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Lubricants
Volume 11
Issue 3
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Lubricants, Volume 11, Issue 3 (March 2023) – 61 articles

Cover Story (view full-size image): Elastohydrodynamic lubrication (EHL) simulations are computationally expensive because the equations that describe the lubricant film pressure and the deformation of the bearing surfaces are coupled and, thus, must be solved simultaneously. We methodically quantify the convergence of soft EHL simulations of textured slider bearings as a function of simulation parameters, including convergence metrics and criteria, cavitation models, texture design parameters, and bearing operating parameters. We conclude that the interplay between discretization, convergence metric, and convergence criterion must be carefully considered to implement numerical simulations that converge to the correct physical solution. A well-designed convergence study can also minimize computational cost. View this paper
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20 pages, 7077 KiB  
Article
Sensitivity of TEHL Simulations to the Use of Different Models for the Constitutive Behaviour of Lubricants
by Peyman Havaej, Joris Degroote and Dieter Fauconnier
Lubricants 2023, 11(3), 151; https://doi.org/10.3390/lubricants11030151 - 21 Mar 2023
Cited by 3 | Viewed by 1934
Abstract
This study compares the film thickness, lubricant temperature, and traction curves of two groups of commonly used constitutive models for lubricants in thermo-elastohydrodynamic lubrication (TEHL) modelling. The first group consists of the Tait equation of state, the Doolittle Newtonian viscosity model, and the [...] Read more.
This study compares the film thickness, lubricant temperature, and traction curves of two groups of commonly used constitutive models for lubricants in thermo-elastohydrodynamic lubrication (TEHL) modelling. The first group consists of the Tait equation of state, the Doolittle Newtonian viscosity model, and the Carreau shear thinning model. The second group includes the Dowson equation of state, the Roelands–Houpert Newtonian viscosity model, and the Eyring shear thinning model. The simulations were conducted using a Computational Fluid Dynamic and Fluid-Structure Interaction (CFD-FSI) approach, which employs a homogeneous equilibrium model for the flow simulation along with a linear elastic solver to describe the deformation of the solid materials. The simulations were conducted under a load range of 100 kN/m to 200 kN/m and a slide-to-roll-ratio (SRR) range between 0 and 2 using Squalane lubricant. The results show up to a 10% deviation in central film thickness, a 31% deviation in coefficient of friction (CoF), and a 38% deviation in maximum lubricant temperature when using the different constitutive models. This study highlights the sensitivity of TEHL simulation results to the choice of constitutive models for lubricants and the importance of carefully selecting the appropriate models for specific applications. Full article
(This article belongs to the Special Issue Accuracy and Reliability of Computational Modelling of Thermo-Elastohydrodynamic Lubrication)
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15 pages, 9630 KiB  
Article
Effects of Tool Plunging Path on the Welded Joint Properties of Pinless Friction Stir Spot Welding
by Xiaole Ge, Di Jiang, Weiwei Song and Hongfeng Wang
Lubricants 2023, 11(3), 150; https://doi.org/10.3390/lubricants11030150 - 21 Mar 2023
Cited by 1 | Viewed by 1399
Abstract
Four tool plunging paths including a one-time plunging path and three step-by-step plunging paths were designed to study the effects of the tool plunging path on the welded joint properties of pinless friction stir spot welding (PFSSW). The appearance, cross-sectional microstructure, welding temperature, [...] Read more.
Four tool plunging paths including a one-time plunging path and three step-by-step plunging paths were designed to study the effects of the tool plunging path on the welded joint properties of pinless friction stir spot welding (PFSSW). The appearance, cross-sectional microstructure, welding temperature, microhardness, and tensile shear failure load of the PFSSW of thin copper sheets under different tool plunging paths were explored. Furthermore, the fracture modes of welded joints under different tool plunging paths were analyzed. Studies showed that path 1 (plunge total depth at one time) produced the largest range of stirring zone, but the grains in the stirring zone were larger and the width of the thermal-mechanical affected zone was smaller. Path 1 obtained the highest peak temperature during the welding process, and path 3 (plunge 1/3 total depth + plunge 2/3 total depth) gained the lowest peak temperature. The greater the initial plunging amount of the tool, the faster the temperature rise rate in the welding stage. The tensile shear failure loads for path 1, path 2 (plunge 1/2 total depth + plunge 1/2 total depth), path 3, and path 4 (plunge 2/3 total depth + plunge 1/3 total depth) were 8.65 kN, 8.15 kN, 8.25 kN, and 8.85 kN, respectively. The tensile shear failure load of path 4 was 2.3% higher than that of path 1. The fracture modes of welded joints under different tool plunging paths were all nugget pullout fractures. The fracture morphology indicated that the fracture type was ductile fracture. The step-by-step plunging path proposed in this work extends the traditional PFSSW process. The findings of this study can provide a reference for the selection and design of tool plunging paths for PFSSW. Full article
(This article belongs to the Special Issue Friction Stir Processing of Structural Metallic Materials)
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13 pages, 4901 KiB  
Article
Viscosity Variations and Tribological Performances of Oleylamine-Modified Fe3O4 Nanoparticles as Mineral Oil Additives
by Xiaoyu Wang, Huanchen Liu, Qilong Zhao, Xiaobo Wang and Wenjing Lou
Lubricants 2023, 11(3), 149; https://doi.org/10.3390/lubricants11030149 - 20 Mar 2023
Cited by 5 | Viewed by 2492
Abstract
In order to improve the flowabilities and anti-friction and anti-wear properties of lubricants, the viscosity variations and tribological performances of oleylamine-modified Fe3O4 nanoparticles as mineral oil additives were systematically investigated via rotational parallel plate rheometer, ball–disc reciprocating tribometer, non-contact three-dimensional [...] Read more.
In order to improve the flowabilities and anti-friction and anti-wear properties of lubricants, the viscosity variations and tribological performances of oleylamine-modified Fe3O4 nanoparticles as mineral oil additives were systematically investigated via rotational parallel plate rheometer, ball–disc reciprocating tribometer, non-contact three-dimensional surface profiler, scanning electron microscope, energy dispersive X-ray spectrometer and X-ray photoelectron spectroscopy. Spherical monodisperse Fe3O4 nanoparticles were synthesized and dispersed into mineral oils to obtain lubricants with mass fractions of 1%, 3%, 5%, 8%, 10% and 20%, respectively. These lubricants have excellent stabilities within 12 months. Interestingly, the dynamic viscosity and kinematic viscosity of the lubricants first decrease and then increase with the increase in Fe3O4 content, and the lubricants’ viscosity is at a minimum when the mass concentration is 5%. The tensile curves also show that with the mass fraction increase, the lubricants’ tackiness and adhesion have the same change law, and both reach the lowest point when the mass concentration is 5%. Meanwhile, Fe3O4 nanoparticles can improve the tribological properties of the base oils. It is worth noting that the maximum reduction in the wear volume at 25 °C is up to 93.8% compared with base oils when the additive concentration of the Fe3O4 nanoparticles is 5 wt%. Full article
(This article belongs to the Special Issue Nanolubrication and Superlubrication)
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17 pages, 5714 KiB  
Article
The Direct-Coupling Method for Analyzing the Performance of Aerostatic Bearings Considering the Fluid–Structure Interaction Effect
by Yangong Wu, Wentao Chen, Qinghui Zhang, Zheng Qiao and Bo Wang
Lubricants 2023, 11(3), 148; https://doi.org/10.3390/lubricants11030148 - 19 Mar 2023
Cited by 1 | Viewed by 1932
Abstract
In the interest of analyzing the effect of the structural deformation root caused by gas pressure on the static features of aerostatic bearings, a fluid–structure interaction (FSI) model based on orifice-type aerostatic bearings is proposed that can predict the characteristics of aerostatic bearings [...] Read more.
