Lubricants

21 pages, 14954 KB

Open AccessArticle

Tribological Behavior and Wear Prediction of Copper-Based Brake Pads for Monorail Cranes Under Complex Hygrothermal Environments

by Minti Xue, Ruihua Tong, Hao Lu, Zhiyuan Shi and Fan Jiang

Lubricants 2026, 14(2), 98; https://doi.org/10.3390/lubricants14020098 - 23 Feb 2026

Viewed by 599

Abstract

A significant amount of frictional heat is generated during the braking process of mine-used monorail cranes under heavy-load and low-speed creeping (or reciprocating speed regulation) conditions, causing thermal softening and performance degradation of the brake pads. Thus, investigating the tribological evolution mechanism is [...] Read more.

A significant amount of frictional heat is generated during the braking process of mine-used monorail cranes under heavy-load and low-speed creeping (or reciprocating speed regulation) conditions, causing thermal softening and performance degradation of the brake pads. Thus, investigating the tribological evolution mechanism is necessary to ensure reliable braking in deep underground environments. In this paper, full-scale tribological testing technology is applied to the brake system, and the friction and wear characteristics of copper-based powder metallurgy (P/M) brake pads under complex hygrothermal environments are studied. A physical experimental model coupling normal load, sliding speed, and humidity is established using a custom-designed open-structure reciprocating tester, revealing the “load weakening effect” under dry conditions and the “dual regulation mechanism” of mixed lubrication and cooling flushing under high humidity. Then, a surrogate prediction model of friction coefficient and wear rate, with respect to the operating parameters, is constructed based on Central Composite Design (CCD) and Response Surface Methodology (RSM). The reliability of the model under non-linear working conditions is estimated based on Analysis of Variance (ANOVA) and blind tests. The results indicate that the model possesses high prediction accuracy (relative error < 5%), and the feasibility of utilizing the high-humidity environment to enhance wear resistance and stability is verified. Full article

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33 pages, 9558 KB

Open AccessReview

Key Technologies and Research Progress of Cemented Carbide Bearings in Marine Environments: Materials, Tribology and Reliability

by Ruichen Liu, Hanhua Zhu, Jian Huang, Ao Chen, Ziyang Yan, Fangxu Sun, Wu Ouyang, Chenxing Sheng, Quan Zou and Hao Xie

Lubricants 2026, 14(2), 97; https://doi.org/10.3390/lubricants14020097 - 23 Feb 2026

Cited by 1 | Viewed by 665

Abstract

This review provides a comprehensive evaluation of the key technologies and latest advances in cemented carbide bearings for marine environments, such as navigation equipment and deep-sea operations. Given the rigorous performance requirements imposed on bearings by the extreme conditions of marine environments, including [...] Read more.

This review provides a comprehensive evaluation of the key technologies and latest advances in cemented carbide bearings for marine environments, such as navigation equipment and deep-sea operations. Given the rigorous performance requirements imposed on bearings by the extreme conditions of marine environments, including high hydrostatic pressure, seawater corrosion and abrasive wear, this paper explores the developments within carbide material systems. It focuses on analyzing the limitations of traditional WC-Co alloys in seawater, as well as the potential and challenges of alternative binder systems such as WC-Ni and WC-high Entropy Alloys (HEAs) in enhancing corrosion resistance and comprehensive mechanical properties. Building on this foundation, the research sorts out the tribological behavior of cemented carbides under seawater lubrication, explaining the influence of the tribocorrosion mechanism on friction characteristics. Meanwhile, it also explores reliability enhancement strategies through surface modifications like coatings and texturing, and discusses the challenges associated with life prediction models. Through tribopair experiments between cemented carbides and various bearing materials, the application orientation of cemented carbides is clarified, which provides a selection framework for carbide bearing applications in different marine scenarios. Finally, the paper summarizes the current technological bottlenecks and core scientific issues, offering insights for future research and development directions in this field. Full article

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16 pages, 5984 KB

Open AccessArticle

Optimization of Surface Quality in Milling of Aluminum Alloy 6030 Under Minimum-Quantity Lubrication Using Response Surface Methodology and Genetic Algorithm

by Qisen Cheng and Zhengcheng Tang

Lubricants 2026, 14(2), 96; https://doi.org/10.3390/lubricants14020096 - 21 Feb 2026

Cited by 1 | Viewed by 527

Abstract

With the development of manufacturing towards stricter precision requirements and increasingly complex geometric shapes, dimensional accuracy has become a key factor affecting precision engineering components used in many industries. Effective cooling and lubrication methods have always been a meaningful way to improve the [...] Read more.

With the development of manufacturing towards stricter precision requirements and increasingly complex geometric shapes, dimensional accuracy has become a key factor affecting precision engineering components used in many industries. Effective cooling and lubrication methods have always been a meaningful way to improve the surface quality of cutting materials. Minimum-quantity lubrication technology mixes compressed air with cutting fluid, produces a spray at ambient temperature, and guides these droplets to the cutting area under the action of high-pressure air to promote penetration into the contact area between the tool, workpiece, and chip. Minimum-quantity lubrication can be used to increase cutting speed, cool workpieces, improve workpiece quality, and significantly reduce the pollution caused by cutting fluid to the environment. However, minimum-quantity lubrication technology still cannot meet the requirements of sustainable machining in cutting processes. A test device platform for milling 6030 aluminum alloy with minimal quantity lubrication was established, and different cooling methods were used to analyze the effect on surface roughness. The spindle speed n, feed rate f, and cutting depth a_p are selected as optimization variables, with surface roughness as the optimization objective. Single-factor experiments were conducted to determine the optimal range for these variables. Subsequently, a model was constructed using the response surface methodology and solved using Design-Expert software. The interaction effects of spindle speed, feed rate, and depth of cut on surface roughness were analyzed. Additionally, genetic algorithms were employed to optimize cutting process parameters for the best combination. The results demonstrated that by combining Response Surface Methodology (RSM)and genetic algorithms, when the spindle speed n was 2520 r/min, the feed rate f was 48 mm/min, and the depth of cut a_p was 0.08 mm, the actual surface roughness after milling reached 0.148 µm, representing a 74.57% reduction compared to the initial surface roughness. This research method provides a theoretical foundation and technical support for optimizing minimal quantity lubrication (MQL) cutting processes. Full article

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20 pages, 4713 KB

Open AccessArticle

Early-Stage Damage Diagnosis of Rolling Bearings Based on Acoustic Emission Signals Interpreted by Friction Behavior and Machine Learning

by Taketo Nakai, Renguo Lu, Hiroshi Tani, Shinji Koganezawa and Jinqing Wang

Lubricants 2026, 14(2), 95; https://doi.org/10.3390/lubricants14020095 - 20 Feb 2026

Viewed by 683

Abstract

Condition monitoring of rolling bearings is essential for ensuring the reliability of mechanical systems operating under severe or insufficient lubrication conditions. This study proposes a fault diagnosis framework that integrates tribological interpretation of wear phenomena, acoustic emission (AE) signal analysis, and machine learning, [...] Read more.

