Lubricants

22 pages, 3420 KiB

Open AccessReview

A Review on the Dynamic Performance Studies of Gas Foil Bearings

by Chaozhe Jin, Changlin Li and Jianjun Du

Lubricants 2024, 12(7), 262; https://doi.org/10.3390/lubricants12070262 - 22 Jul 2024

Cited by 1 | Viewed by 910

Gas foil bearings have important and wide applications in high-speed turbomachinery, generating low frictional lubricating gas film in series with underlying elastic foil structures to support the rotor system. Their dynamic performance is of vital significance in maintaining the rotor stability as well [...] Read more.

Gas foil bearings have important and wide applications in high-speed turbomachinery, generating low frictional lubricating gas film in series with underlying elastic foil structures to support the rotor system. Their dynamic performance is of vital significance in maintaining the rotor stability as well as in depressing rotor vibrations. This paper conducts a comprehensive review on dynamic performance studies conducted on gas foil bearings, including research on the dynamic stiffness and damping coefficients, bearing stability, nonlinear vibrations of the rotor–bearing system, and active methods for controlling rotor dynamic motions. This review provides clear observations towards the developments and iterations of the models, methods, and experiments of these studies. Full article

(This article belongs to the Special Issue Gas Lubrication and Dry Gas Seal)

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11 pages, 8480 KiB

Open AccessArticle

Molecular Dynamics Simulation and Experimental Study of Friction and Wear Characteristics of Carbon Nanotube-Reinforced Nitrile Butadiene Rubber

by Ce Liang, Changgeng Shuai and Xin Wang

Lubricants 2024, 12(7), 261; https://doi.org/10.3390/lubricants12070261 - 22 Jul 2024

Viewed by 947

Abstract

Nitrile butadiene rubber (NBR) and its various composite materials are widely employed as friction materials in mechanical equipment. The use of carbon nanotube (CNT) reinforcement in NBR for improved friction and wear characteristics has become a major research focus. However, the mechanisms underlying [...] Read more.

Nitrile butadiene rubber (NBR) and its various composite materials are widely employed as friction materials in mechanical equipment. The use of carbon nanotube (CNT) reinforcement in NBR for improved friction and wear characteristics has become a major research focus. However, the mechanisms underlying the improvement in the friction and wear characteristics of NBR with different CNT contents remain insufficiently elucidated. Therefore, we conducted a combined analysis of NBR reinforced with varying CNT contents through molecular dynamics (MD) simulations and ring–block friction experiments. The aim is to analyze the extent to which CNTs enhance the water-lubricated friction and dry wear properties of NBR and explore the improvement mechanisms through molecular chain characteristics. The results of this study demonstrate that as the mass fraction of CNTs (0%, 1.25%, 2.5%, 5%) increases, the water-lubricated friction coefficient of NBR continuously decreases. Under water-lubricated conditions, CNTs improve the water storage capacity of the NBR surface and enhance lubrication efficiency. In the dry wear state, CNTs help reduce scratch depth and dry wear volume. Full article

(This article belongs to the Special Issue 2D Materials in Tribology)

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20 pages, 6774 KiB

Open AccessArticle

Sheet Forming via Limiting Dome Height (LDH) Test: Influence of the Application of Lubricants, Location and Sheet Thickness on the Micro-Mechanical Properties of X8CrMnNi19-6-3

by Martin Ovsik, Martin Bednarik, Martin Reznicek and Michal Stanek

Lubricants 2024, 12(7), 260; https://doi.org/10.3390/lubricants12070260 - 21 Jul 2024

Viewed by 861

Abstract

This work is concerned with forming, specifically deep drawing, and its influence on the micro-mechanical properties of sheet metal. In practice, there are several applications in which fractions can occur due to weak spots in the deep-drawn sheet metal, especially after long-term use. [...] Read more.

This work is concerned with forming, specifically deep drawing, and its influence on the micro-mechanical properties of sheet metal. In practice, there are several applications in which fractions can occur due to weak spots in the deep-drawn sheet metal, especially after long-term use. The deep drawing process was carried out on BUP–600 machines using the LHD (Limiting Dome Height) method, which uses a forming tool with a diameter of 100 mm and bead groove. Sheet metals X8CrMnNi19-6-3 (1.4376) with thicknesses of 1, 1.5, and 3 mm were selected for this process. To study the effect of a lubricant on the formability of the sheet metal, deep drawing without and with a lubricant was compared. An FEM analysis was conducted to identify critical points in the deep drawing process, and the results were later compared with real results. The analysis was conducted using the AutoForm program. The micro-mechanical properties of these points were subsequently examined. The specified points on the formed part showed significant differences in their micro-mechanical properties, suggesting a higher strength but also less resistance to fractures. The difference in micro-mechanical properties (indentation and Vickers hardness) in points that were not deep-drawn and points located in critical areas was up to 86%. Significant changes in behavior were found in the indentation modulus and plastic/elastic deformation work as well. This study demonstrates the significant effect of the use of a lubricant in achieving the deep drawing of the sheet metal. The application of a lubricant resulted in a 33% increase in drawing range compared to drawing without lubrication. This study has a significant influence on the deep drawing of sheet metals in practice, showing the fundamental influence of the lubricant on the drawing process and also showing the problem of critical points that need to be eliminated. Full article

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

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37 pages, 32174 KiB

Open AccessArticle

Improved Operating Behavior of Self-Lubricating Rolling-Sliding Contacts under High Load with Oil-Impregnated Porous Sinter Material

by Nicolai Sprogies, Thomas Lohner and Karsten Stahl

Lubricants 2024, 12(7), 259; https://doi.org/10.3390/lubricants12070259 - 21 Jul 2024

Viewed by 1125

Abstract

Resource and energy efficiency are of high importance in gearbox applications. To reduce friction and wear, an external lubricant supply like dip or injection lubrication is used to lubricate tribosystems in machine elements. This leads to the need for large lubricant volumes and [...] Read more.

Resource and energy efficiency are of high importance in gearbox applications. To reduce friction and wear, an external lubricant supply like dip or injection lubrication is used to lubricate tribosystems in machine elements. This leads to the need for large lubricant volumes and elaborate sealing requirements. One potential method of minimizing the amount of lubricant and simplifying sealing in gearboxes is the self-lubrication of tribosystems using oil-impregnation of porous materials. Although well established in low-loaded journal bearings, self-lubrication of rolling-sliding contacts in gears is poorly understood. This study presents the self-lubrication method using oil-impregnated porous sinter material variants. For this, the tribosystem of gear contacts is transferred to model contacts, which are analyzed for friction and temperature behavior using a twin-disk tribometer. High-resolution surface images are used to record the surface changes. The test results show a significant increase in self-lubrication functionality of tribosystems by oil-impregnated porous sinter material and a tribo-performance comparable to injection-lubricated tribosystems of a sinter material with additionally solid lubricant added to the sinter material powder before sintering. Furthermore, the analyses highlight a significant influence of the surface finish, and in particular the surface porosity, on the overall tribosystem behavior through significantly improved friction and wear behavior transferable to gear applications. Full article

(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)

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13 pages, 4867 KiB

Open AccessArticle

Finite Element Analysis of Damage Evolution of Solid Lubrication Film in Rolling–Sliding Contact

by Peng Lv, Changling Tian, Yujun Xue, Yongjian Yu, Haichao Cai and Yanjing Yin

Lubricants 2024, 12(7), 258; https://doi.org/10.3390/lubricants12070258 - 18 Jul 2024

Viewed by 656

Abstract

Based on the cohesive zone model (CZM), a finite element model of the film–substrate bearing system in the rolling–sliding contact state is established. Through analyzing the normal and tangential bearing states of the film–substrate system, the effects of the sliding–rolling ratio and the [...] Read more.

