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Tribology and Hot Corrosion Behavior of MCrAlY-Based Multicomponent Coatings Containing Copper
Low Brine Shrimp Bio-Toxicity Marine Lubricating Hydraulic Fluid with Ultra-Low Friction Coefficient and Enhanced Frictional Heat Suppression
Temperature Characteristics of Axle-Box Bearings Under Wheel Flat Excitation
Intelligent Analysis and Optimization of Lubrication Status Factor Based on Dynamically Loaded Roll Gap in Cold Strip Rolling
MoS2 Additives in Lithium Grease for Electrified Systems

Journal Description

Lubricants

Lubricants is an international, peer-reviewed, open access journal on tribology published monthly online by MDPI.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
Journal Rank: JCR - Q2 (Engineering, Mechanical) / CiteScore - Q2 (Mechanical Engineering)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 14.6 days after submission; acceptance to publication is undertaken in 2.5 days (median values for papers published in this journal in the second half of 2024).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.

Impact Factor: 3.1 (2023); 5-Year Impact Factor: 3.1 (2023)

Imprint Information Journal Flyer Open Access ISSN: 2075-4442

Latest Articles

13 pages, 2998 KiB

Open AccessArticle

Study of Surface Treatment by Ionic Plasma and Self-Protective Pastes of AISI 304 and 316L Stainless Steels: Chemical, Microstructural, and Nanohardness Evaluation

by Francisco Martínez-Baltodano, Juan C. Díaz-Guillén, Lizsandra López-Ojeda, Gregorio Vargas-Gutiérrez and Wilian Pech-Rodríguez

Lubricants 2025, 13(5), 195; https://doi.org/10.3390/lubricants13050195 - 24 Apr 2025

This work studied the effect of self-protective paste nitriding (SPN) and ion plasma nitriding (IPN) on the surface chemistry, microstructure, and nanohardness of AISI 304 and 316L stainless steels, with both treated at 440 °C for 5 h. Surface modifications analyzed using SEM [...] Read more.

This work studied the effect of self-protective paste nitriding (SPN) and ion plasma nitriding (IPN) on the surface chemistry, microstructure, and nanohardness of AISI 304 and 316L stainless steels, with both treated at 440 °C for 5 h. Surface modifications analyzed using SEM and nanoindentation revealed distinct outcomes. SPN induced an oxynitriding effect due to the oxidation properties of the pastes, forming Fe₃O₄ and Fe_xC phases, while IPN produced an expanded austenite layer. Both methods enhanced surface nanohardness, but SPN showed superior results. For 316L SS, SPN increased nanohardness by 367.81% (6.83 GPa) compared to a 133.5% increase (3.41 GPa) with IPN. For 304 SS, SPN improved nanohardness by 26% (2.23 GPa), whereas IPN reduced it by 48% (0.92 GPa). These findings highlight SPN’s potential as an effective anti-wear treatment, particularly for 316L SS. The SPN process utilized a eutectic mixture of sodium cyanate and sodium carbonate, while IPN employed a N₂:H₂ (1:1) gas mixture. SEM analyses confirmed the formation of γ-Fe(N) phases, indicating dispersed iron nitrides (FeN, Fe₃N, Fe₄N). SPN’s simultaneous oxidation and nitrocarburization led to an oxide layer above the nitride diffusion layer, enhancing mechanical properties through iron oxides (Fe₃O₄) and carbides (Fe_xC). Comparative analysis showed that AISI 316L exhibited better performance than AISI 304, underscoring SPN’s effectiveness for surface modification. Full article

(This article belongs to the Special Issue Structural Evolution and Wear of Steels)

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14 pages, 2159 KiB

Open AccessArticle

Discussion on the Non-Linear Stability of Short Hydrodynamic Bearings by Applying Rabinowitsch Fluid Model

by Huaiqing Lu, Chunyan Cheng and Zhuxin Tian

Lubricants 2025, 13(5), 194; https://doi.org/10.3390/lubricants13050194 - 23 Apr 2025

Using the Rabinowitsch fluid model, the effects of dilatant fluids (a non-Newtonian factor less than 0) and pseudo-plastic fluids (a non-Newtonian factor greater than 0) on the non-linear stability of hydrodynamic journal bearings is discussed. The modified Reynolds equation is solved by the [...] Read more.

