Lubricants

18 pages, 3984 KiB

Open AccessArticle

Influence of Titanium Oxide and Calcium Carbonate Powder as Additives on Tribological Characteristics of Lubricants

by Abhinit Shrivastava, Surinder Kumar, Sumit Kumar, Hemant Kumar, Sumika Chauhan, Govind Vashishtha and Rajesh Kumar

Lubricants 2025, 13(5), 229; https://doi.org/10.3390/lubricants13050229 - 20 May 2025

Abstract

The properties of lubricating oils are greatly enhanced by the incorporation of additives. With technological advancements, numerous additives have been developed and proven effective for this purpose. Some additives enhance anti-wear and anti-friction characteristics, while others improve the oil’s viscosity index. It has [...] Read more.

The properties of lubricating oils are greatly enhanced by the incorporation of additives. With technological advancements, numerous additives have been developed and proven effective for this purpose. Some additives enhance anti-wear and anti-friction characteristics, while others improve the oil’s viscosity index. It has been noted that certain additives influence more than one property of the lubricating oil. In this study, a mixture of TiO₂ at 0.2 wt.%, 0.3 wt.%, and 0.4 wt.% and CaCO₃ at 0.4 wt.%, 0.6 wt.%, and 0.8 wt.% was used as an additive in gear oil EP140 to prepare the samples. A pin-on-disc test was conducted for the tribological characterization of the various samples. A combination of 0.2 wt.% TiO₂ and 0.4 wt.% CaCO₃ particles in the gear oil resulted in a remarkable 88.23% reduction in wear compared to the base gear lubricating oil (EP140). The combination of 0.3 wt.% TiO₂ and 0.6 wt.% CaCO₃ particles in the gear oil led to a significant 36.84% reduction in the coefficient of friction. Field Emission Scanning Electron Microscopy (FESEM) revealed that the pin tested with sample S1 (gear oil containing 0.2 wt.% TiO₂ and 0.4 wt.% CaCO₃) exhibited a smoother wear surface than the base lubricating oil. Full article

(This article belongs to the Special Issue Tribology for Lightweighting)

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17 pages, 3656 KiB

Open AccessArticle

Dynamic Motion of a Vane in Six Degrees of Freedom and Its Effect on Wear in a Rotary-Vane Compressor Considering Fluid Lubrication

by Gwanghee Hong, Youngjun Park and Gunhee Jang

Lubricants 2025, 13(5), 228; https://doi.org/10.3390/lubricants13050228 - 19 May 2025

Abstract

Vanes are critical components of a rotary-vane compressor. If the vanes do not achieve sufficient contact with the inner wall of the cylinder, the compression chambers do not form completely. However, excessive contact between the vane and the cylinder wall can produce wear [...] Read more.

Vanes are critical components of a rotary-vane compressor. If the vanes do not achieve sufficient contact with the inner wall of the cylinder, the compression chambers do not form completely. However, excessive contact between the vane and the cylinder wall can produce wear on both, also decreasing the lifespan of the compressor. We applied the Poisson equation and the Reynolds equation to calculate the gas force and fluid-reaction force acting on the vane. We solved the equations for the motion of the rigid vane in six degrees of freedom to determine the dynamic motion of the vane. We operated the rotary-vane compressor for 800 h under the same simulation conditions and measured the wear patterns of the vane, the bottom thrust bearing, and the cylinder wall. Finally, we validated the proposed method by confirming that the simulated contact force matches well with the measured wear patterns on the vane and the inner wall of the cylinder. The proposed method overcomes the limitations of the previous three-degrees-of-freedom analyses of the vane and will contribute to developing a robust and efficient rotary-vane compressor. Full article

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

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19 pages, 4486 KiB

Open AccessArticle

Investigation of the Dynamic Leakage Characteristics of Floating Seal End Faces in Shield Machine Cutters with Consideration of Wear Effects

by Gang Hu, Zhengzhong Zhou, Zhihao Zhang and Haiming Zhao

Lubricants 2025, 13(5), 227; https://doi.org/10.3390/lubricants13050227 - 19 May 2025

Abstract

In slurry shield tunneling projects, leakage from floating seals frequently leads to abnormal failures of disc cutters. To investigate the leakage characteristics at the floating seal end faces of the cutters, a numerical method is proposed for analyzing the dynamic leakage behavior of [...] Read more.

