Lubricants

15 pages, 1980 KB

Open AccessArticle

Optimizing the Artificial Aging Process of Lubricating Oils Contaminated by Alternative Fuel Using Design of Experiments Methodology

by Dominika Pintér and András Lajos Nagy

Lubricants 2025, 13(9), 405; https://doi.org/10.3390/lubricants13090405 - 11 Sep 2025

Abstract

This study aimed to develop an experimental method for producing artificially aged oil with properties—such as coefficient of friction, average wear scar diameter, and antiwear additive content—similar to those of used oil contaminated with alternative fuel, sampled after 129 h of engine test [...] Read more.

This study aimed to develop an experimental method for producing artificially aged oil with properties—such as coefficient of friction, average wear scar diameter, and antiwear additive content—similar to those of used oil contaminated with alternative fuel, sampled after 129 h of engine test bench operation. A design of experiment (DoE) methodology was applied to examine the effects of various parameters and identify optimal settings. Friction and wear tests were conducted using an Optimol SRV5 tribometer in a ball-on-disc configuration, while wear scars were analyzed with a Keyence VHX-1000 digital microscope. Oil analysis was conducted with an Anton Paar 3001 viscometer and a Bruker Invenio-S Fourier-transform infrared spectrometer. The DoE results showed that the heating duration had a negligible effect on oil degradation. Aging time primarily affected changes in the friction coefficient and average wear scar diameter, whereas aging temperature was the primary factor influencing the anti-wear additive content. Gaussian elimination identified the optimal aging parameters as 132.8 °C and 103.1 h. These results were confirmed through surface analysis using a ThermoFisher NexsaG2 X-ray photoelectron spectrometer, which showed that the tribofilm composition of the used oil most closely matched that of artificially aged oils prepared at 120 °C for 96 h and 140 °C for 120 h. The strong correlation between the predicted and experimentally confirmed conditions demonstrates the reliability of the proposed method for replicating realistic aging effects in lubricating oils. Full article

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14 pages, 4502 KB

Open AccessArticle

Synthesis and Performance Study of a New Ether-Polyalphaolefin Base Oil

by Lei Huang and Wumanjiang Eli

Lubricants 2025, 13(9), 404; https://doi.org/10.3390/lubricants13090404 - 11 Sep 2025

Abstract

This study reports the first synthesis of a new type of ether-polyalphaolefin (DVE-PAO) base oil via free radical bulk copolymerization using triethylene glycol divinyl ether (DVE-3) and α-olefin in drip-feed mode. The characteristic structure of DVE-PAO was characterized by Fourier Transform Infrared Spectroscopy [...] Read more.

This study reports the first synthesis of a new type of ether-polyalphaolefin (DVE-PAO) base oil via free radical bulk copolymerization using triethylene glycol divinyl ether (DVE-3) and α-olefin in drip-feed mode. The characteristic structure of DVE-PAO was characterized by Fourier Transform Infrared Spectroscopy (FTIR) and Nuclear Magnetic Resonance Spectroscopy (NMR). The relative molecular weight and molecular weight distribution of DVE-PAO were determined using gel permeation chromatography (GPC). Structurally, it is a new type of base oil that integrates both polyalkylene glycol (PAG) and polyalphaolefin (PAO) structural units. The research shows that the viscosity of DVE-PAO base oil, the conversion rate of α-olefin, and the pour point of the copolymer increase with rising copolymerization temperature. Additionally, results from the rotating oxygen bomb test indicate that the oxidation stability of DVE-PAO also improves with increasing viscosity. Based on the principles of free radical copolymerization, this study provides a preliminary elucidation of the copolymerization patterns between the aforementioned double-ended vinyl ethers and α-olefins. Furthermore, the DVE-PAO base oil exhibits excellent miscibility with both mineral oils and polyalphaolefin (PAO) base oils. As a result, this ether-based polyalphaolefin is expected to find broad applications in the field of lubricants. Full article

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15 pages, 3513 KB

Open AccessArticle

Study on the Formation Mechanism of Oil Sludge in Polyol Esters in Presence of High-Temperature Antioxidant N-Phenyl-α-naphthylamine

by Cheng Cao, Hanglin Li, Shichao Han and Jiusheng Li

Lubricants 2025, 13(9), 403; https://doi.org/10.3390/lubricants13090403 - 10 Sep 2025

Abstract

Compared with traditional lubricants, polyol ester lubricants exhibit superior oxidative stability and have been widely applied in extreme operating conditions such as aviation engines. However, under high-temperature conditions, polyol esters are still susceptible to oxidation and therefore require the addition of antioxidants. N-phenyl-α-naphthylamine [...] Read more.

Compared with traditional lubricants, polyol ester lubricants exhibit superior oxidative stability and have been widely applied in extreme operating conditions such as aviation engines. However, under high-temperature conditions, polyol esters are still susceptible to oxidation and therefore require the addition of antioxidants. N-phenyl-α-naphthylamine is an excellent high-temperature antioxidant used in polyol ester. However, a notable issue is that oil sludge may form when this antioxidant is used at high temperatures. Excessive sludge can lead to a series of problems such as oil circuit blockage, more severe mechanical wear, and poor heat dissipation performance. In this work, oil sludge formation from N-phenyl-α-naphthylamine was simulated via high-temperature oxidation experiments in a polyol ester base oil. The formed sludge was then characterized by various advanced techniques, such as FT-IR, GPC, TGA, MALDI-TOF MS, and XPS. The results showed that the oil sludge was mainly composed of derivatives of polyol esters and N-phenyl-α-naphthylamine, along with some metal components. Further analysis showed that polymerization reactions between antioxidant molecules are the key factors leading to sludge generation, and polycyclic aromatic compounds formed by polymerization are responsible for inducing sludge generation in polyol esters. Full article

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27 pages, 4453 KB

Open AccessArticle

Multi-Objective Optimization of Wet Clutch Groove Structures Based on Response Surface Methodology and Engagement Thermal–Flow Analysis

by Xiangping Liao, Langxin Sun, Ying Zhao and Xinyang Zhu

Lubricants 2025, 13(9), 402; https://doi.org/10.3390/lubricants13090402 - 10 Sep 2025

Abstract

This study addresses the thermal hazards that arise during the initial engagement stage of wet clutches, where rapid heat generation within the transient lubricating film may cause premature film rupture, torque instability, and accelerated wear. To overcome these challenges, a coupled thermo–fluid model [...] Read more.

This study addresses the thermal hazards that arise during the initial engagement stage of wet clutches, where rapid heat generation within the transient lubricating film may cause premature film rupture, torque instability, and accelerated wear. To overcome these challenges, a coupled thermo–fluid model was developed to capture oil film flow, heat transfer, and viscous torque behavior under varying groove structures. A novelty of this work is the first integration of computational fluid dynamics (CFD) with response surface methodology (RSM) to systematically reveal how groove geometry—cross-sectional shape, number, and inclination angle—collectively influences peak temperature and viscous torque during the lubricating film stage. Simulation results show that spiral semi-circular grooves provide superior thermal management, reducing the peak friction plate temperature to 75.5 °C, while the optimized design obtained via RSM (groove depth of 0.89 mm, 19 grooves, and a 5.28° inclination angle) further lowers the maximum temperature to 68.2 °C and sustains torque transmission above 18.5 N·m. These findings demonstrate that rational groove design, guided by multi-objective optimization, can mitigate thermal risks while maintaining torque stability, offering new insights for the high-performance design of wet clutches. Full article

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61 pages, 12556 KB

Open AccessReview

The Recent Advancements in Minimum Quantity Lubrication (MQL) and Its Application in Mechanical Machining—A State-of-the-Art Review

by Aqib Mashood Khan, MD Rahatuzzaman Rahat, Umayar Ahmed, Muhammad Jamil, Muhammad Asad Ali, Guolong Zhao and José V. Abellán-Nebot

Lubricants 2025, 13(9), 401; https://doi.org/10.3390/lubricants13090401 - 9 Sep 2025

Abstract

The move toward environmentally friendly methods in the global manufacturing sector has led to the use of minimum quantity lubrication (MQL) as an eco-friendly alternative to traditional flood cooling. However, the natural limits of MQL in high-performance settings have led to the use [...] Read more.