Using the Rabinowitsch fluid model, the effects of dilatant fluids (a non-Newtonian factor less than 0) and pseudo-plastic fluids (a non-Newtonian factor greater than 0) on the non-linear stability of hydrodynamic journal bearings is discussed. The modified Reynolds equation is solved by the small perturbation method, and the stiffness and damping coefficients and threshold speed of hydrodynamic bearings are obtained. Through the fourth-order Runge–Kutta method, the trajectory of the journal center is traced and the non-linear stability boundary of hydrodynamic bearings with different non-Newtonian lubricants could be confirmed. The results show that the dilatant fluids could increase the threshold speed and enlarge the non-linear stability region of the hydrodynamic bearing, while the influence of pseudo-plastic fluids is positive. And for the lubricants with a larger non-Newtonian factor, the effect is more obvious. It could be confirmed that the stability of hydrodynamic bearings lubricated with dilatant fluids is better than that of bearings with Newtonian and pseudo-plastic lubricants. The results illustrate that selecting a more appropriate lubricant can enhance the stability of hydrodynamic bearings. Full article

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

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15 pages, 7879 KiB

Open AccessArticle

Fabrication of a Composite Groove Array Surface with Gradient Wettability Which Delivers Enhanced Lubrication Performance

by Tianrui Zhang, Chenglong Liu, Xinming Li, Feng Guo and Kongmin Zhu

Lubricants 2025, 13(5), 193; https://doi.org/10.3390/lubricants13050193 - 23 Apr 2025

A novel composite groove array surface was fabricated using femtosecond laser ablation technology to enhance self-replenishment capability. Initially, the driving efficiency of droplets on the composite groove array surface was tested using a high-speed droplet transportation system, characterizing the effect of this surface [...] Read more.

A novel composite groove array surface was fabricated using femtosecond laser ablation technology to enhance self-replenishment capability. Initially, the driving efficiency of droplets on the composite groove array surface was tested using a high-speed droplet transportation system, characterizing the effect of this surface on lubricant backflow characteristics. Simultaneously, measurement of lubricating film thickness was utilized to explore the lubrication enhancement effect of the composite groove array surface on oil film formation under reciprocating motion. The multidimensional gradient wettability, engineered through the composite groove array surface, demonstrated excellent efficiency in lubricant replenishment within the lubrication track. Oil droplet transportation testing demonstrated that the composite groove array surface, which induced gradient wettability at the boundary, attained a maximum driving speed of 123.5 mm/s. This innovative design significantly reduced the barriers associated with lubricant backflow, particularly those induced by cavitation expansion during high-frequency reciprocating motion. Furthermore, the results demonstrated that the film-forming capabilities of this composite groove array surface were enhanced, thereby optimizing the overall lubrication performance. Full article

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11 pages, 2501 KiB

Open AccessArticle

Effect of Micro-Dimple Texture on the Lubrication Characteristics of Elliptical Sliding Pairs Between a Flex Spline and a Novel Forced Wave Generator

by Zixiang Yi and Hongbing Xin

Lubricants 2025, 13(5), 192; https://doi.org/10.3390/lubricants13050192 - 23 Apr 2025

The novel forced wave generator (NFWG) is a critical component of the harmonic drive (HD) without a flexible bearing. Tribological design is required to increase the load-carrying capacity and reduce the frictional resistance in the elliptical sliding pairs (ESPs) between the flex spline [...] Read more.

The novel forced wave generator (NFWG) is a critical component of the harmonic drive (HD) without a flexible bearing. Tribological design is required to increase the load-carrying capacity and reduce the frictional resistance in the elliptical sliding pairs (ESPs) between the flex spline (FS) and the NFWG. As the thin-walled FS operates under cyclic deformation with large displacement in the HD, this paper investigates the effects of the distribution region, depth, shape, and density of micro-dimple textures on the outer contour surface of the NFWG on the load-carrying capacity and the frictional resistance of the ESPs using the CFD method. The analysis reveals that the load capacity and lubrication performances of the ESPs are significantly enhanced when the micro-dimple textures are fully distributed on the outer contour surface of the NFWG, with a depth of 0.1 mm, a radius of 6 mm, and a distribution density of 3.9%. The results provide a reference for the practical design of ESPs in the HD under extreme mechanical transmission conditions. Full article

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18 pages, 4725 KiB

Open AccessArticle

Experimental Study on Thermal Elastohydrodynamic Lubrication Performance Calculation and Take-Off Speed of Thrust Bearing of Canned Motor Pump

by Yanjun Cao, Yingjie Yu, Haiming Gang, Qichen Shang, Xiaozhe Meng, Mohan Yang and Qian Jia

Lubricants 2025, 13(4), 191; https://doi.org/10.3390/lubricants13040191 - 21 Apr 2025

In this paper, the calculation model and method of the lubrication performance of the thrust bearing, which considers the thermal bomb deformation, are constructed based on the working characteristics of the main pump thrust of the nuclear power plant. The key design parameters [...] Read more.

