, obtained when the grinding speed, workpiece feed rate, and grinding depth were set at 15–35 m/s, 40–120 mm/min, and 0.05–0.25 mm, respectively, indicate that, compared with HPGW-MQL, ultrasonic vibration causes periodic “contact-separation” between grains and workpiece. This dynamic process shortens the contact length between grains and workpiece, leading to maximum reductions of 43.85%, 22.15%, 34.16%, and 30.77% in grinding force, grinding force ratio, grinding temperature, and specific grinding energy, respectively. On the other hand, the ultrasonic cavitation effect causes atomization of the lubricating oil film adsorbed on the workpiece surface, leading to a decrease in lubrication performance and resulting in a maximum increase of 27.27% in the friction coefficient. This study provides new theoretical support and technical approaches for the green grinding of nickel-based superalloys. Full article

(This article belongs to the Special Issue Tribology in Cryogenic Machining)

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20 pages, 4469 KB

Open AccessArticle

Numerical Simulation of Wheel–Rail Adhesion Under Wet Conditions and Large Creepage During Braking

by Pengcheng Shi, Bing Wu, Jiaqing Huang, Zhaoyang Wang and Jianyong Zuo

Lubricants 2026, 14(1), 29; https://doi.org/10.3390/lubricants14010029 - 8 Jan 2026

Viewed by 632

Abstract

Low adhesion conditions can lead to significant wheel slip during braking for high-speed trains, resulting in severe wheel–rail rolling contact fatigue issues. The objective of this paper is to reproduce the dynamic wheel–rail adhesion characteristics of high-speed train braking with large creepage using [...] Read more.

Low adhesion conditions can lead to significant wheel slip during braking for high-speed trains, resulting in severe wheel–rail rolling contact fatigue issues. The objective of this paper is to reproduce the dynamic wheel–rail adhesion characteristics of high-speed train braking with large creepage using the transient non-Hertzian ECF model under wet conditions and to clarify the underlying mechanisms. The Kik–Piotrowski (KP) model is used to solve the wheel–rail normal contact problem, and the corresponding non-elliptical adaptive method is adopted to modify the ECF model considering time-dependent effects for solving the tangential contact problem. The dynamic large creepage adhesion characteristics of high-speed trains under wet conditions during braking are analyzed. Furthermore, the effect of braking initial speeds and longitudinal creepage variation curves on dynamic adhesion characteristics is discussed. The results indicate that the large creepage adhesion characteristic curve of high-speed trains during braking exhibits a loading stable phase and an unloading stable phase, both of which effectively enhance the utilization of wheel–rail adhesion. Full article

(This article belongs to the Special Issue Advances in Frictional Interfaces)

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24 pages, 2887 KB

Open AccessArticle

Tribological and Rheological Characterization of 3D Printed Polycarbonate: Effect of Layer Orientation, Surface Topography, and Lubrication Conditions

by Jovana Marković, Marija Matejić, Damjan Rangelov, Milan Banić, Jasmina Skerlić, Nevena Jeremić and Miloš Matejić

Lubricants 2026, 14(1), 28; https://doi.org/10.3390/lubricants14010028 - 8 Jan 2026

Cited by 1 | Viewed by 980

Abstract

Understanding the tribological behavior of additively manufactured polymers is essential for their reliable use in sliding components. Tribological tests were performed on a linear reciprocating tribometer pin-on-plate configuration using a polycarbonate sample (PC–PC). To assess the influence of additive-manufacturing-induced anisotropy, three build orientations [...] Read more.

Understanding the tribological behavior of additively manufactured polymers is essential for their reliable use in sliding components. Tribological tests were performed on a linear reciprocating tribometer pin-on-plate configuration using a polycarbonate sample (PC–PC). To assess the influence of additive-manufacturing-induced anisotropy, three build orientations (0°, 45°, 90°) were examined. Two normal loads of 39.24 N and 58.86 N, and two sliding velocities of 15 and 20 mm/s were selected to represent typical low-load operating conditions of polymeric components. Tests were conducted in dry contact and with two commercial lubricants exhibiting distinct rheological characteristics. Surface topography was characterized before and after testing to evaluate orientation-dependent roughness evolution, while rheological measurements provided effective viscosities at shear rates corresponding to imposed velocities. Frictional behavior was analyzed through the Stribeck parameter, showing that all configurations operated within boundary or early mixed lubrication regimes. Longitudinal specimen layer orientation (90°) was expected to give the lowest friction. In fact, dominant lowest friction in most of the examination regimes gave the 45° build orientation, whereas the 0° orientation hindered lubricant entrainment and produced the highest boundary interaction. Differences in lubricant viscosity influenced Stribeck positioning and the magnitude of friction reduction, demonstrating strong coupling between layer orientation, roughness evolution, and lubrication performance. Full article