In the interest of analyzing the effect of the structural deformation root caused by gas pressure on the static features of aerostatic bearings, a fluid–structure interaction (FSI) model based on orifice-type aerostatic bearings is proposed that can predict the characteristics of aerostatic bearings more accurately by using the direct-coupling method (DCM). By using COMSOL Multiphysics, the governing equation matrix of the finite element model of structural deformation and gas film pressure was solved with the integral solution method, and the orifice boundary conditions were calculated with the root iteration method. At the same time, the static performance of I-shaped orifice-type aerostatic bearing with various supply pressures was analyzed theoretically and tested experimentally. The results show that in comparison with the calculation results without taking account of structural deformation, the theoretical values from the model derived in this paper considering the FSI effect are closer to the experimental values. Finally, by using the orthogonal design method, FSI simulation was carried out to analyze how the key dimension factors influence the structural stiffness of the spindle, and it is concluded that the thrust bearing’s stiffness is strongly influenced by the thickness of the thrust plate. Full article
(This article belongs to the Special Issue Condition Monitoring and Simulation Analysis of Bearings)
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16 pages, 5868 KiB  
Article
Study on the Dispersion and Lubrication Properties of LDH in Lubricating Oil
by Yong Li, Qiang Zhang, Weidong Zhou, Yongwang Huang and Jingbin Han
Lubricants 2023, 11(3), 147; https://doi.org/10.3390/lubricants11030147 - 19 Mar 2023
Cited by 1 | Viewed by 2427
Abstract
The dispersion of nanomaterials in lubricating oil plays an important role in the lubrication and wear-resistance properties. In this work, supramolecular layered double hydroxides (LDHs) were prepared and added to lubricating oil with different dispersants. The content of key elements in the samples [...] Read more.
The dispersion of nanomaterials in lubricating oil plays an important role in the lubrication and wear-resistance properties. In this work, supramolecular layered double hydroxides (LDHs) were prepared and added to lubricating oil with different dispersants. The content of key elements in the samples was measured by an oil element analyzer, and the dispersion properties of different samples were studied. The friction coefficient of the samples was measured by high-frequency linear vibration (SRV), and the morphology and composition were characterized by SEM to study the antiwear performance and action mechanism of LDH. The oxidation induction time of the samples was measured by RBOT to study the antioxygenic properties of LDH in lubricating oil. The results show that LDH can be well-dispersed in lubricating oil with the action of specific dispersants. After adding LDH, the antiwear performance of lubricating oil was improved, as a uniform and dense protective film was formed on the friction surface. Full article
(This article belongs to the Special Issue Nanolubrication and Superlubrication)
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22 pages, 17888 KiB  
Article
Study on the Effect of Oil Supply on the Sound Field Characteristics of Full Ceramic Ball Bearings under Oil Lubrication
by Jian Sun, Xin Fang, Jinmei Yao, Renyun Guan, Zhe Zhang and Guangxiang Zhang
Lubricants 2023, 11(3), 146; https://doi.org/10.3390/lubricants11030146 - 19 Mar 2023
Cited by 5 | Viewed by 1741
Abstract
To study the full sound field distribution characteristics of full ceramic ball bearings, reduce the radiation noise of the bearings, and improve their service performance. In this paper, the sound field distribution characteristics of 6206 silicon nitride ceramic deep groove ball bearings are [...] Read more.
To study the full sound field distribution characteristics of full ceramic ball bearings, reduce the radiation noise of the bearings, and improve their service performance. In this paper, the sound field distribution characteristics of 6206 silicon nitride ceramic deep groove ball bearings are studied under different oil supplies. A mathematical model of the sound field distribution of full ceramic ball bearings under oil lubrication is established, and the validity of the model is verified by experimental data. The bearing cavity simulation model of the full ceramic ball bearing is established, and the influence of oil supply on the operation characteristics of the full ceramic ball bearing is studied. Through theoretical and experimental research, the circular distribution law of the noise signal of ceramic ball bearings under different oil supplies is revealed. It is found that there is an optimal fuel supply when the speed and load are constant. Under optimal oil supply lubrication conditions, the full ceramic ball bearing has the minimum radiation noise, and the bearing exhibits optimal lubrication state, vibration and temperature rise characteristics. The new contribution of this paper: with the increase in oil supply, the sound pressure level of radiation noise of full ceramic ball bearings decreases and then increases. The research results reveal the radiation noise mechanism of full ceramic ball bearings, which is of great significance for enriching its theory and method. Full article
(This article belongs to the Special Issue Advances in Bearing Lubrication and Thermodynamics 2023)
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28 pages, 15978 KiB  
Article
Analysis of Nonlinear Time-Domain Lubrication Characteristics of the Hydrodynamic Journal Bearing System
by Changgang Lin, Fan Jian, Shili Sun, Can Sima, Libo Qi and Mingsong Zou
Lubricants 2023, 11(3), 145; https://doi.org/10.3390/lubricants11030145 - 17 Mar 2023
Cited by 1 | Viewed by 1652
Abstract
The nonlinear time-domain lubrication characteristics of the hydrodynamic journal bearing system are studied in this paper. The motion equation of the hydrodynamic journal bearing system is established based on the balance of the relationship among the water film force, journal inertia force, and [...] Read more.
The nonlinear time-domain lubrication characteristics of the hydrodynamic journal bearing system are studied in this paper. The motion equation of the hydrodynamic journal bearing system is established based on the balance of the relationship among the water film force, journal inertia force, and external load. The water film pressure distribution of the sliding bearing is calculated by the finite difference method. Firstly, the variation law of the water film pressure distribution with time under the external periodic load is calculated considering the inertial force of the journal. The influence of the initial eccentricity on the orbit of the journal center is studied. Secondly, the maximum water film pressure, the orbit of the journal center, eccentricity, water film pressure, and the minimum water film thickness of the bearing under the action of circumferential and unidirectional periodic external loads are calculated, and the effects of inertial force and rotational speed on the dynamic characteristics of the bearing are analyzed. Finally, the water film dynamic characteristics under low speed and heavy load are studied. The result shows that the pressure of the dimensionless water film caused by inertial force is reduced by 7 to 10 percent at the rotational speed between 200 r/min and 800 r/min, which means that the influence of inertia force cannot be ignored. Full article
(This article belongs to the Special Issue Water-Lubricated Bearings)
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25 pages, 7938 KiB  
Article
‘Triangle Ester’ Molecules as Blending Components in Mineral Oil: A Theoretical and Experimental Investigation
by Neha Sharma, Sunil Kumar, Gananath D. Thakre and Anjan Ray
Lubricants 2023, 11(3), 144; https://doi.org/10.3390/lubricants11030144 - 17 Mar 2023
Cited by 1 | Viewed by 1974
Abstract
The present work explored the use of fatty acid ‘Triangle ester’ molecules (Epoxidized Ester (EE), and Thiirane Ester (TE)) as antifriction and antiwear additives at varying levels for Group I and Group II mineral base oils using the standard ASTMD-4172B four-ball test. Relative [...] Read more.
