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Lubricants
Volume 11
Issue 2
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Lubricants, Volume 11, Issue 2 (February 2023) – 56 articles

Cover Story (view full-size image): In railway service, sanding is used to overcome low adhesion conditions in wheel–rail contacts. Despite active research, the physical mechanisms causing the friction-increasing effect of sand are still poorly understood. Advanced models including local effects in the contact are therefore beneficial. As a basis for such models, two types of tests on single sand grains are carried out. Firstly, initial breakage behaviour is investigated with focus on the particle fragments’ size and spread as only fragments remaining within a certain radius can influence friction during roll-over. Secondly, single grain crushing tests are conducted under realistic wheel–rail loads, thus showing the formation of solidified clusters of sand fragments. View this paper
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20 pages, 7076 KiB  
Article
An Unsupervised Vibration Noise Reduction Approach and Its Application in Lubrication Condition Monitoring
by Wani J. Morgan and Hsiao-Yeh Chu
Lubricants 2023, 11(2), 90; https://doi.org/10.3390/lubricants11020090 - 19 Feb 2023
Cited by 1 | Viewed by 1638
Abstract
Accelerometers are sensitive devices that capture vibrational fault signatures from industrial machines. However, noise often contaminates these fault signatures and must be eliminated before analysis. A data-driven (DD) denoising algorithm capable of filtering useful vibrational fault signatures from background noises was derived in [...] Read more.
Accelerometers are sensitive devices that capture vibrational fault signatures from industrial machines. However, noise often contaminates these fault signatures and must be eliminated before analysis. A data-driven (DD) denoising algorithm capable of filtering useful vibrational fault signatures from background noises was derived in this study. The algorithm was first validated by comparing its denoised result with a numerically generated ideal signal with a known exact solution. The DD denoising approach reduced the Mean Squared Error (MSE) from 0.459, when no denoising was performed, to 0.068, indicating an 85.2% decrease in noise. This novel approach outperformed the Discrete Wavelet (DW) denoising approach, which had an MSE of 0.115. The proposed DD denoising algorithm was also applied to preprocess vibration data used for the real-time lubrication condition monitoring of the plastic injection molding machine’s toggle clamping system, thereby reducing false positive relubrication alarms. The false positive rates, when analysis was performed on the raw vibration and the DW denoised vibration, were 10.7% and 7.6%, respectively, whereas the DD denoised vibration yielded the lowest false positive rate at 1%. This low false positive rate of the DD denoised vibration indicates that it is a more reliable condition monitoring system, thereby making this technique suitable for the smart manufacturing industry. Full article
(This article belongs to the Special Issue Tribology in Manufacturing and Design)
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12 pages, 2344 KiB  
Article
Analysis of Changes in Soot Content in Engine Oils under Operating Conditions
by Grzegorz Zając, Wojciech Gołębiowski, Małgorzata Szczepanik, Artur Wolak and Marie Sejkorová
Lubricants 2023, 11(2), 89; https://doi.org/10.3390/lubricants11020089 - 18 Feb 2023
Cited by 2 | Viewed by 1684
Abstract
Oil has an enormous influence on the condition of the engine. Determining its degradation allows companies to maximize the availability of a specific vehicle and fleet of vehicles in general. In the evolution of engine oil degradation, one of the variables considered to [...] Read more.
Oil has an enormous influence on the condition of the engine. Determining its degradation allows companies to maximize the availability of a specific vehicle and fleet of vehicles in general. In the evolution of engine oil degradation, one of the variables considered to be the most important is soot content. This article examines the direction and severity of soot content and dispersion changes in engine oil occurring during actual engine operation during four complete change intervals. The oil under study was operated in a city bus. It belonged to the fleet of vehicles of a transport company from new to the mileage of about 200,000 km. Soot content was determined in accordance with ASTM E2412-10, while dispersion size was determined using the dried drop test in accordance with ASTM D7899. The results obtained provide the basis for the conclusion that the direction of change in soot content in each interval is characterized by a high degree of homogeneity. With respect to the degree of soot build-up, a high level of similarity was observed between the intervals studied. The study of change in the degree of oil dispersion using the “drop on blotter” method made it possible to confirm the trend of decreasing dispersion as the run increases. The obtained results led to the development of a statistical model describing these relationships. Full article
(This article belongs to the Special Issue Advances in Sustainable Machining)
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15 pages, 5147 KiB  
Article
Phenomenological Laws of Single Point Contact: Pre-Rolling Contact Resistance through Pendulum
by Igor. Gilavdary, Samir Mekid and Natalia. Riznookaya
Lubricants 2023, 11(2), 88; https://doi.org/10.3390/lubricants11020088 - 17 Feb 2023
Cited by 1 | Viewed by 1313
Abstract
The development results of a single-point contact system set up as a pendulum to study the laws of rolling resistance to contacting bodies at a distance significantly reduced compared to the elastic contact spot size. The designed device uses a physical pendulum sustained [...] Read more.
The development results of a single-point contact system set up as a pendulum to study the laws of rolling resistance to contacting bodies at a distance significantly reduced compared to the elastic contact spot size. The designed device uses a physical pendulum sustained by only one ball on a flat polished surface. The problem of stability of the pendulum swing plane is solved. A phenomenological theory of rolling resistance is described. The surface tension of solids on the contact zone, parameters of the frequency-independent internal friction and the pressure of the adhesion forces are found. Full article
(This article belongs to the Special Issue Advances in Contact Mechanics)
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15 pages, 4070 KiB  
Article
A Study on the Effects of Hybridized Metal Oxide and Carbonaceous Nano-Cutting Fluids in the End Milling of AA6082 Aluminum Alloy
by Vignesh S, Mohammed Iqbal U and Jaharah A. Ghani
Lubricants 2023, 11(2), 87; https://doi.org/10.3390/lubricants11020087 - 17 Feb 2023
Viewed by 1440
Abstract
Finding an alternate solution for supplanting the existing conventional lubricant in machining is a challenge. This work narrows the search down to the use of nano-cutting fluids, as they exhibit excellent properties such as high thermal conductivity and good lubricity. A technical analysis [...] Read more.