In slurry shield tunneling projects, leakage from floating seals frequently leads to abnormal failures of disc cutters. To investigate the leakage characteristics at the floating seal end faces of the cutters, a numerical method is proposed for analyzing the dynamic leakage behavior of the floating seal end faces, considering the effects of wear. The elastohydrodynamic lubrication problem of the floating seal was addressed using the Reynolds equation and the slicing method, leading to the development of a computational model for the pressure and thickness distribution of the oil film on rough surfaces. Based on the Archard wear equation, a dynamic surface roughness model considering wear was established. Furthermore, a numerical model for dynamic leakage of the floating seal end faces in shield machine cutters, incorporating wear effects, was developed. Simulated friction and wear tests of the floating seal end faces, along with cutter seal leakage experiments, were conducted for validation. The results demonstrate that the dynamic surface roughness model considering wear can effectively predict the roughness evolution of worn surfaces. The trend of the theoretical leakage rate is generally consistent with that of the experimental results, verifying the effectiveness of the proposed model. Full article

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22 pages, 2847 KiB

Open AccessArticle

Research on the Calculation Method for the Contact Stress of Wind Turbine Main Shaft Bearings Based on Finite Element Analysis

by Yi Zou, Wenlei Sun, Hongwei Wang, Tiantian Xu and Bingkai Wang

Lubricants 2025, 13(5), 226; https://doi.org/10.3390/lubricants13050226 - 18 May 2025

Abstract

Under alternating loads, the contact situation for self-aligning roller bearings in the main shaft of a wind turbine is complex. Few methodologies exist for calculating the contact stress of main shaft bearings. We propose a method for calculating the contact stress of main [...] Read more.

Under alternating loads, the contact situation for self-aligning roller bearings in the main shaft of a wind turbine is complex. Few methodologies exist for calculating the contact stress of main shaft bearings. We propose a method for calculating the contact stress of main shaft bearings in wind turbines; by simulating alternating loads that affect the turbine’s lifespan with a probability of 99%, analyzing the operational characteristics of the bearings under these loads using the roller slice method, and establishing a load–displacement model, this model serves as the boundary condition for contact stress simulation. We present the approach for building a three-dimensional finite element simulation model of contact stress, followed by model validation. The findings reveal that the maximum stress within the spindle bearing is concentrated in the contact zone, taking on an elliptical configuration. The maximum contact stress, as computed by the proposed method, amounts to 1356.3 MPa, and the bearing’s load-bearing performance adequately fulfills the design requirements. A comparative analysis with the calculation results documented in the existing literature shows that the average discrepancies in the computed outcomes for the roller’s contact with the inner and outer rings are 2.55% and 2.48%, respectively, and this validates the high reliability of the proposed approach. The research conducted in this thesis can further enhance the credibility of the contact stress calculation method for large-scale wind turbine spindle bearings. Full article

21 pages, 12654 KiB

Open AccessArticle

Numerical Simulation and Experimental Study on the Role of Jet Angle in Controlling the Flow of Transmission Gears

by Tiangang Zou, Qingdong Yan, Wei Hou, Chunyu Wang, Ziqiang Zhang and Junye Li

Lubricants 2025, 13(5), 225; https://doi.org/10.3390/lubricants13050225 - 16 May 2025

Abstract

Gears play an important role in modern machinery and are indispensable transmission components, particularly at high speeds, where lubrication is essential for the reliability and efficiency of the gear unit. In order to study the oil coverage law and heat dissipation mechanism of [...] Read more.