Based on the cohesive zone model (CZM), a finite element model of the film–substrate bearing system in the rolling–sliding contact state is established. Through analyzing the normal and tangential bearing states of the film–substrate system, the effects of the sliding–rolling ratio and the film–substrate adhesion strength on the interfacial stress and the interfacial energy release rate of the film–substrate system are studied. The results show that there is an almost symmetric stress distribution at both sides of the contact zone in rolling contact. In rolling–sliding contact, obvious shear flow along the rolling–sliding direction occurs at the front edge of the contact zone, which results in a significant increase in the shear stress at the interface at the front edge of the contact zone, increasing the risk of interface damage and delamination failure. Meanwhile, the shear flow causes a normal tensile stress concentration along the film surface behind the contact zone, which very easily causes the emergence and expansion of the film surface cracks. In addition, there is a clear positive correlation between the adhesion strength and the load-bearing capacity of the film–substrate interface. The tangential delamination damage mainly occurs at the interface regardless of the rolling or rolling–sliding contact state. Full article

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19 pages, 7143 KiB

Open AccessArticle

Theoretical Evaluation of Lubrication Performance of Thrust-Type Foil Bearings in Liquid Nitrogen

by Hang Dou, Tao Jiang, Longgui He, Shuo Cheng, Xiaoliang Fang and Jimin Xu

Lubricants 2024, 12(7), 257; https://doi.org/10.3390/lubricants12070257 - 17 Jul 2024

Viewed by 689

Abstract

The development of reusable liquid rocket turbopumps has gradually highlighted the disadvantages of rolling bearings, particularly the contradiction between long service life and high rotational speed. It is critical to explore a feasible bearing scheme offering a long wear life and high stability [...] Read more.

The development of reusable liquid rocket turbopumps has gradually highlighted the disadvantages of rolling bearings, particularly the contradiction between long service life and high rotational speed. It is critical to explore a feasible bearing scheme offering a long wear life and high stability to replace the existing rolling bearings. In this study, liquid nitrogen is adopted to simulate the ultra-low temperature environment of liquid rocket turbopumps, and theoretical evaluations of the lubrication performance of thrust-type foil bearings in liquid nitrogen are conducted. A link-spring model for the bump foil structure and a thin-plate finite element model for the top foil structure are established. The static and dynamic characteristics of the bearings are analyzed using methods including the finite difference method, the Newton–Raphson iteration method, and the finite element method. Detailed analysis includes the effects of factors such as rotational speed, fluid film thickness, thrust disk tilt angle, and the friction coefficient of the bump foil interface on the static and dynamic characteristics of thrust-type foil bearings. The research results indicate that thrust-type foil bearings have a good load-carrying capacity and low frictional power consumption. The adaptive deformation of the foil structure increases the fluid film thickness, preventing dry friction due to direct contact between the rotor journal and the bearing surface. When faced with thrust disk tilt, the direct translational stiffness and damping coefficient of the bearing do not undergo significant changes, ensuring system stability. Based on the results of this study, the exceptional performance characteristics of thrust-type foil bearings make them a promising alternative to rolling bearings for the development of reusable liquid rocket turbopumps. Full article

(This article belongs to the Special Issue Aerospace Tribology)

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26 pages, 26815 KiB

Open AccessArticle

Field Study of Asphalt Pavement Texture and Skid Resistance under Traffic Polishing Using 0.01 mm 3D Images

by Guangwei Yang, Kuan-Ting Chen, Kelvin Wang, Joshua Li and Yiwen Zou

Lubricants 2024, 12(7), 256; https://doi.org/10.3390/lubricants12070256 - 17 Jul 2024

Viewed by 1016

Abstract

Pavement texture and skid resistance are pivotal surface features of roadway to traffic safety, especially under wet weather. Engineering interventions should be scheduled periodically to restore these features as they deteriorate over time under traffic polishing. While many studies have investigated the effects [...] Read more.

Pavement texture and skid resistance are pivotal surface features of roadway to traffic safety, especially under wet weather. Engineering interventions should be scheduled periodically to restore these features as they deteriorate over time under traffic polishing. While many studies have investigated the effects of traffic polishing on pavement texture and skid resistance through laboratory experiments, the absence of real-world traffic and environmental factors in these studies may limit the generalization of their findings. This study addresses this research gap by conducting a comprehensive field study of pavement texture and skid resistance under traffic polishing in the real world. A total of thirty pairs of pavement texture and friction data were systematically collected from three distinct locations with different levels of traffic polishing (middle, right wheel path, and edge) along an asphalt pavement in Oklahoma, USA. Data acquisition utilized a laser imaging device to reconstruct 0.01 mm 3D images to characterize pavement texture and a Dynamic Friction Tester to evaluate pavement friction at different speeds. Twenty 3D areal parameters were calculated on whole images, macrotexture images, and microtexture images to investigate the effects of traffic polishing on pavement texture from different perspectives. Then, texture parameters and testing speeds were combined to develop friction prediction models via linear and nonlinear methodologies. The results indicate that Random Forest models with identified inputs achieved excellent performance for non-contact friction evaluation. Last, the friction decrease rate was discussed to estimate the timing of future maintenance to restore skid resistance. This study provides more insights into how engineers should plan maintenance to restore pavement texture and friction considering real-world traffic polishing. Full article

(This article belongs to the Special Issue Friction Assessment in Pavement Engineering)

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15 pages, 4444 KiB

Open AccessArticle

Performance of Aromatic Amine-Modified Metallocene Polyalphaolefin Lubricant Base Oil

by Jian Xu, Qidi Hu and Jiusheng Li

Lubricants 2024, 12(7), 255; https://doi.org/10.3390/lubricants12070255 - 16 Jul 2024

Cited by 1 | Viewed by 1039

Abstract

With the continuous advancement of industrial technology, higher demands have been placed on the properties of gear oils, such as oxidation stability and shear resistance. Herein, the oxidation stability of high-viscosity metallocene poly-

α

-olefins (mPAOs) was improved by chemical modification via aromatic [...] Read more.