The present work explored the use of fatty acid ‘Triangle ester’ molecules (Epoxidized Ester (EE), and Thiirane Ester (TE)) as antifriction and antiwear additives at varying levels for Group I and Group II mineral base oils using the standard ASTMD-4172B four-ball test. Relative to neat base oil, EE blends showed improved antifriction by ~61% and ~42% and antiwear properties by ~32% and ~41% in Group I and Group II base oils, respectively, while the TE blends showed friction reduction by ~65% and ~40% and wear reduction by ~93% and ~50% relative to the same neat base stock. Time evolution of the ‘Triangle ester’ molecules and their blends with mineral oil (modeled as hexadecane) w.r.t. conformational changes, adsorption energy, intermolecular energy, and effect of the applied stress were estimated theoretically using MD simulations. Further, optimized levels of these additives were explored for their effectiveness as a blending component for commercial engine oil (CEO) and could reduce the friction and wear of CEO by ~50% and ~30%, respectively. Full article
(This article belongs to the Special Issue Microstructure, Anti-wear Properties and Numerical Simulation of Lubricants)
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15 pages, 5462 KiB  
Article
Oil Separation of Lubricating Greases under Static Conditions: Analytical Photo-Centrifuge and DIN 51817
by Karl-Heinz Jacob
Lubricants 2023, 11(3), 143; https://doi.org/10.3390/lubricants11030143 - 17 Mar 2023
Viewed by 2830
Abstract
Lubricating greases enclose oil in porous structures of aggregated thickener particles. Their tendency to separate oil under static conditions is evaluated according to DIN 51817 or DIN ISO 22285 in tests of up to 168 h with the mass fraction of separated oil [...] Read more.
Lubricating greases enclose oil in porous structures of aggregated thickener particles. Their tendency to separate oil under static conditions is evaluated according to DIN 51817 or DIN ISO 22285 in tests of up to 168 h with the mass fraction of separated oil as result. With an analytical photo-centrifuge, separated oil mass fractions can be tracked in real time in the instrument operating temperature range from 4–60 °C. Due to the higher mechanical load compared to standard tests, the grease samples separate more and faster oil, significantly speeding up the analysis process. Fitting the measured data from both methods with the function wO = wO,∞ exp(−t/tc), the parameters maximum oil separation wO,∞ and characteristic time tc are obtained as measures of oil separation extent and rate. Both parameters help to compare the two methods and to interpret the oil separation characteristics of greases. Using four commercial greases of NLGI classes 0–2, the analytical photo-centrifuge measuring method is presented in detail and its results are discussed in reference to those of standard DIN 51817. Full article
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16 pages, 20530 KiB  
Article
Effect of Rotational Speed on Tribological Properties of Carbon Fiber-Reinforced Al-Si Alloy Matrix Composites
by Feng Tang, Xiaotao Pan, Yafei Deng, Zhenquan Zhou, Guoxun Zeng and Sinong Xiao
Lubricants 2023, 11(3), 142; https://doi.org/10.3390/lubricants11030142 - 17 Mar 2023
Cited by 5 | Viewed by 1557
Abstract
Porous carbon fiber-reinforced Al-Si alloy matrix composites and carbon fiber felt-reinforced Al-Si alloy matrix composites with carbon content of 10 wt.% were prepared by die casting. The dry tribological properties of these two composites and Al-Si alloy were studied using a ball-on-disc rotational [...] Read more.
Porous carbon fiber-reinforced Al-Si alloy matrix composites and carbon fiber felt-reinforced Al-Si alloy matrix composites with carbon content of 10 wt.% were prepared by die casting. The dry tribological properties of these two composites and Al-Si alloy were studied using a ball-on-disc rotational tribometer in the rotational speed range of 300 r/min to 1000 r/min, and the wear mechanisms were analyzed in combination with the wear morphology. The results show that the friction coefficient and wear rate of these two composites are lower than the Al-Si alloy at different speeds. With the increase in rotational speed, the friction coefficient of the two composites and Al-Si alloy first increases and then decreases, and the wear rate gradually increases. The wear mechanisms of the two composites and Al-Si alloy change from abrasive wear and adhesive wear to delamination wear, but the node speed of the change in the wear mechanism of the composites to delamination wear is higher, and the wear degree is relatively slight. In addition, the comprehensive tribological properties of carbon fiber felt-reinforced Al-Si alloy matrix composites are better than the porous carbon fiber-reinforced Al-Si alloy matrix composites. Full article
(This article belongs to the Special Issue Wear Behavior of Aluminum Matrix Composite)
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24 pages, 19658 KiB  
Article
Insights into the Corrosion Inhibition Performance of Three 2-Isoxazoline-γ-Lactones for Carbon Steel in Acidic Medium: Linking Molecular and Experimental-Level Information with Microscopic-Scale Modeling
by Youssef Youssefi, Abdeslam Ansari, Omar Ou-ani, Lahcen Oucheikh, Ahmad Oubair, Hassane Lgaz, Belkheir Hammouti, Abdelkarim Chaouiki, Young Gun Ko and Mohamed Znini
Lubricants 2023, 11(3), 141; https://doi.org/10.3390/lubricants11030141 - 16 Mar 2023
Cited by 8 | Viewed by 2021
Abstract
The corrosion inhibition properties of three spiro-isoxazoline derivatives, namely 3,4-diphenyl-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (DDA), 3-phenyl-4-(p-tolyl)-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (PDA) and 4-(4-methoxyphenyl)-3-phenyl-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (MDA) on carbon steel in 1.0 mol/L HCl acid medium were experimentally and computationally investigated. The experimental results showed that the inhibitory efficiency reached remarkable values of 76.26, [...] Read more.