Finding an alternate solution for supplanting the existing conventional lubricant in machining is a challenge. This work narrows the search down to the use of nano-cutting fluids, as they exhibit excellent properties such as high thermal conductivity and good lubricity. A technical analysis of the performance of hybrid nano-cutting fluids in the end milling of AA6082 aluminium alloy in a constrained end milling condition is presented. Alumina and carbon nanotubes were chosen in this study for their better physical characteristics and compatibility during machining. Coconut oil was chosen as the base fluid (dispersal medium) as it provides good lubricity and better dispersion of nanoparticles due to its excellent rheological behaviour. The hybrid nanofluid was prepared by mixing alumina-based nanofluid with carbon nanotube nanoparticles in different volumetric concentrations. The thermo-physical properties of the prepared hybrid nanofluid were tested. Furthermore, they were tested for their spread-ability and other mechanical properties. Later, their performances as cutting fluid were studied with the minimum quantity lubrication (MQL) technique, wherein nanoparticle mist was formed and evaluated in the end milling of AA6082 aluminium to reduce the quantity of nanofluids’ usage during end milling. The controllable parameters of speed, feed rate, and type of cutting fluid were chosen, with the levels of cutting speeds and feed rate at 75–125 m/min, and 0.005–0.015 mm/tooth, respectively, and the response parameters studied were surface roughness and tool wear. The results show that better performance is achieved in hybridized nano-cutting fluid, with a sharp improvement of 20%, and 25% in tool wear and surface roughness when compared to the base fluid. This study has explored the concept of hybridization and the capability of nanofluids as cutting fluids that can be used as eco-friendly cutting fluids in manufacturing industries. Full article
(This article belongs to the Special Issue Methods of Application of Cutting Fluids in Machining)
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15 pages, 6645 KiB  
Article
Effect of Cu-Doped Carbon Quantum Dot Dispersion Liquid on the Lubrication Performance of Polyethylene Glycol
by Shusheng Liu, Xiuqian Yu, Enzhu Hu, Enhao Su, Yanjie Chen, Jianping Wang, Kunhong Hu, Yong Xu, Xianguo Hu and Hua Zhong
Lubricants 2023, 11(2), 86; https://doi.org/10.3390/lubricants11020086 - 16 Feb 2023
Cited by 3 | Viewed by 1444
Abstract
Energy saving and reduced consumption of key materials such as bearings in high-end equipment can be realized by synthesizing a new lubricating functional additive, copper-doped carbon quantum dot dispersion liquid (Cu-CQDs) via hydrothermal reaction with glycerol, cupric chloride dihydrate, and choline chloride as [...] Read more.
Energy saving and reduced consumption of key materials such as bearings in high-end equipment can be realized by synthesizing a new lubricating functional additive, copper-doped carbon quantum dot dispersion liquid (Cu-CQDs) via hydrothermal reaction with glycerol, cupric chloride dihydrate, and choline chloride as raw materials. The influence of the dispersion liquid containing Cu-CQDs nanoparticles on the lubricating properties of polyethylene glycol (PEG200) was investigated on a four-ball friction tester. The wear scars of steel balls after friction were analyzed using a scanning electron microscope accompanied by energy dispersive spectroscopy (SEM/EDS), photoelectron microscopy, and Raman spectroscopy. The results revealed the friction and wear mechanism of Cu-CQDs. Cu-CQDs dispersion liquid can significantly enhance the lubrication performance of PEG. The average friction coefficient of PEG containing 2.0 wt% Cu-CQDs dispersion liquid was 40.99% lower than that of pure PEG. The friction and wear mechanism can be ascribed to friction, inducing Cu-CQDs to participate in the formation of boundary lubricating film, resulting in a low friction coefficient and wear scar diameter. Full article
(This article belongs to the Special Issue Advances in Boundary Lubrication)
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20 pages, 7840 KiB  
Article
On the Wear Behavior of Bush Drive Chains: Part I—Characterization of Engine Damage Processes and Development of a Model Test Setup for Pin Wear
by Florian Summer, Philipp Bergmann and Florian Grün
Lubricants 2023, 11(2), 85; https://doi.org/10.3390/lubricants11020085 - 16 Feb 2023
Cited by 1 | Viewed by 1437
Abstract
The present work deals with the tribological characterization of the bush-pin contact in timing chains, with a particular focus on the pin wear processes and the development of a model testing technique suitable for this purpose. With the presented test methodology, both the [...] Read more.
The present work deals with the tribological characterization of the bush-pin contact in timing chains, with a particular focus on the pin wear processes and the development of a model testing technique suitable for this purpose. With the presented test methodology, both the friction and other parameters, such as contact temperatures and the electrical contact resistance between the CrN-coated pin and a steel bush equivalent could be precisely measured during the test procedure, and the input parameters, such as test load, temperature, and test frequency, could be specifically adjusted. In addition, motor components were analyzed in the present study, in order to study the damage processes of application and compare them with those of the model tests. The measured friction and wear processes on the test rig were verified using well-acknowledged design parameters, such as apparent friction energy and linear wear intensity according to Fleischer. The results demonstrated the wear process between the CrN coated spherical steel surface and the plane steel counterpart (mild smoothing wear at moderate loads, and for an advanced wear state with an exposed steel substrate, there was exposed break-outs and deformation, as well as abrasive grooving) and showed that the methodology replicated the wear processes of application and is therefore suitable for characterizing the pin wear of bush drive timing chains. Full article
(This article belongs to the Special Issue Tribology in Mobility, Volume II)
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12 pages, 1641 KiB  
Article
Experimental Verification of the Boundary Element Method for Adhesive Contacts of a Coated Elastic Half-Space
by Iakov A. Lyashenko, Valentin L. Popov and Vadym Borysiuk
Lubricants 2023, 11(2), 84; https://doi.org/10.3390/lubricants11020084 - 15 Feb 2023
Cited by 8 | Viewed by 1355
Abstract
We consider analytical, numerical, and experimental approaches developed to describe the mechanical contact between a rigid indenter and an elastic half-space coated with an elastic layer. Numerical simulations of the indentation process were performed using the recently generalized boundary element method (BEM). Analytical [...] Read more.
We consider analytical, numerical, and experimental approaches developed to describe the mechanical contact between a rigid indenter and an elastic half-space coated with an elastic layer. Numerical simulations of the indentation process were performed using the recently generalized boundary element method (BEM). Analytical approximation of the dependence of contact stiffness on the indenter diameter was used to verify the results of BEM simulations. Adhesive contacts of hard indenters of different shapes with soft rubber layers have been experimentally studied using specially designed laboratory equipment. The comparison of the results from all three implemented methods shows good agreement of the obtained data, thus supporting the generalized BEM simulation technique developed for the JKR limit of very small range of action of adhesive forces. It was shown that the half-space approximation is asymptotical at high ratios of layer thickness h to cylindrical indenter diameter D; however, it is very slowly. Thus, at the ratio h/D = 3.22, the half-space approximation leads to 20% lower contact stiffness compared with that obtained for finite thickness using both an experiment and simulation. Full article
(This article belongs to the Special Issue Advances in Contact Mechanics)
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25 pages, 35869 KiB  
Article
Effect of the Distribution Characteristics of TiC Phases Particles on the Strengthening in Nickel Matrix
by Dingfeng Qu, Min Zheng, Zongxiao Zhu, Wenbang Chen, Weihua Chen, Tianzuo Shi and Jie Chen
Lubricants 2023, 11(2), 83; https://doi.org/10.3390/lubricants11020083 - 15 Feb 2023
Cited by 2 | Viewed by 1090
Abstract
Molecular dynamics (MD) was used to simulate the effect of TiC particles distribution on the tribological behavior of the reinforced composites. The mechanical properties, friction coefficient, number of wear atoms, stress and temperature, and microscopic deformation behavior of TiC/Ni composites during nano-friction were [...] Read more.