With the continuous advancement of industrial technology, higher demands have been placed on the properties of gear oils, such as oxidation stability and shear resistance. Herein, the oxidation stability of high-viscosity metallocene poly-

α

-olefins (mPAOs) was improved by chemical modification via aromatic amine alkylation. The modified mPAO base oils were synthesized separately with diphenylamine (mPAO-DPA) and N-phenyl-

α

-naphthylamine (mPAO-NPA), and their applicability in industrial gear oil formulations was evaluated. The composition and physicochemical properties of the obtained samples were assessed using ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, gel permeation chromatography, and the American Society for Testing and Materials standards (ASTM D445, ASTM D2270, ASTM D92, etc.) confirming the successful completion of the alkylation reaction. The oxidation stability of the samples was also evaluated using pressurized differential scanning calorimetry. The initial oxidation temperature of mPAO-NPA (230 °C) was 53 °C higher than that of mPAO, and the oxidation induction period of mPAO-DPA was nearly twice that of mPAO-NPA. Thermogravimetric analysis in air revealed the increased thermal decomposition temperature and improved thermal stability of modified mPAO. ISO VG 320 industrial gear oils were formulated using mPAO alkylated with N-phenyl-

α

-naphthylamine(Lub-2) and commercially purchased PAO100 (Lub-1) as base oil components. The antioxidant performance of two industrial gear oils was evaluated through oven oxidation and rotating oxygen bomb tests. The oxidation induction period of Lub-2 was 30% higher than that of Lub-1, with the latter having a lower acid number and a smaller increase in viscosity at 40 °C. Finally, the friction performance of the samples was assessed on a four-ball friction tester, revealing the synergistic effect of the mPAO-NPA base oil with the HiTEC 3339 additive, forming a more stable oil film with a smaller wear scar diameter. Full article

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23 pages, 15008 KiB

Open AccessArticle

Investigation on the Static Performance of Surface-Throttling Frictionless Pneumatic Cylinder through Finite Element Method

by Jingfeng Xu, Siyu Gao, Lizi Qi, Qiang Gao, Min Zhu, Hongbin Yang, Yinze Li, Wenyuan Wei and Lihua Lu

Lubricants 2024, 12(7), 254; https://doi.org/10.3390/lubricants12070254 - 14 Jul 2024

Viewed by 800

Abstract

The equilibrium system is essential for the high-precision movement of the ultra-precision vertical axis. However, the complex assembly process makes orifice-throttling frictionless cylinders difficult to manufacture and prone to air hammering. Surface-throttling frictionless pneumatic cylinders effectively avoid these problems. This paper establishes an [...] Read more.

The equilibrium system is essential for the high-precision movement of the ultra-precision vertical axis. However, the complex assembly process makes orifice-throttling frictionless cylinders difficult to manufacture and prone to air hammering. Surface-throttling frictionless pneumatic cylinders effectively avoid these problems. This paper establishes an improved finite element method (FEM) model of a novel surface-throttling frictionless pneumatic cylinder to investigate its static performance. Furthermore, the static equilibrium calculation of the dual-cylinder system is concerned. The radial bearing capacity and support force requirements for the surface-throttling aerostatic bearings are obtained. The outcomes provide theoretical guidance for optimizing cylinder parameters. It ensures that the ultimately optimized cylinder meets the requirements for radial bearing capacity and support force of the ultra-precision vertical axis while minimizing air consumption. Finally, the accuracy of the proposed method is verified through computational fluid dynamics (CFD) calculation and experiments. Full article

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15 pages, 4186 KiB

Open AccessArticle

Numerical Simulations and Experimental Validation of Squeeze Film Dampers for Aircraft Jet Engines

by Markus Golek, Jakob Gleichner, Ioannis Chatzisavvas, Lukas Kohlmann, Marcus Schmidt, Peter Reinke and Adrian Rienäcker

Lubricants 2024, 12(7), 253; https://doi.org/10.3390/lubricants12070253 - 13 Jul 2024

Viewed by 894

Abstract

Squeeze film dampers are used to reduce vibration in aircraft jet engines supported by rolling element bearings. The underlying physics of the squeeze film dampers has been studied extensively over the past 50 years. However, the research on the SFDs is still ongoing [...] Read more.

Squeeze film dampers are used to reduce vibration in aircraft jet engines supported by rolling element bearings. The underlying physics of the squeeze film dampers has been studied extensively over the past 50 years. However, the research on the SFDs is still ongoing due to the complexity of modeling of several effects such as fluid inertia and the modeling of the piston rings, which are often used to seal SFDs. In this work, a special experimental setup has been designed to validate the numerical models of SFDs. This experimental setup can be used with various SFD geometries (including piston ring seals) and simulate almost all conditions that may occur in an aircraft jet engine. This work also focuses on the inertia forces of the fluid. The hydrodynamic pressure distribution of a detailed 3D-CFD model is compared with the solution of the Reynolds equation including inertia effects. Finally, the simulation results are compared with experimental data and good agreement is observed. Full article

(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)

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28 pages, 15385 KiB

Open AccessArticle

Analysis of Rigid-Flexible Coupled Collision Force in a Variable Load Offshore Wind Turbine Main Three-Row Cylindrical Roller Bearing

by Xiaoxu Pang, Dingkang Zhu, Xu Zuo, Dongfeng Wang, Wenlu Hao, Ming Qiu and Duo Liu

Lubricants 2024, 12(7), 252; https://doi.org/10.3390/lubricants12070252 - 11 Jul 2024

Viewed by 808

Abstract

In response to the limitations and one-sidedness of the simulation results of a rigid three-row cylindrical roller bearing for an offshore wind turbine main shaft under constant-load conditions, this paper proposes a simulation analysis method under variable loads. A contact mechanics model and [...] Read more.

In response to the limitations and one-sidedness of the simulation results of a rigid three-row cylindrical roller bearing for an offshore wind turbine main shaft under constant-load conditions, this paper proposes a simulation analysis method under variable loads. A contact mechanics model and a flexible body model are established, and the rigid-flexible coupled treatment is applied to the bearing’s inner and outer ring and cages. Based on variable load conditions, the theoretical speeds, simulated speeds, and acceleration responses of the pure rigid model and the rigid-flexible coupled model are compared, and the model is validated. Finally, the dynamic and transient responses reveal the time-varying characteristics of bearing loads and stress distribution patterns under different driving speeds and contact friction coefficients in the rigid-flexible coupled model. The conclusions are as follows: the rotational error of the rigid model is 1.67 to 3.76 times greater than that of the rigid-flexible coupled model, and the acceleration trend of the rigid-flexible coupled model is more stable with smaller speed fluctuations. The average forces on the thrust roller and cages increase with the driving speed, while those on the radial roller, cages, and inner ring decrease with the driving speed. The average force on the near-blade end cage is approximately 1.19 to 1.59 times that of the far end. The average force on the roller and cages significantly decreases with decreasing friction coefficient, with a reduction ranging from 50.08% to 76.41%. The maximum stress of the bearing increases with increasing driving speed. The novel simulation method for a rigid-flexible, coupled, three-row cylindrical roller bearing model under variable load conditions proposed in this paper can more accurately simulate the dynamic response of offshore wind turbine main shaft bearings during service. The results obtained in this paper provide highly valuable guidance for the research and design of offshore wind turbine main shaft bearings. Full article