Condition monitoring of rolling bearings is essential for ensuring the reliability of mechanical systems operating under severe or insufficient lubrication conditions. This study proposes a fault diagnosis framework that integrates tribological interpretation of wear phenomena, acoustic emission (AE) signal analysis, and machine learning, based on bearing life tests conducted under dry conditions as an accelerated wear environment to capture damage progression within a practical experimental time. Unlike conventional studies relying on artificially introduced defects, this work focuses on AE signals obtained from bearings in which damage initiates and progresses through actual wear processes. Life tests were conducted using deep groove ball bearings under two radial load conditions. The temporal evolution of the coefficient of friction, AE signals, and surface damage was analyzed. Although the coefficient of friction was the most sensitive indicator of wear progression, its direct measurement is impractical for in-service applications. Frequency-domain analysis revealed that AE counts per second and band-specific AE energy exhibit early changes consistent with the evolution of the friction coefficient. Using these physically interpretable AE features, a fully connected neural network was developed to classify bearing conditions into normal, early-stage damage, and damage progression. The proposed model achieved an average classification accuracy of approximately 85%, demonstrating the effectiveness of AE-based machine learning for bearing fault diagnosis under real wear progression conditions rather than artificial defect scenarios. Full article

(This article belongs to the Special Issue Advanced Methods for Wear Monitoring)

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19 pages, 8955 KB

Open AccessArticle

Comparative Wear and Friction Assessment of Nano-Additive Lubricants on Diesel Motors

by Recep Çağrı Orman

Lubricants 2026, 14(2), 94; https://doi.org/10.3390/lubricants14020094 - 19 Feb 2026

Viewed by 892

Abstract

In this study, boron carbide (B₄C), hexagonal boron nitride (hBN), holy super graphene (HSG), and hybrid (B₄C+hBN+HSG) nano-additives were added to SAE 15W-40 diesel engine oil at a range of 0.03–0.24 g per 30 mL of oil, and reciprocating [...] Read more.

In this study, boron carbide (B₄C), hexagonal boron nitride (hBN), holy super graphene (HSG), and hybrid (B₄C+hBN+HSG) nano-additives were added to SAE 15W-40 diesel engine oil at a range of 0.03–0.24 g per 30 mL of oil, and reciprocating tribological tests were conducted on a GG25 (EN-GJL-250) gray cast iron-based diesel piston surface in contact with an Al₂O₃ ball (Ø6 mm) at a load of 20 N, a sliding distance of 500 m, and a temperature of 75 °C. XRD analysis showed that the dominant phase on the piston surface was the α-Fe matrix and that no significant new phase had formed. The results obtained revealed that the nano-additive effect is strongly dependent on both the additive type and the additive level. At a low level (0.03 g/30 mL) of B₄C additive, the average COF decreased by approximately 19%, while at a low level (0.03 g/30 mL) of hBN additive, this decrease amounted to approximately 54%. In the HSG additive, at the highest level (0.24 g/30 mL), the coefficient of friction (COF) decreased to ≈0.032, achieving a friction reduction of approximately 75% compared to the base oil. In the hybrid oil series, COF values remained in the range of approximately 0.082–0.087 at all additive levels and were generally 25–28% lower than those of the base oil. SEM/EDS examinations showed that a tribofilm with high carbon content formed in the HSG-additive oils, while a tribofilm layer containing C, B, and N elements together formed in the hybrid-additive oils. Overall, it was concluded that selecting the appropriate additive type and level can reduce friction and wear losses at the piston interface, thereby contributing to engine efficiency by extending the life of engine components and limiting friction-induced energy losses. Full article

(This article belongs to the Special Issue Preparation, Tribological Behavior, and Applications of Lubricant Additives)

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19 pages, 2374 KB

Open AccessArticle

Adaptive Lubrication Enhancement of Piston Ring Seals via Fluid Pressure-Induced Waviness for High-Power Clutches

by Bochao Wang, Xingyun Jia, Qiaoqiao Bao and Jiang Qiu

Lubricants 2026, 14(2), 93; https://doi.org/10.3390/lubricants14020093 - 18 Feb 2026

Viewed by 662

Abstract

High-power clutches operating under high-frequency engagement–disengagement cycles demand piston ring seals with exceptional leakage control and tribological reliability. Conventional architectures often experience lubrication failure and severe adhesive wear during transient pressure fluctuations. This research proposes an autonomous intelligent sealing strategy leveraging fluid pressure-induced [...] Read more.

High-power clutches operating under high-frequency engagement–disengagement cycles demand piston ring seals with exceptional leakage control and tribological reliability. Conventional architectures often experience lubrication failure and severe adhesive wear during transient pressure fluctuations. This research proposes an autonomous intelligent sealing strategy leveraging fluid pressure-induced morphological evolution. By strategically integrating periodic macroscopic structural relief features on the non-sealing surface, the sealing interface transforms into a micron-scale wavy topography in response to hydraulic loading. This structurally embedded intelligence significantly improves fluid pressure distribution, facilitating a transition toward a more favorable lubrication regime. Furthermore, a “self-healing and positional stagnation” logic is elucidated: upon pressure dissipation, the induced waviness elastically recovers to a planar state to ensure sealing integrity, while the ring maintains its axial position due to the predominant frictional resistance of the secondary seal. This synergistic mechanism effectively precludes deleterious dry friction during the clutch disengagement phase. High-fidelity numerical investigations, benchmarked against established experimental data, identify the rectangular groove configuration as the optimal geometry for maximizing waviness amplitude (≈1.5 µm). This research provides a robust framework for developing responsive, zero-wear intelligent seals in advanced power transmissions. Full article

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17 pages, 5606 KB

Open AccessFeature PaperArticle

Lubricating Properties of Oil-Based Solutions Containing Graphene as Additive

by Luís Vilhena, Barnabas Erhabor, Tsering Wangmo, Bruno Figueiredo and Amílcar Ramalho

Lubricants 2026, 14(2), 92; https://doi.org/10.3390/lubricants14020092 - 16 Feb 2026

Cited by 1 | Viewed by 675

Abstract

Graphene, a 2D carbon allotrope with a hexagonal atomic structure, exhibits an exceptionally low friction coefficient of approximately 0.004, making it a superior alternative to traditional lubricants. This research investigates the performance of graphene as an additive in oil-based lubricants. Experimental trials will [...] Read more.

Graphene, a 2D carbon allotrope with a hexagonal atomic structure, exhibits an exceptionally low friction coefficient of approximately 0.004, making it a superior alternative to traditional lubricants. This research investigates the performance of graphene as an additive in oil-based lubricants. Experimental trials will be conducted using a block-on-ring (B-o-R) setup involving a steel rod pressed against a rotating steel ring under a fixed load. By varying the sliding velocities, the study will map the Stribeck curve across the boundary (BL), mixed (ML), and hydrodynamic (HL) lubrication regimes. Furthermore, the lubricant’s durability under extreme pressure will be assessed via Timken testing. The study identified 0.08 wt.% as the optimal concentration for PAO8, achieving a 21.25% friction reduction in the boundary regime. Furthermore, graphene as an additive mitigated wear volume by up to 90% under extreme pressure conditions (1.3 GPa), whereas epoxidized soybean oil proved to be highly effective as a base lubricant without additional nano-additives. Full article

(This article belongs to the Special Issue Experimental Modelling of Tribosystems)

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5 pages, 131 KB

Open AccessEditorial

Recent Advances in High-Temperature Tribology

by Long Wang, Guanyu Deng and Jun Cheng

Lubricants 2026, 14(2), 91; https://doi.org/10.3390/lubricants14020091 - 15 Feb 2026

Viewed by 684

Abstract

High-temperature tribology is a multidisciplinary science that has evolved rapidly in response to the increasing performance demands of high-technology sectors, including aviation, aerospace, nuclear energy, power generation, and advanced metal forming industries [...] Full article

(This article belongs to the Special Issue Recent Advances in High Temperature Tribology)

22 pages, 9913 KB

Open AccessArticle

Numerical Investigation of Gas Film Performance in Face Dry Gas Seals with Combined Micro-Textured Structures

by Tianyi Shi and Yanting Zhang

Lubricants 2026, 14(2), 90; https://doi.org/10.3390/lubricants14020090 - 15 Feb 2026

Viewed by 680

Abstract

To enhance the load-carrying capacity and operational stability of dry gas seal gas films while reducing gas leakage, and to provide a theoretical basis for structural optimization and innovation of face seals, a numerical model of gas film lubrication in face dry gas [...] Read more.