The corrosion inhibition properties of three spiro-isoxazoline derivatives, namely 3,4-diphenyl-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (DDA), 3-phenyl-4-(p-tolyl)-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (PDA) and 4-(4-methoxyphenyl)-3-phenyl-1,7-dioxa-2-azaspiro[4.4]non-2-en-6-one (MDA) on carbon steel in 1.0 mol/L HCl acid medium were experimentally and computationally investigated. The experimental results showed that the inhibitory efficiency reached remarkable values of 76.26, 80.31, and 82.91%, respectively, for DDA, PDA and MDA at a maximum concentration of 10−3 mol/L. The potentiodynamic polarization curves (PPCs) showed that investigated compounds had a mixed type character, controlling both anodic and cathodic corrosion reactions. In addition, electrochemical impedance spectroscopy (EIS) indicated that the addition of increasing concentration of tested compounds to HCl solutions led to a significant increase in the polarization resistance of the carbon steel, which was accompanied with a simultaneous decrease in the double layer capacitance. On the other hand, the morphological study of the metal surface by scanning electron microscope (SEM) and energy dispersive X-ray (EDX) confirmed the effective protection of the carbon steel by the inhibitors against corrosion through the formation of a protective film on its surface. The adsorption characteristics of investigated compounds on carbon steel were assessed at microscopic level using Density Functional Based Tight Binding (DFTB) simulation, which revealed the formation of covalent bonds between inhibitors’ atoms and Fe atoms. Furthermore, additional insights into the compounds’ reactivity and adsorption configurations on steel surface were obtained from global reactivity descriptors and Monte Carlo simulation. The present work’s outcomes are interesting for further design and performance evaluation of effective organic corrosion inhibitors for acid environments. Full article
(This article belongs to the Special Issue Green Corrosion Inhibitors: Natural and Synthetic Organic Inhibitors)
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14 pages, 4535 KiB  
Article
Contact of Rough Surfaces: An Incremental Model Accounting for Strain Gradient Plasticity
by Chunyun Jiang, Weike Yuan, Yanbin Zheng and Gangfeng Wang
Lubricants 2023, 11(3), 140; https://doi.org/10.3390/lubricants11030140 - 15 Mar 2023
Cited by 2 | Viewed by 2448
Abstract
In the contact of rough surfaces, most contact patches are at the scale of micrometers, and thus, their contact deformation can be dominated by the size-dependent plasticity. In this paper, we propose a new strategy to analyze the role of strain gradient plasticity [...] Read more.
In the contact of rough surfaces, most contact patches are at the scale of micrometers, and thus, their contact deformation can be dominated by the size-dependent plasticity. In this paper, we propose a new strategy to analyze the role of strain gradient plasticity in the contact response between a realistic rough surface and a rigid plane, which modifies the incremental contact model based on the mechanism-based gradient plasticity (MSGP) theory. For several different rough surfaces with their topography measured experimentally, the relations between applied load and real contact area are derived in a simple but effective way. It is found that strain gradient plasticity significantly increases the level of mean contact pressure. The hardening effect caused by strain gradient plasticity weakens somewhat as the contact area increases. Compared with previous methods, the present model might be more efficient and of wider application. Full article
(This article belongs to the Special Issue Advances in Contact Mechanics)
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18 pages, 8812 KiB  
Article
Effect of Characteristic Parameters and Distribution of Friction Pair Surface Texture on Lubrication Properties
by Haowen Qiang, Guangming Gao, Sitong Ye, Linkai Cheng and Quandai Wang
Lubricants 2023, 11(3), 139; https://doi.org/10.3390/lubricants11030139 - 14 Mar 2023
Cited by 4 | Viewed by 1865
Abstract
Based on the basic mechanism and bionics principle that texture affects the dynamic pressure effect of lubricating medium, a V-shaped texture that converges along the sliding direction is designed. Through numerical simulation, the optimal geometric parameters and distribution of the V-shaped and textures [...] Read more.
Based on the basic mechanism and bionics principle that texture affects the dynamic pressure effect of lubricating medium, a V-shaped texture that converges along the sliding direction is designed. Through numerical simulation, the optimal geometric parameters and distribution of the V-shaped and textures are obtained. A textured surface with various texture features is prepared using a nanosecond ultraviolet laser with bearing steel as substrate. Tribological experiments with friction and wear tester are performed to investigate the effect of characteristic parameters and distribution of surface texture on the lubrication performance and the lubrication properties are compared and analyzed with that of circular texture. Hence, this investigation provides a research direction to improve the lubrication performance between frictional pairs under fluid lubrication condition to reduce the frictional wear of mechanical systems. The results show that under the conditions of optimal parameters, due to the effect of convergence and extrusion on the flow of lubrication medium, the V-shape texture is better than the circular texture in improving the lubrication performance. The optimal characteristic parameters of V-shape texture are: 60° for the angle between the two wings, 0.53 for shape parameter, 25.9% for area ratio, 13 μm depth, 60% texture area coverage ratio, and the inlet of flow field of the texture distribution position. Full article
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15 pages, 6262 KiB  
Article
Mathematical Analysis of Transverse Wall-Shearing Motion via Cross Flow of Nanofluid
by Faisal Z. Duraihem, Arif Ullah Khan, Salman Saleem and Shawana
Lubricants 2023, 11(3), 138; https://doi.org/10.3390/lubricants11030138 - 14 Mar 2023
Viewed by 1302
Abstract
The investigation of nanofluid’s cross flow, which is caused by a nonlinear stretching sheet within the boundary layer, is presented. The proper mathematical detail is provided for three distinct cross flow instances with the streamwise flow. A uniform transverse stream located far above [...] Read more.
The investigation of nanofluid’s cross flow, which is caused by a nonlinear stretching sheet within the boundary layer, is presented. The proper mathematical detail is provided for three distinct cross flow instances with the streamwise flow. A uniform transverse stream located far above the stretched plate, in one instance, creates the cross flow. Two further situations deal with cross flows caused by surface transverse shearing motions. Weidman’s work was used to find a similarity solution by making the necessary changes. It has been found that two parameters, namely nanoparticle volume frictions ϕ and a nonlinear stretching parameter β, have a significant impact on the flow of fluids in cross flow scenarios. Graphical representations of transverse and streamwise shear stresses and velocity profiles are provided. From this study, we found that nanoparticle volume fraction ϕ reduces the momentum boundary layer in both streamwise and cross flow scenarios while increasing the temperature of the fluid and, hence, increasing thermal boundary layer thickness. The same is observed for the nonlinear stretching parameter β. Full article
(This article belongs to the Special Issue The Tribological Properties and Mathematical Analysis of Nanofluids)
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12 pages, 1933 KiB  
Review
Frictional Properties of Two-Dimensional Nanomaterials as an Additive in Liquid Lubricants: Current Challenges and Potential Research Topics
by Edgar Leonardo Castellanos-Leal, Angel Osuna-Zatarain and Alejandra Garcia-Garcia
Lubricants 2023, 11(3), 137; https://doi.org/10.3390/lubricants11030137 - 14 Mar 2023
Cited by 7 | Viewed by 2286
Abstract
This paper reports on the trend of studying and applying two-dimensional materials in tribology. Two-dimensional materials have improved the ability of lubricants when used as additives to reduce wear between surfaces through the formation of protective layers by sliding on metal surfaces. The [...] Read more.