In this paper, the calculation model and method of the lubrication performance of the thrust bearing, which considers the thermal bomb deformation, are constructed based on the working characteristics of the main pump thrust of the nuclear power plant. The key design parameters of the tile package Angle θ are analyzed by taking the design parameters of the thrust-bearing tile as the variable. The circumferential fulcrum coefficient of tile, the influence of tile thickness B, and tile elastic modulus E on the lubrication performance of thrust bearing are analyzed to obtain improved design parameters. The lubrication performance of the thrust bearing includes the minimum oil film thickness h_min, the maximum temperature of oil film T_max, total flow Q_x, total power consumption W, maximum thermal deformation of axial bush δT_max, and the maximum elastic deformation of the axial bush δF_max. The scale test of the designed thrust bearing is carried out. The take-off speed of the bearing is tested and compared with the results of the theoretical analysis. The study results show that the influence is becoming more obvious from θo to h_min. Moreover, the impact becomes more obvious from T_max to Q_x, B to hmin, and Q_x to δT_max and δF_max. Lastly, the impact is also obvious from E to Q_x and δF_max. Full article

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20 pages, 8653 KiB

Open AccessArticle

Leakage Flow Characteristics of Novel Two-Stage Brush Seal with Pressure-Equalizing Hole

by Yu Li, Huanze Xu, Jinghan Zhang, Dan Sun and Zemin Yang

Lubricants 2025, 13(4), 190; https://doi.org/10.3390/lubricants13040190 - 19 Apr 2025

Uneven inter-stage pressure drops of the common two-stage brush seal (CBS) lead to a problem that the second stage bristles bear excessive pressure load, and this problem leads to the premature failure of the brush seal. In this paper, a novel two-stage brush [...] Read more.

Uneven inter-stage pressure drops of the common two-stage brush seal (CBS) lead to a problem that the second stage bristles bear excessive pressure load, and this problem leads to the premature failure of the brush seal. In this paper, a novel two-stage brush seal (NBS) with the backing plate holes of the second stage was proposed, and a three-dimensional numerical model of the NBS was established. Then, the effects of the pressure-equalizing (PE) hole on the inter-stage pressure drop distribution of the NBS were numerically analyzed, and an optimal structure was obtained. Finally, the leakage flow characteristics of this optimal structure were studied. The results showed that the NBS with PE hole increased the passage area of the downstream, and so effectively improved the uneven pressure drops of the CBS, and the pressure drop balance ratio of the NBS was obviously smaller than that of the CBS. For the structural parameters studied in this paper, the pressure drop balance ratio of the NBS was improved by 45.6~67.9% compared to the CBS. Moreover, when PE holes were 0.4 mm in diameter, 5.95 mm in height, and the number of rows was 1, the NBS had the best pressure drop balance and its leakage was only 8.7% higher than that of the CBS. Full article

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16 pages, 7371 KiB

Open AccessArticle

Anisotropic Wear Resistance of Heat-Treated Selective Laser-Melted 316L Stainless Steel

by Menghui Sun, Qianqian Zhang, Jinxiu Wu, Hao Wang, Xu Wang, Hao Zhang, Yinong An, Yujie Liu and Long Ma

Lubricants 2025, 13(4), 189; https://doi.org/10.3390/lubricants13040189 - 19 Apr 2025

Anisotropic microstructures and wear resistance are caused by large thermal gradients during selective laser melting (SLM). Investigating the wear resistance in different planes of SLM specimens is crucial. Hence, the effect of heat treatment on the anisotropy of the microstructure, density, microhardness, and [...] Read more.

Anisotropic microstructures and wear resistance are caused by large thermal gradients during selective laser melting (SLM). Investigating the wear resistance in different planes of SLM specimens is crucial. Hence, the effect of heat treatment on the anisotropy of the microstructure, density, microhardness, and wear resistance of SLM 316L stainless steel was studied. Specimens subjected to solution + aging treatment exhibited γ austenite and α ferrite phases with lower microstrain, as determined via X-ray diffraction (XRD) analysis. Microstructure observations demonstrated that SLM 316L appears as intersecting melt pools on the XOY plane and fish scale-like melt pools on the XOZ plane. After heat treatment, the melt boundaries disappeared, carbides (M₂₃C₆) precipitated at grain boundaries and within the grains, and the microstructures coarsened and became more uniform. The microhardness and wear resistance of the XOY plane were shown to be superior to those of the XOZ plane, and the microhardness decreased following heat treatment. Compared with SLM 316L, the microhardness of the XOY and XOZ planes of the specimen subjected to solution + aging treatment decreased by 5.96% and 4.98%. The friction and wear test results revealed that the specimen after solution + aging treatment had the lowest friction coefficient and the smallest wear rate. The wear rates of specimens from the XOY and XOZ planes after solution + aging treatment were 21.1% and 27.1% lower than that of SLM 316L, exhibiting the best wear resistance. Full article