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25 pages, 6445 KiB

Open AccessArticle

Enhancing Lubrication Performance of Plastic Oil Lubricant with Oleic Acid-Functionalized Graphene Nanoplatelets and Hexagonal Boron Nitride Solid Lubricant Additives

by Soumya Sikdar and Pradeep L. Menezes

Lubricants 2024, 12(7), 251; https://doi.org/10.3390/lubricants12070251 - 10 Jul 2024

Cited by 1 | Viewed by 1028

Abstract

The study explored the viability of using waste plastic oil (PO) as an alternative lubricant to petroleum-based lubricants in industrial settings. To enhance the lubrication performance of the PO, this study incorporated cost-efficient, oleic acid-modified, graphene nano platelets [GNP (f)] and hexagonal boron [...] Read more.

The study explored the viability of using waste plastic oil (PO) as an alternative lubricant to petroleum-based lubricants in industrial settings. To enhance the lubrication performance of the PO, this study incorporated cost-efficient, oleic acid-modified, graphene nano platelets [GNP (f)] and hexagonal boron nitride [hBN (f)] nano solid lubricant additives into the PO in various concentrations, forming functionalized nano lubricants. The PO and its functionalized nano lubricant’s rheological, dispersion stability, thermal degradation, friction, and wear performance were investigated. Results manifest that incorporating GNP (f) and hBN (f) into the PO significantly enhanced the viscosity and dispersion stability. In addition, it was seen that GNP (f) and hBN (f) nano lubricants lowered the coefficient of friction (COF) by 53% and 63.63% respectively, compared to the PO. However, the GNP (f) and hBN (f) nano lubricants demonstrated a 3.16% decrease and a 50.08% increase in wear volume relative to the PO. Overall, the GNP (f) and hBN (f) nano lubricants displayed a synergistic friction behavior, while they exhibited an antagonistic behavior pertaining to the wear volume. The study elucidated the mechanisms underlying friction and wear performance of the nano lubricants. Full article

(This article belongs to the Collection Rising Stars in Tribological Research)

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17 pages, 5142 KiB

Open AccessArticle

Modelling of Static and Dynamic Elastomer Friction in Dry Conditions

by Fabian Kaiser, Daniele Savio and Ravindrakumar Bactavatchalou

Lubricants 2024, 12(7), 250; https://doi.org/10.3390/lubricants12070250 - 9 Jul 2024

Cited by 1 | Viewed by 1222

Abstract

Understanding the tribological behavior of elastomers in dry conditions is essential for sealing applications, as dry contact may occur even in lubricated conditions due to local dewetting. In recent decades, Persson and co-authors have developed a comprehensive theory for rubber contact mechanics and [...] Read more.

Understanding the tribological behavior of elastomers in dry conditions is essential for sealing applications, as dry contact may occur even in lubricated conditions due to local dewetting. In recent decades, Persson and co-authors have developed a comprehensive theory for rubber contact mechanics and dry friction. In this work, their model is implemented and extended, particularly by including static friction based on the bond population model by Juvekar and coworkers. Validation experiments are performed using a tribometer over a wide range of materials, temperatures and speeds. It is shown that the friction model presented in this work can predict the static and dynamic dry friction of various commercial rubber materials with different base polymers (FKM, EPDM and NBR) with an average accuracy of 10%. The model is then used to study the relevance of different elastomer friction contributions under various operating conditions and for different roughness of the counter surface. The present model will help in the development of novel optimized sealing solutions and provide a foundation for future modeling of lubricated elastomer friction. Full article

(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)

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20 pages, 21189 KiB

Open AccessArticle

The Tribological and Adsorption Performance of Chlorophenyl Silicone Oil Using Different Ceramic Materials under High Temperature

by Jie Cheng, Yan Meng, Fangxu Sun, Luo Yue, Xue Zhou, Peng Wei, Hui Zhao, Xiangli Wen, Pengpeng Bai, Qian Zhao, Yonggang Meng and Yu Tian

Lubricants 2024, 12(7), 249; https://doi.org/10.3390/lubricants12070249 - 6 Jul 2024

Viewed by 968

Abstract

With the development of technical requirements, the current challenges faced by bearing materials mainly revolve around high-temperature conditions and the trend towards material lightweighting. Full ceramic bearings are the new candidate due to their excellent properties. This article details the tribological and adsorption [...] Read more.

With the development of technical requirements, the current challenges faced by bearing materials mainly revolve around high-temperature conditions and the trend towards material lightweighting. Full ceramic bearings are the new candidate due to their excellent properties. This article details the tribological and adsorption performance of chlorophenyl silicone oil (CPSO) as a high-temperature lubricant in ceramic tribological systems (ZrO₂, Al₂O₃, and Si₃N₄). Among the three ceramic tribological systems, the lubrication performance can be ordered as Si₃N₄ > Al₂O₃ > ZrO₂, as the wear rates of the ZrO₂ and Al₂O₃ tribo-systems are almost 1135.67 and 283.33 times larger than that of the Si₃N₄ tribo-system, respectively. The observed results can be explained by the superior adsorption performance of CPSO on a Si₃N₄ ceramic surface, which was calculated by molecular dynamic simulation. The molecular dynamic simulation results show the adsorption energy of CPSO/Si₃N₄ is almost 54.09 and 61.18 times higher compared to that on ZrO₂ and Al₂O₃ ceramics. These findings provide experimental and theoretical insights for understanding the lubrication performance of CPSO in a full ceramic tribo-system. Full article

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15 pages, 8290 KiB

Open AccessArticle

Multi-Response Optimization and Experimental Investigation of the Influences of Various Coolant Conditions on the Milling of Alloy 20

by Youlei Zhao, Na Cui, Zhenxian Hou, Jing Li, Junqiang Liu and Yapeng Xu

Lubricants 2024, 12(7), 248; https://doi.org/10.3390/lubricants12070248 - 5 Jul 2024

Viewed by 877

Abstract

This study investigates the machining processes of Alloy 20 under different cooling conditions: Minimum Quantity Lubrication (MQL), Carbon Dioxide (CO₂), and the hybrid MQL + CO₂ approach. The research focuses on optimizing the cutting parameters, understanding the surface characteristics, analysing [...] Read more.