This paper reports on the trend of studying and applying two-dimensional materials in tribology. Two-dimensional materials have improved the ability of lubricants when used as additives to reduce wear between surfaces through the formation of protective layers by sliding on metal surfaces. The morphology and chemical nature of 2D materials are among the important factors that influence their dispersion in the lubricant medium and determine the final performance of the lubricant for various applications. The mentioned materials in this work are h-BN, graphene, graphene oxide, and MoS2 as part of the transition metal dichalcogenides. The most studied material to date is graphene and its analogs, such as graphene oxide, which, under controlled conditions, can present superlubricity, with COF values less than 0.01. Some methodologies applied to modify two-dimensional materials and examples of the application and characterization of their performance in tribology are mentioned. This review also shows the benefits of using 2D nanomaterials and the synergy generated when two or more of them are combined to not only achieve superlubricity but also improve corrosion resistance and mechanical properties at the interfaces found in contact. Full article
(This article belongs to the Special Issue Tribological Applications of Nano & Submicro Structured Materials)
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14 pages, 3391 KiB  
Article
Analysis of Circulation Characteristics and Heat Balance of High-Speed Rolling Bearing under Oil-Air Lubrication
by Xiqiang Ma, Mian Zhang, Fang Yang, Yujun Xue, Ruijie Gu and Nan Guo
Lubricants 2023, 11(3), 136; https://doi.org/10.3390/lubricants11030136 - 14 Mar 2023
Cited by 3 | Viewed by 2490
Abstract
Aiming to solve the problem of oil-air lubrication failure caused by the high working temperature of high-speed rolling bearings, this study proposes a method, based on the theory of gas-solid two-phase flow and bearing tribology, of predicting the dynamic temperature rise of nonlinear [...] Read more.
Aiming to solve the problem of oil-air lubrication failure caused by the high working temperature of high-speed rolling bearings, this study proposes a method, based on the theory of gas-solid two-phase flow and bearing tribology, of predicting the dynamic temperature rise of nonlinear high-speed rolling bearings under oil-air lubrication conditions. The accuracy of the fluid–structure coupling model is verified by comparing the temperature rise test results of angular contact ball bearing at different speeds. The characteristics of oil-air lubrication circulation and the relationship between the lubrication parameters and the heat balance of the high-speed rolling bearings have been studied. The results show that the gas supply pressure of the system has a significant influence on the continuity and fluctuation of the oil film in the oil pipe nozzle. The initial rise in temperature of the inner and outer rings of the bearing and the fluid domain has a speed threshold value, and the temperature increases linearly with the bearing speed. With the increase in the oil supply and lube oil viscosity of the system, the temperature rise of the outer ring of the bearing increases first, then decreases, and finally increases again. There is an optimal oil supply 5.5 mL and optimize viscosity 68 cSt for the bearing in the work condition. Full article
(This article belongs to the Special Issue Advances in Bearing Lubrication and Thermodynamics 2023)
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15 pages, 3858 KiB  
Article
Running-In Effects of Lubricated Polyether Ether Ketone on Steel for Different Spreading and Sorption Tendencies
by Christof Koplin, Bernadette Schlüter and Raimund Jaeger
Lubricants 2023, 11(3), 135; https://doi.org/10.3390/lubricants11030135 - 13 Mar 2023
Viewed by 1510
Abstract
Polyether ether ketone is a highly resilient thermoplastic that can withstand as an unfilled or filled polymer tribological high loads in high-temperature applications, as it has a high glass and melting temperature. Currently, it attracts interest as a lubricated material for drive systems [...] Read more.
Polyether ether ketone is a highly resilient thermoplastic that can withstand as an unfilled or filled polymer tribological high loads in high-temperature applications, as it has a high glass and melting temperature. Currently, it attracts interest as a lubricated material for drive systems to minimize noise, as a lightweight solution improving the CO2 balance, or in combination with novel lubricants. We have produced friction and wear maps with pin-on-disk tests on steel axial bearing rings and investigated the interaction and running-in behavior with different lubricants, such as different polyalkylene glycols, polyalphaolefin, and various esters. In general, the behavior of polyether ether ketone is hardly influenced by the frictional heat when loaded at room temperature. It shows a lubricant-specific polymer transfer and surface softening. This running-in impact is enhanced if a loading strategy with initial high friction power is applied. The beneficial transfer forms on the track in mixed lubrication on the rough counterpart until an increasing adhesive contact limits this effect. The appearance of a minimal wear coefficient was found below the glass temperature with lubricants strongly sorbing in polyether ether ketones, such as polar polyalkylenglycol or trimellitic acid ester-based lubricants. Using the interfacial energy of the system to derive an energy term describing the tendency to form a stable transfer, systematic trends in the tribological behavior of polyether ether ketone and polyketone could be identified that can be projected on other systems. Full article
(This article belongs to the Special Issue Assessment of Adhesive Wear)
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20 pages, 5659 KiB  
Article
Theoretical and Experimental Flow Characteristics of a Large-Scale Annular Channel in Terms of Deformation Gradient, Eccentricity, and Water Compressibility
by Shendan Zhao, Yinshui Liu, Defa Wu, Chuanmin Wang and Zhenyao Wang
Lubricants 2023, 11(3), 134; https://doi.org/10.3390/lubricants11030134 - 13 Mar 2023
Cited by 7 | Viewed by 2104
Abstract
Hydraulic water plunger pumps have come to be widely used in coal mining, seawater desalination, and oil exploitation due to their high output pressure and large flow characteristics. In a high-pressure large-flow plunger pump, the leakage of the annular channel of the plunger [...] Read more.
Hydraulic water plunger pumps have come to be widely used in coal mining, seawater desalination, and oil exploitation due to their high output pressure and large flow characteristics. In a high-pressure large-flow plunger pump, the leakage of the annular channel of the plunger pair is an essential factor affecting volume efficiency. The axial pressure gradient exists in the fluid inside the annular channel, resulting in the plunger and plunger sleeve forming similar funnel-like shapes. Moreover, the characteristics of large diameter, high working pressure, and low fluid viscosity of the plunger pump will lead to the complicated flow of the annular channel. The influence of eccentricity and structural deformation on leakage is difficult to evaluate. Therefore, considering the deformation gradient and eccentricity of the plunger pair and the compressibility of the water, the deformation equations and leakage equations of the annular channel under the laminar and turbulent flow state are derived in this study. The eccentricity and leakage of the annular channel under different pressure conditions are measured using a built sealing test bench. It is proved that the discrepancy between the calculated model and the experimental results is less than 6% under different pressures, which effectively predicts the sealing performance of plunger pumps. The results show that under the laminar flow condition, the effects of eccentricity, structural deformation, and medium compressibility on leakage are 148%, 4.92%, and 0.92%, respectively. In turbulent conditions, they were 31%, 2.84%, and 1.19%, respectively. Besides, the reasonable material pairing of the plunger friction pair can reduce the variation of leakage due to structural deformation. Full article
(This article belongs to the Special Issue Fluid–Structure Interaction in Bearings and Seals)
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22 pages, 8457 KiB  
Article
Study of the Plastic Behavior of Rough Bearing Surfaces Using a Half-Space Contact Model and the Fatigue Life Estimation According to the Fatemi–Socie Model
by Flavien Foko Foko, Lukas Rüth, Oliver Koch and Bernd Sauer
Lubricants 2023, 11(3), 133; https://doi.org/10.3390/lubricants11030133 - 13 Mar 2023
Cited by 3 | Viewed by 2822
Abstract
A multiscale approach for the fatigue life estimation of rolling bearings is presented in this paper and applied to inner rings of cylindrical roller bearings of the type NU208. The forces acting in the rolling contact are determined from system-oriented modeling at the [...] Read more.