To enhance the load-carrying capacity and operational stability of dry gas seal gas films while reducing gas leakage, and to provide a theoretical basis for structural optimization and innovation of face seals, a numerical model of gas film lubrication in face dry gas seals considering the geometric effects of combined micro-textures is developed based on the governing equations of gas lubrication. The finite difference method is employed to numerically solve the gas film pressure distribution. With the objectives of maximizing the opening force and minimizing the leakage rate, the influences of combined micro-texture structural parameters on gas film performance under typical operating conditions are systematically investigated, and favorable parameter ranges are identified. The results show that the proposed model exhibits high accuracy and reliability, with good agreement with published data. Different combined groove textures significantly affect the gas film thickness and pressure distributions, leading to distinct bearing and stability characteristics. When opening force and leakage are jointly considered, the sealing performance ranks as triangular composite texture, semicircular composite texture, rectangular composite texture, and trapezoidal composite texture. Quantitatively, the trapezoidal texture exhibits the largest increase in the opening force–leakage ratio of approximately 0.29%, whereas the triangular texture shows the smallest increase of about 0.19%. Reasonable design of combined micro-textures can effectively improve the comprehensive gas film performance of face dry gas seals, achieving a coordinated enhancement of opening force and reduction in leakage. The present study provides theoretical guidance for the structural design and engineering application of high-performance dry gas seals. Full article

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30 pages, 41827 KB

Open AccessArticle

A Novel Assessment Model for the Sustainability of Clean Cutting Technology Based on Game Theory

by Zewen Li, Wei Zhao, Junjie Hu, Peng Zhao, Liang Li and Feng Kong

Lubricants 2026, 14(2), 89; https://doi.org/10.3390/lubricants14020089 - 14 Feb 2026

Viewed by 542

Abstract

To enhance the sustainability of manufacturing, various clean cutting technologies have been developed, yet their sustainability assessment faces challenges in balancing multiple conflicting objectives and stakeholder interests. This paper proposes a game theory-based evaluation framework that treats environmental, technical, economic, and social dimensions [...] Read more.

To enhance the sustainability of manufacturing, various clean cutting technologies have been developed, yet their sustainability assessment faces challenges in balancing multiple conflicting objectives and stakeholder interests. This paper proposes a game theory-based evaluation framework that treats environmental, technical, economic, and social dimensions as cooperative players. The Nash equilibrium model is employed to dynamically reconcile subjective weights from the analytic hierarchy process and objective weights from the entropy method, thus achieving optimal weight allocation. Experimental studies on Ti-6Al-4V titanium alloy milling compared dry milling, minimum quantity lubrication, and cryogenic minimum quantity lubrication (CMQL) under different parameters. Results demonstrate that the game-theoretic model effectively integrates preferences and achieves Nash equilibrium. CMQL showed superior performance, increasing tool life by approximately 40% and reducing surface roughness by about 25% compared to dry milling. Coated inserts reduced carbon emissions by nearly 30% versus end mills. The Nash equilibrium analysis demonstrates that dry milling with coated inserts attains the highest level of processing sustainability under high-speed conditions due to synergistic environmental and economic advantages, while simultaneously revealing practical trade-offs among competing objectives. This study confirms that the proposed framework enables scientific weight coordination and provides a quantifiable, interpretable decision-making system for sustainable process selection. Full article

(This article belongs to the Special Issue Minimum Quantity Lubrication (MQL): Advances, Applications, and Future Perspectives)

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19 pages, 10597 KB

Open AccessArticle

Numerical Simulation of Startup Performance in High-Power Diesel Engine Lubrication Systems Under High-Altitude and Cold Conditions

by Zhonghao Gao, Yiqiao Guo, Wendi Zhu, Wei Du, Lanjie Huang and Hao Zhang

Lubricants 2026, 14(2), 88; https://doi.org/10.3390/lubricants14020088 - 12 Feb 2026

Viewed by 637

Abstract

With the significant increase in the number of motor vehicles in plateau regions, the adaptability and reliability requirements of diesel engines operating under high-altitude and cold conditions have become increasingly critical. In this study, a one-dimensional transient simulation model of the overall engine [...] Read more.

With the significant increase in the number of motor vehicles in plateau regions, the adaptability and reliability requirements of diesel engines operating under high-altitude and cold conditions have become increasingly critical. In this study, a one-dimensional transient simulation model of the overall engine lubrication system was developed based on a physical experimental prototype. The multiphysics-coupled lubrication system was numerically modeled and analyzed, with particular emphasis on elucidating the influence mechanisms of high-altitude and cold environments on the startup performance of diesel engine lubrication systems. System responses under different ambient pressures (0.88 bar, 0.92 bar, 0.96 bar, and standard atmospheric pressure) and oil temperatures (30 °C, 55 °C, and 100 °C) were systematically investigated. In addition, variations in the opening degree of the oil pump pressure relief valve (closed, 4%, 30%, 60%, and 100%) were incorporated to reveal the governing effects of high-altitude and cold environments on lubrication system startup behavior. The results indicate that under high-altitude and cold conditions, the decrease in oil temperature is the dominant factor and exerts the most significant influence on the steady-state oil pressure and flow rate of the lubrication system. Variations in ambient pressure lead only to an equivalent shift in absolute oil pressure, with negligible effects on relative oil pressure, steady-state flow rate, response time, or filling rate. However, a reduction in atmospheric pressure leads to a decrease in the peak oil flow rate at the outlet of the oil pump. The opening degree of the pressure relief valve exhibits a nonlinear influence on the startup performance of the lubrication system, and significantly decreases the oil filling rate. This study innovatively develops a lubrication system performance prediction model under high-altitude, low-pressure, and low-temperature conditions. Calibrated using vehicle road-test data, the model quantifies for the first time the relative contributions of the three key factors to start-up lubrication performance, thereby providing a clear decision-making framework and prioritized improvement directions for the reliability-oriented design and safety threshold calibration of lubrication systems in high-altitude diesel engines. Full article

(This article belongs to the Special Issue Challenges and Advances in Internal Combustion Engines Lubrication)

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26 pages, 4799 KB

Open AccessArticle

Tribological and Micro-Mechanical Behaviors of Advanced Polyethylene (HDPE) by Radiation

by Martin Ovsik, Adam Cesnek, Adam Pis, Klara Fucikova and Michal Stanek

Lubricants 2026, 14(2), 87; https://doi.org/10.3390/lubricants14020087 - 12 Feb 2026

Viewed by 577

Abstract

This study examines the tribological and micro-mechanical behavior of high-density polyethylene (HDPE), which has been advanced to the class of advanced polymers through electron beam irradiation (irradiation dose of 33 kGy to 198 kGy). The tribological and mechanical behaviors were analyzed at the [...] Read more.