(This article belongs to the Special Issue Machine Design and Tribology)

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16 pages, 4519 KB

Open AccessArticle

A Complex Multi-Working-Condition Bearing Fault Diagnosis Model Based on Sparse Representation Classification

by Jing Yang, Yanping Bai, Xia Ma, Jie Yang, Lichen Chai and Xiaoling Meng

Lubricants 2026, 14(1), 27; https://doi.org/10.3390/lubricants14010027 - 6 Jan 2026

Cited by 1 | Viewed by 602

Abstract

This article proposes a new method for bearing fault diagnosis based on sparse representation classification to address the challenges of fault identification under complex working conditions with different degrees of damage. The core of this method lies in directly using the original vibration [...] Read more.

This article proposes a new method for bearing fault diagnosis based on sparse representation classification to address the challenges of fault identification under complex working conditions with different degrees of damage. The core of this method lies in directly using the original vibration signal to construct an overcomplete dictionary without the need for signal denoising or manual feature extraction in advance, thus avoiding the information loss and subjective bias introduced by denoising and feature engineering in traditional methods. Firstly, all training samples are used as a dictionary to sequentially solve for sparse coefficients for each test sample. Secondly, the corresponding parts of each category in the sparse coefficients are filtered out. Then, the category error is calculated based on the sparse coefficients corresponding to each category. Finally, the fault classification of bearings is carried out by comparing the category errors. The experimental results show that this method can maintain high diagnostic accuracy and robustness in complex scenarios with various working conditions and damage levels, verifying its effectiveness and universality for bearing fault diagnosis. Full article

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21 pages, 5717 KB

Open AccessArticle

Film Thickness and Friction of Textured Surfaces in Hydrodynamic Inclined and Parallel Gaps—An Experimental Study

by Petr Šperka, Jan Knotek, Milan Omasta, Ivan Křupka, Pavel Polach and Martin Hartl

Lubricants 2026, 14(1), 26; https://doi.org/10.3390/lubricants14010026 - 6 Jan 2026

Cited by 1 | Viewed by 1050

Abstract

This paper presents an experimental study on the influence of surface texturing on friction and film thickness in the hydrodynamic lubrication regime. Using a pin-on-disk tribometer equipped with light-induced fluorescence microscopy, simultaneous measurements were conducted on smooth and textured samples under parallel and [...] Read more.

This paper presents an experimental study on the influence of surface texturing on friction and film thickness in the hydrodynamic lubrication regime. Using a pin-on-disk tribometer equipped with light-induced fluorescence microscopy, simultaneous measurements were conducted on smooth and textured samples under parallel and inclined surface conditions. The circular faces of the pins were partially or fully covered by circular laser-machined textures consisting of dimples with depths of 5 or 10 µm, diameters of 50 or 100 µm, and coverage density of 20%. The results demonstrate that while texturing significantly reduces friction and increases film thickness in parallel gaps, with partial inlet coverage being the most effective, its impact is minimal in inclined wedge gaps. The study further reveals that the global geometric wedge dominates over texture effects in inclined contacts and that in-texture cavitation, prevalent in parallel conditions, is suppressed by surface inclination. Three distinct contributions of the textures were discussed: a global hydrodynamic effect, a local hydrodynamic effect, and the influence of surface non-flatness (waviness). The findings suggest that texturing is primarily beneficial for acting as a pseudo-wedge or as surface roughness in contacts where a physical wedge is absent. Full article

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21 pages, 2517 KB

Open AccessArticle

Deep Learning Data-Driven Model for Stribeck Curve Prediction of Lubricated Tribo-Pairs

by Victoria Granja and C. Fred Higgs III

Lubricants 2026, 14(1), 25; https://doi.org/10.3390/lubricants14010025 - 6 Jan 2026

Cited by 1 | Viewed by 1063

Abstract

The prediction of tribological behavior in engineering systems based on output data streams is often considered empirical, as it is difficult to fully describe the underlying processes using closed-form mathematical models. For instance, accurately predicting the coefficient of friction (COF) across the three [...] Read more.