The move toward environmentally friendly methods in the global manufacturing sector has led to the use of minimum quantity lubrication (MQL) as an eco-friendly alternative to traditional flood cooling. However, the natural limits of MQL in high-performance settings have led to the use of nanotechnology, which has resulted in the creation of nanofluids, engineered colloidal suspensions that significantly improve the thermophysical and tribological properties of base fluids. This paper gives a complete overview of the latest developments in nanofluid technology for use in machining. It starts with the basics of MQL and the rules for making, describing, and keeping nanofluids stable. The review examines the application and effectiveness of single and hybrid nanofluids in various machining processes. It goes into detail about how they improve tool life, surface integrity, and overall efficiency. It also examines the benefits of integrating nanofluid-assisted MQL (NMQL) with more advanced and hybrid systems, including cryogenic cooling (cryo-NMQL), ultrasonic atomization, electrostatic–magnetic assistance, and multi-nozzle delivery systems. The paper also gives a critical look at the main problems that these technologies face, such as the long-term stability of nanoparticle suspensions, their environmental and economic viability as measured by life cycle assessment (LCA), and the important issues of safety, toxicology, and disposal. This review gives a full picture of the current state and future potential of nanofluid-assisted sustainable manufacturing by pointing out important research gaps, like the need for real-time LCA data, cost-effective scalability, and the use of artificial intelligence (AI) to improve processes, and by outlining future research directions. Full article

(This article belongs to the Special Issue Nanofluid Minimum Quantity Lubrication)

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Graphical abstract

13 pages, 2002 KB

Open AccessArticle

Thermal Elastohydrodynamic Lubrication Analysis of Grease in Tripod Sliding Universal Couplings

by Xinchen Chen, Xia Xiu, Ye Zhou, Chenxin Dong and Degong Chang

Lubricants 2025, 13(9), 400; https://doi.org/10.3390/lubricants13090400 - 9 Sep 2025

Abstract

The tripod sliding universal coupling (TSUC) is a novel type of coupling developed through independent research. This study theoretically investigates the effects of the grease flow index and initial viscosity on thermal elastohydrodynamic lubrication (TEHL) properties. Three common grease formulations were evaluated for [...] Read more.

The tripod sliding universal coupling (TSUC) is a novel type of coupling developed through independent research. This study theoretically investigates the effects of the grease flow index and initial viscosity on thermal elastohydrodynamic lubrication (TEHL) properties. Three common grease formulations were evaluated for TSUC lubrication. The numerical results yielded the following insights: a larger flow index increases film thickness and elevates the secondary pressure peak. A higher initial viscosity enhances film thickness yet significantly elevates the temperature distribution due to quadratic growth in viscous dissipation. It also intensifies the secondary pressure peak, which may exceed the central Hertzian pressure under heavy loads, thereby accelerating surface fatigue. The lubrication performance varies significantly across grease types. When pressure–viscosity coefficients and densities are similar, the initial viscosity becomes the dominant factor. These findings provide a theoretical basis for optimizing grease selection in TSUC systems to improve the efficiency and durability of lubrication. Full article

(This article belongs to the Special Issue Modeling and Simulation of Elastohydrodynamic Lubrication)

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13 pages, 3731 KB

Open AccessArticle

Improving the Wear Properties of Ductile Iron by Introducing Ultrafine Graphite Nodules

by Chen Liu, Yuzhou Du, Haohao Li, Caiyin You, Chao Yang, Na Tian and Bailing Jiang

Lubricants 2025, 13(9), 399; https://doi.org/10.3390/lubricants13090399 - 9 Sep 2025

Abstract

The tribological behavior of ferritic ductile iron without ultrafine graphite nodules (FDI) and ferritic ductile iron with ultrafine graphite nodules (FDI-UG) was investigated in the present study. Ultrafine graphite nodules with a count of 3400 nod/mm² were introduced by annealing treatment of [...] Read more.

The tribological behavior of ferritic ductile iron without ultrafine graphite nodules (FDI) and ferritic ductile iron with ultrafine graphite nodules (FDI-UG) was investigated in the present study. Ultrafine graphite nodules with a count of 3400 nod/mm² were introduced by annealing treatment of quenched ductile iron, which effectively reduced the friction coefficient of ferritic ductile iron from approximately 0.3 to 0.15. This improvement was attributed to the ultrafine graphite nodules, which, due to their small spacing, facilitated a more uniform distribution on the tribological surface. Additionally, the formation of ultrafine graphite nodules in ferritized ductile iron refined the grain size (15 μm) and enhanced the hardness of ferritic ductile iron (183 HV), thereby significantly reducing abrasive wear. The more uniform graphite lubrication on the tribosurface and high hardness of fine ferrite grains in FDI-UG further enhanced wear resistance between the frictional pairs, effectively suppressing adhesion wear at high loads (6 N). Consequently, the ferritic ductile iron containing ultrafine graphite nodules and fine ferrite grains exhibited a superior wear resistance (6.84 × 10⁻³ mm³ and 9.47 × 10⁻³ mm³) compared to its untreated counterpart (9.22 × 10⁻³ mm³ and 11.95 × 10⁻³ mm³). These findings suggest that the incorporation of ultrafine graphite nodules was an effective strategy to enhance the tribological properties of ductile iron. Full article

(This article belongs to the Special Issue Advances in Wear-Resistant Fe-Based Materials)

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15 pages, 4353 KB

Open AccessArticle

Simulation Study on the Effect of Molecular Structure Characteristics of Lubricant Base Oils on Lubrication Performance

by Boxi Tian, Yixi Shao, Feng Zhu, Chengzhi Hu, Tiedong Zhang, Jiaxin Liu, Honglin Xu, Chengyuan Cao, Hongliang Yu and Weiwei Wang

Lubricants 2025, 13(9), 398; https://doi.org/10.3390/lubricants13090398 - 8 Sep 2025

Viewed by 216

Abstract

The complex composition of lubricating base oils makes it difficult to analyze the influence of specific molecular structure on lubricating performance. To achieve this target, nine kinds of poly α-olefin molecules with different structure characteristics were designed, which prepared the lubricant models. Molecular [...] Read more.