Gears play an important role in modern machinery and are indispensable transmission components, particularly at high speeds, where lubrication is essential for the reliability and efficiency of the gear unit. In order to study the oil coverage law and heat dissipation mechanism of high-speed rotating meshing gears by injection angle, this paper adopts the moving particle semi-implicit method to establish a high-speed rotating gear lubrication model, study the intrinsic effect of different jet angles on gear lubrication, and build a gear lubrication bench for experimental verification. Numerical simulation found that with an increase in spray angle, the gear surface coverage and heat transfer coefficient of the high-speed rotating transmission gears initially increase and then decrease. They reflect the same lubrication law characteristics. When the injection angle was 90°, the surface coverage and heat transfer coefficient values were at their greatest, resulting in the best spray lubricating effect. According to the experimental results, under the conditions of 0.5 MPa injection pressure and high-speed rotation of the transmission gear with vertical injection, the lubricant covers the largest surface area of the gear and the least power loss. Simultaneously, in our previous study, we experimentally obtained the optimal parameter conditions on the basis of which we derived. The effect of nozzle diameter on jet lubrication was investigated in a previous study, and in this article, the effect of nozzle angle and distance on gear lubrication is investigated; the optimal conditions for high-speed lubrication of gears are the incident distance of 3.5 cm, incident angle of 90°, incident diameter of 1.5 mm, and gear speed of 2000 r/min, and the lubrication effect reaches the best ideal state; reduction in oil loss due to oil injection lubrication and power loss due to different parameters of the lubrication system. Lubrication design provides a theoretical foundation for the transmission system. Full article

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

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14 pages, 4128 KiB

Open AccessArticle

Laser Texturing to Improve Wear Resistance of 65Mn Steel Rotary Tiller Blades: Effects of Scanning Speed

by Heng Xiao, Dongyan Yang, Yiding Ou, Junlan Zhang, Yue Hu and Lei Ma

Lubricants 2025, 13(5), 224; https://doi.org/10.3390/lubricants13050224 - 16 May 2025

Abstract

With rapid advancements in agricultural mechanization, enhancing the wear resistance and lifespan of rotary tiller blades is crucial for boosting productivity. This study examines how surface textures affect the friction and wear of 65Mn steel in quartz sand slurry. The results show that [...] Read more.

With rapid advancements in agricultural mechanization, enhancing the wear resistance and lifespan of rotary tiller blades is crucial for boosting productivity. This study examines how surface textures affect the friction and wear of 65Mn steel in quartz sand slurry. The results show that laser processing treatment significantly improves the wear resistance of 65Mn steel blades through the lubrication effect due to the wear debris capturing ability of the laser-processed micro-pits. Samples with surface textures processed using a laser scanning speed of 200 mm/s exhibit the best anti-wear property under loads of both 70 N and 100 N, reducing the wear loss by approximately 44.19% and 36.22%, respectively, compared to the non-textured samples. With the applied load increase to 100 N, laser-processed textures can still reduce wear damage but with an impaired anti-wear effect due to the gradually flattening of some textures due to long-term friction and crush damage by high load conditions. These findings help to augment wear resistance and prolong the operational lifespan of 65Mn steel rotary tiller blades, thereby contributing to a more robust understanding of the tribological enhancements achievable through the laser surface texturing process. Full article

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20 pages, 11694 KiB

Open AccessArticle

Quantifying Dynamic Oil Immersion in a Spiral Bevel Gear via Image Processing for Improved Churning Loss Prediction

by Yu Dai, Xin Huang, Jianfeng Zhong, Caihua Yang and Xiang Zhu

Lubricants 2025, 13(5), 223; https://doi.org/10.3390/lubricants13050223 - 15 May 2025

Abstract

This paper investigates the special phenomenon that the practical immersed depth of a spiral bevel gear as the driving gear under splash lubrication is significantly less than the static depth. To quantify the practical immersion depth, a computational fluid dynamics (CFD) approach integrated [...] Read more.

This paper investigates the special phenomenon that the practical immersed depth of a spiral bevel gear as the driving gear under splash lubrication is significantly less than the static depth. To quantify the practical immersion depth, a computational fluid dynamics (CFD) approach integrated with image processing techniques is utilized to determine the dynamic immersion depth and the associated churning power loss. First, a theoretical method is developed to estimate the churning losses of the bevel gear by replacing the static immersion depth with the practical dynamic immersion depth. Subsequently, the CFD method, which incorporates the overset mesh technique and the volume-of-fluid (VOF) method, is employed to simulate the gear churning phenomenon. Meanwhile, the dynamic immersion depth is determined through image processing techniques that analyze the oil distribution characteristics in the splash-lubricated bevel gear. Finally, experimental results obtained from a dedicated lubrication test rig are favorably compared with the numerical results, confirming that the practical dynamic immersion depth is an accurate and effective parameter for calculating power losses. Full article

(This article belongs to the Special Issue Gearbox Lubrication)

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16 pages, 3986 KiB

Open AccessArticle

Study on Secondary Remelting Modification of Laser Cladding Ni60/WC Composite Coatings

by Jianwen Zhang, Gui Wang, Jingquan Wu, Jiang Huang, Wenqing Shi, Fenju An and Xianglin Wu

Lubricants 2025, 13(5), 222; https://doi.org/10.3390/lubricants13050222 - 15 May 2025

Abstract

In this study, laser melting experiments of Ni60/WC composite powder coatings were carried out using a laser, and the surface morphology and microstructure of the coatings were analyzed using a scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). In addition, [...] Read more.