This study examines the tribological and micro-mechanical behavior of high-density polyethylene (HDPE), which has been advanced to the class of advanced polymers through electron beam irradiation (irradiation dose of 33 kGy to 198 kGy). The tribological and mechanical behaviors were analyzed at the surface and at various depths beneath the surface to verify the extent of radiation effects across the entire cross-section of the specimen. Changes in tribological and mechanical behavior are closely related to changes in the structure of the material, mainly changes in crystallinity. As this study shows, 99 kGy appears to be the ideal radiation dose in terms of the properties examined. An increase in absorbed radiation dose leads to a deterioration of tribological and mechanical performance, which correlates with material degradation and a concomitant reduction in crystallinity. The improvement in the properties examined between unirradiated and irradiated HDPE at a dose of 99 kGy is 18% for mechanical behaviors and 8% for tribological behaviors on the surface of the sample. A maximum deviation of 39% was identified between the surface and the center of the material. There was also a change in crystallinity of up to 12%. These modifications result in enhanced surface wear resistance and increased overall stiffness, effectively shifting commodity-grade HDPE toward the performance domain of advanced polymers with only minimal cost implications. Full article

(This article belongs to the Special Issue Tribological Behaviours of Advanced Polymeric Materials)

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29 pages, 8793 KB

Open AccessArticle

Research on Load Distribution and Fatigue Life Under Elliptical Deformation of Four-Point Contact Slewing Bearing Rings for Excavators

by Haisheng Yang, Run Zhang, Jiahang Zhang, Zhanwang Shi and Yingbin Wei

Lubricants 2026, 14(2), 86; https://doi.org/10.3390/lubricants14020086 - 12 Feb 2026

Viewed by 509

Abstract

Excavators are critical equipment in mining, construction, and other fields. The four-point contact slewing bearings used in their slewing mechanisms operate under harsh conditions such as heavy loads and impacts. Furthermore, the bearing rings are prone to elliptical deformation after installation, making them [...] Read more.

Excavators are critical equipment in mining, construction, and other fields. The four-point contact slewing bearings used in their slewing mechanisms operate under harsh conditions such as heavy loads and impacts. Furthermore, the bearing rings are prone to elliptical deformation after installation, making them susceptible to premature failure. To address this issue, this paper establishes a mechanical bearing model to investigate the load distribution among balls and the fatigue life of the bearing under elliptical deformation of the rings. It systematically analyzes the influence of key design parameters. The research finds that elliptical deformation of the rings leads to contact angle deviation and a reduction in load-bearing balls, resulting in severe degradation of bearing fatigue life; therefore, its occurrence must be strictly controlled. Designing with a groove curvature radius coefficient within the range of 0.51 to 0.52 achieves an optimal balance between fatigue life and the four-point contact geometry of the balls. There exists an “optimal clearance” that maximizes bearing fatigue life; when considering significant elliptical deformation, the clearance design should be appropriately increased. Increasing the design contact angle enhances load capacity and helps mitigate the effects of elliptical deformation. However, an excessively large contact angle can cause ellipse truncation in the raceway contact zone; thus, the contact angle should be designed based on practical conditions. Increasing the number of balls can improve the influence of ovality on load distribution and enhance the bearing’s fatigue life. This study provides a theoretical reference for the design of high-reliability slewing bearings for excavators. Full article

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22 pages, 10720 KB

Open AccessArticle

Return to the Roots—Experimental Work on Water-Lubricated Bearings with Lignum Vitae Wood Bearing Bushes and Comparison with Other Similar Solutions

by Michał Wasilczuk, Bob Shortridge and Wojciech Litwin

Lubricants 2026, 14(2), 85; https://doi.org/10.3390/lubricants14020085 - 12 Feb 2026

Viewed by 865

Abstract

The results of experimental tests of six various water-lubricated bearings are described. Tests were performed under conditions typical for marine stern tube bearings. The acquired low-friction coefficient values indicated that the bearings operated in the fluid friction regime over a wide range of [...] Read more.

The results of experimental tests of six various water-lubricated bearings are described. Tests were performed under conditions typical for marine stern tube bearings. The acquired low-friction coefficient values indicated that the bearings operated in the fluid friction regime over a wide range of sliding speeds and loads. Due to elastic deformations of the flexible non-metal bushings, it was not possible to measure the lubricant film thickness to confirm this phenomenon. Studying measured hydrodynamic pressure distribution profiles, and thanks to lifting force calculation, it was proven that hydrodynamic phenomena occur between strongly deformed, rough surfaces lubricated by a low-viscosity fluid. Full article

(This article belongs to the Special Issue Water Lubricated Bearings)

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20 pages, 6979 KB

Open AccessArticle

Macroscale Superlubricity in Water-Based Systems on Electroless Ni–P Coatings via P-Content Optimization and Tribofilm Control

by Qinglin Ye, Huijie Zhang, Yuzhen Liu, Juan Jin, Kai Le, Shusheng Xu, Xiaoming Gao and Lijun Weng

Lubricants 2026, 14(2), 84; https://doi.org/10.3390/lubricants14020084 - 12 Feb 2026

Viewed by 598

Abstract

Electroless Ni–P coatings are widely used for corrosion and wear protection, yet their ability to deliver water-based superlubricity and the role of phosphorus content remain insufficiently understood. Here, electroless Ni–P coatings with four P contents (3.4, 6.4, 9.0, and 12.4 wt%) were deposited [...] Read more.

Electroless Ni–P coatings are widely used for corrosion and wear protection, yet their ability to deliver water-based superlubricity and the role of phosphorus content remain insufficiently understood. Here, electroless Ni–P coatings with four P contents (3.4, 6.4, 9.0, and 12.4 wt%) were deposited on GCr15 steel with nearly constant thickness and comparable initial roughness, and were tested against Si₃N₄ balls in neutral 0.5 M NaH₂PO₂ solution. Friction measurements, together with surface topography characterization and tribofilm analysis, were used to link P content with tribofilm chemistry and superlubricity. All coatings achieved macroscale superlubricity, exhibiting steady-state friction coefficients below 0.01, while the running-in time decreased markedly as P content increased. During sliding, the wear tracks underwent mechano-chemical polishing to Sa ≈ 11–12 nm and formed phosphate–silicate tribofilms enriched in P–O and Si–O species on both the coating and the counterface. These findings establish a composition–tribofilm–superlubricity relationship in the Ni–P/NaH₂PO₂ system and demonstrate that P-content optimization is an effective internal design lever to accelerate running-in, mitigate wear, and achieve robust superlubricity under neutral aqueous lubrication. Full article

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19 pages, 3805 KB

Open AccessArticle

Rotordynamic System-Level Effects of Three-Lobe Journal Bearings Including Manufacturing Variations

by Leonardo Ubiola-Soto and Adolfo Delgado

Lubricants 2026, 14(2), 83; https://doi.org/10.3390/lubricants14020083 - 11 Feb 2026

Viewed by 743

Abstract

This paper examines the impact of pad-to-pad manufacturing variations in three-lobe journal bearings on system-level rotordynamics. Two sources of non-uniform clearance were studied: dissimilar pad clearance and preload. Both were varied independently within standard manufacturing tolerances. The results show that the conventional assumption [...] Read more.