(This article belongs to the Special Issue Friction and Wear of Alloys)

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20 pages, 4320 KiB

Open AccessArticle

The Impact of Oil Viscosity and Fuel Quality on Internal Combustion Engine Performance and Emissions: An Experimental Approach

by Milton Garcia Tobar, Kevin Pinta Pesantez, Pablo Jimenez Romero and Rafael Wilmer Contreras Urgiles

Lubricants 2025, 13(4), 188; https://doi.org/10.3390/lubricants13040188 - 18 Apr 2025

The automotive industry faces increasing challenges due to fuel scarcity and pollutant emissions, necessitating the implementation of strategies that optimize engine performance while minimizing the environmental impact. This study aimed to analyze the influence of oil viscosity and fuel quality on the engine [...] Read more.

The automotive industry faces increasing challenges due to fuel scarcity and pollutant emissions, necessitating the implementation of strategies that optimize engine performance while minimizing the environmental impact. This study aimed to analyze the influence of oil viscosity and fuel quality on the engine performance and pollutant emissions in an internal combustion engine. A Response Surface Methodology (RSM)-based experimental design was employed. Three oil viscosity levels (SAE 5W-30, 10W-30, and 20W-50) and three fuel quality levels (87, 92, and 95 octane) were evaluated using a Chevrolet Grand Vitara 2.0L (General Motors, Quito, Ecuador) tested on a dynamometer. The oil grades were selected to represent a practical range of viscosities commonly used in commercial vehicles operating under local conditions. The results indicate that using lower-viscosity oil (SAE 5W-30) increased the engine power by up to 6.25% compared to when using SAE 20W-50. Additionally, using higher-octane fuel led to an average power increase of 1.49%, attributed to improved combustion stability and the ability to operate at a more advanced ignition timing without knocking. The emissions analysis revealed that high-viscosity oil at high RPMs increased CO₂ emissions to 14.4% vol, whereas low-viscosity oil at low RPMs reduced CO₂ emissions to 13.4% vol. Statistical analysis confirmed that the engine speed (RPM) was the most influential factor in emissions (F = 163.11 and p < 0.0001 for CO₂; F = 247.02 and p < 0.0001 for NOx), while fuel quality also played a significant role. These findings suggest that optimizing the oil viscosity and selecting the appropriate fuel can enhance engine efficiency and reduce emissions, thereby contributing to the development of more sustainable automotive technologies. Future research should explore the use of ultra-low-viscosity lubricants (SAE 0W-20) and assess their long-term effects on engine wear. Full article

(This article belongs to the Special Issue Advances in Hydrodynamic Friction in Combustion Engines)

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16 pages, 9284 KiB

Open AccessArticle

The Impact of Surface Roughness on the Friction and Wear Performance of GCr15 Bearing Steel

by Tiantian He, Wenbo Chen, Zeyuan Liu, Zhipeng Gong, Sanming Du and Yongzhen Zhang

Lubricants 2025, 13(4), 187; https://doi.org/10.3390/lubricants13040187 - 18 Apr 2025

Surface roughness plays a crucial role in determining surface quality, influencing factors such as vibration, noise, assembly precision, lubrication, and wear resistance in bearings. This research examines how surface roughness (Sa) affects the friction and wear characteristics of GCr15 steel under conditions with [...] Read more.

Surface roughness plays a crucial role in determining surface quality, influencing factors such as vibration, noise, assembly precision, lubrication, and wear resistance in bearings. This research examines how surface roughness (Sa) affects the friction and wear characteristics of GCr15 steel under conditions with adequate oil lubrication while varying the applied load. The findings indicate that with an increase in Sa, the friction coefficient of GCr15 steel also increases. As the load rises from 15 N to 35 N, the friction coefficient remains relatively constant. However, higher loads lead to more severe wear of the microprotrusions on the surface of GCr15 steel. The wear area first decreases and then increases as Sa increases. The minimum wear area occurs when Sa is 0.5 μm. Additionally, a back propagation neural network (BPNN) model has been developed to predict the wear performance of GCr15 steel. Validation experiments show that the average prediction error for the BPNN model is 10.64%. Full article

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24 pages, 24408 KiB

Open AccessArticle

Pin-on-Disc Experimental Study of Thermomechanical Processes Related to Squeal Occurrence

by Quentin Caradec, Sacha Durain, Maël Thévenot, Mathis Briatte, Merten Stender, Jean-François Brunel and Philippe Dufrénoy

Lubricants 2025, 13(4), 186; https://doi.org/10.3390/lubricants13040186 - 18 Apr 2025

Squeal refers to a sustained high-intensity noise resulting from friction-induced vibrations. Although it is known that it originates from mode coupling, the conditions under which it occurs are still unclear, especially regarding the contact conditions. In this paper, pin-on-disc experimental tests are conducted [...] Read more.