A multiscale approach for the fatigue life estimation of rolling bearings is presented in this paper and applied to inner rings of cylindrical roller bearings of the type NU208. The forces acting in the rolling contact are determined from system-oriented modeling at the macro level. The microscale contact simulations are carried out in a half-space contact model. The stresses on the inner ring are determined and used in the local fatigue approach, according to Fatemi–Socie, for fatigue life estimation. Four surface variants were investigated, one ideally smooth surface and three real (rough) surfaces. The three rough surface variants used different finishing processes: fine ground, hard turned, and rough ground were produced. A load case with a maximum pressure of 2.4 GPa in the roller-inner ring contact was investigated. In addition to the fatigue life estimation, the plasticity behavior (surface topography, resulting contact pressure, and residual stress) of the three manufactured surfaces stood in the focus of the work. As the comparison between experimental and simulated results confirms, good predictions can be made with the simulation model. Full article
(This article belongs to the Special Issue Tribological Studies of Roller Bearings)
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14 pages, 6081 KiB  
Article
Tribological Properties of Nanoparticles in the Presence of MoDTC
by Weiwei Wang, Miao Yu, Jiandong Ma and Yuanming Jia
Lubricants 2023, 11(3), 132; https://doi.org/10.3390/lubricants11030132 - 13 Mar 2023
Cited by 4 | Viewed by 1585
Abstract
Nanoparticles can reduce the friction coefficient and present a self-restorative effect and MoDTC is important as a friction-reducing additive. Both are important for improving lubricating performance. In this study, the tribological performances of nanoparticles in the presence of MoDTC were studied. The chemical [...] Read more.
Nanoparticles can reduce the friction coefficient and present a self-restorative effect and MoDTC is important as a friction-reducing additive. Both are important for improving lubricating performance. In this study, the tribological performances of nanoparticles in the presence of MoDTC were studied. The chemical synthetic and ball-milled nanoparticles were selected as test samples, and tribological performances were evaluated by a block-ring friction test rig. Experimental results show that the synthetic serpentine particle with a 200–800 nm diameter exhibits the lowest friction coefficient and wear, while the ball-milled kaolin particle shows the highest friction and wear. A synergistic lubricating effect has been shown when mixing the synthetic nano serpentine particle and MoDTC. The friction coefficient of “BD + synthetic serpentine” reduced from 0.011 to 0.055 after the compound with MoDTC. At 150 °C, the “BD + synthetic serpentine + MoDTC” improves the production of MoS2 on the friction surface, which further reduced the friction coefficient and wear, while the ball-milled kaolin reduced the production of MoS2, which leads to a high friction coefficient. The synthetic serpentine shows a round surface without any sharp edge, which shows the minimal ploughing effect on the friction surface. Based on the experimental results, the synthetic nanoparticles have the best antiwear and friction reduction performance when compounded with MoDTC. Full article
(This article belongs to the Special Issue Matching Ability and Anti-Wear Properties of Lubricants)
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16 pages, 4124 KiB  
Article
Investigation of Wear Behavior in Self-Lubricating ABS Polymer Composites Reinforced with Glass Fiber/ABS and Glass Fiber/Carbon Fiber/ABS Hybrid
by Aravind Dhandapani, Senthilkumar Krishnasamy, Rajini Nagarajan, Anto Dilip Albert Selvaraj, Senthil Muthu Kumar Thiagamani, Chandrasekar Muthukumar, Faruq Mohammad, Hamad A. Al-Lohedan and Sikiru Oluwarotimi Ismail
Lubricants 2023, 11(3), 131; https://doi.org/10.3390/lubricants11030131 - 13 Mar 2023
Cited by 6 | Viewed by 2248
Abstract
A new hybrid fabrication technique was introduced to manufacture composite laminates made of glass fiber, carbon fiber, and acrylonitrile butadiene styrene (ABS) as the matrix. The fabrication process utilized two different techniques: fused deposition modeling and hot press molding. The composite laminates were [...] Read more.
A new hybrid fabrication technique was introduced to manufacture composite laminates made of glass fiber, carbon fiber, and acrylonitrile butadiene styrene (ABS) as the matrix. The fabrication process utilized two different techniques: fused deposition modeling and hot press molding. The composite laminates were produced using five layers of glass fibers to form glass fiber-reinforced composites (GF/ABS) and five layers of glass fiber and carbon fiber to form glass fiber, carbon fiber-reinforced hybrid composites (GF/CF/ABS), with three layers of glass fibers and two layers of carbon fibers. The fabricated composite laminates were subjected to wear testing at velocities of 2 m/s, 3 m/s, and 4 m/s and under loads of 5 N and 10 N. The results indicated that GF/ABS samples had the lowest wear loss at 5 N and a velocity of 4 m/s. Additionally, the GF/CF/ABS hybrid samples had the lowest coefficient of friction (COF) of 0.28 at 4 m/s. The GF/ABS samples also exhibited the lowest friction force of 1.7 at 5 N and a velocity of 4 m/s. The worn samples were analyzed using a scanning electron microscope to examine the fiber-to-matrix adhesion behavior. GF/ABS and GF/CF/ABS composites are widely used in various applications due to their high strength-to-weight ratio and resistance to wear. These materials could be used in automotive parts, sporting goods, and marine applications. Full article
(This article belongs to the Special Issue Tribology in the Processing of Composite Materials)
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27 pages, 10086 KiB  
Article
The Influences of Different Parameters on the Static and Dynamic Performances of the Aerostatic Bearing
by Jianbo Zhang, Zhifang Deng, Kun Zhang, Hailiang Jin, Tao Yuan, Ce Chen, Zhimin Su, Yitao Cao, Zhongliang Xie, Danyang Wu and Jingping Sui
Lubricants 2023, 11(3), 130; https://doi.org/10.3390/lubricants11030130 - 13 Mar 2023
Cited by 1 | Viewed by 1797
Abstract
Aerostatic bearings have been widely applied to high-rotating speed machines due to their low friction and high rotational speed advantages. The geometry parameters, supply pressure and rotational speed play important roles in the static and dynamic performances of the aerostatic bearings. In this [...] Read more.
Aerostatic bearings have been widely applied to high-rotating speed machines due to their low friction and high rotational speed advantages. The geometry parameters, supply pressure and rotational speed play important roles in the static and dynamic performances of the aerostatic bearings. In this paper, the steady state and dynamic Reynolds equations are solved by the finite difference method (FDM) and used to study the static and dynamic performances of the aerostatic bearings. Then, combined with the motion equation of the rigid rotor-aerostatic bearing system, the linear stability of the aerostatic bearing is also studied. Moreover, based on the theory mentioned above, the influences of the geometry parameters (such as orifice diameter, radial clearance and eccentricity), rotational speed and supply pressure are investigated in detail. It was found that aerostatic bearing geometries, rotational speed and supply pressure had a significant effect on the steady and dynamic performances. Under the low-speed conditions and high supple pressure, the static pressure effect plays the main role in the performances of the aerostatic bearings, while on the contrary, the rotational effect plays the main role. Furthermore, a half-speed whirl may generate under certain conditions. The results also provide useful design guidelines for aerostatic bearings in high-speed machines. Full article
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17 pages, 3253 KiB  
Article
Viscosity and Friction Reduction of Double-End-Capped Polyalkylene Glycol Nanolubricants for Eco-Friendly Refrigerant
by Mohd Zaki Sharif, Wan Hamzah Azmi, Mohd Fairusham Ghazali, Nurul Nadia Mohd Zawawi and Hafiz Muhammad Ali
Lubricants 2023, 11(3), 129; https://doi.org/10.3390/lubricants11030129 - 12 Mar 2023
Cited by 14 | Viewed by 1869
Abstract
In sustainable tribology, researchers are investigating methods to enhance tribological performance by incorporating nanoparticles into lubricants. However, one potential drawback of this strategy is increased lubricant viscosity. The current study aimed to assess the impact of these nanoparticles on the viscosity and coefficient [...] Read more.