In this study, laser melting experiments of Ni60/WC composite powder coatings were carried out using a laser, and the surface morphology and microstructure of the coatings were analyzed using a scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). In addition, hardness testing equipment was used to assess the hardness of the coatings and an electrochemical workstation was used to characterize their corrosion resistance. The key findings demonstrate substantial variations in coating performance based on remelting parameters. The coatings processed without secondary laser remelting exhibited an average hardness of 501.36 (standard deviation 154.46) HV_0.2, a self-corrosion potential of −0.039 V, and a self-corrosion current density of 8.11 × 10⁻⁴ A/cm². In contrast, some coatings were subjected to secondary remelting at 800 mm/min (S 800). The laser is used to scan the surface of the cladding with the laser on the surface of the cladding, and the speed is the feed rate of the laser scanning. XRD analysis revealed intensified main peaks, indicative of elevated solid solution and carbide content. SEM micrographs displayed fishbone-like and feather-like morphologies, with the hardness increasing to 622.98 (standard deviation 9.60) HV_0.2 and the corrosion metrics improving to −0.038 V and 2.86 × 10⁻⁵ A/cm². In contrast, coatings remelted at 600 mm/min (S600) exhibited broader but less intense XDR peaks, alongside diminished reticulation in SEM imagery. These samples demonstrated marginally lower hardness 599.91 (standard deviation 8.35) HV_0.2 but superior corrosion resistance, with a self-corrosion potential of −0.012 V and current density of 2.64 × 10⁻⁵ A/cm². The results underscore the critical influence of laser scanning velocity and remelting frequency on microstructural evolution, mechanical strength, and electrochemical stability. Enhanced hardness correlates with refined microstructural features, while enhanced corrosion resistance arises from reduced defect density and stabilized electrochemical activity. Full article

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21 pages, 7284 KiB

Open AccessArticle

Complex Working Condition Bearing Fault Diagnosis Based on Multi-Feature Fusion and Improved Weighted Balance Distribution Adaptive Approach

by Jing Yang, Yanping Bai, Ting Xu, Rong Cheng, Wendong Zhang and Guojun Zhang

Lubricants 2025, 13(5), 221; https://doi.org/10.3390/lubricants13050221 - 15 May 2025

Abstract

In order to improve the accuracy and generalization ability of fault diagnosis for rotating machinery bearings under complex working conditions, a new model based on multi-feature fusion and improved weighted balance distribution adaptation is proposed. Firstly, an optimized variational mode decomposition algorithm is [...] Read more.

In order to improve the accuracy and generalization ability of fault diagnosis for rotating machinery bearings under complex working conditions, a new model based on multi-feature fusion and improved weighted balance distribution adaptation is proposed. Firstly, an optimized variational mode decomposition algorithm is introduced to denoise the fault signal. Secondly, in order to complement fault information from multiple dimensions, thirteen frequency features and four entropy features are extracted. Then, the 17 features are directly concatenated by dimension to form a high-dimensional feature vector that better adapts to complex working conditions and multiple fault modes. Finally, the improved weighted balance distribution adaptive algorithm is used to reduce the distribution difference between the source domain and the target domain. K-nearest neighbors is used as a classifier to determine the fault category. Using the Case Western Reserve University dataset for validation, the experimental results show that the proposed model achieves an average diagnostic accuracy of 99.34% under 12 complex working conditions. Full article

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13 pages, 5691 KiB

Open AccessArticle

An Analysis of Flow Field Characteristics Under the Start-Up Condition of a Subway Gearbox

by Zhijian Wang, Liwei Guo, Xinglin Li, Feng Wu and Jianguo Ye

Lubricants 2025, 13(5), 220; https://doi.org/10.3390/lubricants13050220 - 15 May 2025

Abstract

This study investigates the transient lubrication dynamics of subway gearboxes during acceleration phases through computational fluid dynamics (CFD) modeling. A simplified gearbox model with helical gears, bearings, and oil-guide channels was developed using STAR-CCM+^®. Simulations evaluated the effects of three acceleration [...] Read more.