The complex composition of lubricating base oils makes it difficult to analyze the influence of specific molecular structure on lubricating performance. To achieve this target, nine kinds of poly α-olefin molecules with different structure characteristics were designed, which prepared the lubricant models. Molecular dynamic simulation was used to analyze the tribological performance under pressure of 500 MPa, temperature 353 K, and shear velocity of 20 m/s; the volume compression and shear stress of lubricant films were obtained. Molecular volume, adsorption energies, radius of gyration, and mean square displacement were used to analyze the relationship between molecular structure and lubricant performance. Results show that the characteristic of the Iso and Mid type have the best friction reduction performance. The molecules of the Iso structure have the highest oil film thickness and the best load-bearing performance. The radius of gyration increases with the shear simulation for most of the molecules. The adsorption energy of End is the highest, and the Mid is the smallest. Among the nine molecules, C20Iso shows excellent performance both in load-bearing and friction reduction, which provides a reference for the molecular design of high-performance lubricant base oils. Full article

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24 pages, 1799 KB

Open AccessArticle

Lubricant Performance in Wind Turbines: A Data Study in Real-Use Conditions

by A. E. Jiménez, H. J. Barajas, M. D. Avilés, I. J. Martínez-Mateo and F. J. Carrión-Vilches

Lubricants 2025, 13(9), 397; https://doi.org/10.3390/lubricants13090397 - 7 Sep 2025

Viewed by 230

Abstract

An extensive statistical study was conducted on a 10-year dataset (2014–2023) containing the lubrication condition monitoring results from wind turbine gearboxes in the Iberian Peninsula. The dataset includes two mineral and two synthetic lubricants; all four were sampled and analyzed regularly in accordance [...] Read more.

An extensive statistical study was conducted on a 10-year dataset (2014–2023) containing the lubrication condition monitoring results from wind turbine gearboxes in the Iberian Peninsula. The dataset includes two mineral and two synthetic lubricants; all four were sampled and analyzed regularly in accordance with the ISO 14830-1 standard. This dataset comprises over 25,000 records across 24 distinct parameters, as defined by the standard maintenance procedure of lubricants in wind turbine gearboxes. To reduce dimensionality, the analysis begins with principal component analysis, followed by discussion of Spearman correlations and finishing with comparation of trends. Performance differences, correlations and typical trends will be evaluated and compared for mineral and synthetic lubricants. This data-driven study presents a significant contribution to supporting maintenance decision-making processes in wind farms. Despite the differences, P, Pb and K have been identified as having a major influence on the variance in the dataset for all the lubricants, although no significant correlations with these elements have been found. Mineral lubricants showed very few correlations between elements and lubricant parameters, with Fe as the major element to be considered. Meanwhile, synthetic lubricants showed several correlations between elements (Fe, Mn, Cu, Ba) and lubricant parameters denoting complex tribochemical reactions. Full article

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23 pages, 8724 KB

Open AccessArticle

Comparative Analysis of Emulsion, Cutting Oil, and Synthetic Oil-Free Fluids on Machining Temperatures and Performance in Side Milling of Ti-6Al-4V

by Hui Liu, Markus Meurer and Thomas Bergs

Lubricants 2025, 13(9), 396; https://doi.org/10.3390/lubricants13090396 - 6 Sep 2025

Viewed by 148

Abstract

During machining, most of the mechanical energy is converted into heat. A substantial part of this heat is transferred to the cutting tool, causing a rapid rise in tool temperature. Excessive thermal loads accelerate tool wear and lead to displacement of the tool [...] Read more.

During machining, most of the mechanical energy is converted into heat. A substantial part of this heat is transferred to the cutting tool, causing a rapid rise in tool temperature. Excessive thermal loads accelerate tool wear and lead to displacement of the tool center point, reducing machining accuracy and workpiece quality. This challenge is particularly pronounced when machining titanium alloys. Due to their low thermal conductivity, titanium alloys impose significantly higher thermal loads on the cutting tool compared to conventional carbon steels, making the process more difficult. To reduce temperatures in the cutting zone, cutting fluids are widely employed in titanium machining. They have been shown to significantly extend tool life. Cutting fluids are broadly categorized into cutting oils and water-based cutting fluids. Owing to their distinct thermophysical properties, these fluids exhibit notably different cooling and lubrication performance. However, current research lacks comprehensive cross-comparative studies of different cutting fluid types, which hinders the selection of optimal cutting fluids for process optimization. This study examines the influence of three cutting fluids—emulsion, cutting oil, and synthetic oil-free fluid—on tool wear, temperature, surface quality, and energy consumption during flood-cooled end milling of Ti-6Al-4V. A novel experimental setup incorporating embedded thermocouples enabled real-time temperature measurement near the cutting edge. Tool wear, torque, and surface roughness were recorded over defined feed lengths. Among the tested fluids, emulsion achieved the best balance of cooling and lubrication, resulting in the longest tool life with a feed travel path of 12.21 m. This corresponds to an increase of approximately 200% compared to cutting oil and oil-free fluid. Cutting oil offered superior lubrication but limited cooling capacity, resulting in localized thermal damage and edge chipping. Water-based cutting fluids reduced tool temperatures by over 300 °C compared to dry cutting but, in some cases, increased notch wear due to higher mechanical stress at the entry point. Power consumption analysis revealed that the cutting fluid supply system accounted for 60–70% of total energy use, particularly with high-viscosity fluids like cutting oil. Complementary thermal and CFD simulations were used to quantify heat partitioning and convective cooling efficiency. The results showed that water-based fluids achieved heat transfer coefficients up to 175 kW/m²·K, more than ten times higher than those of cutting oil. These findings emphasize the importance of selecting suitable cutting fluids and optimizing their supply to enhance tool performance and energy efficiency in Ti-6Al-4V machining. Full article

(This article belongs to the Special Issue Friction and Wear Mechanism Under Extreme Environments)

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12 pages, 4448 KB

Open AccessArticle

Effect of Low Concentrations of Organophosphorus Additives on Tribological Performance of Polyalkylene Glycol-Based Oils for Tin Bronze on Tungsten Carbide Applications

by Elena Torskaya, Vlada Petrova, Aleksey Morozov, Ivan Shkalei and Dmitrii Kozhevnikov

Lubricants 2025, 13(9), 395; https://doi.org/10.3390/lubricants13090395 - 5 Sep 2025

Viewed by 203

Abstract

Low concentrations of organophosphorus additives in PAG oil for friction units are under consideration. Concentrations of 0.1–0.5 percent maintain the environmental friendliness of the oil, but can improve its tribological properties. The friction pair (tin bronze versus tungsten carbide) was made from a [...] Read more.

Low concentrations of organophosphorus additives in PAG oil for friction units are under consideration. Concentrations of 0.1–0.5 percent maintain the environmental friendliness of the oil, but can improve its tribological properties. The friction pair (tin bronze versus tungsten carbide) was made from a plunger and compressor seal. It was tested in the reciprocating sliding mode under a load of 600 N (contact pressure ≈ 13 P), a frequency of 8.33 Hz, an amplitude of 15 mm and a temperature of +70 °C. It was found that the phosphate concentration of 0.2 percent provides the most stable values of the friction coefficient (0.04). The mechanism of action of the modifier was determined by analyzing the results of SEM and profilometry. Organophosphates make both interacting surfaces smoother; and there is an optimal concentration of additives that provides optimal roughness. Full article

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26 pages, 8399 KB

Open AccessArticle

Discharge Coefficient and Pressure Loss Characteristics of Multi-Branch Oil Jet Nozzles

by Yanyang Zhang, Xinyuan Yang, Hongmei Wu, Xin Huang, Yu Dai and Xiang Zhu

Lubricants 2025, 13(9), 394; https://doi.org/10.3390/lubricants13090394 - 4 Sep 2025

Viewed by 246

Abstract

In aeronautic industry applications, multi-branch oil jet nozzles are commonly employed to supply lubricating oil, ensuring adequate thermal regulation and friction control for high-speed gears or bearings. The geometric and operational parameters of these nozzles significantly affect the internal flow dynamics and discharge [...] Read more.