The prediction of tribological behavior in engineering systems based on output data streams is often considered empirical, as it is difficult to fully describe the underlying processes using closed-form mathematical models. For instance, accurately predicting the coefficient of friction (COF) across the three major lubrication regimes using a single model remains elusive. Machine learning (ML) offers a powerful data-driven approach for modeling complex tribological processes by learning nonlinear relationships between operating conditions and performance metrics. This work develops a high-accuracy deep learning model for predicting the COF in lubricated tribosystems across boundary, mixed, and hydrodynamic lubrication regimes. Extensive experimental data were collected using a ball-on-disk tribometer, which generated a large and diverse dataset spanning multiple materials, lubricants, temperatures, loads, and sliding speeds and covered the full Stribeck curve. These data were then used to train and optimize a neural network capable of accurately reproducing frictional transitions across lubrication regimes. The breadth of the dataset not only allows for the full Stribeck behavior to be captured, but also enables generalization across distinct tribosystems. The resulting model demonstrates strong predictive performance and is deployed using a graphical user interface as a practical tool for estimating COF in ball-on-disk lubricated sliding contacts. Full article

(This article belongs to the Special Issue New Horizons in Machine Learning Applications for Tribology)

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12 pages, 2467 KB

Open AccessArticle

First-Principles Insights into Lubrication Behaviors of Gallium-Matrix Liquid Metal for Bearing Steel and Albronze Frictional Pairs

by Xing Li, Ruizhi Wang, Yunqing Tang, Yukui Cai, Xiaoliang Liang, Jiaqian Li, Guijiang Diao and Dongyang Li

Lubricants 2026, 14(1), 24; https://doi.org/10.3390/lubricants14010024 - 5 Jan 2026

Viewed by 780

Abstract

The lubrication properties of gallium-matrix liquid metal (GLM) are intimately connected to the tribofilms formed through frictional processes. Physico-chemical properties of the tribofilms depend on the interfacial interactions between GLM and the surfaces of frictional pairs. Therefore, it is significant to reveal the [...] Read more.

The lubrication properties of gallium-matrix liquid metal (GLM) are intimately connected to the tribofilms formed through frictional processes. Physico-chemical properties of the tribofilms depend on the interfacial interactions between GLM and the surfaces of frictional pairs. Therefore, it is significant to reveal the process of interfacial interactions. In this study, considering that Ga and In atoms are the main components of GLM lubricant, the adsorption processes of Ga and In atoms on Fe (111) and Cu (111) surfaces are, respectively, investigated at the atomic level by the density functional theory (DFT) method to have an insight into the lubrication behaviors of GLM for bearing steel and albronze metals. It is found that the adsorptions of Ga atom on both Fe (111) and Cu (111) surfaces are stronger than that of In atom, and thus forming Fe-Ga bond and Cu-Ga bond. Furthermore, interfacial interactional experiments and tribological experiments are conducted to verify the results of first-principles calculations. Tribological experiments demonstrate that with FeGa₃ film on the bearing steel surface, the friction coefficient and wear rate can be reduced by 30% and 82%, while with CuGa₂ film on the albronze surface, the friction coefficient and wear rate can be reduced by 27% and 94%. Full article

(This article belongs to the Special Issue Tribology of Metals and Alloys)

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25 pages, 10778 KB

Open AccessArticle

Research on Friction and Structural Optimization Design of Segmented Annular Seal

by Zhenpeng He, Hongyu Wang, Shijun Zhao, Jiaxin Si, Ning Li, Baichun Li and Wendong Luo

Lubricants 2026, 14(1), 23; https://doi.org/10.3390/lubricants14010023 - 5 Jan 2026

Viewed by 724

Abstract

As a critical sealing component in aero-engines, the segmented annular seal is prone to friction and wear during the running-in stage, which seriously impairs its sealing performance and service life. To address this issue, this study takes the three-petal segmented annular seal made [...] Read more.