This study investigates the machining processes of Alloy 20 under different cooling conditions: Minimum Quantity Lubrication (MQL), Carbon Dioxide (CO₂), and the hybrid MQL + CO₂ approach. The research focuses on optimizing the cutting parameters, understanding the surface characteristics, analysing the tool wear patterns, and evaluating the chip formation. Face-centred CCD-based response surface methodology (RSM) is applied in order to identify the optimized cutting conditions. Surface roughness, tool wear, and chip morphology are examined through SEM imaging. Surface roughness characteristics reveal distinctive characteristics for each coolant condition: MQL cooling results in a relatively rough surface with tool nose degradation, CO₂ cooling shows scratches on the surface and tool chipping, and MQL + CO₂ cooling yields a smoother finish with close and continuous chip formation under the optimized conditions. This study contributes valuable insights into the complex interactions between cutting parameters and coolants, aiding in the optimization of machining processes for improved outcomes of the machining of Alloy 20. Based on the RSM outcomes, the optimal parametric settings obtained are V_c = 44 m/min, f = 0.04 mm/rev, and a_p = 0.43 mm. Full article

(This article belongs to the Special Issue Minimum Quantity Lubrication: Environmental Alternatives in Processing, 2nd Edition)

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15 pages, 5677 KiB

Open AccessArticle

Assessing the Potential of Bio-Based Friction Modifiers for Food-Grade Lubrication

by Rosa Maria Nothnagel, Guido Boidi, Rainer Franz and Marcella Frauscher

Lubricants 2024, 12(7), 247; https://doi.org/10.3390/lubricants12070247 - 4 Jul 2024

Viewed by 865

Abstract

The objective of this research is to identify a bio-based friction modifier (FM) with tribological performance comparable to conventional FMs. Promising alternatives to conventional FMs, such as the FMs derived from natural sources, including rapeseed and salmon oil, were selected. Increasing concerns about [...] Read more.

The objective of this research is to identify a bio-based friction modifier (FM) with tribological performance comparable to conventional FMs. Promising alternatives to conventional FMs, such as the FMs derived from natural sources, including rapeseed and salmon oil, were selected. Increasing concerns about crude oil prices, environmental impact, and the depletion of fossil resources have further fueled the search for renewable, biodegradable, and environmentally friendly raw materials for lubricants Tribological tests were conducted using a rheometer under non-conformal contact. The normal force, temperature, and sliding speed were varied to simulate conditions such as those found in a food extruder. To simulate cold extrusion applications, water and bio-based FM mixtures were used. The best-performing bio-based FMs were then mixed with a polyalphaolefin to simulate warm extrusion conditions. The results were compared to those obtained from mixtures of a polyalphaolefin and selected conventional FMs. The main finding of this study demonstrated that rapeseed and salmon oils, with a peak coefficient of friction (COF) of 0.16, are the best-performing bio-based FMs for reducing friction. When mixed with distilled water for cold extrusion (case 1) and with polyalphaolefin for warm extrusion (case 2), they performed similarly to the conventional FM, tallow amine, also with a maximum COF of 0.16, and significantly better than polyalphaolefin alone (maximum COF of 0.25). Consequently, rapeseed and salmon oils are suitable bio-based FM candidates to replace conventional FMs in food-grade lubrication. Full article

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

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25 pages, 23912 KiB

Open AccessArticle

Parameter Effects on the Static Characteristics of the Multi-Foil Aerodynamic Journal Bearing with Bump-Backing Foils

by Yulong Jiang, Bo Xu, Qianjing Zhu, Zhongwen Huang and Dongyan Gao

Lubricants 2024, 12(7), 246; https://doi.org/10.3390/lubricants12070246 - 4 Jul 2024

Cited by 1 | Viewed by 991

Abstract

Due to the complexity of lubricating characteristics in the variable-sectional and multiscale clearance, the absence of an effective prediction method and theoretical basis of multi-foil aerodynamic journal bearing with bump-backing foils needs to be further developed. Hence, a modified efficient static characteristics model [...] Read more.

Due to the complexity of lubricating characteristics in the variable-sectional and multiscale clearance, the absence of an effective prediction method and theoretical basis of multi-foil aerodynamic journal bearing with bump-backing foils needs to be further developed. Hence, a modified efficient static characteristics model has been established, of which the one-dimensional curved beam theory is integrated and the elasto-hydrodynamic influence is intelligently concerned. It can be used to well predict the influential mechanisms of operational, geometric, and physical parameter effects on the static characteristics, and the important variation laws are systemically clarified. It aims to furnish a more effective and computationally efficient method and theoretical foundation for this significant type of bearing and promote its engineering design and performance optimization. Full article

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14 pages, 5527 KiB

Open AccessArticle

Impact of Interatomic Potentials on Atomic-Scale Wear of Graphene: A Molecular Dynamics Study

by Xueqi Ye, Jie Zhang and Ping Chen

Lubricants 2024, 12(7), 245; https://doi.org/10.3390/lubricants12070245 - 4 Jul 2024

Viewed by 941

Abstract

Selecting an appropriate empirical interatomic potential is essential for accurately describing interatomic interactions and simulating the friction and wear of graphene. Four empirical potentials—Tersoff, REBO, AIREBO, and LCBOP—were employed in molecular dynamics simulations to study the wear process of graphene at the atomic [...] Read more.

Selecting an appropriate empirical interatomic potential is essential for accurately describing interatomic interactions and simulating the friction and wear of graphene. Four empirical potentials—Tersoff, REBO, AIREBO, and LCBOP—were employed in molecular dynamics simulations to study the wear process of graphene at the atomic scale. The frictional process of graphene was found to be divisible into three distinct phases: elastic deformation, plastic deformation, and wear. Using a progressively increasing load method, the critical load for each phase of graphene under four different empirical potentials was identified. Furthermore, the formation of Stone–Wales (SW) defects, bond distribution, bond breaking and healing, and wrinkle formation were analyzed in detail. Finally, a comparison was made with previous experimental results regarding friction coefficient and wear morphology. Full article

(This article belongs to the Special Issue Advanced Computational Studies in Frictional Contact)

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17 pages, 3685 KiB

Open AccessArticle

Evaluation of Aromatic Organic Compounds as Additives on the Lubrication Properties of Castor Oil

by María Teresa Hernández-Sierra, José E. Báez, Luis Daniel Aguilera-Camacho, J. Santos García-Miranda and Karla J. Moreno

Lubricants 2024, 12(7), 244; https://doi.org/10.3390/lubricants12070244 - 4 Jul 2024

Viewed by 1016

Abstract

In the quest for sustainable lubrication solutions, the present research explored the potential of five organic compounds as additives in castor oil (CO) to improve its lubricating properties. The compounds tested were curcumin, eugenol, 1,3-Diphenyl-2-propanone, 1,3-Diphenyl-2-propenone, and 1,3-Diphenyl-1,3-propanedione. The main results showed that [...] Read more.