This study investigates the transient lubrication dynamics of subway gearboxes during acceleration phases through computational fluid dynamics (CFD) modeling. A simplified gearbox model with helical gears, bearings, and oil-guide channels was developed using STAR-CCM+^®. Simulations evaluated the effects of three acceleration levels (7.4 m/s², 4.4 m/s², and 3.2 m/s²) and three different oil temperatures (−10 °C, 10 °C, and 70 °C) on pressure distribution, churning torque, and oil supply dynamics. The results show that higher acceleration levels intensify transient pressure fluctuations in gear meshing regions and expedite oil supply initiation to bearings. However, the steady-state lubrication performance remains consistent across acceleration magnitudes. Elevated oil temperatures significantly decrease the initial churning torque of a gearbox but increase the steady-state churning torque. There exists an optimal temperature that maximizes the oil supply in the gear meshing zone. In addition, the initial oil supply times for bearings are slightly reduced under lower temperatures. These findings highlight the critical role of transient acceleration and temperature effects in gearbox lubrication optimization, providing insights for enhancing reliability under dynamic operating conditions. Full article

(This article belongs to the Special Issue Tribological Research on Transmission Systems)

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17 pages, 4085 KiB

Open AccessArticle

Comprehensive Evaluation of the Rheological, Tribological, and Thermal Behavior of Cutting Oil and Water-Based Metalworking Fluids

by Florian Pape, Belal G. Nassef, Stefan Schmölzer, Dorothea Stobitzer, Rebekka Taubmann, Florian Rummel, Jan Stegmann, Moritz Gerke, Max Marian, Gerhard Poll and Stephan Kabelac

Lubricants 2025, 13(5), 219; https://doi.org/10.3390/lubricants13050219 - 15 May 2025

Abstract

Metalworking fluids (MWFs) are crucial in the manufacturing industry, playing a key role in facilitating various production processes. As each machining operation comes with distinct requirements, the properties of the MWFs have to be tailored to meet these specific demands. Understanding the properties [...] Read more.

Metalworking fluids (MWFs) are crucial in the manufacturing industry, playing a key role in facilitating various production processes. As each machining operation comes with distinct requirements, the properties of the MWFs have to be tailored to meet these specific demands. Understanding the properties of different MWFs is fundamental for optimizing processes and improving performance. This study centered on characterizing the thermal behavior of various cutting oils and water-based cutting fluids over a wide temperature range and sheds light on the specific tribological behavior. The results indicate that water-based fluids exhibit significant shear-thinning behavior, whereas cutting oils maintain nearly Newtonian properties. In terms of frictional performance, cutting oils generally provide better lubrication at higher temperatures, particularly in mixed and full-fluid film regimes, while water-based fluids demonstrate greater friction stability across a wider range of conditions. Among the tested fluids, water-based formulations showed a phase transition from solid to liquid near 0 °C due to their high water content, whereas only a few cutting oils exhibited a similar behavior. Additionally, the thermal conductivity and heat capacity of water-based fluids were substantially higher than those of the cutting oils, contributing to more efficient heat dissipation during machining. These findings, along with the reported data, intend to guide future researchers and industry in selecting the most appropriate cutting fluids for their specific applications and provide valuable input for computational models simulating the influence of MWFs in the primary and secondary shear zones between cutting tools and the workpiece/chiplet. Full article

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

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24 pages, 10171 KiB

Open AccessArticle

Analysis of Skidding Characteristics of Solid-Lubricated Angular Contact Ball Bearings During Acceleration

by Shijie Zhang, Yuhao Zhao, Jing Wei and Yanyang Zi

Lubricants 2025, 13(5), 218; https://doi.org/10.3390/lubricants13050218 - 14 May 2025

Abstract

Solid-lubricated rolling bearings are widely used in the aerospace field and are key components to support spacecraft rotors. During the start-up of the engine, the sharp acceleration may cause bearing skidding, resulting in damage of the solid lubricating film and a reduction in [...] Read more.