This paper examines the impact of pad-to-pad manufacturing variations in three-lobe journal bearings on system-level rotordynamics. Two sources of non-uniform clearance were studied: dissimilar pad clearance and preload. Both were varied independently within standard manufacturing tolerances. The results show that the conventional assumption that all pads having equal clearances at tolerance extremes does not capture worst-case conditions. Instead, specific non-uniform pad combinations caused the most significant amplification factors and the lowest stability margin. By applying a Surface Response Design of Experiments (SRDOE) method, surrogate models were developed to represent the nonlinear influence of the pads’ dissimilarity. The models identified the most critical combinations of pad and journal variables, revealing that industry-standard practice does not provide the most adverse system behavior. Worst-case conditions arise from non-uniform pad geometry: SRDOE models predict critical combinations, while uniform assumptions of industry-based standards underestimate risk. Incorporating realistic manufacturing variability in rotordynamic models provides a more reliable basis for turbomachinery design. Full article

(This article belongs to the Special Issue Advances in Lubricated Bearings, 2nd Edition)

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17 pages, 1973 KB

Open AccessArticle

Synthesis and Characterization of Trimethylolpropane Esters via Guanidine Carbonate-Catalyzed Transesterification of Sunflower Oil Methyl Esters

by Dimosthenis Filon, George Anastopoulos, Ypatia Zannikou and Dimitrios Karonis

Lubricants 2026, 14(2), 82; https://doi.org/10.3390/lubricants14020082 - 10 Feb 2026

Viewed by 686

Abstract

This study investigates the synthesis and physicochemical characterization of biolubricant base oils derived from sunflower oil methyl esters (SUNOMEs) via transesterification with trimethylolpropane (TMP) using guanidine carbonate (GNDC) as a green and efficient catalyst. The transesterification process was optimized to achieve high conversion [...] Read more.

This study investigates the synthesis and physicochemical characterization of biolubricant base oils derived from sunflower oil methyl esters (SUNOMEs) via transesterification with trimethylolpropane (TMP) using guanidine carbonate (GNDC) as a green and efficient catalyst. The transesterification process was optimized to achieve high conversion and desirable physicochemical properties suitable for lubrication applications. The synthesized esters were characterized by viscosity, density, pour point, and oxidation stability, confirming their suitability as environmentally friendly lubricants. Reaction parameters, such as catalyst concentration (3.0–5.0 wt%), were optimized under both solvent-free and vacuum-assisted conditions. The use of guanidine carbonate achieved enhanced physicochemical properties with significantly reduced reaction times (≈6 h) and eliminated soap formation. The resulting TMP triesters exhibited kinematic viscosities in ranges of 41.27–52.73 cSt (40 °C) and 8.668–10.02 cSt (100 °C), a viscosity index in the range of 180–196, and excellent oxidation stability (RSSOT: up to 54.27 min). Fourier transform infrared (FTIR) analysis confirmed the formation of complete triester structures with characteristic carbonyl and C–O stretching bands at 1735 cm⁻¹ and 1050 cm⁻¹, respectively. Spectra showed also distinct stretching vibrations near 1640–1670 cm⁻¹ and 3300–3400 cm⁻¹, which correspond to amide carbonyl and N–H characteristic groups. The tribological performance was evaluated using Four-Ball Standard Test Method, demonstrating significant improvements compared to commercial mineral oils. The results indicate that guanidine carbonate is an effective catalyst for producing sunflower-oil-derived esters with favorable lubricating properties, highlighting their potential as sustainable biolubricants for industrial applications. Full article

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48 pages, 10325 KB

Open AccessReview

Toward Reliable Triboelectric Nanogenerators: Roles of Lubricants

by P. R. Deshmukh and Dae-Hyun Cho

Lubricants 2026, 14(2), 81; https://doi.org/10.3390/lubricants14020081 - 10 Feb 2026

Viewed by 1081

Abstract

Triboelectric nanogenerators (TENGs) are a newly adopted technology designed to harvest freely available mechanical energy from the environment and convert it into electricity that can help to meet future demands for clean and sustainable energy. TENGs represent a promising next-generation renewable energy technology, [...] Read more.

Triboelectric nanogenerators (TENGs) are a newly adopted technology designed to harvest freely available mechanical energy from the environment and convert it into electricity that can help to meet future demands for clean and sustainable energy. TENGs represent a promising next-generation renewable energy technology, an alternative to traditional non-renewable fossil fuel sources, with a wide range of applications, including smart sensors, wearable devices, internet of things (IoT), and portable electronics. Through contact/triboelectrification and electrostatic induction, TENGs convert mechanical energy into electrical energy. Broadly, TENGs are classified into contact–separation mode and sliding mode. In contact–separation mode, the electric output is achieved through the contact and separation of triboelectric layers, while in the sliding mode, it is generated by the sliding of one triboelectric layer over another. Sliding-mode TENGs have demonstrated better electrical output compared to the contact–separation mode; however, they suffer low durability and cannot operate for long periods due to severe wear. In addition, their electrical output performance is reduced owing to air breakdown. Lubricants have demonstrated their potential in TENGs by overcoming these limitations and improving both tribological and triboelectric performance. This review provides a discussion on the fundamental modes of TENGs, followed by a comprehensive summary of the tribological and triboelectrical performance of existing TENGs under liquid lubrication, along with a comparison of their performance under dry conditions. The effects of load, frequency, mass fraction, and volume of the liquid lubricant on both tribology and electrical output are examined. Durability is identified as a key factor for the long-term practical application of TENGs; hence, this paper also focuses on it. Furthermore, strategies for improving TENG performance and the working mechanisms under liquid lubrication are discussed. Finally, the paper summarizes demonstrations of TENG applications based on various TENG designs. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Triboelectrification)

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22 pages, 5318 KB

Open AccessArticle

Study on Deformation Characteristics of Hollow Shaft of Grinding Mill’s Sliding Shoe Bearing Based on Fluid–Structure Interaction

by Yikai Zheng, Lun Li, Yujun Xue, Hanqi Wu, Yipeng Ren and Jiayi Zhao

Lubricants 2026, 14(2), 80; https://doi.org/10.3390/lubricants14020080 - 10 Feb 2026

Viewed by 578

Abstract

The sliding shoe bearing serves as a critical rotary support component in large grinding mills. The deformation of the hollow shaft under operating conditions is a pivotal factor governing the uniformity and stability of the lubricating oil film thickness in sliding shoe bearings. [...] Read more.