In the quest for sustainable lubrication solutions, the present research explored the potential of five organic compounds as additives in castor oil (CO) to improve its lubricating properties. The compounds tested were curcumin, eugenol, 1,3-Diphenyl-2-propanone, 1,3-Diphenyl-2-propenone, and 1,3-Diphenyl-1,3-propanedione. The main results showed that each additive enhanced at least one characteristic of CO. Most of the additives lowered the density of the castor oil but increased the viscosity by up to 20%. Curcumin and eugenol were particularly effective in creating thicker lubricant films and higher film thickness ratios. Eugenol and 1,3-Diphenyl-2-propanone significantly reduced the friction coefficient by up to 25%. Wear rate and wear mechanisms were significantly reduced with all the additives, achieving a reduction in wear rate of up to 50% (CO+curcumin). All the additives, except the 1,3-Diphenyl-1,3-propanedione, enhanced the oxidation onset temperature up to 8 °C. The influence of chemical structure was also addressed. The optimal additive combination for a specific application that demands minimal friction and wear, as well as strong oxidation stability, was eugenol, followed by curcumin and 1,3-Diphenyl-2-propanone. Overall, the research contributes to the development of eco-friendly lubricants, aligning with the growing demand for green industrial applications, and highlights the significant tribological benefits of these substances as sustainable additives in biolubricant formulations. Full article

(This article belongs to the Special Issue Recent Advances in Green Lubricants)

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4 pages, 147 KiB

Open AccessEditorial

Additives for Lubricating Oil and Grease: Mechanism, Properties and Applications

by Jingbin Han

Lubricants 2024, 12(7), 243; https://doi.org/10.3390/lubricants12070243 - 4 Jul 2024

Viewed by 2155

Abstract

Since the industrial revolution, science and technology, as well as industry of human society, have developed rapidly [...] Full article

(This article belongs to the Special Issue Additives for Lubricating Oil and Grease: Mechanism, Properties and Applications)

20 pages, 5239 KiB

Open AccessArticle

Multi-Objective Deep Q-Network Control for Actively Lubricated Bearings

by Denis Shutin and Yuri Kazakov

Lubricants 2024, 12(7), 242; https://doi.org/10.3390/lubricants12070242 - 3 Jul 2024

Viewed by 923

Abstract

This paper aims to study and demonstrate the possibilities of using reinforcement learning for the synthesis of multi-objective controllers for radial actively lubricated hybrid fluid film bearings (ALHBs), which are considered to be complex multi-physical systems. In addition to the rotor displacement control [...] Read more.

This paper aims to study and demonstrate the possibilities of using reinforcement learning for the synthesis of multi-objective controllers for radial actively lubricated hybrid fluid film bearings (ALHBs), which are considered to be complex multi-physical systems. In addition to the rotor displacement control problem being typically solved for active bearings, the proposed approach also includes power losses due to friction and lubricant pumping in ALHBs among the control objectives to be minimized by optimizing the lubrication modes. The multi-objective controller was synthesized using the deep Q-network (DQN) learning technique. An optimal control policy was determined by the DQN agent during its repetitive interaction with the simulation model of the rotor system with ALHBs. The calculations were sped up by replacing the numerical model of an ALHB with its surrogate ANN-based counterpart and by predicting the shaft displacements in response to operation of two independent control loops. The controller synthesized considering the formulated reward function for DQN agent is able to find a stable shaft position that reduces power losses by almost half compared to the losses observed when using a passive system. It also is able to prevent the established limit of the minimum fluid film thickness being exceeded to avoid possible system damage, for example, when the rotor is unbalanced during the operation. Analysis of the development process and the results obtained allowed us to draw conclusions about the main advantages and disadvantages of the considered approach, and also allowed us to identify some important directions for further research. Full article

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22 pages, 32625 KiB

Open AccessArticle

Numerical Optimization Analysis of Floating Ring Seal Performance Based on Surface Texture

by Zhenpeng He, Yuhang Guo, Jiaxin Si, Ning Li, Lanhao Jia, Yuchen Zou and Hongyu Wang

Lubricants 2024, 12(7), 241; https://doi.org/10.3390/lubricants12070241 - 3 Jul 2024

Viewed by 1000

Abstract

Much research and practical experience have shown that the utilization of textures has an enhancing effect on the performance of dynamic seals and the dynamic pressure lubrication of gas bearings. In order to optimize the performance of floating ring seals, this study systematically [...] Read more.

Much research and practical experience have shown that the utilization of textures has an enhancing effect on the performance of dynamic seals and the dynamic pressure lubrication of gas bearings. In order to optimize the performance of floating ring seals, this study systematically analyzes the effects of different texture shapes and their parameters. The Reynolds equation of the gas is solved by the successive over-relaxation (SOR) iteration method. The pressure and thickness distributions of the seal gas film are solved to derive the floating force, end leakage, friction, and the ratio of buoyancy to leakage within the seal. The effects of various texture shapes, including square, 2:1 rectangle, triangle, hexagon, and circle, as well as their parameters, such as texture depth, angle, and area share, on the sealing performance are discussed. Results show that the texture can increase the air film buoyancy and reduce friction, but it also increases the leakage by a small amount. Square textures and rectangular textures are relatively effective. The deeper the depth of the texture within a certain range, the better the overall performance of the floating ring seal. As the texture area percentage increases, leakage tends to increase and friction tends to decrease. A fractal roughness model is developed, the effect of surface roughness on sealing performance is briefly discussed, and finally the effect of surface texture with roughness is analyzed. Some texture parameters that can significantly optimize the sealing performance are obtained. Rectangular textures with certain parameters enhance the buoyancy of the air film by 81.2%, which is the most significant enhancement effect. This rectangular texture reduces friction by 25.8% but increases leakage by 79.5%. The triangular textures increase buoyancy by 28.02% and leakage increases by only 10.08% when the rotation speed is 15,000 r/min. The results show that texture with appropriate roughness significantly optimizes the performance of the floating ring seal. Full article

(This article belongs to the Special Issue Mechanical Tribology and Surface Technology)

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25 pages, 12647 KiB

Open AccessArticle

Impact of Mid-to-Low-Ash, Low-Viscosity Lubricants on Aftertreatment Systems after 210,000-Kilometer Real-World Road Endurance Trials

by Heng Shao, Hua Hu, Yitao Luo, Lun Hua, Jinchong Pan, Gezhengting Zhu, Yan Jiao, Jingfeng Yan and Guangyuan Wei

Lubricants 2024, 12(7), 240; https://doi.org/10.3390/lubricants12070240 - 3 Jul 2024

Viewed by 845

Abstract

Engine lubricants globally face the challenge of meeting the demands of new engine technologies while enhancing energy efficiency and reducing emissions. Lubricants must enhance their performance and sustainability, improve reliability in complex and harsh environments, and minimize environmental impact and health risks. This [...] Read more.