Solid-lubricated rolling bearings are widely used in the aerospace field and are key components to support spacecraft rotors. During the start-up of the engine, the sharp acceleration may cause bearing skidding, resulting in damage of the solid lubricating film and a reduction in the remaining useful life of the bearing. However, the existing research on the tribo-dynamic responses of solid-lubricated ball bearings mostly relies on semi-empirical tribological models, which are limited in their ability to reveal the micro–macro sliding mechanisms of the ball–raceway contact interface. In this paper, a novel tribo-dynamic model for solid-lubricated angular contact ball bearings is developed by applying Kalker’s rolling contact theory to the Gupta dynamic model. The interpolation method is adopted to calculate contact parameters to improve the model’s efficiency. Using the proposed model, the dynamic response of the bearing in the acceleration process is studied, and the mechanism and influence characteristics of skidding, over-skidding, and creepage of the rolling element are analyzed. The results show that the main reason for skidding is that the traction force is not enough to overcome the resistance, and the gyroscopic effect is the main cause of over-skidding, which follows the principle of conservation of the angular momentum of the ball. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 3rd Edition)

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15 pages, 4664 KiB

Open AccessArticle

Simulation Study on the Surface Texturing Design of COC Hip Joints Based on Elastohydrodynamic Lubrication Model

by Zhenxing Wu, Leiming Gao, Xiuling Huang and Zikai Hua

Lubricants 2025, 13(5), 217; https://doi.org/10.3390/lubricants13050217 - 14 May 2025

Abstract

Post-operative feedback from hip replacement surgeries indicates that implanted ceramic artificial hip joints may produce abnormal noises during movement. This occurrence of joint noise is highly correlated with insufficient lubrication of ceramic-on-ceramic (COC) prostheses. Studies have shown that surface texture design can improve [...] Read more.

Post-operative feedback from hip replacement surgeries indicates that implanted ceramic artificial hip joints may produce abnormal noises during movement. This occurrence of joint noise is highly correlated with insufficient lubrication of ceramic-on-ceramic (COC) prostheses. Studies have shown that surface texture design can improve lubrication performance. In this study, the elastohydrodynamic lubrication model was established with designing textures on the surface of the COC hip joint, using Matlab R2018b and GNU FORTRAN in Codeblocks 20.03 programming. Iterative calculations were performed to determine the average bearing capacity of the oil film and the friction coefficient. The study explored the impact of texture parameters, including the aspect ratio and density, on the lubrication and friction performance of the hip joints. The results indicate that the textured surface generally has a higher fluid film bearing capacity by 161.5~637.7% and a lower friction coefficient by 10.7~60% than the smooth surface. The average bearing capacity of the fluid film increases with an increasing texture aspect ratio, while the trend of the friction coefficient is identical to the average bearing capacity results. As the texture density increases, the average bearing capacity of the fluid film first decreases and then increases, and the trend of the friction coefficient also increases accordingly. Among the nine design groups (

S p = 0.05, 0.15, 0.35, ε = 0.075, 0.1, 0.15

), based on the fuzzy comprehensive evaluation, the local optimal solution is

S p = 0.15

,

ε = 0.075

for lubrication and wear resistance. Full article

(This article belongs to the Special Issue Tribology in Artificial Joints)

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22 pages, 18733 KiB

Open AccessArticle

An Approach for Predicting the Vibro-Impact Behavior of Angular Contact Ball Bearing Considering Variable Clearance

by Yuqi Zhou, Xu Peng and Yu Chen

Lubricants 2025, 13(5), 216; https://doi.org/10.3390/lubricants13050216 - 14 May 2025

Abstract

This work develops a comprehensive analysis method to examine the nonlinear dynamic response of angular contact ball bearings (ACBBs) with variable clearance. Based on the elastic contact theory and friction principle, the nonlinear contact-impact behavior of the ACBB is systematically investigated. A multibody [...] Read more.