In aeronautic industry applications, multi-branch oil jet nozzles are commonly employed to supply lubricating oil, ensuring adequate thermal regulation and friction control for high-speed gears or bearings. The geometric and operational parameters of these nozzles significantly affect the internal flow dynamics and discharge coefficient characteristics. This study presents a numerical investigation into the flow behavior and discharge coefficient of multi-branch oil jet nozzles under typical pressure conditions (0–0.5 MPa) for various orifice sizes and angles. Then, compared to the original theoretical method, the pressure correction equation leveraging the fitting curve method is determined to improve the prediction accuracy of the theoretical method of oil mass flow rate and enhanced by over an order of magnitude. Furthermore, the flow behavior and mass flow properties of multi-branch nozzles, featuring various configurations and distinct orifice angles, are also investigated amply by comparing the numerical and theoretical findings. Full article

(This article belongs to the Special Issue Gearbox Lubrication)

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22 pages, 9885 KB

Open AccessArticle

A Hyperspectral Analysis-Based Approach for Estimation of Wear Metal Content in Lubricating Oil

by Mengjie Li, Lifu Zhang, Deshuai Yuan, Xuejian Sun and Qingxi Tong

Lubricants 2025, 13(9), 393; https://doi.org/10.3390/lubricants13090393 - 4 Sep 2025

Viewed by 308

Abstract

Lubricating oil reflects mechanical component aging and wear. Accurate quantification of its wear metals is essential for equipment safety and intelligent maintenance. This study introduces a rapid, non-destructive method for detecting wear metal content in lubricating oil using hyperspectral technology to overcome limitations [...] Read more.

Lubricating oil reflects mechanical component aging and wear. Accurate quantification of its wear metals is essential for equipment safety and intelligent maintenance. This study introduces a rapid, non-destructive method for detecting wear metal content in lubricating oil using hyperspectral technology to overcome limitations such as bulky, expensive instruments and destructive testing in current spectroscopic techniques. Absorption spectra of 98 marine gearbox oil samples were acquired using Hach UV-Vis and GLT optical fiber spectrometers. We propose a multi-head attention mechanism enhanced genetic algorithm (MHA-GA) for deep feature extraction, integrating attention weights into band selection and fitness evaluation to identify key features under multi-element interference. Wear metal prediction models were constructed using random forest (RF), support vector regression (SVR), and extreme gradient boosting (XGBoost). Results demonstrate MHA-GA outperformed traditional genetic algorithm (GA) and competitive adaptive reweighted sampling (CARS) in feature selection. The MHA-GA-XGBoost model performed best. Fe prediction R² reached 0.96 (Hach) and 0.93 (GLT), with RPDs of 5.33 and 3.90. For Cu, R² reached 0.91 and 0.83, with RPDs of 3.35 and 2.42. The results indicate that hyperspectral technology combined with machine learning enables effective non-destructive wear metal quantification, offering a promising strategy for intelligent maintenance and condition monitoring of lubricating oil. Full article

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23 pages, 5372 KB

Open AccessArticle

Lubrication Reliability and Evolution Laws of Gear Transmission Considering Uncertainty Parameters

by Jiaxing Pei, Yuanyuan Tian, Hongjuan Hou, Yourui Tao, Miaojie Wu and Leilei Wang

Lubricants 2025, 13(9), 392; https://doi.org/10.3390/lubricants13090392 - 3 Sep 2025

Viewed by 339

Abstract

To address the challenge of predicting lubrication states and reliability caused by the uncertainty of gear materials and structural parameters, a lubrication reliability analysis method considering the randomness of gear parameters is proposed. Firstly, a nonlinear dynamic model of a gear pair is [...] Read more.

To address the challenge of predicting lubrication states and reliability caused by the uncertainty of gear materials and structural parameters, a lubrication reliability analysis method considering the randomness of gear parameters is proposed. Firstly, a nonlinear dynamic model of a gear pair is established to derive the dynamic meshing force. The geometric and kinematic analyses are then performed to determine time-varying equivalent curvature radius and entrainment velocity. The minimum film thickness during meshing is further calculated. Considering gear parameters as random variables, a gear lubrication reliability model is formulated. Monte Carlo Simulation method is employed to accurately analyze the dynamic response, dynamic meshing force, equivalent curvature radius, entrainment velocity, probability distribution of minimum film thickness, and gear lubrication failure probability. Additionally, a specialized wear test device is designed to investigate the evolution of tooth surface roughness with wear and to forecast trends in gear lubrication failure probability as wear progresses. The results indicate that the uncertainty in gear parameters have minimal impact on the equivalent curvature radius and entrainment velocity, but significantly affect the dynamic meshing force. The gear speed and root mean square roughness are critical factors affecting lubrication reliability, and the early wear of the teeth enhances the lubrication reliability. The present work provides valuable insights for the design, maintenance, and optimization of high-performance gear systems in practical engineering applications. Full article

(This article belongs to the Special Issue Novel Tribology in Drivetrain Components)

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24 pages, 10817 KB

Open AccessArticle

Pavement Friction Prediction Based Upon Multi-View Fractal and the XGBoost Framework

by Yi Peng, Jialiang Kai, Xinyi Yu, Zhengqi Zhang, Qiang Joshua Li, Guangwei Yang and Lingyun Kong

Lubricants 2025, 13(9), 391; https://doi.org/10.3390/lubricants13090391 - 2 Sep 2025

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Abstract

The anti-slip performance of road surfaces directly affects traffic safety, yet existing evaluation methods based on texture features often suffer from limited interpretability and low accuracy. To overcome these limitations, a portable 3D laser surface analyzer was used to acquire road texture data, [...] Read more.

The anti-slip performance of road surfaces directly affects traffic safety, yet existing evaluation methods based on texture features often suffer from limited interpretability and low accuracy. To overcome these limitations, a portable 3D laser surface analyzer was used to acquire road texture data, while a dynamic friction coefficient tester provided friction measurements. A multi-view fractal dimension index was developed to comprehensively describe the complexity of texture across spatial, cross-sectional, and depth dimensions. Combined with road surface temperature, this index was integrated into an XGBoost-based prediction model to evaluate friction at driving speeds of 10 km/h and 70 km/h. Comparative analysis with linear regression, decision tree, support vector machine, random forest, and backpropagation (BP) neural network models confirmed the superior predictive performance of the proposed approach. The model achieved backpropagation (R²) values of 0.80 and 0.82, with root mean square errors (RMSEs) of 0.05 and 0.04, respectively. Feature importance analysis indicated that fractal characteristics from multiple texture perspectives, together with temperature, significantly influence anti-slip performance. The results demonstrate the feasibility of using non-contact texture-based methods to replace traditional contact-based friction testing. Compared with traditional statistical indices and alternative machine learning algorithms, the proposed model achieved improvements in R² (up to 0.82) and reduced RMSE (as low as 0.04). This study provides a robust indicator system and predictive model to advance road surface safety assessment technologies. Full article

(This article belongs to the Special Issue Tire/Road Interface and Road Surface Textures)

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17 pages, 3153 KB

Open AccessReview

Fabrication and Properties of Hard Coatings by a Hybrid PVD Method

by Rui Zhang, Qimin Wang, Yuxiang Xu, Lisheng Li and Kwang Ho Kim

Lubricants 2025, 13(9), 390; https://doi.org/10.3390/lubricants13090390 - 1 Sep 2025

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Abstract

By integrating cathodic arc evaporation (CAE) with magnetron sputtering (MS) or high-power impulse magnetron sputtering (HiPIMS), hard coatings with diverse multicomponent compositions can be fabricated. Depending on the deposition conditions, the coatings with nano-composite or nano-multilayered microstructures are produced. During the mixing deposition [...] Read more.