Engine lubricants globally face the challenge of meeting the demands of new engine technologies while enhancing energy efficiency and reducing emissions. Lubricants must enhance their performance and sustainability, improve reliability in complex and harsh environments, and minimize environmental impact and health risks. This study explores the influence of two different formulations of low viscosity lubricants, tested through actual road endurance trials, on a hybrid vehicle’s aftertreatment system performance and overall emission levels. The study includes 120,000 km of endurance testing in four different challenging environments in China, as well as 90,000 km of endurance testing in a typical urban and highway driving cycle in a large city. Results indicate that emissions from the test vehicles during the 120,000 km and 210,000 km durable Worldwide harmonized Light vehicle Test Cycles (WLTCs) meet China’s Stage 6 light-duty vehicle emission standards, with the 210,000 km Real Driving Emission test (RDE) results also conforming to these standards. Relative to fresh TWC, the light-off temperature increased by a mere 60 °C, and the oxygen storage capacity declined by around 19% following endurance testing. Additionally, the GPF exhibited satisfactory performance after 210,000 km of endurance testing, showing lower backpressure values compared to the fresh-coated samples, with no notable ash buildup observed in the substrate. Drawing on the outcomes of actual road endurance testing, this study illustrates that employing low-to-mid-ash-content, low-viscosity lubricants is both compatible and reliable for aftertreatment systems in present or advanced hybrid technologies. Premium lubricants facilitate vehicles in sustaining compliant and stable emission performance, even amid harsh environments and complex operating conditions. Furthermore, the tested lubricants effectively inhibit excessive aging of the aftertreatment system over prolonged mileage. Moreover, this study discusses the feasibility of rapid aging evaluation methods for aftertreatment systems based on engine test benches, juxtaposed with actual road endurance testing. These findings and conclusions offer crucial references and guidance for enhancing lubricant performance and sustainability. Subsequent studies can delve deeper into the correlation between lubricant performance and environmental impact, alongside optimization strategies for lubricants across various vehicle models and usage scenarios. Full article

(This article belongs to the Special Issue Tackling Emissions from the Internal Combustion Engine: Advances in Piston/Bore Tribology)

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27 pages, 5605 KiB

Open AccessArticle

Optimization of Variational Mode Decomposition-Convolutional Neural Network-Bidirectional Long Short Term Memory Rolling Bearing Fault Diagnosis Model Based on Improved Dung Beetle Optimizer Algorithm

by Weiqing Sun, Yue Wang, Xingyi You, Di Zhang, Jingyi Zhang and Xiaohu Zhao

Lubricants 2024, 12(7), 239; https://doi.org/10.3390/lubricants12070239 - 2 Jul 2024

Cited by 1 | Viewed by 944

Abstract

(1) Background: Rolling bearings are important components in mechanical equipment, but they are also components with a high failure rate. Once a malfunction occurs, it will cause mechanical equipment to malfunction and may even affect personnel safety. Therefore, studying the fault diagnosis methods [...] Read more.

(1) Background: Rolling bearings are important components in mechanical equipment, but they are also components with a high failure rate. Once a malfunction occurs, it will cause mechanical equipment to malfunction and may even affect personnel safety. Therefore, studying the fault diagnosis methods for rolling bearings is of great significance and is also a current research hotspot and frontier. However, the vibration signals of rolling bearings usually exhibit nonlinear and non-stationary characteristics, and are easily affected by industrial environmental noise, making it difficult to accurately diagnose bearing faults. (2) Methods: Therefore, this article proposes a rolling bearing fault diagnosis model based on an improved dung beetle optimizer (DBO) algorithm-optimized variational mode decomposition-convolutional neural network-bidirectional long short-term memory (VMD-CNN-BiLSTM). Firstly, an improved DBO algorithm named CSADBO is proposed by integrating multiple strategies such as chaotic mapping and cooperative search. Secondly, the optimal parameter combination of VMD was adaptively determined through the CSADBO algorithm, and the optimized VMD algorithm was used to perform modal decomposition on the bearing vibration signal. Then, CNN-BiLSTM was used as the model for fault classification, and hyperparameters of the model were optimized using the CSADBO algorithm. (3) Results: Finally, multiple experiments were conducted on the bearing dataset of Case Western Reserve University, and the proposed method achieved an average diagnostic accuracy of 99.6%. (4) Conclusions: Experimental comparisons were made with other models to verify the effectiveness of the proposed model. The experimental results show that the proposed model based on an improved DBO algorithm optimized VMD-CNN-BiLSTM can effectively be used for rolling bearing fault diagnosis, with high diagnostic accuracy, and can provide a theoretical reference for other related fault diagnosis problems. Full article

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

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16 pages, 6431 KiB

Open AccessArticle

Calculation Method and Experimental Study on Circumferential Total Clearance of Cageless Bearings

by Xiaofeng Zhao, Shuidian Xu, Tao Xu, Qianqian Xu and Kai Huang

Lubricants 2024, 12(7), 238; https://doi.org/10.3390/lubricants12070238 - 28 Jun 2024

Viewed by 663

Abstract

This paper addresses the issue of the frequent collision and grinding of rolling elements in cageless bearings during operation by proposing a method to calculate the total circumferential clearance. The calculation is based on the maximum orbital speed difference in the bearing rolling [...] Read more.

This paper addresses the issue of the frequent collision and grinding of rolling elements in cageless bearings during operation by proposing a method to calculate the total circumferential clearance. The calculation is based on the maximum orbital speed difference in the bearing rolling elements to determine the minimum clearance needed to prevent collision. The study analyzes the impact of the rolling element diameter, bearing pitch diameter, contact angle, and number of rolling elements on the total circumferential clearance. The discussion then focuses on optimizing the number of rolling elements in cageless bearings. The optimization results demonstrate that the proposed calculation reduces collisions between rolling elements and bearing stress. Additionally, a total circumferential clearance test was conducted on a logarithmic spiral bearing, showing significant improvements in wear, average temperature, and temperature rise when designed according to the method presented in this article. These findings offer valuable insights into the design of cageless bearings. Full article

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28 pages, 22903 KiB

Open AccessArticle

Cold Spray Deposition of MoS₂- and WS₂-Based Solid Lubricant Coatings

by Jeffrey R. Lince, Peter Woods, Eric Woods, Wai H. Mak, Scott D. Sitzman and Andrew J. Clough

Lubricants 2024, 12(7), 237; https://doi.org/10.3390/lubricants12070237 - 28 Jun 2024

Viewed by 918

Abstract

The cold spray deposition technique has been used to produce a new class of solid lubricant coatings using powder feedstocks of the metal disulfides WS₂ or MoS₂, either pure or mixed with Cu and Ni metal powders. Friction and cycle [...] Read more.