Molecular dynamics (MD) was used to simulate the effect of TiC particles distribution on the tribological behavior of the reinforced composites. The mechanical properties, friction coefficient, number of wear atoms, stress and temperature, and microscopic deformation behavior of TiC/Ni composites during nano-friction were systematically investigated by MD to reveal the effect of TiC distribution on the friction removal mechanism of the material. It was found that the larger the radius of the TiC particles, or the shallower the depth of the TiC particles, the easier it was to generate stress concentrations around the TiC particles, forming a high dislocation density region and promoting the nucleation of dislocations. This leads to severe friction hardening, reducing the atomic number of abrasive chips and reducing the friction coefficient by approximately 6% for every 1 nm reduction in depth, thus improving the anti-wear capacity. However, when the radius of the TiC particles increases and the thickness from the surface deepens, the elastic recovery in material deformation is weakened. We also found that the presence of the TiC particles during the friction process changes the stress state inside the workpiece, putting the TiC particles and the surrounding nickel atoms into a high-temperature state and increasing the concentrated temperature by 30 K for every 1 nm increase in depth. Nevertheless, the workpiece atoms below the TiC particles invariably exist in a low-temperature state, which has a great insulation effect and improves the high-temperature performance of the material. The insight into the wear characteristics of TiC particles distribution provides the basis for a wide range of TiC/Ni applications. Full article
(This article belongs to the Special Issue Friction and Wear on the Atomic Scale)
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22 pages, 41774 KiB  
Article
Investigation on Machinability Characteristics of Inconel 718 Alloy in Cryogenic Machining Processes
by Le Gong, Yu Su, Yong Liu, Wei Zhao, Aqib Mashood Khan and Muhammad Jamil
Lubricants 2023, 11(2), 82; https://doi.org/10.3390/lubricants11020082 - 15 Feb 2023
Cited by 4 | Viewed by 1372
Abstract
In this innovative work, Inconel 718 alloy turning simulation models under dry and cryogenic machining (Cryo) conditions are developed. The machinability characteristics of the aforementioned alloy were assessed with relation to cutting temperature (Tct) and cutting force ( [...] Read more.
In this innovative work, Inconel 718 alloy turning simulation models under dry and cryogenic machining (Cryo) conditions are developed. The machinability characteristics of the aforementioned alloy were assessed with relation to cutting temperature (Tct) and cutting force (Fcf). The comparison of the Tct and Fcf results from simulation with those obtained under the identical experimental conditions served as additional evidence of the effectiveness of the suggested simulation model. By varying the cutting speed, the reduction in Tct under Cryo conditions was 9.36% to 11.98% compared to dry cutting. Regarding the force comparison under experiment and simulation, the average difference between the simulation and experimental values for the main cutting force (Fc) was 13.73%, whereas the average deviation for the feed force (Ff) was 14.63%. Response surface methodology (RSM) was employed to build the forecasting models for Tct and Fcf in cryogenic settings. These mathematical models showed excellent predictive performance and were able to estimate the Tct and Fcf under machining operations settings, according to the present research. When compared to dry cutting, Cryo reduced the cutting temperature, which had a positive impact on the alloy’s machinability. Full article
(This article belongs to the Special Issue Advances in Sustainable Cooling/Lubrication Techniques for Improving the Tribological Characteristics and Machining Performance)
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15 pages, 4470 KiB  
Article
Accelerated Thermo-Catalytic Degradation of Perfluoropolyether (PFPE) Lubricants for Space Applications
by Milena Gleirscher, Archim Wolfberger, Sandra Schlögl, Małgorzata Hołyńska and Andreas Hausberger
Lubricants 2023, 11(2), 81; https://doi.org/10.3390/lubricants11020081 - 14 Feb 2023
Cited by 5 | Viewed by 2251
Abstract
Perfluoropolyethers (PFPE) are a class of frequently used lubricants in space applications due to their high stability under demanding conditions. However, they are susceptible to aging, with the aging mechanism being dependent on the specific material combination and storage condition. A Lewis-acid-induced thermo-catalytic [...] Read more.
Perfluoropolyethers (PFPE) are a class of frequently used lubricants in space applications due to their high stability under demanding conditions. However, they are susceptible to aging, with the aging mechanism being dependent on the specific material combination and storage condition. A Lewis-acid-induced thermo-catalytic degradation mechanism is of concern, for example, under steel-on-steel sliding contact, and can be relevant for long-term storage (LTS). Accelerated aging experiments were performed on Fomblin® Z25 and Krytox™ 143AC to investigate thermal stability under the influence of iron(III) fluoride (FeF3) at elevated temperatures (180 °C, 200 °C, and 220 °C) up to a total duration of 2000 h. The degradation effects were monitored via selected analysis techniques: mass loss of the samples due to degradation and subsequent evaporation during aging, FTIR spectroscopy to investigate changes to the chemical structure, dynamic viscosity measurements for the investigation of a potential impact due to changes in molecular mass, and a ball-on-disc tribological test setup to obtain friction behavior of the aged lubricants. Distinct differences between the two types of PFPE lubricants regarding stability to thermo-catalytic degradation were found. Fomblin® Z25 was highly affected by the presence of FeF3 within the selected aging conditions, exhibiting high mass loss, a significant drop in dynamic viscosity, and an increased coefficient of friction due to degradation reactions. Full article
(This article belongs to the Special Issue New Challenges in Tribology of Space Mechanisms)
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13 pages, 2032 KiB  
Article
A Computational Study on the Role of Lubricants under Boundary Lubrication
by Walter Holweger, Luigi Bobbio, Zhuoqiong Mo, Jörg Fliege, Bernd Goerlach and Barbara Simon
Lubricants 2023, 11(2), 80; https://doi.org/10.3390/lubricants11020080 - 13 Feb 2023
Cited by 2 | Viewed by 1122
Abstract
The knowledge of how lubricants contribute to the operational life of a drive train is unclear until now, despite the fact that plenty of literature is available. A novel concept is presented in order to estimate the wear appearing in bearings addressed to [...] Read more.
The knowledge of how lubricants contribute to the operational life of a drive train is unclear until now, despite the fact that plenty of literature is available. A novel concept is presented in order to estimate the wear appearing in bearings addressed to the regime of mixed friction with respect to the composition and the so-called “inner” structure of the lubricant. In doing so, the composition is turned into a set of predictors describing the dipolar and inducible dipolar properties of all components as an activity amongst them and toward the surface. The results show that the activity of the solvated specie apparent, stated as the “inner” structure of the lubricant, is closely related to the surface activity and the expected wear. The technique presented here allows a fast computational procedure such that a given lubricant, once known by its constituents, could be explored with respect to the expected wear. Reducing time-consuming tests is desirable by the fact that new materials are forthcoming as a consequence of regulations and evolving green technology. Full article
(This article belongs to the Special Issue Sustainable Elastohydrodynamic Lubrication)
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21 pages, 6354 KiB  
Article
Sustainable Vegetable Oil-Based Minimum Quantity Lubrication Assisted Machining of AZ91 Magnesium Alloy: A Grey Relational Analysis-Based Study
by Assem Alshibi, Abdelrahman Nasreldin and Salman Pervaiz
Lubricants 2023, 11(2), 79; https://doi.org/10.3390/lubricants11020079 - 12 Feb 2023
Cited by 4 | Viewed by 1697
Abstract
The implementation of magnesium alloys in a multitude of industries has been proven to be a mere effect of their attractive light weight, corrosion resistant, and biodegradable properties. These traits allow these materials to portray an excellent sustainable machinability. However, with increasing demand, [...] Read more.