As a critical sealing component in aero-engines, the segmented annular seal is prone to friction and wear during the running-in stage, which seriously impairs its sealing performance and service life. To address this issue, this study takes the three-petal segmented annular seal made of T482 graphite as the research object, adopting a combined method of high-speed ring-block friction and wear tests and thermal–fluid–solid coupling simulation to investigate its friction and wear mechanisms and optimize its structural design. The results show that the segmented annular seal undergoes more severe friction and wear in the low-speed running-in stage; the wear rate increases with the rise in loading force and decreases with the increase in rotational speed, and the variation trend of surface roughness is consistent with that of the friction coefficient. Frictional heat and wear-induced scratches intensify the deformation and leakage of the seal, thereby leading to the risk of seal failure. Optimizing the depth of radial dynamic pressure grooves can significantly improve the opening performance of the seal, while optimizing the width of axial grooves mainly affects the seal leakage. This research provides a theoretical basis for improving the service life and sealing performance of segmented annular seals in aero-engines. Full article

(This article belongs to the Special Issue Mechanical Tribology and Surface Technology, 2nd Edition)

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18 pages, 4209 KB

Open AccessArticle

Data-Driven AI Model for Time-Based Prediction of Friction and Wear in Lubricated Tribosystems

by Victoria Granja and C. Fred Higgs III

Lubricants 2026, 14(1), 22; https://doi.org/10.3390/lubricants14010022 - 5 Jan 2026

Cited by 1 | Viewed by 1030

Abstract

Accurately predicting friction and wear in lubricated tribosystems is essential for improving mechanical performance and durability. However, models that simultaneously predict the COF and wear remain scarce due to the complex, non-linear nature of these phenomena and the absence of a direct correlation [...] Read more.

Accurately predicting friction and wear in lubricated tribosystems is essential for improving mechanical performance and durability. However, models that simultaneously predict the COF and wear remain scarce due to the complex, non-linear nature of these phenomena and the absence of a direct correlation between them. Tribology has traditionally relied on experimental methods to quantify these properties. In this study, a data-driven machine learning model is developed to predict the COF and WSD over time using data from four-ball tester experiments with lubricants containing various additives. Input parameters include lubricant properties, additive properties, and operating conditions. The data-driven model effectively captures the complex interactions among these variables, demonstrating high predictive accuracy for both the COF and WSD. These findings underscore the potential of deep learning in partnership with large data sets, overcoming modeling limitations in tribology, offering a valuable tool for predictive maintenance and lubricant optimization in industrial applications. Full article

(This article belongs to the Special Issue New Horizons in Machine Learning Applications for Tribology)

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18 pages, 5921 KB

Open AccessArticle

Enhancing the Lubrication Performance of Steel–Steel Contacts Using a Novel Ionic Liquid Based on Phosphate Ammonium Salt as an Oil Additive

by Junjie Xie, Shuai Hu, Cunqiang Liu, Ziqiang Gao, Faxue Zhang, Chaoyang Zhang and Mohamed Kamal Ahmed Ali

Lubricants 2026, 14(1), 21; https://doi.org/10.3390/lubricants14010021 - 4 Jan 2026

Viewed by 794

Abstract

Oil additives are essential for improving anti-wear (AW) properties and durability of mechanical components. In this study, a novel ionic liquid based on phosphate ammonium salt (coded as IL-NPAS) was designed using organic synthesis methods. The high-level objective of this work is to [...] Read more.