The cold spray deposition technique has been used to produce a new class of solid lubricant coatings using powder feedstocks of the metal disulfides WS₂ or MoS₂, either pure or mixed with Cu and Ni metal powders. Friction and cycle lives were obtained using ball-on-flat reciprocating tribometry of coated 304 SS flats in dry nitrogen and vacuum at higher Hertzian contact stresses (S_max = 1386 MPa (201 ksi)). The measured friction and thickness of the coatings were much lower than for previous studies (COF = 0.03 ± 0.01 and ≤1 µm, respectively), which is due to their high metal disulfide:metal ratios. Cu-containing metal sulfide coatings exhibited somewhat higher cycle lifetimes than the pure metal sulfide coatings, even though the Cu content was only ~1 wt%. Profiling of wear tracks for coatings tested to 3000 cycles (i.e., pre-failure) yielded specific wear rates in the range 3–7 × 10⁻⁶ mm³N⁻¹m⁻¹, similar to other solid lubricant coatings. When compared to other coating techniques, the cold spray method represents a niche that has heretofore been vacant. In particular, it will be useful in many precision ball-bearing applications that require higher throughput and lower costs than sputter-deposited MoS₂-based coatings. Full article

(This article belongs to the Special Issue New Challenges in Tribology of Space Mechanisms)

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26 pages, 1185 KiB

Open AccessReview

A Review of the Rheological Consistency of Materials

by Alan Gurt and Michael Khonsari

Lubricants 2024, 12(7), 236; https://doi.org/10.3390/lubricants12070236 - 28 Jun 2024

Viewed by 1136

Abstract

Despite the ubiquity and prevalence of rheological consistency across a wide range of industries, there is no clear consensus on its meaning or on one particular technique for quantifying it. Instead, there exist various definitions of “consistency” that are each specific to a [...] Read more.

Despite the ubiquity and prevalence of rheological consistency across a wide range of industries, there is no clear consensus on its meaning or on one particular technique for quantifying it. Instead, there exist various definitions of “consistency” that are each specific to a given context, and each industry has its own procedure for measuring it. This paper organizes the many subjects and terminologies associated with consistency, providing a comprehensive guide of fundamental mechanics, fundamental properties, modeling techniques, and standardized tests that describe consistency. This includes outlining the rheological models that describe the behavior of viscoelastic and non-Newtonian materials as well as the identification of numerous parameters that can be individually evaluated to comprehensively understand and quantify consistency. Such an understanding of consistency and its underlying mechanical properties encourages the refinement of current consistency test methods and development of new ones. Full article

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17 pages, 6096 KiB

Open AccessArticle

Holistic Measurement of the Friction Behavior of Wet Clutches

by Patrick Strobl, Georg Johann Meingassner, Hermann Pflaum, Katharina Voelkel, Thomas Schneider and Karsten Stahl

Lubricants 2024, 12(7), 235; https://doi.org/10.3390/lubricants12070235 - 25 Jun 2024

Viewed by 1209

Abstract

The safe and efficient torque transmission of wet disk clutch systems requires high coefficients of friction. To achieve good controllability and high comfort, a positive slope of the coefficient of friction over sliding velocity is ensured by a reasonable formulation of the lubricant [...] Read more.

The safe and efficient torque transmission of wet disk clutch systems requires high coefficients of friction. To achieve good controllability and high comfort, a positive slope of the coefficient of friction over sliding velocity is ensured by a reasonable formulation of the lubricant and choice of the friction pairing. This results in low transmittable torque at low sliding velocities. Thus, the occurrence of unwanted micro-slip in dynamic operation modes must be considered for the design of safety-relevant clutch systems. This work presents a methodology for the holistic measurement of the friction behavior of wet disk clutches. It is suitable for numerous applications and supports a sound understanding of frictional properties in the range of sliding velocities occurring in brake shifts through forced slip operation down to static torque transmission. The experimental determination of the holistic friction behavior is crucial for developing optimized design guidelines for modern clutch systems. Full article

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16 pages, 15735 KiB

Open AccessArticle

Study on the Friction Characteristics and Fatigue Life of Carbonitriding-Treated Needle Bearings

by Yong Chen, Xiangrun Pu, Lijie Hao, Guangxin Li and Li Luo

Lubricants 2024, 12(7), 234; https://doi.org/10.3390/lubricants12070234 - 24 Jun 2024

Viewed by 999

Abstract

Being a key component of the transmission system, the needle bearing’s performance and service life affects the overall service life of mechanical equipment. This study takes needle bearings composed of AISI 52100 steel as the research object and studies the effect of carbonitriding [...] Read more.

Being a key component of the transmission system, the needle bearing’s performance and service life affects the overall service life of mechanical equipment. This study takes needle bearings composed of AISI 52100 steel as the research object and studies the effect of carbonitriding surface strengthening treatment on the bearing friction, wear, and fatigue life. The carbon and nitrogen co-infiltration surface-strengthening method was employed to prepare cylindrical and disc samples. The surface hardness, residual austenite content, microscopic morphology and organization composition, coefficient of friction, and wear scar were studied to analyze the effect on the wear performance of the material. The bearing fatigue wear comparison test was conducted on a test bench to compare the actual fatigue life and surface damage of the needle bearing through conventional martensitic quenching heat treatment and carbonitriding treatment. The results demonstrate that the carbonitriding strengthening method enhances the toughness of the material while improving its surface hardness. It also improves the wear resistance of the needle roller bearings, and the fatigue life of the bearings is significantly improved. In conclusion, carbon and nitrogen co-infiltration treatment is a strengthening method that effectively extends the service life of needle roller bearings, indicating its high practical value. Full article

(This article belongs to the Special Issue Tribological Characteristics of Bearing System, 2nd Edition)

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17 pages, 7505 KiB

Open AccessArticle

Effect of Hydrogen Pressure on the Fretting Behavior of Rubber Materials

by Géraldine Theiler, Natalia Cano Murillo and Andreas Hausberger

Lubricants 2024, 12(7), 233; https://doi.org/10.3390/lubricants12070233 - 23 Jun 2024

Cited by 1 | Viewed by 1463

Abstract

Safety and reliability are the major challenges to face for the development and acceptance of hydrogen technology. It is therefore crucial to deeply study material compatibility, in particular for tribological components that are directly in contact with hydrogen. Some of the most critical [...] Read more.

Safety and reliability are the major challenges to face for the development and acceptance of hydrogen technology. It is therefore crucial to deeply study material compatibility, in particular for tribological components that are directly in contact with hydrogen. Some of the most critical parts are sealing materials that need increased safety requirements. In this study, the fretting behavior of several elastomer materials were evaluated against 316L stainless steel in an air and hydrogen environment up to 10 MPa. Several grades of cross-linked hydrogenated acrylonitrile butadiene (HNBR), acrylonitrile butadiene (NBR) and ethylene propylene diene monomer rubbers (EPDM) were investigated. Furthermore, aging experiments were conducted for 7 days under static conditions in 100 MPa of hydrogen followed by rapid gas decompression. Fretting tests revealed that the wear of these compounds is significantly affected by the hydrogen environment compared to air, especially with NBR grades. After the aging experiment, the friction response of the HNBR grades is characterized by increased adhesion due to elastic deformation, leading to partial slip. Full article

(This article belongs to the Special Issue Tribology in Germany: Latest Research and Development)

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