The implementation of magnesium alloys in a multitude of industries has been proven to be a mere effect of their attractive light weight, corrosion resistant, and biodegradable properties. These traits allow these materials to portray an excellent sustainable machinability. However, with increasing demand, it is essential to explore sustainable means of increasing production while mitigating reductions in sustainability. The current work aims to assess and optimize the high-speed machinability of AZ91 with the use of a vegetable oil-based minimum quantity lubrication (MQL) system using the grey relational analysis (GRA) on the basis of chip morphology and tool wear. The investigation entailed a full factorial design with MQL flow rate, cutting speed, and feed rate as the control parameters and flank wear, land width, chip contact length, saw-tooth pitch, chip segmentation ratio, chip compression ratio, and shear angle as the output responses. The optimal control parameters predicted and experimentally confirmed were an MQL flow rate of 40 mL/h, cutting speed of 300 m/min, and feed rate of 0.3 mm/rev. The usage of said optimal parameters results in a grey relational grade improvement of 0.2675 in comparison to the referenced first experimental run. Moreover, the MQL flow rate was regarded as the critical variable with a contribution percentage of 20% for the grey relational grade. Full article
(This article belongs to the Special Issue Minimum Quantity Lubrication: Environmental Alternatives in Processing)
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17 pages, 5344 KiB  
Article
Numerical Analysis of Friction Reduction and ATSLB Capacity of Lubricated MTS with Textured Micro-Elements
by Xigui Wang, Hui Huang, Jingyu Song, Yongmei Wang and Jiafu Ruan
Lubricants 2023, 11(2), 78; https://doi.org/10.3390/lubricants11020078 - 11 Feb 2023
Viewed by 1074
Abstract
The simulation analysis numerically investigates the thermoelastic lubricated interfacial Textured Micro-Element (TME) load-bearing contact, a theoretical model is proposed, and the effective friction reduction and Anti-Thermoelastic Scuffing Load bearing (ATSLB) capacity between random rough Meshing Teeth Surfaces (MTS) are presented, the mechanism linking [...] Read more.
The simulation analysis numerically investigates the thermoelastic lubricated interfacial Textured Micro-Element (TME) load-bearing contact, a theoretical model is proposed, and the effective friction reduction and Anti-Thermoelastic Scuffing Load bearing (ATSLB) capacity between random rough Meshing Teeth Surfaces (MTS) are presented, the mechanism linking interfacial thermoelastic lubrication, TME meshing friction reduction and ATSLB is revealed. The real contact domain area between MTS with multi-scale Micro-Element Textures (MET) is obtained for the numerical calculation of the three-dimensional equivalent TME contact volume, which is the correlation bridge between friction reduction and ATSLB of the thermoelastic lubrication interface. The proposed theoretical model predicts the time-varying behaviour of the textured meshing interface friction reduction with TME contact load under thermoelastic lubrication conditions. Numerical simulations show that the textured interface meshing volume is the key to solving the load-bearing problem of line contact between randomly rough teeth surfaces. The friction coefficients of the MTS are reduced by 13–24%. The lubricated load-bearing and friction reduction behaviour between the textured MTS is quantified by the thermoelastic voids of TME interface and actual meshing volume ratio, which provides a new perspective for further insight into the lubrication and friction reduction behaviour between the MTS with multi-scale MET-ATSLB coupling mechanism. Full article
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17 pages, 16399 KiB  
Article
Simulation Study on Bearing Lubrication Mechanism and Friction Characteristics of the Biomimetic Non-Smooth Surface of a Cross-Scale, Second-Order Compound Microstructure
by Yingna Liang, Cunyuan Wang, Zongyi Zhang, Zhepeng Zhang, Wei Wang, Hao Xing, Tianyuan Guan and Dianrong Gao
Lubricants 2023, 11(2), 77; https://doi.org/10.3390/lubricants11020077 - 11 Feb 2023
Cited by 3 | Viewed by 1194
Abstract
The reasonable design of biomimetic non-smooth surfaces is a novel and effective way to solve problems such as the poor lubricity and serious friction and wear of friction pairs of seawater axial piston pumps. Inspired by cross-scale, second-order compound microstructures on the surfaces [...] Read more.
The reasonable design of biomimetic non-smooth surfaces is a novel and effective way to solve problems such as the poor lubricity and serious friction and wear of friction pairs of seawater axial piston pumps. Inspired by cross-scale, second-order compound microstructures on the surfaces of some living organisms, a hydrodynamic lubrication model of a slipper pair with a surface featuring spherical pits containing spherical convex hulls was built. This study analyzed the bearing lubrication mechanism and friction characteristics of cross-scale, second-order compound microstructure from the microflow perspective via the CFD method and optimized the working and geometric parameters using a hybrid orthogonal test scheme. The study’s results show that the cross-scale, second-order compound microstructure can produce a superimposed hydrodynamic pressure effect to improve the bearing capacity of the lubrication film of a slipper pair, reducing the friction coefficient. The orders of factors (the working parameter and geometric parameters) under multiple indices (the total pressure-bearing capacity and the friction coefficient) were found. The optimal combination is a spherical pit with a first order diameter of 0.7 mm, a first order depth-to-diameter ratio of 0.1, an area rate of 20%, an arrangement angle of α/3 and a spherical convex hull with a second order diameter of 0.13 mm, and a second order depth-to-diameter ratio of 0.3. Compared to a smooth surface and a first-order, non-smooth microstructure, the cross-scale, second-order compound microstructure has an 11.0% and 8.9% higher total pressure-bearing capacity, respectively, and the friction coefficient decreased by 9.5% and 5.4%, respectively. Full article
(This article belongs to the Topic Advanced Manufacturing and Surface Technology)
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15 pages, 9523 KiB  
Article
Experimental Investigation of Oil Transport during Low Load to High Load Transient in Internal Combustion Engines
by Mo Li and Tian Tian
Lubricants 2023, 11(2), 76; https://doi.org/10.3390/lubricants11020076 - 11 Feb 2023
Cited by 1 | Viewed by 1091
Abstract
Reducing the Lubricating Oil Consumption (LOC) has been a critical focus for engine manufacturers. LOC not only depends on engine operating condition but also the history of the operating condition variations. This work seeks to understand the oil transport in the ring pack [...] Read more.
Reducing the Lubricating Oil Consumption (LOC) has been a critical focus for engine manufacturers. LOC not only depends on engine operating condition but also the history of the operating condition variations. This work seeks to understand the oil transport in the ring pack during the low load to high load transient through experimental investigations. An optical engine with 2D Laser Induced Fluorescence (2D-LIF) technique, equipped with a modern low-tension Three-Piece Oil Control Ring (TPOCR), was applied to investigate the oil transport in the ring pack. It was found that, after the engine stayed under the blowby separation line long enough, a sudden increase to high load can result in a huge increase of oil ejection to the liner from the top ring groove in the expansion strokes. The mechanism behind it is that, when the load is increased, the oil accumulated inside the top ring groove during the low load condition is pushed out by the gas flow after the peak cylinder pressure is reached. Different combinations of load, speed, rate of change in load and time duration at low load were tested to examine their influence on this leakage mechanism. An operation with a gradual increase of engine load was found to be able to reduce the amount of oil leaked to the liner by releasing more oil to the second land. These findings can help the effort to reduce the oil emission (OE) generated from Spark Ignited (SI) engines equipped with TPOCR in the real-world transient driving conditions as well as the emission tests. Full article
(This article belongs to the Special Issue Gear Load-Independent Power Losses)
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23 pages, 8619 KiB  
Article
Establishment and Calibration of a Digital Twin to Replicate the Friction Behaviour of a Pin-on-Disk Tribometer
by Erik Hansen, Gerda Vaitkunaite, Johannes Schneider, Peter Gumbsch and Bettina Frohnapfel
Lubricants 2023, 11(2), 75; https://doi.org/10.3390/lubricants11020075 - 10 Feb 2023
Cited by 4 | Viewed by 1693
Abstract
While the modification of surface contacts offers significant potential for friction reduction, obtaining an underlying consistent friction behaviour of real-life experiments and virtual simulations is still an ongoing challenge. In particular, most works in the literature only consider idealised geometries that can be [...] Read more.