In sustainable tribology, researchers are investigating methods to enhance tribological performance by incorporating nanoparticles into lubricants. However, one potential drawback of this strategy is increased lubricant viscosity. The current study aimed to assess the impact of these nanoparticles on the viscosity and coefficient of friction (COF) of the nanolubricants. Three different nanolubricants were synthesized through a two-step process, including mono-nanolubricants (Al2O3/DEC PAG and SiO2/DEC PAG) and hybrid nanolubricants (Al2O3-SiO2/DEC PAG), at volume concentrations between 0.01% and 0.05%. The viscosity and shear flow behavior of these nanolubricants were evaluated using a digital rheometer, while the COF was measured using a Koehler four-ball tribometer. All the nanolubricants showed Newtonian behavior during the experiments. The dynamic viscosity velocity increment of SiO2/DEC PAG was found to be the lowest (1.88%), followed by Al2O3-SiO2/DEC PAG (2.74%) and Al2O3/DEC PAG (3.56%). The viscosity indices of all the nanolubricants were improved only at higher concentrations. At a volume concentration of 0.03%, the Al2O3-SiO2/DEC PAG nanolubricant reduced the COF by up to 8.1%. The results showed that the combination of nanoparticles, temperature, and volume concentration significantly influenced the viscosity and COF of nanolubricants. This study provides essential information for developing high-performance nanolubricants with improved viscosity and COF and advancing environmentally friendly tribology solutions. Full article
(This article belongs to the Special Issue Green Tribology: New Insights toward a Sustainable World 2023)
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22 pages, 5162 KiB  
Article
A Feature-Extraction-Based Adaptive Refinement Method for Solving the Reynolds Equation in Piston–Cylinder System
by Jiashu Yang, Bingquan Zuo, Huixin Luo and Weikang Xie
Lubricants 2023, 11(3), 128; https://doi.org/10.3390/lubricants11030128 - 10 Mar 2023
Viewed by 1420
Abstract
A fast local refinement algorithm based on feature extraction is developed. In the mesh-based Reynolds equation solutions, two refinement features based on the physical parameters of fluid lubrication are firstly defined, namely, pressure value feature and pressure gradient feature. Then, a fast adaptive [...] Read more.
A fast local refinement algorithm based on feature extraction is developed. In the mesh-based Reynolds equation solutions, two refinement features based on the physical parameters of fluid lubrication are firstly defined, namely, pressure value feature and pressure gradient feature. Then, a fast adaptive strategy different from the traditional methods based on residuals or recovery errors is constructed according to the features, which are expected to determine the element needed to be refined. Considering the update requirement of the feature parameters, an adaptive update strategy for feature parameters is also developed. Finally, the feasibility of the scheme is verified on a single-cylinder gasoline engine. Results show that the current algorithm can effectively reduce the computational scale while ensuring the computational accuracy of the mesh-based model, compared with the traditional global and local refinement strategy. Full article
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21 pages, 12028 KiB  
Article
Tribological Performance of a Composite Cold Spray for Coated Bores
by Eduardo Tomanik, Laurent Aubanel, Michael Bussas, Francesco Delloro and Thomas Lampke
Lubricants 2023, 11(3), 127; https://doi.org/10.3390/lubricants11030127 - 10 Mar 2023
Cited by 2 | Viewed by 1971
Abstract
The tribological performance of a thermal sprayed, mirror-like surface with localized protuberances was investigated through tribotests and computational simulation. A composite coating with a 410L steel matrix and M2 tool steel hard particles was applied by the cold spray process as a bore [...] Read more.
The tribological performance of a thermal sprayed, mirror-like surface with localized protuberances was investigated through tribotests and computational simulation. A composite coating with a 410L steel matrix and M2 tool steel hard particles was applied by the cold spray process as a bore coating for combustion engines. The presence of protuberances promoted the quick formation of an antifriction tribofilm when tested with an SAE 0W-16 containing ZDDP and MoDTC, which significantly reduced the asperity friction in comparison to the conventional engine coated bores in reciprocating tribological tests. An in-house computational model using deterministic numerical methods was used for the mixed and hydrodynamic lubrication regime. Lubricant film thickness and friction were simulated for a piston ring versus the proposed coating. The computer simulations showed that the protuberances reduced the hydrodynamic friction by increasing the otherwise very thin oil film thickness of mirror-like surfaces. Although not intuitive, this result was caused by the reducing of the oil film shear rate. Full article
(This article belongs to the Special Issue Tribology in Mobility, Volume II)
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14 pages, 5563 KiB  
Article
Study on Adhesion Force of Graphene under Cylinder–Plane Contact
by Kai Shi, Manfeng Hu and Ping Huang
Lubricants 2023, 11(3), 126; https://doi.org/10.3390/lubricants11030126 - 10 Mar 2023
Viewed by 1899
Abstract
There are many cylinder–plane contacts in microaccelerators, microgyroscopes, and RF switches. Adhesion is one of the main factors affecting the manufacture and use of these micro–nano devices, but its research is insufficient. Graphene is expected to be used in these fields due to [...] Read more.
There are many cylinder–plane contacts in microaccelerators, microgyroscopes, and RF switches. Adhesion is one of the main factors affecting the manufacture and use of these micro–nano devices, but its research is insufficient. Graphene is expected to be used in these fields due to its excellent electrical and mechanical properties. Therefore, it is significant to research the adhesion force of graphene under cylinder–plane. Firstly, the meniscus formation process was introduced using the variable-water-contact-angle method. Secondly, the adhesion force of the graphene surface was measured with a cylindrical atomic-force-microscope probe. Finally, the contact area was considered as a number of nanoscale cylinders in contact with the plane, and the adhesion force of the cylinder–plane model was obtained. The results showed that there was a maximum adhesion force at a relative humidity of 65%. The adhesion force was evidently not time-dependent when the relative humidity was below 45%, because the meniscus cannot be formed on the graphene surface at low relative humidity. While the graphene contact surface formed a meniscus for higher relative humidity, and the adhesion force-versus-time curves first increased and then decreased to stability. Moreover, the relationship between adhesion force and substrate contact angle, roughness, relative humidity, and dwell time was established, and the number of cylinders was determined. The error between the modified theoretical model and the experimental values was only 6%. Full article
(This article belongs to the Special Issue Assessment of Adhesive Wear)
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15 pages, 13301 KiB  
Article
Pivot Stiffness Effect on Transient Dynamic Characteristic of Tilting Pad Journal Bearing-Rotor System Passing through Critical Speed
by Yingze Jin, Qiuli Niu, Yuanpeng Qu and Xiaoyang Yuan
Lubricants 2023, 11(3), 125; https://doi.org/10.3390/lubricants11030125 - 10 Mar 2023
Cited by 3 | Viewed by 1872
Abstract
Tilting pad journal bearings (TPJBs) are widely applied in the high-speed rotor system whose working speed is higher than its critical speed due to excellent hydrodynamic lubrication and stability. Pivot stiffness is one of the key design parameters of TPJBs compared to other [...] Read more.
