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1
Kato, S., E. Marui, A. Kobayashi i S. Senda. "The Influence of Lubricants on Static Friction Characteristics Under Boundary Lubrication". Journal of Tribology 107, nr 2 (1.04.1985): 188–94. http://dx.doi.org/10.1115/1.3261018.
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Based on a new boundary lubrication model, the characteristics of lubricants under boundary lubrication at low sliding speed and low contact pressure such as in machine tool slideways are investigated in relation to surface topography. It is clarified theoretically and ascertained experimentally that the property of lubricants under boundary lubrication can be estimated by the newly defined appraisal coefficient of boundary lubrication property determined by the thickness and load carrying capacity of adsorbed lubricant film and the surface topography.
2
Liu, Xiaoyan, i Per M. Claesson. "Bioinspired Bottlebrush Polymers for Aqueous Boundary Lubrication". Polymers 14, nr 13 (3.07.2022): 2724. http://dx.doi.org/10.3390/polym14132724.
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An extremely efficient lubrication system is achieved in synovial joints by means of bio-lubricants and sophisticated nanostructured surfaces that work together. Molecular bottlebrush structures play crucial roles for this superior tribosystem. For example, lubricin is an important bio-lubricant, and aggrecan associated with hyaluronan is important for the mechanical response of cartilage. Inspired by nature, synthetic bottlebrush polymers have been developed and excellent aqueous boundary lubrication has been achieved. In this review, we summarize recent experimental investigations of the interfacial lubrication properties of surfaces coated with bottlebrush bio-lubricants and bioinspired bottlebrush polymers. We also discuss recent advances in understanding intermolecular synergy in aqueous lubrication including natural and synthetic polymers. Finally, opportunities and challenges in developing efficient aqueous boundary lubrication systems are outlined.
3
Xu, Rong-Guang, i Yongsheng Leng. "Squeezing and stick–slip friction behaviors of lubricants in boundary lubrication". Proceedings of the National Academy of Sciences 115, nr 26 (13.06.2018): 6560–65. http://dx.doi.org/10.1073/pnas.1805569115.
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The fundamental questions of how lubricant molecules organize into a layered structure under nanometers confinement and what is the interplay between layering and friction are still not well answered in the field of nanotribology. While the phase transition of lubricants during a squeeze-out process under compression is a long-standing controversial debate (i.e., liquid-like to solid-like phase transition versus amorphous glass-like transition), recent different interpretations to the stick–slip friction of lubricants in boundary lubrication present new challenges in this field. We carry out molecular dynamics simulations of a model lubricant film (cyclohexane) confined between molecularly smooth surfaces (mica)––a prototypical model system studied in surface force apparatus or surface force balance experiments. Through fully atomistic simulations, we find that repulsive force between two solid surfaces starts at about seven lubricant layers (n= 7) and the lubricant film undergoes a sudden liquid-like to solid-like phase transition atn< 6 monolayers thickness. Shear of solidified lubricant films at three- or four-monolayer thickness results in stick–slip friction. The sliding friction simulation shows that instead of shear melting of the film during the slip of the surface, boundary slips at solid–lubricant interfaces happen, while the solidified structure of the lubricant film is well maintained during repeated stick–slip friction cycles. Moreover, no dilation of the lubricant film during the slip is observed, which is surprisingly consistent with recent surface force balance experimental measurements.
4
Arif, Mohammad, Saurabh Kango i Dinesh Kumar Shukla. "Effect of slip boundary condition and non-newtonian rheology of lubricants on the dynamic characteristics of finite hydrodynamic journal bearing". Surface Topography: Metrology and Properties 10, nr 1 (11.01.2022): 015002. http://dx.doi.org/10.1088/2051-672x/ac4403.
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Abstract In the present study, the influence of various slip zone locations on the dynamic stability of finite hydrodynamic journal bearing lubricated with non-Newtonian and Newtonian lubricants has been investigated. Linearized equation of motion with free vibration of rigid rotor has been used to find the optimum location of the slip region with maximum stability margin limit. It has been observed that bearing with interface of slip and no-slip region near the upstream side of minimum film-thickness location is effective in improving the direct and cross stiffness coefficient, critical mass parameter, and critical whirling speed. The magnitude of dynamic performance parameters with slip effect is highly dependent on the rheology of lubricant. Shear-thinning lubricants combined with slip boundary condition shows higher dynamic stability as compared to the Newtonian lubricants under the conventional boundary condition. For all considered rheology of lubricants, the dynamic stability of bearing with slip effect is improving by increasing the eccentricity ratio.
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Carré, D. J. "Perfluoropolyalkylether lubricants under boundary conditions: Iron catalysis of lubricant degradation". Journal of Synthetic Lubrication 6, nr 1 (kwiecień 1989): 1–15. http://dx.doi.org/10.1002/jsl.3000060102.
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Boiko, M., T. Boiko i I. Kolesnikov. "Influence of aldol condensation processes on the formation of surface films during friction in ester lubricants". Journal of Physics: Conference Series 2131, nr 5 (1.12.2021): 052037. http://dx.doi.org/10.1088/1742-6596/2131/5/052037.