While the modification of surface contacts offers significant potential for friction reduction, obtaining an underlying consistent friction behaviour of real-life experiments and virtual simulations is still an ongoing challenge. In particular, most works in the literature only consider idealised geometries that can be parametrised with simple analytical functions. In contrast to this approach, the current work describes the establishment of a digital twin of a pin-on-disk tribometer whose virtual geometry is completely replicated from real-life post-test topography measurements and fed into a two-scale mixed lubrication solver. Subsequently, several calibration steps are performed to identify the sensitivities of the friction behaviour towards certain geometry features and enable the digital twin to robustly represent the Stribeck curve of the physical experiments. Furthermore, a derivation of the Hersey number is used to generalise the obtained friction behaviour for different dynamic viscosities and allow the validation of the presented method. Full article
(This article belongs to the Special Issue Fundamentals in Building Tribological Digital Twins of Machine Elements)
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21 pages, 2349 KiB  
Review
Improvement of Generative Adversarial Network and Its Application in Bearing Fault Diagnosis: A Review
by Diwang Ruan, Xuran Chen, Clemens Gühmann and Jianping Yan
Lubricants 2023, 11(2), 74; https://doi.org/10.3390/lubricants11020074 - 10 Feb 2023
Cited by 8 | Viewed by 2459
Abstract
A small sample size and unbalanced sample distribution are two main problems when data-driven methods are applied for fault diagnosis in practical engineering. Technically, sample generation and data augmentation have proven to be effective methods to solve this problem. The generative adversarial network [...] Read more.
A small sample size and unbalanced sample distribution are two main problems when data-driven methods are applied for fault diagnosis in practical engineering. Technically, sample generation and data augmentation have proven to be effective methods to solve this problem. The generative adversarial network (GAN) has been widely used in recent years as a representative generative model. Besides the general GAN, many variants have recently been reported to address its inherent problems such as mode collapse and slow convergence. In addition, many new techniques are being proposed to increase the sample generation quality. Therefore, a systematic review of GAN, especially its application in fault diagnosis, is necessary. In this paper, the theory and structure of GAN and variants such as ACGAN, VAEGAN, DCGAN, WGAN, et al. are presented first. Then, the literature on GANs is mainly categorized and analyzed from two aspects: improvements in GAN’s structure and loss function. Specifically, the improvements in the structure are classified into three types: information-based, input-based, and layer-based. Regarding the modification of the loss function, it is sorted into two aspects: metric-based and regularization-based. Afterwards, the evaluation metrics of the generated samples are summarized and compared. Finally, the typical applications of GAN in the bearing fault diagnosis field are listed, and the challenges for further research are also discussed. Full article
(This article belongs to the Special Issue Recent Advances in Machine Learning in Tribology)
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28 pages, 5057 KiB  
Article
Effect of Chamfer Form and Parameters on the Characteristics of Finite Length Journal Bearing under Impact Load
by Hazim U. Jamali, Hakim S. Sultan, Oday I. Abdullah, Adnan Naji Jameel Al-Tamimi, Luay Hashem Abbud, Alessandro Ruggiero and Zahraa A. Al-Dujaili
Lubricants 2023, 11(2), 73; https://doi.org/10.3390/lubricants11020073 - 10 Feb 2023
Cited by 4 | Viewed by 1306
Abstract
Journal bearings in typical applications are subjected to misalignment due to several causes, such as shaft deformation under load and errors related to the installation and manufacturing processes. Misalignment has well-known severe negative consequences on the performance of the bearings. This paper deals [...] Read more.
Journal bearings in typical applications are subjected to misalignment due to several causes, such as shaft deformation under load and errors related to the installation and manufacturing processes. Misalignment has well-known severe negative consequences on the performance of the bearings. This paper deals with the bearing chamfer to reduce these consequences of misalignment, and two forms of bearing edge modification are considered in the analysis. These forms are linear and curved chamfering of the bearing edges, where the height of the chamfer in the circumferential direction and the length of the modification in the longitudinal direction are considered as geometrical design parameters. The investigation includes a numerical solution of the hydrodynamic lubrication problem of finite length journal bearing, considering 3D misalignment cases using the finite difference method. This includes the assessment of the chamfer forms and their effects on the bearing performance in terms of the main bearing design parameters. Furthermore, the stability of the chamfered bearings is also investigated under impact load. Results showed that both chamfer forms are beneficial for a certain limit of the design parameters in reducing the maximum pressure and coefficient of friction and in elevating the film thickness levels, extending the range of misalignment in which the journal bearing can operate safely. In addition, the chamfered bearings in both forms showed more stability range in terms of the critical speed and shaft center trajectories under impact load. The bearings with the curved chamfer, where the slope is continuous at the start of modification, showed more uniform film thickness levels, and their shaft center trajectories were closer to the perfectly aligned bearing in the stable operating range of the system. Full article
(This article belongs to the Special Issue Tribology Problems in Rotating Machinery)
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23 pages, 29574 KiB  
Article
Effect of Sliding on the Relation of Tribofilm Thickness and Wear
by Martin Jech, Maria L. Miranda-Medina, Thomas Wopelka, Christian Tomastik and Carsten Gachot
Lubricants 2023, 11(2), 72; https://doi.org/10.3390/lubricants11020072 - 10 Feb 2023
Cited by 2 | Viewed by 1259
Abstract
The formation of tribofilms depends on temperature, shear stress, availability of the related chemical components, and characteristics of the near surface region, e.g., roughness and surface chemistry. The purpose of a tribofilm is to separate two sliding surfaces, thus preventing or limiting wear. [...] Read more.