Oil additives are essential for improving anti-wear (AW) properties and durability of mechanical components. In this study, a novel ionic liquid based on phosphate ammonium salt (coded as IL-NPAS) was designed using organic synthesis methods. The high-level objective of this work is to enhance the wear resistance ability of oil-lubricated steels with low-cost additives in terms of materials and manufacturing methods. The IL-NPAS additive was incorporated at concentrations of 0.1 wt% and 0.5 wt% in 150 SN oil, which served as the base oil. Additionally, the commercial oil additive (coded as AW6110) was utilized as a reference to evaluate the effectiveness of the synthesized additive. The frictional behaviour was evaluated with an SRV tribometer at test temperatures of 25 °C and 100 °C. After that, SEM, 3D profilometry, XPS, and TOF-SIMS techniques were employed to show the wear modes and determine the chemical composition of the lubricating tribolayer. Noticeably, the formulated lubricant based on the 0.5 wt% IL-NPAS additive provided AW performance almost identical to the AW6110 additive. The results showed that the 0.5 wt% IL-NPAS additive reduced the coefficient of friction (COF) and improved AW properties by 34–36% and 80–90%, respectively, compared to the 150 SN base oil. Overall, this study holds significant promise for the development of low-cost lubricating oil additives. Full article

(This article belongs to the Special Issue Advances in Ionic Liquids as New Lubricant Materials)

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27 pages, 6768 KB

Open AccessArticle

Design and Performance Analysis of a New Variable Friction Pipeline Magnetic Flux Leakage Detection Robot

by Haichao Liu, Dongliang Cao, Shining Yuan, Jie Liu and Yufang Li

Lubricants 2026, 14(1), 20; https://doi.org/10.3390/lubricants14010020 - 1 Jan 2026

Viewed by 785

Abstract

To meet the requirements of in-pipeline inspection tasks, this paper designs a fluid-driven pipeline magnetic flux leakage (MFL) inspection robot with controllable speed. Based on the operating conditions of the robot, a combined solution with variable friction and drainage speed regulation devices is [...] Read more.

To meet the requirements of in-pipeline inspection tasks, this paper designs a fluid-driven pipeline magnetic flux leakage (MFL) inspection robot with controllable speed. Based on the operating conditions of the robot, a combined solution with variable friction and drainage speed regulation devices is developed. A mechanical equilibrium model of the robot is established. Through theoretical calculations and ANSYS 19.0 simulations, the structural parameters of the cup seals are determined. FLUENT fluid simulations are employed to optimize the drainage area, and the relationships between the valve opening, flow velocity, and torque are analyzed. Furthermore, the speed regulation characteristics of the variable friction device are evaluated. Experimental results demonstrate that the robot can achieve effective speed control and possesses reliable anti-jamming capability. The findings confirm the feasibility of the designed robot for pipeline magnetic flux leakage inspection tasks. Full article

(This article belongs to the Special Issue Tribology in Pipeline Transport Engineering)

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15 pages, 2805 KB

Open AccessArticle

Mechanism of Inner Rail Corrugation on Large-Radius Curves in Metro Systems

by Qifeng Song, Yan Hu, Feng Wen, Hutang Sang, Xi Kang and Dapeng Zhang

Lubricants 2026, 14(1), 19; https://doi.org/10.3390/lubricants14010019 - 1 Jan 2026

Viewed by 597

Abstract

This paper investigates the underlying cause of inner rail corrugation on large-radius curved tracks in metro systems. A dynamic model of the vehicle–track system (VTS) was developed to analyze the creep characteristics between the guiding wheelset and the rails when the vehicle negotiates [...] Read more.

This paper investigates the underlying cause of inner rail corrugation on large-radius curved tracks in metro systems. A dynamic model of the vehicle–track system (VTS) was developed to analyze the creep characteristics between the guiding wheelset and the rails when the vehicle negotiates large-radius curves under coasting, traction, and braking conditions. A finite element-based complex eigenvalue analysis was conducted to evaluate the stability of the wheel–rail frictional system. The results reveal that under coasting conditions, the wheel–rail creep forces on large-radius curves remain unsaturated, substantially reducing the likelihood of corrugation formation. In contrast, during braking, the creep force may approach saturation on the guiding inner wheel, increasing the possibility of wheel–rail sliding. This braking-induced sliding can trigger friction-induced self-excited vibrations at the wheel–rail interface, leading to the development of inner rail corrugation on large-radius curves. Full article

(This article belongs to the Special Issue Tribology in Railway Engineering)