Tilting pad journal bearings (TPJBs) are widely applied in the high-speed rotor system whose working speed is higher than its critical speed due to excellent hydrodynamic lubrication and stability. Pivot stiffness is one of the key design parameters of TPJBs compared to other journal bearings and has become particularly important for optimizing the performance of TPJB-rotor systems. In order to improve the vibration and critical characteristics of rotor systems, the transient dynamic characteristic of a TPJB-rotor system passing through the critical speed is investigated considering different pivot stiffness ratios. A time-varying dynamics model of a symmetrical single-disc rotor supported by four-pad TPJBs is established considering constant acceleration conditions and nonlinear hydrodynamic bearing force. The disc vibration characteristic, journal vibration characteristic, pad vibration characteristic, and hydrodynamic bearing force are analyzed by using Bode plot, shaft center orbit, pad phase orbit, waterfall plot, and time history. The results show that the pivot stiffness plays a major role in the suppression of resonance amplitude and working amplitude of a TPJB-rotor system, without changing the frequency characteristic of the system. This study provides a theoretical basis for the pivot stiffness design of TPJBs and the vibration suppression of rotor systems. Full article
(This article belongs to the Special Issue Tribological Characteristics of Bearing System)
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20 pages, 18897 KiB  
Article
Tribological Behaviour and Microstructure of an Aluminium Alloy-Based g-SiC Hybrid Surface Composite Produced by FSP
by Jun Liang Tan and Kia Wai Liew
Lubricants 2023, 11(3), 124; https://doi.org/10.3390/lubricants11030124 - 10 Mar 2023
Cited by 3 | Viewed by 1871
Abstract
In this work, the microstructure and wear characteristics of a surface-reinforced composite based on an aluminium alloy with a mixture of graphene nanoplatelets (GNP) and silicon carbide (SiC), referred to as g-SiC, fabricated by Friction Stir Processing (FSP), are investigated. To further improve [...] Read more.
In this work, the microstructure and wear characteristics of a surface-reinforced composite based on an aluminium alloy with a mixture of graphene nanoplatelets (GNP) and silicon carbide (SiC), referred to as g-SiC, fabricated by Friction Stir Processing (FSP), are investigated. To further improve the tribological performance, different volume fractions (0 vol%, 5 vol%, 10 vol% and 15 vol%) of g-SiC-reinforced aluminium alloy are prepared by FSP. It is concluded that the Friction Stir Processed (FSPed) AA5083/g-SiC (15 vol%) specimen has optimum reduction in average friction coefficient (61.13%) and optimum reduction in specimen weight (72.97%). In summary, such hybrid reinforcements effectively improve the mechanical and tribological properties of metals with minimal negative impact on the environment and humans, while reducing material loss and overall manufacturing costs. Full article
(This article belongs to the Special Issue Advances in Surface Engineering and Tribology)
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18 pages, 4906 KiB  
Article
Influence of Tribolayer on Rolling Bearing Fatigue Performed on an FE8 Test Rig—A Follow-up
by Joerg W. H. Franke, Janine Fritz, Thomas Koenig and Daniel Merk
Lubricants 2023, 11(3), 123; https://doi.org/10.3390/lubricants11030123 - 9 Mar 2023
Cited by 2 | Viewed by 2718
Abstract
The tribological contact between raceways and rolling elements is essential for rolling bearing performance and lifetime. The geometrical description of these contacts is well known and can be used in several mechanical simulation tools. The material description, especially of the near-surface volume after [...] Read more.
The tribological contact between raceways and rolling elements is essential for rolling bearing performance and lifetime. The geometrical description of these contacts is well known and can be used in several mechanical simulation tools. The material description, especially of the near-surface volume after interaction with lubricants, is not as simple. In particular, the Schaeffler FE8-25 test with cylindrical roller thrust bearings exhibits different failure modes depending on the lubricant chemistry. The main failure mechanisms of this test are sub-surface fatigue damage due to WECs (White Etching Cracks) and/or surface-induced fatigue damage (SIF). The harsh test conditions with mixed friction at high speeds and multiple slip conditions over the raceway width additionally provides different tribological conditions on a small area. This leads finally to the formation of certain tribological layers on the raceway because of the interaction of the surface with the lubricant chemistry under local frictional energies, which are worth investigating. The characterization of the layers was performed by the two less time-consuming, spatially resolved analysis methods of µXRF and ATR FTIR microscopy adapted by Schaeffler. This paper shows the results of this research and offers new approaches to optimizing rolling bearing testing and predicting the risk of early failures. Full article
(This article belongs to the Special Issue Tribological Studies of Roller Bearings)
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52 pages, 18335 KiB  
Review
A Critical Review of High-Temperature Tribology and Cutting Performance of Cermet and Ceramic Tool Materials
by Ali Elgazzar, Sheng-Jian Zhou, Jia-Hu Ouyang, Zhan-Guo Liu, Yu-Jin Wang and Ya-Ming Wang
Lubricants 2023, 11(3), 122; https://doi.org/10.3390/lubricants11030122 - 9 Mar 2023
Cited by 15 | Viewed by 4388
Abstract
Cermet materials exhibit advanced mechanical and tribological properties, and are widely used for tribology, elevated temperature, and machining applications due to their unique amalgamation of hardness, strength, and toughness. This paper presents a comprehensive overview of various cermet systems and recent advances in [...] Read more.
Cermet materials exhibit advanced mechanical and tribological properties, and are widely used for tribology, elevated temperature, and machining applications due to their unique amalgamation of hardness, strength, and toughness. This paper presents a comprehensive overview of various cermet systems and recent advances in high-temperature tribology and cutting performance of cermet and ceramic tool materials. It outlines microstructural properties, such as lessening grain sizes, obtaining extended grains, lowering grain boundary phase content, amorphous grain boundary phases crystallizing, inter-granular phase strengthening, and managing crack propagation path. Additionally, surface processing or surface modifications, such as surface texturing, appropriate roughness, or coating technique, can optimize the ceramic and cermet tribological performances. The purpose of this study is to present some guidelines for the design of ceramics and cermets with reduced friction and wear and increased cutting performance. The current research progress concerning tribological properties and surface texturing of cutting tool inserts is critically identified. Lubrication techniques are required in commercial applications to increase the lifetime of cutting tools used in harsh conditions. Liquid lubricants are still commonly utilized in relative motion; however, they have the limitations of not working in extreme settings, such as high-temperature environments. As a result, global research is presently underway to produce new solid lubricants for use in a variety of such conditions. This review also provides a quick outline of current research on this topic. Full article
(This article belongs to the Special Issue Recent Advances in High Temperature Tribology)
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