The formation of tribofilms depends on temperature, shear stress, availability of the related chemical components, and characteristics of the near surface region, e.g., roughness and surface chemistry. The purpose of a tribofilm is to separate two sliding surfaces, thus preventing or limiting wear. This research article aims for the first time at a systematic approach to elucidate on a fundamental level the interplay between tribofilm formation in particular thickness and wear behavior in the boundary and mixed lubrication regime. For this, load, temperature and sliding frequency as most relevant parameters are taken into consideration. For that purpose, a piston ring and cylinder liner configuration in an oscillating tribometer was chosen as a model system, with the top dead centre conditions in internal combustion engines of passenger cars as the testing regime. The amount of wear produced during the tribotests is continuously monitored by means of the Radio-Isotope Concentration (RIC) method. The tribofilm is investigated via Atomic Force Microscopy (AFM), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) and X-ray Photoelectron Spectroscopy (XPS). The results clearly indicate that the impact of load on the wear rate can be seen in an Archard-like dependency, but changes of temperature and sliding velocity in the boundary to mixed lubrication regime imply a non-linear ratio between wear and tribofilm formation. Full article
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16 pages, 7612 KiB  
Article
New Optimized Lubricating Blend of Peanut Oil and Naphthenic Oil Additivated with Graphene Nanoparticles and MoS2: Stability Time and Thermal Conductivity
by Rashmi Walvekar, Shubrajit Bhaumik, Thachnatharen Nagarajan, Mohammad Khalid, Abdul Khaliq Rasheed, Thummalapalli Chandra Sekhara Manikyam Gupta and Viorel Paleu
Lubricants 2023, 11(2), 71; https://doi.org/10.3390/lubricants11020071 - 09 Feb 2023
Cited by 1 | Viewed by 2023
Abstract
Lubricants are essential to machinery life, as they play a crucial role in controlling and diminishing the friction and wear between moving parts when operated under extreme conditions. To this end, due to tight environmental conditions, manufacturers are looking for alternative solid lubricants [...] Read more.
Lubricants are essential to machinery life, as they play a crucial role in controlling and diminishing the friction and wear between moving parts when operated under extreme conditions. To this end, due to tight environmental conditions, manufacturers are looking for alternative solid lubricants to be dispersed in base liquid lubricants. MoS2 and graphene are solid lubricants that provide low frictional properties and high thermal stability in both oxidizing and non-oxidizing environments. This research offers a new lubricant with improved thermal conductivity that combines the synergistic effect of graphene and MoS2 in a blend of vegetable oil (peanut) and naphthenic oil. The ratio of peanut oil and naphthenic oil varies from 1:3–3:1. A fixed composition of 4.34 wt.% palm oil methyl ester (POME) is added to enhance the anti-wear property further. Graphene and MoS2 concentrations varied between 1:2–5:2, respectively. This nanoparticle additive oil blend is physically mixed using a water bath sonication for 4 h. The stability of the blend lubricant dispersed with MoS2 and graphene is studied using a UV-Vis spectrophotometer for 25 days. The effect of various concentrations of graphene, MoS2, peanut oil, and naphthenic oil on the thermal conductivity of the nanolubricant is also studied as a function of temperature (25 °C–55 °C). Artificial neural network models were used for the parametric investigation of the nanolubricant. It is found that the stability of the formulated nanolubricant increased with peanut oil composition above 25 wt.%. The results show that the 3:1 blend ratio showed higher stability for hybrid MoS2-based lubricants. Similarly, the highest thermal conductivity is observed for 100 wt.% naphthenic oil with a 1:2 ratio of graphene–MoS2 at 55 °C. Full article
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14 pages, 8469 KiB  
Article
Numerical Simulation of a New Designed Mechanical Seals with Spiral Groove Structures
by Tao He, Qiangqiang Zhang, Ying Yan, Jintong Dong and Ping Zhou
Lubricants 2023, 11(2), 70; https://doi.org/10.3390/lubricants11020070 - 09 Feb 2023
Cited by 4 | Viewed by 1679
Abstract
The spiral groove seal has a strong hydrodynamic effect, but it has poor pollution resistance at the seal’s end and has unfavorable sealing stability. Circumferential waviness seals can use the fluid to clean the surface and have a strong ability to self-rush, protecting [...] Read more.
The spiral groove seal has a strong hydrodynamic effect, but it has poor pollution resistance at the seal’s end and has unfavorable sealing stability. Circumferential waviness seals can use the fluid to clean the surface and have a strong ability to self-rush, protecting the main cover from contamination. This study presents a novel wave-tilt-dam seal design that integrates spiral groove structures to enhance the hydrodynamic performance of circumferential waviness seals. The objective of the research is to evaluate the mechanical effectiveness of this new design through simulation modeling, with a focus on the impact of structural parameters such as rotational speed and seal pressure on the hydrodynamic behavior under various operating conditions. The results of the study indicate that the new structure effectively improves the hydrodynamic performance of the liquid seal, resulting in a significant increase in film rigidity. Additionally, the study identifies optimal values for structural parameters under specific conditions. By addressing the limitations of traditional spiral groove seals and improving their hydrodynamic performance, this research contributes to the advancement of seal technology. Full article
(This article belongs to the Special Issue Fluid–Structure Interaction in Bearings and Seals)
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23 pages, 5578 KiB  
Article
Research on Shaft Current Damage Identification of Variable Condition Motor Bearings Based on Multiscale Feature Label Propagation and Manifold Metric Transfer
by Guangbin Wang, Shubiao Zhao, Zhixian Zhong and Dong Zeng
Lubricants 2023, 11(2), 69; https://doi.org/10.3390/lubricants11020069 - 09 Feb 2023
Cited by 1 | Viewed by 1061
Abstract
The current damage is the most stubborn and difficult fault of high-power motor bearings because its vibration characteristics are easily confused with those of ordinary bearing mechanical faults. If it is discriminated as an ordinary mechanical fault without electrical insulation protection, the current [...] Read more.
The current damage is the most stubborn and difficult fault of high-power motor bearings because its vibration characteristics are easily confused with those of ordinary bearing mechanical faults. If it is discriminated as an ordinary mechanical fault without electrical insulation protection, the current damage of bearing shafts will still repeatedly appear. Aiming at the problem that it is difficult to identify the bearing current damage fault under variable working conditions, a bearing shaft current damage identification method based on multiscale feature label propagation and manifold metric transfer (MFLP-MMT) is proposed. Firstly, the multiscale sub-band signal is obtained by wavelet packet decomposition, and the multiscale sub-band fuzzy entropy is obtained by calculating its fuzzy entropy. Then, according to the extracted features, a neighbor graph is constructed on the source domain of the known fault label to obtain the pseudo label of the target domain sample, and the source domain label information is gradually diffused by way of the graph label propagation. The multiscale sub-band fuzzy entropy of the sample is mapped to the low-dimensional manifold space by locality preserving projections (LPP), and the source domain samples close to the target domain are given higher weights by cross-domain density ratio estimation to solve the problem of domain offset. Combined with the label samples of the target domain in label propagation, the manifold distance metric is learned to minimize the intra-class distance and maximize the inter-class distance in the domain and eliminate the overlapping phenomenon in the domain. By increasing the range of label propagation after each iteration, the label propagation error of the leading graph is gradually reduced, and unsupervised metric transfer learning is realized. The experimental results show that the new method is superior to the semi-supervised transfer learning method in fault identification ability; the highest fault identification accuracy can reach 100% and it has a good robustness. Full article
(This article belongs to the Special Issue Condition Monitoring and Simulation Analysis of Bearings)
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20 pages, 14497 KiB  
Article
Improvement of Frictional Property of AISI D2 Tool Steel Surface against JIS SPFC 980Y Advanced High-Strength Steel by Using Laser Texturing Process
by Witthaya Daodon and Viboon Saetang
Lubricants 2023, 11(2), 68; https://doi.org/10.3390/lubricants11020068 - 08 Feb 2023
Cited by 4 | Viewed by 1447
Abstract
Surface friction in metal forming processes can be reduced by creating lubricant reservoirs at the interface between surfaces in contact, and a laser texturing process can be employed to produce the micro-dimples that act as the reservoirs on the surfaces. However, the role [...] Read more.