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33 pages, 3071 KB

Open AccessSystematic Review

Friction and Cartilage Wear in Hemiarthroplasty: A Systematic Review of Key Influencing Factors

by Victoria P. Marino, Francesca De Vecchi, Dominik J. Federl, Landon M. Begin, Afton K. Limberg, Douglas C. Moore, Joseph J. Crisco, Douglas W. Van Citters and Markus A. Wimmer

Lubricants 2026, 14(1), 18; https://doi.org/10.3390/lubricants14010018 - 31 Dec 2025

Viewed by 815

Abstract

Hemiarthroplasty addresses joint damage confined to one side, preserving native cartilage and bone, but accelerated degeneration of the opposing cartilage can compromise outcomes. This systematic review should clarify whether coefficient of friction (COF) reliably predicts cartilage wear when evaluating hemiarthroplasty bearing materials (HBMs). [...] Read more.

Hemiarthroplasty addresses joint damage confined to one side, preserving native cartilage and bone, but accelerated degeneration of the opposing cartilage can compromise outcomes. This systematic review should clarify whether coefficient of friction (COF) reliably predicts cartilage wear when evaluating hemiarthroplasty bearing materials (HBMs). Thirty in vitro studies reporting both outcomes were identified. Data were extracted on COF, wear, and testing parameters, and wear was standardized using a 0–4 rubric to enable cross-study comparison. Three analytical approaches were applied: linear model fits, Pearson’s correlations, and predictive modeling. Reported COFs increased significantly with testing time, while contact stress and sliding velocity showed variable associations with COF. Predictive models for cobalt–chromium (CoCr), the most studied HBM, showed moderate fit, suggesting that mechanical parameters explain only part of COF variability. For wear, linear models showed poor fit with COF, but correlations indicated positive associations with contact stress. Inconsistent effects of velocity and distance were found. Predictive models explained little variability. Together, these findings suggest that outcomes are strongly influenced by testing conditions, lubricants, and HBM selection, and COF alone is an unreliable predictor of cartilage wear in an experimental setting. Full article

(This article belongs to the Special Issue Tribology of Medical Devices)

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25 pages, 6890 KB

Open AccessArticle

Development of Oleic Acid-Assisted Nanolubricants from Palm Kernel Oil for Boundary Lubrication Performance Under Extreme Pressure

by Aiman Yahaya, Syahrullail Samion, Zulhanafi Paiman, Nurul Farhanah Azman and Shunpei Kamitani

Lubricants 2026, 14(1), 17; https://doi.org/10.3390/lubricants14010017 - 30 Dec 2025

Viewed by 854

Abstract

The stability of nanolubricants is critical for ensuring effective performance under extreme pressure (EP) conditions, where severe boundary lubrication governs friction and wear behaviour. This study examines palm kernel oil (PKO)-based nanolubricants enhanced with carbon graphene (CG), hexagonal boron nitride (hBN), and molybdenum [...] Read more.

The stability of nanolubricants is critical for ensuring effective performance under extreme pressure (EP) conditions, where severe boundary lubrication governs friction and wear behaviour. This study examines palm kernel oil (PKO)-based nanolubricants enhanced with carbon graphene (CG), hexagonal boron nitride (hBN), and molybdenum disulfide (MoS₂), with and without oleic acid (OA) as a surfactant. OA incorporation improved CG dispersion stability, reducing agglomerate size by 30.4% (17.61 μm to 12.23 μm) and increasing the viscosity index from ~176 to 188, compared to 152 for the commercial hydrogen engine oil baseline. Under EP conditions, PKO + CG + OA achieved a 51.7% reduction in the coefficient of friction (0.58 to 0.28) and 18.2% improvement in weld load resistance, while wear scar diameter decreased by 13.4%. Surface and elemental analyses indicated the formation of a composite tribofilm containing oxide species, graphene platelets, and carboxylate-derived compounds from OA, consistent with iron–oleate-like chemistry that enhances load-carrying capacity and wear protection. These findings demonstrate the potential of OA-assisted PKO nanolubricants as sustainable, high-performance formulations for extreme pressure boundary lubrication, contributing to the advancement of green tribology. Full article

(This article belongs to the Special Issue Tribological Impacts of Sustainable Fuels in Mobility Systems)

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