By integrating cathodic arc evaporation (CAE) with magnetron sputtering (MS) or high-power impulse magnetron sputtering (HiPIMS), hard coatings with diverse multicomponent compositions can be fabricated. Depending on the deposition conditions, the coatings with nano-composite or nano-multilayered microstructures are produced. During the mixing deposition conditions, nano-composite coatings are fabricated, which can be tailored to possess combining properties of super hardness, low friction coefficient, and excellent thermal/chemical stability. For the deposition with larger rotating periods, layer-by-layer deposition was observed. By the nano-multilayered coating design, superior mechanical properties (hardness ≥ 35 GPa), modulated residual stresses, and enhanced high-temperature properties can be obtained. In addition, lubricious elements, low friction (friction coefficient < 0.4), and low wear (<10⁻⁵ mm³/N∙m) both at ambient temperature and high temperature can be realized. Among these coatings, some have been specifically designed to achieve outstanding cutting performance in high-speed cutting applications. Several nitride and oxide hard coatings, such as AlTiN, TiAlN/TiSiN, AlCrN/Cu, and AlCrO, were deposited using a hybrid industrial physical vapor deposition (PVD) coating system. The microstructure, mechanical properties, and cutting performance of these coatings will be discussed. Full article

(This article belongs to the Special Issue Wear and Friction of High-Performance Coatings and Hardened Surfaces)

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23 pages, 3472 KB

Open AccessArticle

Smart Oil Management with Green Sensors for Industry 4.0

by Kübra Keser

Lubricants 2025, 13(9), 389; https://doi.org/10.3390/lubricants13090389 - 1 Sep 2025

Viewed by 394

Abstract

Lubricating oils are utilised in equipment and machinery to reduce friction and enhance material utilisation. The utilisation of oil leads to an increase in its thickness and density over time. Current methods for assessing oil life are slow, expensive, and complex, and often [...] Read more.

Lubricating oils are utilised in equipment and machinery to reduce friction and enhance material utilisation. The utilisation of oil leads to an increase in its thickness and density over time. Current methods for assessing oil life are slow, expensive, and complex, and often only applicable in laboratory settings and unsuitable for real-time or field use. This leads to unexpected equipment failures, unnecessary oil changes, and economic and environmental losses. A comprehensive review of the extant literature revealed no studies and no national or international patents on neural network algorithm-based oil life modelling and classification using green sensors. In order to address this research gap, this study, for the first time in the literature, provides a green conductivity sensor with high-accuracy prediction of oil life by integrating real-time field measurements and artificial neural networks. This design is based on analysing resistance change using a relatively low-cost, three-dimensional, eco-friendly sensor. The sensor is characterised by its simplicity, speed, precision, instantaneous measurement capability, and user-friendliness. The MLP and LVQ algorithms took as input the resistance values measured in two different oil types (diesel, bench oil) after 5–30 h of use. Depending on their degradation levels, they classified the oils as ‘diesel’ or ‘bench oil’ with 99.77% and 100% accuracy. This study encompasses a sensing system with a sensitivity of 50 µS/cm, demonstrating the proposed methodologies’ efficacy. A next-generation decision support system that will perform oil life determination in real time and with excellent efficiency has been introduced into the literature. The components of the sensor structure under scrutiny in this study are conducive to the creation of zero waste, in addition to being environmentally friendly and biocompatible. The developed three-dimensional green sensor simultaneously detects physical (resistance change) and chemical (oxidation-induced polar group formation) degradation by measuring oil conductivity and resistance changes. Measurements were conducted on simulated contaminated samples in a laboratory environment and on real diesel, gasoline, and industrial oil samples. Thanks to its simplicity, rapid applicability, and low cost, the proposed method enables real-time data collection and decision-making in industrial maintenance processes, contributing to the development of predictive maintenance strategies. It also supports environmental sustainability by preventing unnecessary oil changes and reducing waste. Full article

(This article belongs to the Special Issue Future of Digital Tribology: Prediction of Tribological Performance Using Sensors, Signal Processing and Machine Learning)

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27 pages, 13580 KB

Open AccessArticle

Understanding the Lubrication and Wear Behavior of Agricultural Components Under Rice Interaction: A Multi-Scale Modeling Study

by Honglei Zhang, Zhong Tang, Xinyang Gu and Biao Zhang

Lubricants 2025, 13(9), 388; https://doi.org/10.3390/lubricants13090388 - 30 Aug 2025

Viewed by 346

Abstract

This study investigates the tribological behavior and wear mechanisms of Q235 steel components subjected to abrasive interaction with rice, a critical challenge in agricultural machinery performance and longevity. We employed a comprehensive multi-scale framework, integrating bench-top tribological testing, advanced Discrete Element Method (DEM) [...] Read more.

This study investigates the tribological behavior and wear mechanisms of Q235 steel components subjected to abrasive interaction with rice, a critical challenge in agricultural machinery performance and longevity. We employed a comprehensive multi-scale framework, integrating bench-top tribological testing, advanced Discrete Element Method (DEM) coupled with a wear model (DEM-Wear), and detailed surface characterization. Bench tests revealed a composite wear mechanism for the rice–steel tribo-pair, transitioning from mechanical polishing under mild conditions to significant soft abrasive micro-cutting driven by the silica particles inherent in rice during high-load, high-velocity interactions. This elucidated fundamental friction and wear phenomena at the micro-level. A novel, calibrated DEM-Wear model was developed and validated, accurately predicting macroscopic wear “hot spots” on full-scale combine harvester header platforms with excellent geometric similarity to real-world wear profiles. This provides a robust predictive tool for component lifespan and performance optimization. Furthermore, fractal analysis was successfully applied to quantitatively characterize worn surfaces, establishing fractal dimension (Ds) as a sensitive metric for wear severity, increasing from ~2.17 on unworn surfaces to ~2.3156 in severely worn regions, directly correlating with the dominant wear mechanisms. This study offers a valuable computational approach for understanding and mitigating wear in tribosystems involving complex particulate matter, contributing to improved machinery reliability and reduced operational costs. Full article

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13 pages, 11786 KB

Open AccessArticle

Self-Lubricating Ni-Based Composite Coating with Core-Shell Structured Mo@Ag@Ni Addition: Tribological Behaviors and Interface Evolution over Multi-Thermal Cycles

by Nairu He, Yuanhai Zhai, Ziwen Fang, Jie Yang and Wei Chen

Lubricants 2025, 13(9), 387; https://doi.org/10.3390/lubricants13090387 - 29 Aug 2025

Viewed by 399

Abstract

The rapid dissipation of soft metal lubricants would deteriorate the self-lubricating properties of the coatings at elevated temperatures. In this study, the core-shell structured Mo@Ag@Ni particles were prepared via electroless plating to suppress the rapid dissipation of Ag and facilitate tribochemical reactions at [...] Read more.