Squeal refers to a sustained high-intensity noise resulting from friction-induced vibrations. Although it is known that it originates from mode coupling, the conditions under which it occurs are still unclear, especially regarding the contact conditions. In this paper, pin-on-disc experimental tests are conducted in order to investigate the conditions of squeal occurrence. The tests are highly instrumented: they involve in particular a detailed measurement of near-surface temperature evolution in the pin using 16 thermocouples and a discrete monitoring of the evolution of surface profiles. As expected, the squealing frequency is closely related to the temperature level. However, the mean temperature level alone is not sufficient to predict the occurrence of squeal, especially at low temperatures. The study of local temperature elevations over the pin surface coupled with surface observations allows for assessing the evolution of macroscopic contact localization during tests at low temperatures. The contact localization is shown to be related to squeal episodes: at low temperatures, the contact is localized near the corners of the pin surface, and squeal is found to occur only in situations where the contact is evenly balanced over the corners, which is highly influenced by the initial pin surface profile. This shows that the conditions of squeal occurrence are driven in a significant extent by thermomechanical processes. Full article

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14 pages, 5772 KiB

Open AccessArticle

Study on the Tribological Behaviors of a Wave Glider’s Wing’s Rotating Shaft Using Fractal and Chaotic Analysis

by Shihui Lang, Hua Zhu and Xuehai Lian

Lubricants 2025, 13(4), 185; https://doi.org/10.3390/lubricants13040185 - 16 Apr 2025

This paper conducts wear tests of rotating shafts and bearings, and collects the wear amount, surface morphology, and friction force signals to study its tribological behaviors using the fractal and chaotic analysis. The rotation shaft surface fractal dimension were calculated to characterize the [...] Read more.

This paper conducts wear tests of rotating shafts and bearings, and collects the wear amount, surface morphology, and friction force signals to study its tribological behaviors using the fractal and chaotic analysis. The rotation shaft surface fractal dimension were calculated to characterize the self-similarity and smoothness, the signals’ phase trajectories were constructed, and its correlation dimension and phase-point saturation were calculated to reveal the dynamic evolution of the system. The results show that the surface fractal dimension increases from low to high. The phase trajectory fluctuates and then maintains in a finite space, and the correlation dimension increases and stabilizes near the larger value while the phase-point saturation has the opposite evolution. The changes in surface fractal dimension, phase trajectories, correlation dimension, and phase-point saturation are similar to the wear rate, exhibiting a transition from instability to stability, which is more objective and sensitive than traditional representation methods. According to the fractal and chaotic characterization results of the worn surface and friction force signal, the material of CrNiMoN has better friction and wear properties than GCr15. The results reveal the tribological behaviors and wear mechanisms of the rotating shaft and provide guidance for material selection and designing, along with a basis for characterizing the wear status of the rotating shaft of wave glider wing. Full article

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17 pages, 2619 KiB

Open AccessArticle

Optimizing Hyaluronan-Based Lubricants for Treating Thoracolumbar Fascia Pathologies: Insights from Tribological and Pharmacokinetic Studies

by Alexandra Streďanská, Matěj Šimek, Jana Matonohová, David Nečas, Martin Vrbka, Jakub Suchánek, Veronika Pavliňáková, Lucy Vojtová, Martin Hartl, Ivan Křupka and Kristina Nešporová

Lubricants 2025, 13(4), 184; https://doi.org/10.3390/lubricants13040184 - 16 Apr 2025

In a world where the incidence of non-specific lower back pain (LBP) is steadily increasing, researchers are still searching for effective solutions for patients. Hyaluronic acid (HA) viscosupplementation is commonly used to restore lubrication in osteoarthritis (OA) and other medical applications, but its [...] Read more.

In a world where the incidence of non-specific lower back pain (LBP) is steadily increasing, researchers are still searching for effective solutions for patients. Hyaluronic acid (HA) viscosupplementation is commonly used to restore lubrication in osteoarthritis (OA) and other medical applications, but its rapid metabolism limits efficacy. This study evaluates whether an HA derivative can replace native HA for the treatment of non-specific LBP while maintaining or enhancing its frictional properties and improving in vivo stability. Six HA-based lubricants, both native and derivatized, were tested in a tribological rabbit fascia model and a new synthetic model. Reduced HA derivative showed better tribological properties and longer in vivo residence time compared to native HA, as demonstrated in pharmacokinetic studies in rabbits. The 316 kDa HA and reduced HA exhibited the most stable tribological properties, which were influenced by their molecular weight and concentration. These findings suggest that both native and reduced HA are promising viscosupplements for intrafascial injection in the treatment of LBP, with reduced HA potentially enhancing effectiveness through a prolonged effect. Full article

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21 pages, 8225 KiB

Open AccessArticle

Contact Load Calculation Models for Finite Line Contact Rollers in Bearing Dynamic Simulation Under Dry and Lubricated Conditions

by Yongxu Hu, Liu He, Yan Luo, Andy Chit Tan and Cai Yi

Lubricants 2025, 13(4), 183; https://doi.org/10.3390/lubricants13040183 - 15 Apr 2025

The key to exploring the behavior of bearings through dynamic methods lies in establishing an accurate model for calculating the contact load between the roller and the raceway. Based on the half-space theory of Boussinesq, this study developed a full-order model for calculating [...] Read more.