The sliding shoe bearing serves as a critical rotary support component in large grinding mills. The deformation of the hollow shaft under operating conditions is a pivotal factor governing the uniformity and stability of the lubricating oil film thickness in sliding shoe bearings. To address this, a finite element model of the sliding shoe bearing system, comprising the lubricating oil film and hollow shaft, was established based on fluid–structure interaction (FSI). The model’s predictions for oil cavity pressure and hollow shaft radial displacement were validated using a custom-built test rig designed for single-shoe sliding shoe bearing oil pressure measurements. Utilizing this finite element model, the relationship between hollow shaft deformation and oil film pressure distribution was systematically investigated. The study analyzed the effects of key parameters—specifically the area ratio of the primary and secondary oil chambers, radial load, secondary oil chamber supply pressure, and primary oil chamber supply orifice diameter—on the axial and circumferential deformation of the hollow shaft. The results indicate that the oil film pressure distribution directly influences the deformation of the hollow shaft. The area ratio of the oil chambers emerges as the dominant factor affecting this deformation. Furthermore, radial load exerts a significant impact, whereas the influence of the secondary oil chamber supply pressure is relatively minor. Conversely, the inner diameter of the primary oil chamber supply orifice exhibits a negligible effect on the hollow shaft deformation. Full article

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23 pages, 2882 KB

Open AccessArticle

The Influence of Misalignment on the Performance of the Herringbone Groove Journal Bearing-Rotor System

by Yubin Zhang, Fengtao Wang, Chunlan Yu, Huomei Zhu and Xiaoyun Zhao

Lubricants 2026, 14(2), 79; https://doi.org/10.3390/lubricants14020079 - 10 Feb 2026

Viewed by 629

Abstract

Misalignment of the herringbone groove radial bearing can lead to changes in performance and system abnormalities. To investigate the effects of different misalignment modes and magnitudes on the HGJB-rotor system, a coupled dynamic model was established. Based on this model, the influences of [...] Read more.

Misalignment of the herringbone groove radial bearing can lead to changes in performance and system abnormalities. To investigate the effects of different misalignment modes and magnitudes on the HGJB-rotor system, a coupled dynamic model was established. Based on this model, the influences of parallel misalignment and angular misalignment on bearing performance were analyzed, and the variation law of rotor vibration was revealed. The results indicate that the rotor motion trajectory and bearing dynamic coefficients (including critical journal mass and critical whirl frequency) exhibit time-varying characteristics. Specifically, compared with the aligned condition, a parallel misalignment of δ = 8.0 × 10⁻⁶ m reduces the relative film thickness by 17.8% and increases the maximum film pressure by 1.85%. Meanwhile, an angular misalignment of θ₀ = 8.0 × 10⁻⁴ rad results in a 45.9% reduction in relative film thickness and a 33.1% increase in maximum film pressure. Additionally, the increased misalignment magnitude enhances the rotor vibration amplitude significantly. For instance, the Y-direction displacement amplitude increases by 59.4% under the maximum parallel misalignment. Moreover, the misalignment also alters the axial trajectory of the rotor. Overall, different misalignment modes and magnitudes exert significant effects on the rotor vibration characteristics. The research findings provide theoretical support and technical references for the further development and engineering application of HGJBs. Full article

(This article belongs to the Special Issue Advances in Hydrodynamic Bearings)

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22 pages, 3356 KB

Open AccessArticle

Effect of TiO₂ and SiO₂ Nanoparticles on Traction, Wear, and High-Shear Viscosity of PAG Lubricants Under Elastohydrodynamic (EHL) Conditions for Refrigeration Systems

by Mohd Zaki Sharif, Mohd Syafiq Abd Aziz, Mohd Farid Ismail, Mohd Fadzli Bin Abdollah, Abdul Aziz Mohamad Redhwan, Nor Azazi Ngatiman and Anwar Ilmar Ramadhan

Lubricants 2026, 14(2), 78; https://doi.org/10.3390/lubricants14020078 - 9 Feb 2026

Viewed by 653

Abstract

This study tests TiO₂ and SiO₂ nanolubricants in PAG oil using a Mini Traction Machine and an Ultra Shear Viscometer. The loads were 20 N and 40 N. The entrainment speeds ranged from 2.5 to 500 mm/s. The slide-to-roll ratio (SRR) [...] Read more.

This study tests TiO₂ and SiO₂ nanolubricants in PAG oil using a Mini Traction Machine and an Ultra Shear Viscometer. The loads were 20 N and 40 N. The entrainment speeds ranged from 2.5 to 500 mm/s. The slide-to-roll ratio (SRR) ranged from 25 to 150%. The nanoparticle concentrations were 0.01, 0.03, and 0.05%. The ball size was 19.05 mm, and the disc was 46 mm. All tests were run at 40 °C. Only the 0.05% concentration lowered traction compared with PAG at a fixed SRR. TiO₂ at 0.05% showed the largest drop, up to 4.89% at 20 N and 2.99% at 40 N. However, lower concentrations increased traction. All the nanolubricants reduced wear. TiO₂ at 0.03% gave the lowest wear, with a reduction of about 35 µm at 40 N. Nanolubricant samples stayed between 40.2 and 40.5 °C, while PAG reached about 41.0 °C. TiO₂ produced slightly lower temperatures than SiO₂. Ultra-shear tests from 40 to 100 °C showed shear thinning. In most conditions, TiO₂ at 0.05% kept the highest viscosity at 40 and 60 °C, up to 12% above PAG. SiO₂ showed smaller changes. TiO₂ delivered better friction, wear, temperature, and viscosity performance. Overall, both nanolubricants at 0.03% are suitable when wear reduction and thermal stability are prioritised over traction reduction, such as in refrigeration applications, while the 0.05% suits high-load or high-shear use. Full article

(This article belongs to the Special Issue Tribological Behavior of Nanolubricants: Do We Know Enough?)

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28 pages, 2783 KB

Open AccessReview

Tribological Properties of Biolubricants: A Comprehensive Bibliometric and Trend Analysis

by M. Marliete F. Melo Neta, Rodolpho R. C. Monteiro, Paulo R. C. F. Ribeiro Filho, Célio L. Cavalcante, Jr. and Francisco Murilo Tavares Luna

Lubricants 2026, 14(2), 77; https://doi.org/10.3390/lubricants14020077 - 7 Feb 2026

Viewed by 1274

Abstract

Interest in replacing petroleum-based lubricants with bio-based alternatives is driven by growing demand for lubricants, in contrast to a decreasing supply of products derived from fossil resources, coupled with environmental concerns. Biolubricants offer several advantages over conventional petroleum-based lubricants, such as biodegradability and [...] Read more.

Interest in replacing petroleum-based lubricants with bio-based alternatives is driven by growing demand for lubricants, in contrast to a decreasing supply of products derived from fossil resources, coupled with environmental concerns. Biolubricants offer several advantages over conventional petroleum-based lubricants, such as biodegradability and renewability. Researchers have been seeking solutions for these challenges over the years, employing various approaches, including the use of different raw materials, chemical modifications, and different types of additives. This review evaluates a total of 504 articles published between 2010 and 2025 in the Scopus database, with the help of RStudio, using the bibliometrix package. The objective is to provide an integrated bibliometric and systematic analysis, presenting the research landscape on the tribological properties of biolubricants, which may contribute to the development of novel investigation initiatives in the field. The main thematic trends, researchers, journals, and most active countries and institutions have been evaluated. Additionally, the most cited studies, recent advances and existing gaps are presented and discussed. Full article

(This article belongs to the Special Issue Tribological Performance and Applications of Environmentally Friendly Biolubricants)

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18 pages, 9942 KB

Open AccessArticle

Experimental Investigation of a Highly Loaded Half-Journal Bearing

by James Layton, Humberto Medina, Hasna Fadhila, Benjamin C. Rothwell, Stephen Ambrose, Katrina Farbrother and Carol Eastwick

Lubricants 2026, 14(2), 76; https://doi.org/10.3390/lubricants14020076 - 6 Feb 2026

Viewed by 652

Abstract

A dedicated experimental rig is presented for a half-journal bearing operating under highly loaded, well-controlled hydrodynamic lubrication conditions relevant to turbomachinery. The apparatus combines pressure measurements in the film, distributed temperature measurements in the shaft and bush, and ultrasonic film-thickness measurements that map [...] Read more.