The rapid dissipation of soft metal lubricants would deteriorate the self-lubricating properties of the coatings at elevated temperatures. In this study, the core-shell structured Mo@Ag@Ni particles were prepared via electroless plating to suppress the rapid dissipation of Ag and facilitate tribochemical reactions at high temperatures. The NiCrAlY-Mo@Ag@Ni composite coating was sprayed on the substrate of Inconel 718 alloy using atmospheric plasma spraying technology. The results of this study show that the structural design of Mo@Ag@Ni can enhance the bonding strength of the particle interface, resulting in a high microhardness of approximately 332.2 HV. During high-temperature friction tests, Mo@Ag@Ni can provide excellent tribological properties by promoting the silver molybdate formation on the worn surface. At 800 °C, the friction coefficient and wear rate are only about 0.32 and 1.58 × 10⁻⁵ mm³N⁻¹m⁻¹, respectively. Moreover, the Ni shell layer can inhibit the rapid diffusion of Ag and provide sufficient Ag₂O to maintain the continuity of Ag₂MoO₄ lubricating film, which endows the coating with a longer lubrication life. Over multi-thermal cycles, the friction coefficient and wear rate constantly maintain at about 0.3 and 2.5 × 10⁻⁵ mm³N⁻¹m⁻¹, respectively. Full article

(This article belongs to the Special Issue Tribological Properties of Sprayed Coatings)

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33 pages, 20297 KB

Open AccessArticle

Mechanical and Tribological Performance of Additively Manufactured Nanocrystalline Aluminum via Cryomilling and Cold Spray

by Amanendra K. Kushwaha, Manoranjan Misra and Pradeep L. Menezes

Lubricants 2025, 13(9), 386; https://doi.org/10.3390/lubricants13090386 - 28 Aug 2025

Viewed by 396

Abstract

In this study, nanocrystalline (NC) aluminum (Al) and magnesium (Mg)-doped Al bulk components were fabricated using a hybrid manufacturing process that combines cryomilling and high-pressure cold spray (HPCS) additive deposition techniques. Yttria-stabilized zirconia (YSZ) was also added during the HPCS process to improve [...] Read more.

In this study, nanocrystalline (NC) aluminum (Al) and magnesium (Mg)-doped Al bulk components were fabricated using a hybrid manufacturing process that combines cryomilling and high-pressure cold spray (HPCS) additive deposition techniques. Yttria-stabilized zirconia (YSZ) was also added during the HPCS process to improve deposition efficiency and build-up thickness via peening. The evolution of morphology, crystallite size, and elemental composition of both cryomilled powders and cold-sprayed (CS’ed) components was systematically characterized using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). Mechanical characterization was performed using Vickers microhardness and uniaxial tensile testing, while the tribological behavior was assessed using sliding wear tests under dry/lubricated conditions. XRD analysis revealed that increased cryomilling duration led to significant crystallite refinement, which directly correlated with enhanced hardness and strength. This mechanical strengthening was accompanied by an increase in coefficient of friction (COF) and lower wear rates. The results also showed that the Mg-doped Al exhibited superior hardness, tensile strength, and tribological performance compared to pure Al. The study further explores the underlying mechanisms responsible for these enhancements, highlighting the potential of solute-assisted grain boundary stabilization in tailoring high-performance NC Al alloys. Full article

(This article belongs to the Special Issue Wear and Friction in Hybrid and Additive Manufacturing Processes)

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16 pages, 9956 KB

Open AccessArticle

Fabrication of Novel Porous Thin Plates by Rolling and Vacuum Sintering for Aerostatic Bearings

by Chaozhong Li and Zhaoyao Zhou

Lubricants 2025, 13(9), 385; https://doi.org/10.3390/lubricants13090385 - 28 Aug 2025

Viewed by 451

Abstract

To develop a new porous metal for aerostatic bearing, herein, novel porous thin plates (PTPs) with micron-scale porous structures are fabricated. The pore size distribution and air permeability of PTPs are measured. A tensile test is carried out and the fractography is observed. [...] Read more.

To develop a new porous metal for aerostatic bearing, herein, novel porous thin plates (PTPs) with micron-scale porous structures are fabricated. The pore size distribution and air permeability of PTPs are measured. A tensile test is carried out and the fractography is observed. The load capacity and stiffness of aerostatic bearings utilizing PTPs as porous restrictors are tested. The results show that the phenomenon of the uneven distribution of powders can be significantly improved by decreasing the roller speed. Fine powder porous thin plates (FPTPs) effectively balance permeability and mechanical properties, achieving an ultimate tensile strength of 157 MPa while maintaining favorable permeability, significantly exceeding existing porous restrictors. Aerostatic bearings employing PTPs as restrictors demonstrate substantial load capacity and stiffness. Notably, aerostatic bearings utilizing coarse powder porous thin plates (CPTPs) as restrictors deliver 511 N load capacity and 22 N/μm stiffness with a considerably smaller porous restrictor area. It is worth noting that the novel PTPs not only exhibit a straightforward and environmentally friendly manufacturing process but also preserve the micron-scale porous structure while meeting the practical requirements of aerostatic bearings, holding significant promise for gas lubrication applications. Full article

(This article belongs to the Special Issue Gas Lubrication and Dry Gas Seal, 2nd Edition)

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21 pages, 8665 KB

Open AccessArticle

Impact of Lubricating Oil Leakage Characteristics of a Bearing Cavity Sealing System Based on an Oil–Gas Two-Phase Flow

by Guozhe Ren, Rui Wang, Dan Sun, Wenfeng Xu and Yu Li

Lubricants 2025, 13(9), 384; https://doi.org/10.3390/lubricants13090384 - 28 Aug 2025

Viewed by 416

Abstract

In this paper, we aim to study the oil–gas two-phase flow characteristics, leakage characteristics, and critical oil sealing characteristics of the bearing cavity sealing system of aero-engine bearings. For this purpose, the unsteady solution models of the conventional bearing cavity sealing system and [...] Read more.

In this paper, we aim to study the oil–gas two-phase flow characteristics, leakage characteristics, and critical oil sealing characteristics of the bearing cavity sealing system of aero-engine bearings. For this purpose, the unsteady solution models of the conventional bearing cavity sealing system and the graphite with oil-return groove bearing cavity sealing system based on the Euler–Euler two-phase flow method were established. The experimental device for the oil–gas two-phase flow for the bearing cavity was designed and constructed. Thus, the oil–gas two-phase oil sealing characteristics of both systems under different structural and working condition parameters were studied. The results show that the change in the sealing length does not affect the leakage of lubricating oil for the conventional bearing cavity sealing system. It was observed that the higher the rotate speed is, the greater the oil leakage and the greater the critical sealing pressure difference. The graphite with oil-return groove structure can significantly reduce the leakage of lubricating oil and the critical sealing pressure difference. The increase in the length and number of oil-return groove can effectively reduce the leakage of lubricating oil. The width of the oil-return groove has no obvious effect on the sealing and leakage characteristics of the lubricating oil. Full article

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23 pages, 5290 KB

Open AccessArticle

Fuzzy Identification of Lubrication Degradation State Based on Multi-Index Fusion

by Chan Xu, Qianqian Zhang, Qiuxia Fan and Yunqi Tong

Lubricants 2025, 13(9), 383; https://doi.org/10.3390/lubricants13090383 - 27 Aug 2025

Viewed by 386

Abstract

Lubrication failure has become a predominant failure mode in aviation roller bearings. Timely identification of lubrication degradation is critical for preventing premature bearing failure. This paper presents a fuzzy identification method of lubrication degradation stages by fusing multiple indicators. Firstly, four monitoring indicators, [...] Read more.