Surface friction in metal forming processes can be reduced by creating lubricant reservoirs at the interface between surfaces in contact, and a laser texturing process can be employed to produce the micro-dimples that act as the reservoirs on the surfaces. However, the role of the laser texturing parameters in the friction reduction of tool steel surfaces has still received very little attention. Therefore, this study aims to reduce the friction of the AISI D2 tool steel surface on which a nanosecond pulse laser was applied to create an array of micro-lubricant pockets for trapping lubricant. The effects of laser power, irradiation duration, and spacing distance between pockets on the pocket diameter, size of the heat-affected zone, surface friction, and wettability were investigated in this work. The average laser power in the range from 5 to 10 W and laser irradiation duration of 0.02 to 0.10 s were applied. The results showed that the increase in laser power and irradiation duration enlarged the pocket diameter and heat-affected zone. The largest pocket diameter of 40 µm was achievable by using 10 W laser power together with 0.10 s irradiation time. The pin-on-disc method was employed to determine the friction coefficient of the tool steel, where JIS SPFC 980Y advanced high-strength steel was used as a disc. The friction coefficient of laser-textured with different spacing distances of 150, 200, and 250 µm versus untextured surfaces was compared and found to vary depending on the applied normal load. The laser-textured surface having a pocket spacing distance of 150 µm and pocket density of 5.6%, offered the lowest friction coefficient of 0.097 on average for all tested loads, whereas the average friction coefficient of the untextured surface was 0.117. In addition, the wettability of textured surfaces was insignificantly changed compared to that of untextured ones, so the micro-lubricant pockets did not cause oleophobicity affecting the performance of lubrication. Well-defined micro-pockets using the most appropriate laser parameters, i.e., 10 W laser power with 0.10 s irradiation duration and 150 µm spacing distance, successfully reduced the sliding friction of contacting couples between the laser-textured tool steel and advanced high-strength steel surfaces. The low surface friction induced by the laser-fabricated micro-lubricant pockets has been feasible for the forming tool and die applications where the energy consumed in their operations can be minimized. Full article
(This article belongs to the Special Issue Friction, Wear and Lubrication of Tool Steels in Metal Forming and Machining)
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18 pages, 2531 KiB  
Article
Extensive Stability Assessment of TiO2/Polyvinyl Ether Nanolubricant with Physical Homogenization
by Mohd Farid Ismail, Wan Hamzah Azmi, Rizalman Mamat, Korada Viswanatha Sharma and Hafiz Muhammad Ali
Lubricants 2023, 11(2), 67; https://doi.org/10.3390/lubricants11020067 - 08 Feb 2023
Viewed by 1072
Abstract
Proper preparation and stability evaluation of the nanolubricant shall be established when applying the nanoparticle dispersion technique in a two-phase system. The stability of the nanolubricant ensures the maximum benefit gained from the dispersion of nanoparticles in specified Polyvinyl ether (PVE). In this [...] Read more.
Proper preparation and stability evaluation of the nanolubricant shall be established when applying the nanoparticle dispersion technique in a two-phase system. The stability of the nanolubricant ensures the maximum benefit gained from the dispersion of nanoparticles in specified Polyvinyl ether (PVE). In this study, TiO2/PVE nanolubricant was prepared using two methods of physical homogenization: high-speed homogenizer (HSH) and ultrasonication bath. The HSH used a preparation time of up to 300 s in the stability assessment. Meanwhile, the ultrasonication bath had a preparation time of 1, 3, 5, and 7 h. The stability condition of the nanolubricant was evaluated using photo capturing, ultraviolet-visible (UV-Vis) spectrophotometer, zeta potential, and zeta sizer. A sample with 180 s of preparation time shows the best stability condition from HSH. The nanolubricant with ultrasonication offers excellent stability at 5 h of homogenizing time with a concentration ratio of more than 90% for up to 30 days of observation. In conclusion, ultrasonication homogenizing methods show better results than HSH with a zeta potential of more than 60 mV. In addition, HSH can be recommended as an optional method to produce nanolubricant with a low preparation time for immediate use. Full article
(This article belongs to the Special Issue Nanolubrication and Superlubrication)
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20 pages, 221764 KiB  
Article
Tuning the Parameters of Cu–WS2 Composite Production via Powder Metallurgy: Evaluation of the Effects on Tribological Properties
by Marco Freschi, Lara Dragoni, Marco Mariani, Oskari Haiko, Jukka Kömi, Nora Lecis and Giovanni Dotelli
Lubricants 2023, 11(2), 66; https://doi.org/10.3390/lubricants11020066 - 06 Feb 2023
Cited by 2 | Viewed by 1535
Abstract
Metal matrix self-lubricating composites exhibit outstanding performance in various environments, reaching the required properties by modifying the reinforcement–matrix ratio and the production method. The present research investigated the effects on tribological performance and electrical properties of different pressure loads, maintaining pressing time, and [...] Read more.
Metal matrix self-lubricating composites exhibit outstanding performance in various environments, reaching the required properties by modifying the reinforcement–matrix ratio and the production method. The present research investigated the effects on tribological performance and electrical properties of different pressure loads, maintaining pressing time, and sintering temperatures during the production of copper–10 wt% tungsten disulfide (Cu–WS2) composite via powder metallurgy. Moreover, additional thermo-mechanical treatments were evaluated, namely second pressing and second sintering steps. The density and the hardness of the produced composites were measured, as well as the electrical resistivity, considering sliding electrical contacts as possible employment. The outputs of the wear tests were considered together with the analysis of the wear track via scanning electron microscopy and confocal laser scanning microscopy to understand wear mechanisms. Different production routes were compared in terms of electrical resistivity, wear coefficient, and specific wear rate, calculated by the confocal laser scanning microscopy, and friction coefficient, measured during the wear test. The main results highlighted that the increase in sintering temperature was detrimental to the hardness and tribological properties; higher load and additional pressing step determined a general improvement in the tested properties. Full article
(This article belongs to the Special Issue Assessment of Adhesive Wear)
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12 pages, 2265 KiB  
Article
Halloysite Reinforced Natural Esters for Energy Applications
by Jose Jaime Taha-Tijerina, Karla Aviña, Victoria Padilla-Gainza and Aditya Akundi
Lubricants 2023, 11(2), 65; https://doi.org/10.3390/lubricants11020065 - 05 Feb 2023
Cited by 3 | Viewed by 1469
Abstract
Recently, environmentally friendly and sustainable materials are being developed, searching for biocompatible and efficient materials which could be incorporated into diverse industries and fields. Natural esters are investigated and have emerged as eco-friendly high-performance alternatives to mineral fluids. This research shows the evaluations [...] Read more.