A dedicated experimental rig is presented for a half-journal bearing operating under highly loaded, well-controlled hydrodynamic lubrication conditions relevant to turbomachinery. The apparatus combines pressure measurements in the film, distributed temperature measurements in the shaft and bush, and ultrasonic film-thickness measurements that map the circumferential film-thickness profile across the lubrication region. Experiments are reported for normal loads of 5–20 kN and shaft speeds of 1000–4000 rpm with controlled oil supply conditions. The measured pressure and temperature trends are consistent with established hydrodynamic lubrication behaviour. The film thickness measurements confirm full-film operation across the tested operating envelope, while indicating increased uncertainty in regions affected by cavitation. A correlation for the temperature rise due to viscous heating is proposed as a compact representation of the data. The rig design and accompanying measurements provide a benchmark-quality data set intended for validation and development of thermal elasto-hydrodynamic lubrication (TEHL)/computational fluid dynamics (CFD) models under high load and speed conditions. Full article

(This article belongs to the Special Issue Advances in Hydrodynamic Bearings)

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16 pages, 2820 KB

Open AccessArticle

Reliability Assessment of Spherical Assembly Mechanical Seals in Turbo Pumps

by Tianzhao Li, Muming Hao, Yongfan Li, Yong Song, Baojie Ren, Chenyin Wang and Xiaozu Li

Lubricants 2026, 14(2), 75; https://doi.org/10.3390/lubricants14020075 - 6 Feb 2026

Viewed by 564

Abstract

The spherical assembly mechanical end-face seal, a pivotal component of the liquid rocket engine turbopump, holds direct influence over the performance of the turbopump. This paper introduces a approach for assessing the reliability of mechanical seals. The proposed method formulates a dimensionless reliability [...] Read more.

The spherical assembly mechanical end-face seal, a pivotal component of the liquid rocket engine turbopump, holds direct influence over the performance of the turbopump. This paper introduces a approach for assessing the reliability of mechanical seals. The proposed method formulates a dimensionless reliability factor, R, derived from multiple sets of monitoring data collected during the operation of the seal. The health status of the seal can be evaluated based on the value of R. The computation of R is contingent on two main elements: firstly, it relies on the threshold of evaluation parameters obtained from laboratory tests, and secondly, it incorporates the weight of parameters derived from expert experience using fuzzy set theory. And then R can be calculated by substituting real-time monitoring data of the seal. The efficacy of the proposed method was substantiated through testing and verification using two sets of real-world engineering data, and was subsequently compared with methods currently employed in engineering. The results indicate that the proposed method surpasses existing methods in terms of accuracy and sensitivity. Furthermore, the data upon which it is based can be easily monitored in an engineering context, thereby enhancing its relevance and potential for widespread application in engineering. Full article

(This article belongs to the Special Issue Recent Advances in Sealing Technologies)

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17 pages, 5957 KB

Open AccessArticle

Wear of Lubricated Point and Line Contacts at Matched Hertzian Contact Stress

by Jiazhen Chen and Ashlie Martini

Lubricants 2026, 14(2), 74; https://doi.org/10.3390/lubricants14020074 - 5 Feb 2026

Cited by 1 | Viewed by 845

Abstract

Wear, a critical factor governing the performance and durability of mechanical systems, is typically characterized using point-contact and line-contact test configurations. However, it remains unclear whether the wear trends observed in one test configuration would be observed in the other configuration under the [...] Read more.

Wear, a critical factor governing the performance and durability of mechanical systems, is typically characterized using point-contact and line-contact test configurations. However, it remains unclear whether the wear trends observed in one test configuration would be observed in the other configuration under the same nominal conditions. In this study, ball-on-disk (ASTM G99) and block-on-ring (ASTM G77) tests were conducted under an identical maximum Hertzian contact stress and sliding speed, using the same material pair and lubricating oil, to clarify which contact configuration exhibits more wear and why. The results show that, under the same Hertzian contact stress, the line-contact configuration exhibits a specific wear rate two orders of magnitude higher than the point-contact configuration, despite exhibiting a lower and more stable coefficient of friction. The disk wear is negligible and the ball shows only mild material loss, whereas the line-contact system displays wear rates several orders of magnitude higher, with the rotating ring contributing the dominant share of the total wear. White-light interferometry and scanning electron microscopy observations reveal directional, groove-dominated surface morphologies on the ball and disk, while wear on the block is confined to edge-localized regions and the worn ring surface has smooth, polished morphology. Energy-dispersive X-ray spectroscopy confirms that a Zn- and P-rich tribofilm forms exclusively on the ring surface. Finite element analysis shows stress amplification at the finite line-contact edges, explaining the observed wear severity. These results demonstrate that matching Hertzian contact stress alone is insufficient to ensure comparable wear behavior between point and line contacts. Full article

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25 pages, 3002 KB

Open AccessArticle

Research on Contact Performance and Friction Force of VL Seal of Aviation Actuator Under High Pressure Conditions

by Yanan Wang, Wenjun Yu, Jianping Ai, Xihui Tao, Qingyun Guo, Dongye Wang, Junying Suo and Xiuxu Zhao

Lubricants 2026, 14(2), 73; https://doi.org/10.3390/lubricants14020073 - 4 Feb 2026

Viewed by 766

Abstract

To elucidate the contact performance and friction force variation characteristics of VL seals for aviation actuators under high-pressure conditions, this study adopted a fluid–structure interaction (FSI)-coupled finite element model to analyze the maximum contact pressure and contact width and their respective variation trends [...] Read more.

To elucidate the contact performance and friction force variation characteristics of VL seals for aviation actuators under high-pressure conditions, this study adopted a fluid–structure interaction (FSI)-coupled finite element model to analyze the maximum contact pressure and contact width and their respective variation trends across varying oil pressures and reciprocating velocities. Subsequently, friction force tests of the seals were conducted under matching operating parameters, and the friction coefficients of polytetrafluoroethylene (PTFE) were measured and compared under different normal pressures. The results demonstrate that the friction force of the seals during both extending and retracting strokes increases with rising oil pressure, which is highly correlated with the theoretically predicted conclusion that the seal contact width expands as oil pressure increases. Further analysis confirms that reciprocating velocity exerts no significant influence on the aforementioned variation trends. This study provides a critical basis for the selection and optimal design of VL seals used in high-pressure aviation hydraulic actuators. Full article

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

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26 pages, 1858 KB

Open AccessReview

Artificial Intelligence in Lubricant Research—Advances in Monitoring and Predictive Maintenance

by Raj Shah, Kate Marussich, Vikram Mittal and Andreas Rosenkranz

Lubricants 2026, 14(2), 72; https://doi.org/10.3390/lubricants14020072 - 3 Feb 2026

Viewed by 1714

Abstract

Artificial intelligence transforms lubricant research by linking molecular modeling, diagnostics, and industrial operations into predictive systems. In this regard, machine learning methods such as Bayesian optimization and neural-based Quantitative Structure–Property/Tribological Relationship (QSPR/QSTR) modeling help to accelerate additive design and formulation development. Moreover, deep [...] Read more.