Lubrication failure has become a predominant failure mode in aviation roller bearings. Timely identification of lubrication degradation is critical for preventing premature bearing failure. This paper presents a fuzzy identification method of lubrication degradation stages by fusing multiple indicators. Firstly, four monitoring indicators, including the oil film thickness (OFT), wear surface roughness (WSR), contact resonance frequency (CRF), and amplitude of CRF (CRFA), are extracted through numerical simulations to characterize the lubrication degradation process. Then, a fuzzy evaluation method is proposed to identify the lubrication degradation stages by integrating these indicators. The results indicate that these four indicators can identify three typical stages of the lubrication degradation process—good lubrication, normal wear, and severe wear, with an accuracy rate exceeding 92%. Finally, lubrication degradation experiments are carried out on a sliding-rolling test rig to verify the method’s effectiveness. This work provides superior interpretability of the multifactorial coupled lubrication degradation process analysis. Full article

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22 pages, 4316 KB

Open AccessArticle

Surface Property and Braking Reliability Analyses of YSZ Thermal Barrier-Coated Brake Disc of Kilometer-Deep Well Hoist

by Wanzi Yan, Hao Lu, Yu Tang, Zhencai Zhu and Fengbin Ren

Lubricants 2025, 13(9), 382; https://doi.org/10.3390/lubricants13090382 - 26 Aug 2025

Viewed by 405

Abstract

A significant amount of heat is generated during the braking process of a kilometer-deep well hoist, which causes a large temperature rise and then thermal deformation and cracks in the brake disc. Thus, improving the surface performance of the brake disc is necessary [...] Read more.

A significant amount of heat is generated during the braking process of a kilometer-deep well hoist, which causes a large temperature rise and then thermal deformation and cracks in the brake disc. Thus, improving the surface performance of the brake disc is necessary to ensure reliable braking under high-speed and heavy-load conditions. In this paper, thermal barrier coating technology is applied to a brake disc, and the friction and wear characteristics of a yttria-stabilized zirconia (YSZ) thermal barrier-coated brake disc is studied. A coupled thermomechanical model of the hoist disc brake is established, and a temperature field simulation analysis of uncoated and coated brake discs under emergency braking conditions is carried out. Then, a surrogate model of the maximum temperature of the brake disc surface with respect to the random parameters of the brake disc is constructed based on a Latin hypercube experimental design and the Kriging method. The reliability of the brake disc under emergency braking conditions is estimated based on saddlepoint approximation (SPA), and the feasibility of applying a YSZ thermal barrier coating to a hoist disc brake is verified. Full article

(This article belongs to the Special Issue Tribological Behavior of Wire Rope)

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19 pages, 10881 KB

Open AccessArticle

Simulation Analysis and Structural Improvements of Oil Return in Main Bearing Chamber of Aero-Engine

by Yanhong Ma, Wanfei Zheng, Xueqi Chen, Zihao Leng and Jie Hong

Lubricants 2025, 13(9), 381; https://doi.org/10.3390/lubricants13090381 - 26 Aug 2025

Viewed by 465

Abstract

Modern advanced aero-engine bearing systems typically exhibit structural and loading characteristics with high DN values. The harsh thermal environment and multi-physics loads under operating conditions render the reliability of bearing structural systems particularly sensitive to lubrication efficiency and bearing chamber temperature. This study [...] Read more.

Modern advanced aero-engine bearing systems typically exhibit structural and loading characteristics with high DN values. The harsh thermal environment and multi-physics loads under operating conditions render the reliability of bearing structural systems particularly sensitive to lubrication efficiency and bearing chamber temperature. This study performs simulation analyses of oil return processes and their influencing factors in an aero-engine main bearing chamber with complex structural features. The results show two primary causes of reduced scavenging performance. On the one hand, the local low-speed region at the inlet of the scavenge pipe causes some oil to fail to enter the scavenge pipe normally. On the other hand, the air in the bearing chamber is disturbed by the rotation of the rotor, which makes oil enter the oil sump with a tendency to return to the oil collection annulus, thereby causing poor oil return. Furthermore, two structural improvements of the oil sump are proposed. These improvements avoid the disruptive effects of circumferential fluid motion in the oil collection annulus on the pressure and velocity distribution within the bearing chamber, thereby improving scavenging performance. Full article

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21 pages, 2401 KB

Open AccessArticle

Comparative Evaluation of the Tribological Performance of Al-MMC and GCI Brake Rotors Through AK Master Dynamometer Testing

by Samuel A. Awe and Lucia Lattanzi

Lubricants 2025, 13(9), 380; https://doi.org/10.3390/lubricants13090380 - 26 Aug 2025

Viewed by 436

Abstract

The increasing demand for lightweight and high-performance brake rotors has led to the exploration of aluminum–metal matrix composites (Al-MMCs) as alternatives to conventional cast iron rotors. This study evaluated the tribological performance of squeeze-cast Al-MMC brake rotors using an AK Master dynamometer test [...] Read more.

The increasing demand for lightweight and high-performance brake rotors has led to the exploration of aluminum–metal matrix composites (Al-MMCs) as alternatives to conventional cast iron rotors. This study evaluated the tribological performance of squeeze-cast Al-MMC brake rotors using an AK Master dynamometer test and compared it with that of conventional gray cast iron (GCI) rotors. The Al-MMC rotors demonstrated stable coefficients of friction (CoFs) with reduced wear rates, compared to the GCI rotors. Surface analysis identified the predominant wear mechanisms, including abrasive and oxidative wear. The Al-MMC rotors exhibited sensitivity to pressure and speed, with a CoF range of 0.35–0.47 that decreased at higher pressures and speeds, whereas the GCI rotors maintained a stable CoF range of 0.38–0.44. At elevated temperatures, the GCI rotors displayed superior thermal stability and fade resistance compared to the Al-MMCs, which experienced a 40–60% loss in CoF. Wear analysis indicated material transfer from brake pads to Al-MMC rotors, resulting in protective tribofilm formation, whereas GCI rotors exhibited conventional abrasive wear. These findings highlight the potential of squeeze-cast Al-MMCs for automotive braking applications, offering advantages in weight reduction and wear resistance, but also suggest the need for further material optimization to enhance high-temperature performance and friction stability. Full article

(This article belongs to the Special Issue Recent Advancements in Friction Research for Disc Brake Systems)

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17 pages, 13580 KB

Open AccessArticle

Investigation of the Lubrication Performance of Petal-Shaped Micro-Pit Texture on the Surface of Stator Rubber in Screw Pumps

by Xiaoming Wu, Xinfu Liu, Guoqing Han, Xiangzhi Shi, Jiuquan An, Xiaoli Yin and Li Geng

Lubricants 2025, 13(9), 379; https://doi.org/10.3390/lubricants13090379 - 26 Aug 2025

Viewed by 533

Abstract

This study proposed a surface modification method, based on petal-shaped micro-pit texture, allowing to solve the problem of significant wear of the stator caused by the oil film rupture in the metal-rubber friction pair of the screw pump under complex conditions in the [...] Read more.