Recently, environmentally friendly and sustainable materials are being developed, searching for biocompatible and efficient materials which could be incorporated into diverse industries and fields. Natural esters are investigated and have emerged as eco-friendly high-performance alternatives to mineral fluids. This research shows the evaluations on thermal transport and tribological properties of halloysite nanotubular structures (HNS) reinforcing natural ester lubricant at various filler fractions (0.01, 0.05, and 0.10 wt.%). Nanolubricant tribotestings were evaluated under two configurations, block-on-ring, and 4-balls, to obtain the coefficient of friction (COF) and wear scar diameter (WSD), respectively. Results indicated improvements, even at merely 0.01 wt.% HNS concentration, where COF and WSD were reduced by ~66% and 8%, respectively, when compared to pure natural ester. The maximum significant improvement was observed for the 0.05 wt.% concentration, which resulted in a reduction of 87% in COF and 37% in WSD. Thermal conductivity was analyzed under a temperature scan from room temperature up to 70 °C (343 K). Results indicate that thermal conductivity is improved as the HNS concentration and testing temperature are increased. Results revealed improvements for the nanolubricants in the range of 8–16% at 50 °C (323 K) and reached a maximum of 30% at 70 °C (343 K). Therefore, this research suggests that natural ester/HNS lubricants might be used in industrial applications as green lubricants. Full article
(This article belongs to the Special Issue Functional Lubricating Materials)
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30 pages, 1354 KiB  
Review
State-of-the-Art in Sustainable Machining of Different Materials Using Nano Minimum Quality Lubrication (NMQL)
by Avinash Kumar, Anuj Kumar Sharma and Jitendra Kumar Katiyar
Lubricants 2023, 11(2), 64; https://doi.org/10.3390/lubricants11020064 - 03 Feb 2023
Cited by 19 | Viewed by 2582
Abstract
In the manufacturing industry, during machining, the conventional cutting fluid plays a vital role; however, extravagant use of cutting fluids due to its disposal affects the environment badly. Nowadays, due to these advantages of conventional cutting fluids, alternative methods of conventional cutting fluids [...] Read more.
In the manufacturing industry, during machining, the conventional cutting fluid plays a vital role; however, extravagant use of cutting fluids due to its disposal affects the environment badly. Nowadays, due to these advantages of conventional cutting fluids, alternative methods of conventional cutting fluids or alternative methods are preferred. One of the most preferred methods may be the minimum quantity lubrication technique with conventional or nanoparticle-enriched cutting fluids. The present paper has a compilation of the investigations based on MQL application in different machining processes such as turning, milling, grinding, and drilling. The machining also involves hard-to-machine alloys. The paper discusses cryogenic MQL in brief and opens the domain for work in future. The purpose of this paper is to provide a quick reference for researchers working on the practical use of MQL lubricants with nanopowders dissolved and their application in machining for different materials. Full article
(This article belongs to the Special Issue Biolubricants in Machining)
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12 pages, 10343 KiB  
Article
Measurement for Lubricant Distribution in an Angular Contact Ball Bearing and Its Influence Investigation
by Baogang Wen, Yemin Li, Meiling Wang and Yang Yang
Lubricants 2023, 11(2), 63; https://doi.org/10.3390/lubricants11020063 - 03 Feb 2023
Cited by 4 | Viewed by 1826
Abstract
Oil lubrication is widely adopted in rolling bearings, the characteristics of which affect the oil film formation and friction state, and also the heat generation and dissipation characteristics. However, it is difficult to measure the internal lubrication of rolling bearings in practice, which [...] Read more.
Oil lubrication is widely adopted in rolling bearings, the characteristics of which affect the oil film formation and friction state, and also the heat generation and dissipation characteristics. However, it is difficult to measure the internal lubrication of rolling bearings in practice, which is of great importance for lubrication and structure design. In this work, one measurement system for lubricant distribution was built and installed on a test rig to obtain original pictures of the lubricant in bearings. Grayscale images were obtained by picture processing to characterize the lubricant distribution, and the image pixels were evaluated for the characterization of lubricant volume. Finally, the measurement of the lubricant distribution in the angular ball bearing was carried out under different lubrication and cage groove conditions, and their influences were investigated. The results show that the lubricant distribution is affected by the oil jet nozzle angle, operating speed, and cage structure. The lubricant capacity among balls and the cage pocket in bearings gradually increased with the increase in the nozzle angle and the depth of the cage grooves, but decreased with the increasing operating speed. The experimental results are helpful to provide a basis for the structure and lubrication design of ball bearings. Full article
(This article belongs to the Special Issue Friction and Lubrication of Sliding Bearings, Volume II)
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13 pages, 997 KiB  
Article
Oil Detection Fault Tree Analysis Based on Improved Expert’s Own Weight–Aggregate Fuzzy Number
by Junjie Sheng and Haijun Wei
Lubricants 2023, 11(2), 62; https://doi.org/10.3390/lubricants11020062 - 02 Feb 2023
Viewed by 1075
Abstract
Oil detection technology improves the reliability of machinery or equipment. The physical and chemical indicators of the fluid can reflect the cause of the failure in various aspects, which can prevent major accidents to the greatest extent by setting up a fault tree. [...] Read more.
Oil detection technology improves the reliability of machinery or equipment. The physical and chemical indicators of the fluid can reflect the cause of the failure in various aspects, which can prevent major accidents to the greatest extent by setting up a fault tree. Owing to the lack of data, it is difficult to accurately obtain the basic event probabilities, which makes it difficult to diagnose faults. The expert evaluation method and aggregated fuzzy numbers are used to exact the failure probability, where the event probability is evaluated as the subjective will of the expert. To improve the probabilistic accuracy, weights are improved by the combined assignment method as well as the reasonableness analysis. A fault tree diagnostic model is constructed for qualitative and quantitative analysis, taking the ship engine oil viscosity high fault as an example. According to the results, the model can provide a comprehensive analysis of physical and chemical indicators. Experts’ own weights have a large impact on the failure probability, with their weight changes leading to a change in the failure ranking. From the discrimination, following a Bland–Altman analysis of the results, the selected combined empowerment method improved the discrimination of the results by 4.8% compared to the traditional method, with 100% data consistency, which proved that the improvement was reliable and effective. The structure of this fault diagnosis model is clear, which can quickly give the fault cause and probability reference value. Full article
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25 pages, 2322 KiB  
Article
Exact Model Order Reduction for the Full-System Finite Element Solution of Thermal Elastohydrodynamic Lubrication Problems
by Jad Mounayer and Wassim Habchi
Lubricants 2023, 11(2), 61; https://doi.org/10.3390/lubricants11020061 - 02 Feb 2023
Cited by 2 | Viewed by 1267
Abstract
The derivation of fast, reliable, and accurate modeling procedures for the solution of thermal elastohydrodynamic lubrication problems is a topic of significant interest in the Tribology community. In this paper, a novel model order reduction technique is introduced for the analysis of thermal [...] Read more.
The derivation of fast, reliable, and accurate modeling procedures for the solution of thermal elastohydrodynamic lubrication problems is a topic of significant interest in the Tribology community. In this paper, a novel model order reduction technique is introduced for the analysis of thermal elastohydrodynamic lubrication problems. The method uses static condensation to reduce the size of the linear elasticity part within the overall matrix system, followed by a splitting algorithm to avoid the burden of solving a semi-dense matrix system. The results reveal the exactness of the proposed methodology, which does not introduce any additional model-reduction approximations to the overall solution. They also reveal the reduction in computational times, which is in the order of 10–20% for line contacts, while it is in excess of 50% for circular contacts. The robustness of the proposed method is displayed by using it to model some relatively highly loaded contacts whose numerical solution is known to be rather challenging. Full article
(This article belongs to the Special Issue Accuracy and Reliability of Computational Modelling of Thermo-Elastohydrodynamic Lubrication)
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