This work develops a comprehensive analysis method to examine the nonlinear dynamic response of angular contact ball bearings (ACBBs) with variable clearance. Based on the elastic contact theory and friction principle, the nonlinear contact-impact behavior of the ACBB is systematically investigated. A multibody dynamics model incorporating three-dimensional clearance effects is developed. First, the nonlinear vibro-impact dynamics model of the ACBB is presented considering the influence of variable clearance. Second, the kinematic analysis of the ACBB with clearance is planned, and performance tests are performed under variable conditions, which demonstrate the effectiveness of the proposed method. Furthermore, a comparative analysis of a numerical simulation of the ACBBs with variable clearance is performed. The results show that the increase in rotation speed and external load would cause the high-frequency contact impact between ball and raceway. The decline of the deviation ratio for the cage’s mass center velocity illustrates that the motion trajectory of ACBB would be irregular. Full article

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

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13 pages, 2986 KiB

Open AccessArticle

Prediction of Lubrication Performance of Hyaluronic Acid Aqueous Solutions Using a Bayesian-Optimized BP Network

by Xia Li and Feng Guo

Lubricants 2025, 13(5), 215; https://doi.org/10.3390/lubricants13050215 - 14 May 2025

Abstract

The present study proposes a Bayesian-optimized back-propagation (BP) neural network framework for predicting the tribological performance of hyaluronic acid (HA) aqueous solutions under hydrodynamic lubrication conditions. The model addresses the complex rheological behavior of HA and limitations of traditional trial-and-error methods. It integrates [...] Read more.

The present study proposes a Bayesian-optimized back-propagation (BP) neural network framework for predicting the tribological performance of hyaluronic acid (HA) aqueous solutions under hydrodynamic lubrication conditions. The model addresses the complex rheological behavior of HA and limitations of traditional trial-and-error methods. It integrates four operational parameters—applied load, sliding speed, fluid viscosity and contact surface inclination. These enable the simultaneous prediction of two critical lubrication characteristics: film thickness and load-carrying capacity. Bayesian optimization was used to automate hyperparameter tuning. This can significantly improve computational efficiency. The optimized model showed a coefficient of determination (R²) of 0.938 and a mean square error (MSE) of 0.0025 on the test dataset, indicating its ability for accurate prediction. The results indicated a significant positive correlation between HA viscosity and lubrication performance. This framework can be used as a screening tool for HA-based lubricants. The integration of machine learning with biotribology may offer opportunities to improve data-driven approaches to analyzing complex fluid behavior, where traditional models have limitations. Full article

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

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14 pages, 2106 KiB

Open AccessArticle

Intricacies of Thrust Collar Simulation

by Christian Heinrich and Armin Lohrengel

Lubricants 2025, 13(5), 214; https://doi.org/10.3390/lubricants13050214 - 13 May 2025

Abstract

This paper presents a number of thrust-collar-specific effects to consider when simulating the elastohydrodynamic lubrication state. Plate bending can lead to edge loading and can be considered via an FEM model of the solids. When bending is of no concern, the effect of [...] Read more.

This paper presents a number of thrust-collar-specific effects to consider when simulating the elastohydrodynamic lubrication state. Plate bending can lead to edge loading and can be considered via an FEM model of the solids. When bending is of no concern, the effect of the close outside edge needs to be corrected in half-space deformation theory. Track heating requires a unique version of the Carslaw/Jaeger flash temperature solution for curved trajectories. Especially, the adapted treatment of stiffness effects leads to vastly different results in, e.g., lubrication gap height. Full article

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25 pages, 8216 KiB

Open AccessArticle

Influence of a Walnut Shell Biochar Additive on the Tribological and Rheological Properties of Vegetable Lubricating Grease

by Rafal Kozdrach and Pawel Radulski

Lubricants 2025, 13(5), 213; https://doi.org/10.3390/lubricants13050213 - 13 May 2025

Abstract

This paper presents the results of a study on the effect of a biochar additive produced via pyrolysis at 400 °C and 500 °C from waste biomass, i.e., walnut shells, on the tribological and rheological properties of vegetable lubricating compositions. Sunflower oil and [...] Read more.