The key to exploring the behavior of bearings through dynamic methods lies in establishing an accurate model for calculating the contact load between the roller and the raceway. Based on the half-space theory of Boussinesq, this study developed a full-order model for calculating the contact load of the finite line contact roller. The model adopted an iterative procedure to calculate the contact load of each roller slice according to deformations. According to the comparisons between the contact loads obtained by the proposed model and those obtained by FEA, the average error for a cylindrical roller was approximately 2%, while that for a tapered roller was approximately 17%. By neglecting the influences of inter-slice contact stresses on the deformation of local roller slice, a fast-calculating method for the full-order model was developed, thereby reducing the calculation time by approximately 77%. By integrating the fast method with the Dowson–Higginson’s formula, another model was developed to calculate the contact load under lubrication conditions. The proposed models were utilized to investigate the dynamic characteristics of a double-row tapered roller bearing, and the results were validated through experiments. The proposed method could be utilized to assess dynamic performances of bearings across different operating scenarios. Full article

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

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25 pages, 8753 KiB

Open AccessArticle

Research on RV Reducer Shaft Bearing Force and Structural Optimization

by Xiaoxu Pang, Dingkang Zhu, Xinlong Wang, Minghao Yang, Qiaoshuo Li, Duo Liu and Hai Wu

Lubricants 2025, 13(4), 182; https://doi.org/10.3390/lubricants13040182 - 15 Apr 2025

This paper addresses the unclear bearing force of an RV reducer shaft by establishing a transmission model and analyzing the force situation of each component. Three force models for the crank support bearing, swivel arm bearing, and main bearing are developed. The force [...] Read more.

This paper addresses the unclear bearing force of an RV reducer shaft by establishing a transmission model and analyzing the force situation of each component. Three force models for the crank support bearing, swivel arm bearing, and main bearing are developed. The force variations under different working conditions and the impact of structural parameters on shaft bearing forces are analyzed. Structural optimization is performed using Kriging-NSGA-II to minimize bearing forces. The results show similar load patterns for the bearings, with the force magnitude being ranked in the following order: rotating arm > crank support > main bearing. After optimization, the bearing forces are reduced by 8.26% for the crank support shaft, 10.35% for the rotating arm shaft, and 5.15% for the main shaft. Full article

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

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17 pages, 15797 KiB

Open AccessArticle

Unbalance Response of a Hydrogen Fuel Cell Vehicle Air Compressor Rotor Supported by Gas Foil Bearings: Experimental Study and Analysis

by Ming Ying and Xinghua Liu

Lubricants 2025, 13(4), 181; https://doi.org/10.3390/lubricants13040181 - 14 Apr 2025

In rotating machinery, unbalanced mass is one of the most common causes of system vibration. This paper presents an experimental investigation of the unbalance response of a gas foil bearing-rotor system, based on a 30 kW-rated commercial hydrogen fuel cell vehicle air compressor. [...] Read more.

In rotating machinery, unbalanced mass is one of the most common causes of system vibration. This paper presents an experimental investigation of the unbalance response of a gas foil bearing-rotor system, based on a 30 kW-rated commercial hydrogen fuel cell vehicle air compressor. The study examines the response of the system to varying unbalanced masses at different rotational speeds. Experimental results show that, after adding unbalanced mass, subsynchronous vibration of the rotor is relatively slight, while synchronous vibration is the main source of vibration; when unbalanced mass is added to one side of the rotor, the synchronous vibration on that side initially decreases and then increases with speed, while synchronous vibration on the opposite side continuously increases with speed; when unbalanced mass is added to both sides, the synchronous vibration on each side increases with the phase difference of the unbalanced mass at low speed, while the opposite trend occurs at high speed. The analysis of the gas foil bearing-rotor system dynamics model established based on the dynamic coefficient of the bearing shows that the bending of the rotor offsets the displacement caused by the unbalanced mass, which is the primary reason for the nonlinear behavior of the synchronous vibration of the rotor. These findings contribute to an improved understanding of GFB-rotor interactions under unbalanced conditions and provide practical guidance for optimizing dynamic balancing strategies in hydrogen fuel cell vehicle compressors. Full article

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24 pages, 18010 KiB

Open AccessArticle

Reducing the Friction Coefficient of Heavy-Load Spherical Bearings in Bridges Using Surface Texturing—A Numerical Study

by Qian Hu, Qingxiang Pei and Pei Li

Lubricants 2025, 13(4), 180; https://doi.org/10.3390/lubricants13040180 - 13 Apr 2025

Spherical bearings play a crucial role in maintaining the safety of bridge systems. The frequent operation and wear rate over their lifespan highlight the necessity for methods to improve their tribological performance. In this study, GQZ-60000 unidirectionally movable spherical bearings were the research [...] Read more.