This study proposed a surface modification method, based on petal-shaped micro-pit texture, allowing to solve the problem of significant wear of the stator caused by the oil film rupture in the metal-rubber friction pair of the screw pump under complex conditions in the later stages of oilfield extraction. A geometric model of the petal-shaped micro-pit texture on the stator rubber surface and a mathematical model of the hydrodynamic lubrication flow field based on the Reynolds equation were developed. Computational Fluid Dynamics (CFD) simulations and friction tests were conducted to systematically study the influence of the medium flow direction, texture area ratio, and texture size on the lubrication performance. The obtained results showed that compared with the flow in the x-direction, the load-carrying capacity of the oil film was increased by more than 0.93% when the medium flowed in y-direction, and it reached its optimal value at an area of 10%. When the area ratio reached 60%, the interference effect of the flow field reduced the pressure by 6.98%. The increase of the size of the petals allowed to expand the positive pressure zone and increase the net load-carrying capacity. Furthermore, friction tests demonstrated that the friction coefficient was decreased with the increase of the texture size and increased with the increase of the texture area ratio. The petal-shaped micro-pit texture with size of 350 μm and an area ratio of 10% demonstrated the lowest friction coefficient and highest wear resistance. Full article

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

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37 pages, 38721 KB

Open AccessArticle

A Neural Network-Based Feature Recognition Method in Adaptive Refinement for Efficient Reynolds Equation Solving

by Gang Rao, Lei Ma, Bingquan Zuo, Jiashu Yang and Weikang Xie

Lubricants 2025, 13(9), 378; https://doi.org/10.3390/lubricants13090378 - 25 Aug 2025

Viewed by 503

Abstract

This study proposes an adaptive refinement method based on feature recognition to rapidly obtain solutions of the Reynolds equation. Leveraging an isogeometric analysis (IGA) solution framework supporting local refinement, three natural refinement features tailored to solving the Reynolds equation in fluid lubrication, including [...] Read more.

This study proposes an adaptive refinement method based on feature recognition to rapidly obtain solutions of the Reynolds equation. Leveraging an isogeometric analysis (IGA) solution framework supporting local refinement, three natural refinement features tailored to solving the Reynolds equation in fluid lubrication, including two physical features, a pressure value, a pressure gradient, and an element size feature for discretization, are introduced first to identify mesh elements. Then a neural network model is trained on feature data to predict element classifications effectively. Finally, this model is integrated into the adaptive refinement solution framework and validated through simulations. Comparative validation was conducted on two distinct Reynolds equation instances, with the results demonstrating that the proposed algorithm can effectively evaluate refinement regions globally, avoiding issues such as mesh non-conformity often caused by conventional independent element marking algorithms. The distribution of degrees of freedom is more rational, and the parallel prediction model enhances the speed of the refinement solution. Full article

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15 pages, 9186 KB

Open AccessArticle

Al₂O₃/PTFE Composites for Marine Self-Lubricating Bearings: Modulation Mechanism of Alumina Particle Size on Material Mechanical Properties and Tribological Behavior

by Guofeng Zhao and Shifan Zhu

Lubricants 2025, 13(9), 377; https://doi.org/10.3390/lubricants13090377 - 23 Aug 2025

Viewed by 478

Abstract

Polytetrafluoroethylene (PTFE) is one of the alternative materials suitable for seawater-lubricated bearings, favored for its excellent corrosion resistance and good self-lubricating properties. As marine equipment develops towards higher load, higher reliability, and longer service life, more stringent requirements are imposed on the wear [...] Read more.

Polytetrafluoroethylene (PTFE) is one of the alternative materials suitable for seawater-lubricated bearings, favored for its excellent corrosion resistance and good self-lubricating properties. As marine equipment develops towards higher load, higher reliability, and longer service life, more stringent requirements are imposed on the wear resistance of bearing materials. However, traditional PTFE materials struggle to meet the performance requirements for long-term stable operation in modern marine environments. To improve the wear resistance of PTFE, this study used alumina (Al₂O₃) particles with three different particle sizes (50 nm, 3 μm, and 80 μm) as fillers and prepared Al₂O₃/PTFE composites via the cold pressing and sintering process. Tribological performance tests were conducted using a ball-on-disk reciprocating friction and wear tester, with Cr12 steel balls as counterparts, under an artificial seawater lubrication environment, applying a normal load of 10 N for 40 min. The microstructure and wear scar morphology were characterized by scanning electron microscopy (SEM), and mechanical properties were measured using a Shore hardness tester. A systematic study was carried out on the microstructure, mechanical properties, friction coefficient, wear rate, and limiting PV value of the composites. The results show that the particle size of Al₂O₃ particles significantly affects the mechanical properties, friction coefficient, wear rate, and limiting PV value of the composites. The 50 nm Al₂O₃/PTFE formed a uniformly spread friction film and transfer film during the friction process, which has better friction and wear reduction performance and load bearing capacity. The 80 μm Al₂O₃ group exhibited poor friction properties despite higher hardness. The nanoscale Al₂O₃ filler was superior in improving the wear resistance, stabilizing the coefficient of friction, and prolonging the service life of the material, and demonstrated good seawater lubrication bearing suitability. This study provides theoretical support and an experimental basis for the design optimization and engineering application of PTFE-based composites in harsh marine environments. Full article

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21 pages, 4542 KB

Open AccessArticle

Tribo-Dynamics and Fretting Behavior of Connecting Rod Big-End Bearings in Internal Combustion Engines

by Yinhui Che, Meng Zhang, Qiang Chen, Hebin Ren, Nan Li, Shuo Liu and Yi Cui

Lubricants 2025, 13(9), 376; https://doi.org/10.3390/lubricants13090376 - 23 Aug 2025

Viewed by 455

Abstract

With the increased power density of internal combustion engines (ICE) and growing demands for lightweight design, the connecting rod big-end bearings are subjected to significant alternating loads. Consequently, the interference–fit interfaces become susceptible to fretting damage, which can markedly shorten engine service life [...] Read more.

With the increased power density of internal combustion engines (ICE) and growing demands for lightweight design, the connecting rod big-end bearings are subjected to significant alternating loads. Consequently, the interference–fit interfaces become susceptible to fretting damage, which can markedly shorten engine service life and impair reliability. In the present study, the effects of the big end manufacturing process, bolt preload, and bearing bush interference fit are considered to develop a coupled lubrication–dynamic model of the connecting rod big-end bearing. This model investigates the fretting damage issue in the bearing bush of a marine diesel engine’s connecting rod big end. The results indicate that the relatively low stiffness of the big end is the primary cause of bearing bush fretting damage. Interference fit markedly affects fretting wear on the bush back, whereas the influence of bolt preload is secondary; nevertheless, a decrease in either parameter enlarges the fretting distance. Based on these findings, an optimized design scheme is proposed. Full article

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Lubricants, Volume 13, Issue 9 (September 2025) – 33 articles

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