This paper presents the results of a study on the effect of a biochar additive produced via pyrolysis at 400 °C and 500 °C from waste biomass, i.e., walnut shells, on the tribological and rheological properties of vegetable lubricating compositions. Sunflower oil and amorphous silica, used as a thickener, were used to prepare the lubricants. To the base lubricant prepared in this way, 1 and 5% biochar additive were introduced, and for comparison, we took the same amounts of graphite. Tests were carried out on the anti-wear properties, coefficient of friction, and changes in dynamic viscosity during the tribological test, as well as on the anti-scuffing properties for the tested lubricant compositions. The effect of the applied modifying additive on the lubricating and rheological properties of the prepared lubricating greases was evaluated. On the basis of the study of vegetable greases, it was found that the addition of 5% biochar from walnut shells produced during pyrolysis in 500 °C had the most favorable effect on the anti-wear properties of the tested greases, while the 5% biochar from walnuts shell prepared via pyrolysis at 400 °C had the best anti-scuffing protection. The use of the biochar additive in vegetable greases resulted in a reduction in the dynamic viscosity of the tested greases, particularly for greases modified with 5% walnut shell biochar produced at 500 °C, which is particularly important with respect to the work of steel friction nodes, as well as in central lubrication systems. Full article

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

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16 pages, 7401 KiB

Open AccessArticle

Analytical Method for Predicting Wear Life of Angular Contact Ball Bearings Under Variable Loading Based on Mixed Lubrication

by Xiaoyan Mu, Gong Cheng, Shaojiang Dong, Liang Yi and Hongliang Liu

Lubricants 2025, 13(5), 212; https://doi.org/10.3390/lubricants13050212 - 12 May 2025

Abstract

In aerospace technology, angular contact ball bearings are required to exhibit extremely high operational precision, necessitating real-time monitoring of their wear status to conduct pre-failure analysis. Although extensive studies have been conducted on the wear characteristics of angular contact bearings, further in-depth research [...] Read more.

In aerospace technology, angular contact ball bearings are required to exhibit extremely high operational precision, necessitating real-time monitoring of their wear status to conduct pre-failure analysis. Although extensive studies have been conducted on the wear characteristics of angular contact bearings, further in-depth research is still required to enhance the accuracy of bearing life predictions. To address the imprecision in wear life prediction for angular contact ball bearings, this article proposes a refined wear calculation model based on dynamic load distribution. The model calculates the dynamic load distribution between the inner and outer rings and the raceway under mixed lubrication conditions. Integrating the dynamic load distribution methodology with the wear calculation model, the dynamic contact characteristics of angular contact bearings can be more accurately characterized. Building on this foundation, a dynamic analysis model considering dynamic wear in the bearing contact zone is established. The vibration characteristics of bearings under varying loads are analyzed, and vibration experiments under different load conditions are conducted. Through vibration spectrum analysis, the influence patterns of wear characteristic frequency bands in the wear model on the pre-failure state of bearings are further elucidated. This study provides a theoretical basis for bearing wear life prediction analysis. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 3rd Edition)

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11 pages, 3839 KiB

Open AccessArticle

Potassium Titanate Whisker/Graphene Multi-Dimensional Fillers to Improve the Wear Resistance of Poly(Ether Ether Ketone) Composite

by Zhengjia Ji, Mingliang Ji, Qiuchen Lv, Minggui Liang and Chao Xu

Lubricants 2025, 13(5), 211; https://doi.org/10.3390/lubricants13050211 - 11 May 2025

Abstract

To improve the tribological performance of poly(ether ether ketone) (PEEK), a potassium titanate whisker/graphene multi-dimensional hybrid filler was proposed. Hybrid fillers with one-dimensional (1D) potassium titanate whiskers and two-dimensional (2D) graphene nanosheets in different ratios were fabricated using direct mixing and grafting methods. [...] Read more.

To improve the tribological performance of poly(ether ether ketone) (PEEK), a potassium titanate whisker/graphene multi-dimensional hybrid filler was proposed. Hybrid fillers with one-dimensional (1D) potassium titanate whiskers and two-dimensional (2D) graphene nanosheets in different ratios were fabricated using direct mixing and grafting methods. The potassium titanate whiskers and graphene nanosheets are an excellent combination, as confirmed by SEM and FTIR. Furthermore, PEEK/hybrid filler composites with different mass percentages of fillers were prepared and investigated systematically. It was found that introducing multi-dimensional hybrid PTWs–GNPs (volume ratio 1:3) fillers led to the wear rate being as low as 3.214 × 10⁻⁶ mm³N⁻¹m⁻¹, reduced by 60% compared with pure PEEK. In addition, the wear mechanism of PEEK composites was also investigated. The results demonstrate the superior tribological properties of the PEEK composites with multi-dimensional hybrid PTWs–GNPs fillers. Full article

(This article belongs to the Special Issue Tribology of Polymeric Composites)

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