Lubricants

18 pages, 10596 KiB

Open AccessArticle

The Influence of Pulsed Electron Beam Processing on the Quality of Working Surfaces of Titanium Alloy Products

by Undrakh Mishigdorzhiyn, Aleksey Pyatykh, Andrey Savilov, Nikolay Ulakhanov, Ivan Galetsky, Kirill Demin, Alexander Tikhonov, Maxim Vorobyov, Elizaveta Petrikova and Shunqi Mei

Lubricants 2025, 13(5), 199; https://doi.org/10.3390/lubricants13050199 - 28 Apr 2025

Abstract

Titanium alloys are widely used in medicine due to their unique properties, including inertness with respect to living tissues, light weight, high strength, and impact toughness. For successful implementation, titanium alloy implants should possess high wear resistance and hydrophilicity. This article investigates the [...] Read more.

Titanium alloys are widely used in medicine due to their unique properties, including inertness with respect to living tissues, light weight, high strength, and impact toughness. For successful implementation, titanium alloy implants should possess high wear resistance and hydrophilicity. This article investigates the surface modification process of VT-1 and VT-6 titanium alloys by electron-beam processing (EBP). The EBP effect on the modified surface′s wear resistance, roughness, and hydrophilicity was analyzed. The specimens were made by machining them at a CNC turning center. The specimen surfaces were modified at the SOLO facility by a submillisecond modulated electron beam with a controlled power density of thermal impact, allowing it to reach and stabilize 1400 °C in 400 µs and then maintain it on the surface for 600 µs. A friction machine with a counterbody was used to study the wear resistance of the specimen surface. The study revealed that EBP reduces the roughness parameters of the surface. EBP also decreases the contact angle of wetting, indicating an increase in hydrophilicity compared to the original surface. Experimentally, it was shown that the formation of a nanostructure consisting of needle-like α-strips induced by EBP improves the wear resistance of the surface layer. Full article

(This article belongs to the Special Issue Development Trends in Surface Engineering Modification for Improving Tribological Properties of Alloys and Composite Polymer Materials)

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21 pages, 7985 KiB

Open AccessArticle

Study on the Influence of Inertial Force on the Performance of Aerostatic Thrust Bearings

by Shuo Jia, Chenhui Jia and Yanhui Lu

Lubricants 2025, 13(5), 198; https://doi.org/10.3390/lubricants13050198 - 28 Apr 2025

Abstract

Firstly, the Reynolds equation considering gas inertia force is theoretically deduced in the cylindrical coordinate system, and then a mathematical model of aerostatic thrust bearing with three degrees of freedom (3-DOF) is constructed. Secondly, the Reynolds equation and velocity control equation are solved [...] Read more.

Firstly, the Reynolds equation considering gas inertia force is theoretically deduced in the cylindrical coordinate system, and then a mathematical model of aerostatic thrust bearing with three degrees of freedom (3-DOF) is constructed. Secondly, the Reynolds equation and velocity control equation are solved by the finite difference method (FDM), and the characteristics of gas pressure and velocity distribution in the gas film under steady-state conditions are revealed. On this basis, in the single-factor analysis, the bearing capacity error and recovery torque error caused by the inertia force term are quantitatively analyzed. It is found that the bearing rotating speed has a significant influence on the inertial force error, and the bearing radius also has a certain influence on the inertial force error, while the initial clearance, gas supply pressure, and torsion angle have relatively little influence on the inertial force error. Finally, in the multi-factor analysis, the sample regression equation of relative error of bearing capacity and relative error of restoring torque is established by using the multiple regression analysis method. By comparing the estimated values with the simulation results, the validity of the constructed regression equation is verified. Full article

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11 pages, 458 KiB

Open AccessArticle

A Numerical Investigation of Non-Ideal Gas Effects on the Saturation Pressure of Water Under High Pressure and Temperature

by Roshan Mathew Tom, Sukumar Rajauria, Qing Dai and Qilong Cheng

Lubricants 2025, 13(5), 197; https://doi.org/10.3390/lubricants13050197 - 27 Apr 2025

Abstract

A typical head–disk interface of hard drives can feature pressures exceeding 50 atmospheres, where the non-ideal gas effects can play an important role. One possible consequence is a change in the rate of water evaporation from the disk. This report describes a semi-analytical [...] Read more.

A typical head–disk interface of hard drives can feature pressures exceeding 50 atmospheres, where the non-ideal gas effects can play an important role. One possible consequence is a change in the rate of water evaporation from the disk. This report describes a semi-analytical procedure that employs the concept of fugacity to investigate the non-ideal gas effects on the saturation pressure of water at an elevated temperature and pressure. A vapor–liquid equilibrium equation is solved to derive the saturation pressure. The results show a deviation from the ideal gas law, which is further examined through saturation pressure isotherms. At areas of low temperature and high pressure, lighter gases such as helium show about a 10% deviation from the ideal gas law, whereas heavier gases such as nitrogen deviate by up to 100%. As temperature increases, the differences between the gases decrease. Full article

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15 pages, 2493 KiB

Open AccessArticle

Inertial and Linear Re-Absorption Effects on a Synovial Fluid Flow Through a Lubricated Knee Joint

by Abdul Majeed Siddiqui, Khadija Maqbool, Afifa Ahmed and Amer Bilal Mann

Lubricants 2025, 13(5), 196; https://doi.org/10.3390/lubricants13050196 - 27 Apr 2025

Abstract

This study examines the flow dynamics of synovial fluid within a lubricated knee joint during movement, incorporating the effect of inertia and linear re-absorption at the synovial membrane. The fluid behavior is modeled using a couple-stress fluid framework, which accounts for mechanical phenomena [...] Read more.

This study examines the flow dynamics of synovial fluid within a lubricated knee joint during movement, incorporating the effect of inertia and linear re-absorption at the synovial membrane. The fluid behavior is modeled using a couple-stress fluid framework, which accounts for mechanical phenomena and employs a lubricated membrane. synovial membrane plays a crucial role in reducing drag and enhancing joint lubrication for the formation of a uniform lubrication layer over the cartilage surfaces. The mathematical model of synovial fluid flow through the knee joint presents a set of non-linear partial differential equations solved by a recursive approach and inverse method through the software Mathematica 11. The results indicate that synovial fluid flow generates high pressure and shear stress away from the entry point due to the combined effects of inertial forces, linear re-absorption, and micro-rotation within the couple-stress fluid. Axial flow intensifies at the center of the knee joint during activity in the presence of linear re-absorption and molecular rotation, while transverse flow increases away from the center and near to synovium due to its permeability. These findings provide critical insights for biomedical engineers to quantify pressure and stress distributions in synovial fluid to design artificial joints. Full article

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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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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

Abstract

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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