Spherical bearings play a crucial role in maintaining the safety of bridge systems. The frequent operation and wear rate over their lifespan highlight the necessity for methods to improve their tribological performance. In this study, GQZ-60000 unidirectionally movable spherical bearings were the research object, and three different surface textures—spherical cap, ellipsoidal cap, and double spherical cap—were incorporated into a curved PTFE surface to enhance its tribological performance, with the major focus being on reducing the friction coefficient. The Jakobsson–Floberg–Olsson cavitation boundary condition was used to solve the Reynolds equation numerically to obtain the elastohydrodynamic lubrication pressure, and the parametric effect of the three textures on the friction coefficient were analyzed. Based on the simulation results, a rational texture with rational geometric values are recommended to obtain the minimum friction coefficient of the bearing. However, it was also found that the deformation of the lubricated surface significantly affects the lubricant film thickness, and cavitation of the lubricant film may also affect the selection of rational textures, especially when the relative sliding velocity between lubricated surfaces is high. Full article

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12 pages, 2493 KiB

Open AccessArticle

Predicting the Viscosity of Ester Biolubricants by the Functional Groups of Their Compounds Using a Sensitivity Parameter Model

by F. Javier Ramos, Juan Carlos de Haro, Juan Francisco Rodríguez, Ángel Pérez and Manuel Carmona

Lubricants 2025, 13(4), 179; https://doi.org/10.3390/lubricants13040179 - 12 Apr 2025

Oleic-based trimethylolpropane (TMP) ester mixtures can be produced via esterification reaction between oleic acid (OA) and TMP, presenting important application as biobased lubricants. In this study, a new mathematical model that allows us to predict kinematic viscosities of such mixtures based on kinematic [...] Read more.

Oleic-based trimethylolpropane (TMP) ester mixtures can be produced via esterification reaction between oleic acid (OA) and TMP, presenting important application as biobased lubricants. In this study, a new mathematical model that allows us to predict kinematic viscosities of such mixtures based on kinematic viscosity sensitivity parameters from product functional groups was developed, and it was also checked by fitting the experimental kinematic viscosities of the biolubricant products at 40 and 100 °C. This way, it is possible to predict kinematic viscosities and the viscosity index of these biolubricant mixtures and even pure TMP-esters without the availability to measure purified compounds. Moreover, the influence on the viscosity properties of the different chemical functional groups can be assessed with this physical model. So, the deleterious or beneficial effects of intermediate products and unreacted OA on the biolubricant viscosity index (VI) were quantified, showing that Trioletate and also Dioleate TMP-ester and their mixtures meet very interesting lubricant properties (VI up to 218), whereas the Monooleate TMP-ester and the unreacted OA decrease dramatically the viscosity properties. We believe that these findings can pave the way for the improvement and development of bio-based lubricant formulations towards effective industrial development. Full article

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17 pages, 11217 KiB

Open AccessArticle

Research on Feature Extraction Method and Process Optimization of Rolling Bearing Faults Based on Electrostatic Monitoring

by Ruochen Liu, Han Yin, Jianzhong Sun and Lanchun Zhang

Lubricants 2025, 13(4), 178; https://doi.org/10.3390/lubricants13040178 - 12 Apr 2025

Electrostatic detection is a highly accurate way to monitor system performance failures at an early stage. However, due to the weak electrostatic signal, it can be easily interfered with under complex real-world conditions, leading to a reduction in its monitoring capability. During the [...] Read more.