Artificial intelligence transforms lubricant research by linking molecular modeling, diagnostics, and industrial operations into predictive systems. In this regard, machine learning methods such as Bayesian optimization and neural-based Quantitative Structure–Property/Tribological Relationship (QSPR/QSTR) modeling help to accelerate additive design and formulation development. Moreover, deep learning and hybrid physics–AI frameworks are now capable to predict key lubricant properties such as viscosity, oxidation stability, and wear resistance directly from molecular or spectral data, reducing the need for long-duration field trials like fleet or engine endurance tests. With respect to condition monitoring, convolutional neural networks automate wear debris classification, multimodal sensor fusion enables real-time oil health tracking, and digital twins provide predictive maintenance by forecasting lubricant degradation and optimizing drain intervals. AI-assisted blending and process control platforms extend these advantages into manufacturing, reducing waste and improving reproducibility. This article sheds light on recent progress in AI-driven formulation, monitoring, and maintenance, thus identifying major barriers to adoption such as fragmented datasets, limited model transferability, and low explainability. Moreover, it discusses how standardized data infrastructures, physics-informed learning, and secure federated approaches can advance the industry toward adaptive, sustainable lubricant development under the principles of Industry 5.0. Full article

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30 pages, 4060 KB

Open AccessArticle

Experimental Investigation of Lubrication Effects in High-Feed Face Milling Using DOE-Based Cutting Force and Surface Analysis

by Gyula Varga, István Sztankovics and Antal Nagy

Lubricants 2026, 14(2), 71; https://doi.org/10.3390/lubricants14020071 - 3 Feb 2026

Viewed by 642

Abstract

High-feed face milling is widely adopted in industry for its productivity advantages, especially when machining medium carbon steels. However, the combined effects of lubrication regimes on both the cutting forces and surface quality remain insufficiently explored, creating a research gap in optimizing process [...] Read more.

High-feed face milling is widely adopted in industry for its productivity advantages, especially when machining medium carbon steels. However, the combined effects of lubrication regimes on both the cutting forces and surface quality remain insufficiently explored, creating a research gap in optimizing process parameters for improved performance. This study presents an experimental investigation into the effects of lubrication on cutting forces and surface topography during the high-feed face milling of C45 steel. Using a design of experiments (DOE) approach, eight distinct machining setups were developed by varying the cutting speed, depth of cut, and feed per tooth. Each setup was tested under two lubrication conditions: with flood coolant and under dry machining. Cutting forces in the X, Y, and Z directions were recorded using a dynamometer, while the post-machining surface quality was evaluated using 3D areal surface topography measurements. The results revealed that feed per tooth was the primary factor affecting both the cutting forces and surface roughness, with depth of cut having a moderate effect and cutting speed a minor influence. Flood lubrication reduced the peak forces, stabilized force fluctuations, and improved surface uniformity, particularly in the valley depths and skewness parameters. This work provides (i) a combined analysis of cutting forces and surface topography under high-feed milling, (ii) quantitative evidence of lubrication effects on force and surface consistency, and (iii) identification of dominant process parameters for optimization, offering practical guidance for enhancing productivity, surface quality, and tribological performance in high-feed milling operations. Full article

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

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27 pages, 2466 KB

Open AccessReview

Application of Cryogenic Minimum Quantity Lubrication Technology in Different Machining Processing for Titanium Alloys: A Review

by Xiangke Tian, Tai Ma, Jie Yang and Qinglong An

Lubricants 2026, 14(2), 70; https://doi.org/10.3390/lubricants14020070 - 3 Feb 2026

Viewed by 1085

Abstract

Titanium alloys face challenges such as high temperatures, high forces, and tool wear during turning, milling, drilling, and grinding operations. Cryogenic minimum quantity lubrication (CMQL) technology, which combines cryogenic cooling with micro-lubrication, offers an effective solution to these challenges through its synergistic mechanism [...] Read more.

Titanium alloys face challenges such as high temperatures, high forces, and tool wear during turning, milling, drilling, and grinding operations. Cryogenic minimum quantity lubrication (CMQL) technology, which combines cryogenic cooling with micro-lubrication, offers an effective solution to these challenges through its synergistic mechanism of heat suppression via cooling and friction reduction via lubrication. This paper first elucidates the cooling and lubrication principles of various CMQL technologies and their adaptability process. It then reviews CMQL applications across four titanium alloy machining processes, systematically analyzing their effects on cutting forces, temperatures, tool wear, surface integrity, and chip morphology. Research indicates that CMQL technology demonstrates universal advantages over minimum quantity lubrication (MQL) across diverse titanium alloy machining processes. Furthermore, incorporating nanofluids or integrating ultrasonic vibration to form enhanced composite processes can further improve medium permeability, reduce machining loads, and enhance surface quality. Future developments in this field will advance toward intelligent and sustainable directions, providing critical technological support for high-performance green manufacturing of titanium alloys. Full article

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

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30 pages, 12752 KB

Open AccessArticle

Study on Influence of Roller Profile Modification on Wear of Tapered Roller Bearing

by Zhaoxia Luo, Dingkang Zhu, Wenjing Zhang, Weisong Tian, Yu Zhang, Koucheng Zuo and Lai Hu

Lubricants 2026, 14(2), 69; https://doi.org/10.3390/lubricants14020069 - 2 Feb 2026

Viewed by 857

Abstract

Addressing the scientific problem that the profile modification design of tapered roller bearings primarily focuses on contact stress and fatigue life while neglecting its impact on wear evolution, this paper, based on Hertzian contact theory and the Archard wear theory, and considering centrifugal [...] Read more.

Addressing the scientific problem that the profile modification design of tapered roller bearings primarily focuses on contact stress and fatigue life while neglecting its impact on wear evolution, this paper, based on Hertzian contact theory and the Archard wear theory, and considering centrifugal force, gyroscopic effect, and the complex contact state between rollers and raceways, constructed a comprehensive analysis framework integrating a quasi-static model for profiled rollers and a wear depth calculation model. This framework is novel in that it systematically couples roller profile modification parameters with raceway wear evolution under both pure axial and combined radial–axial loads. The validity and effectiveness of the proposed model were verified by comparing the results of the quasi-static model with load distribution data from existing literature and through measurements conducted on a specially designed bearing wear test platform. The main findings are as follows: (1) When the logarithmic modification parameter f₁ increases from 0.7 μm to 3.6 μm, the maximum wear depth of the inner raceway increases by 133% under pure axial load and 144% under combined load, while that of the outer raceway increases by 142% under pure axial load and expands from 0.1–0.2 μm to 0.23–0.52 μm under combined load. (2) Combined load induces significant asymmetric wear on the outer raceway, and the difference between the two wear peaks increases from 0.13 μm to 0.35 μm as f₁ rises from 0.7 μm to 3.6 μm. (3) The wear peak shifts toward the midpoint of the roller generatrix with increasing modification amount. These results provide important guidance for the wear-oriented optimization design of tapered roller bearings. Full article

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

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