Electrostatic detection is a highly accurate way to monitor system performance failures at an early stage. However, due to the weak electrostatic signal, it can be easily interfered with under complex real-world conditions, leading to a reduction in its monitoring capability. During the electrostatic monitoring of rolling bearings, noise can easily drown out the effective signal, making it difficult to extract fault characteristics. In order to solve this problem, a sparse representation based on cluster-contraction stagewise orthogonal matching pursuit (CcStOMP) is proposed to extract the fault features in the electrostatic signals of rolling bearings. The method adds a clustering contraction mechanism to the stagewise orthogonal matching pursuit (StOMP) algorithm, performs secondary filtering based on atom similarity clustering on the selected atoms in the atom search process, updates the support set, and finally solves the weights and updates the residuals, so as to reconstruct the original electrostatic signals and extract the fault feature components of rolling bearings. The method maintains fast convergence while analysing the extraction effect by comparing the measured signals of rolling bearing outer ring and bearing roller faults with the traditional StOMP algorithm, and the results show that the CcStOMP algorithm has obvious advantages in accurately extracting the fault features in the electrostatic monitoring signals of rolling bearings. Full article

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14 pages, 6751 KiB

Open AccessArticle

Corrosion Resistance of SAE 5160 Steel Deposited by Duplex Simultaneous Treatment with Hastelloy Cathodic Cage

by Marcos Cristino de Sousa Brito, Juliermes Carvalho Pereira, Lauriene Gonçalves da Luz Silva, Renan Matos Monção, Ediones Maciel de Sousa, Weslley Rick Viana Sampaio, Igor Oliveira Nascimento, Anthunes Íkaro de Araújo, Michelle Cequeira Feitor, Thercio Henrique de Carvalho Costa and Rômulo Ribeiro Magalhães de Sousa

Lubricants 2025, 13(4), 177; https://doi.org/10.3390/lubricants13040177 - 12 Apr 2025

SAE 5160 steel, classified as high-strength, low-alloy steel, is widely used in the automotive sector due to its excellent mechanical strength and ductility. However, its inherently low corrosion resistance limits its broader application. This study explores the application of the cathodic cage plasma [...] Read more.

SAE 5160 steel, classified as high-strength, low-alloy steel, is widely used in the automotive sector due to its excellent mechanical strength and ductility. However, its inherently low corrosion resistance limits its broader application. This study explores the application of the cathodic cage plasma deposition (CCPD) technique to enhance the corrosion resistance of SAE 5160 steel. The treatment was performed using a Hastelloy cathodic cage under two atmospheric conditions: hydrogen-rich (75%H₂/25%N₂) and nitrogen-rich (25%H₂/75%N₂). Comprehensive analyses revealed significant improvements in surface properties and corrosion resistance. The hydrogen-rich condition (H25N) facilitated the formation of Cr_0.4Ni_0.6 and CrN phases, associated with a nanocrystalline structure (37.6 nm) and a thicker coating (45.5 μm), resulting in polarization resistance over 290 times greater than that of untreated steel. Conversely, nitrogen-rich treatment (H75N) promoted the formation of Fe₃N and Fe₄N phases, achieving a dense but thinner layer (19.6 μm) with polarization resistance approximately 20 times higher than that of untreated steel. These findings underscore the effectiveness of CCPD as a versatile and scalable surface engineering technique capable of tailoring the properties of SAE 5160 steel for use in highly corrosive environments. This study highlights the critical role of optimizing gas compositions and treatment parameters, offering a foundation for advancing plasma-assisted technologies and alloying strategies. The results provide a valuable framework for developing next-generation corrosion-resistant materials, promoting the longevity and reliability of high-strength steels in demanding industrial applications. Full article

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

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21 pages, 6182 KiB

Open AccessArticle

Assessing the Compatibility of PAO and POE with Fluoroelastomer (FKM) for Potential EVs Application

by Bernardo Tormos, José M. Liñeira Del Río, Adbeel Balaguer and Enrique Giménez

Lubricants 2025, 13(4), 176; https://doi.org/10.3390/lubricants13040176 - 11 Apr 2025

The accelerated growth of electric vehicle (EV) powertrains has prompted the development of specialized fluids that meet stringent thermal and electrical requirements for immersion cooling systems, including interactions with non-metallic components like fluoroelastomer (FKM). This research investigates the interactions between fluoroelastomer (FKM) and [...] Read more.

The accelerated growth of electric vehicle (EV) powertrains has prompted the development of specialized fluids that meet stringent thermal and electrical requirements for immersion cooling systems, including interactions with non-metallic components like fluoroelastomer (FKM). This research investigates the interactions between fluoroelastomer (FKM) and two potential base fluids—polyalphaolefin (PAO4) and a polyol ester (POE)—to assess their suitability for immersion cooling applications. Immersion tests, following an adapted ASTM D7216 standard, evidenced changes in FKM’s mass, Shore A hardness, and tensile strength. Furthermore, the physical, electrical, and thermal properties of the tested fluids were analyzed before and after immersion to determine whether contact with the FKM elastomer compromised their performance. The findings of this study reveal that the fluid exerts a greater influence on the elastomer than vice versa. This study bridges a knowledge gap in regards to EV fluid development and material science, contributing to the development of durable and efficient thermal management solutions. Full article

(This article belongs to the Special Issue Tribology of Electric Vehicles)

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