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Abstract The boundary lubrication mode is usually implemented in conditions of low sliding speeds and high loads. The formation of strong boundary lubricating films under this friction mode determines the operability and durability of the friction units. It is believed that the formation of surface boundary films during friction includes the stages of the lubricant oxidation, and the aldol condensation reaction of oxidized molecules. As a result, high-molecular substances called “friction polymers” are formed. The paper studies the formation of surface films in the presence of substances with different reactivity in the aldol condensation and Claisen condensation reactions. Sunflower oil, bis (2-ethylhexyl) sebacate (DEHS), triisodecyl benzene-1,2,4-tricarboxylate (TC) were used as lubricants. It is shown by ATR IR-spectroscopy of that the common thing for the studied oils is that the C=O and C-O groups participate in the formation of boundary films in these oils. The addition of substances, active in aldol condensation reactions, into lubricants does not accelerate the formation of boundary films. Additives that can chemically interact with iron contribute to the dissolution of the surface oxide film and accelerate the formation of boundary layers. The formation of “friction polymers” occurs when the lubricant molecules interact with the metal surface.
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García-Miranda, J. Santos, Luis Daniel Aguilera-Camacho, María Teresa Hernández-Sierra i Karla J. Moreno. "A Comparative Analysis of the Lubricating Performance of an Eco-Friendly Lubricant vs Mineral Oil in a Metallic System". Coatings 13, nr 8 (27.07.2023): 1314. http://dx.doi.org/10.3390/coatings13081314.
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Eco-friendly lubricant research continues to increase since it has a comparative performance to commercial mineral lubricants to overcome the effects of environmental impact. However, the efficiency of these green lubricants depends on specific applications. In this study, we analyzed the friction and wear performance of a castor/sesame oil mixture as an eco-friendly lubricant and its comparison to a commercial mineral lubricant tested in a metallic system employed in bearing elements. For this purpose, AISI 8620 steel against ISO 100Cr6 was used as tribological pair. The friction and wear tests were carried out through a Tribometer of ball-on-disk configuration under boundary lubricating conditions, whereas the worn surfaces were investigated by using optical and electron microscopy. The physical properties and the rheological properties of the lubricants were also determined. The friction and wear performance between the eco-friendly lubricant and mineral oil were similar so that the CLE were comparable. The CLE values in terms of friction and wear ranged from 86% to 99.4%, respectively.
8
Kobayashi, A., N. Unno i T. Yonemoto. "Study on the Adhesion Force of Lubricants—Adhesion Force Characteristics Under Boundary Lubrication". Journal of Tribology 119, nr 1 (1.01.1997): 107–11. http://dx.doi.org/10.1115/1.2832443.
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The mechanisms that generate adhesion forces in liquid lubricants are studied under various experimental conditions. These forces occur between two surfaces when they are detached in the normal direction under static boundary lubrication conditions. The adhesion force is not influenced by the speed at which the upper specimen is pulled up, but is influenced by the viscosity of the lubricant. The adhesion force under boundary lubrication is much greater than that under hydrodynamic lubrication, and it is closely related to the compressibility of the lubricant.
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Voronin, Serhii, Ivan Hrunyk, Bashir Asadov, Dmytro Onopreychuk i Volodymyr Stefanov. "Study of the Process of Lubricant Application on the Friction Surface Using Aerosol Lubricators". International Journal of Engineering & Technology 7, nr 4.3 (15.09.2018): 20. http://dx.doi.org/10.14419/ijet.v7i4.3.19546.
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The problem of calculation and forecasting main parameters of aerosol lubricators designed for applying lubricants on angled to the horizon friction surfaces e.g. the lateral surfaces of a rail and a wheel flange of railway rolling stock is solved in the article. The main parameters of lubricators being considered in the article are compressed air supply, the geometry of a spray nozzle and the boundary thickness of a lubricant layer applied to the friction surface where there is no creep of a lubricant under the action of gravity. A structural model of application and retention of a lubricant on a friction surface has been proposed. A mathematical model to calculate main parameters of aerosol lubricators has been developed. The model establishes the connection between the geometry of lubricated friction surfaces, physico-chemical properties of lubricants and the diameter of nozzle aperture and the compressed air supply. The example of calculation of the boundary thickness of a lubricant layer applied to the friction surface under the condition of the absence of its creeping under the action of gravity has been presented in the article. The article presents the results of experimental studies the process of aerosol application of a lubricant to the friction surface.
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Koplin, Christof, Sherif Ahmed Abdel-Wahed, Raimund Jaeger i Matthias Scherge. "The Transition from Static to Dynamic Boundary Friction of a Lubricated Spreading and a Non-Spreading Adhesive Contact by Macroscopic Oscillatory Tribometry". Lubricants 7, nr 1 (9.01.2019): 6. http://dx.doi.org/10.3390/lubricants7010006.
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Lubricated poly(ether ether ketone) (PEEK) and polyamide (PA46)–steel tribosystems were investigated. They show a complex but systematic transition behavior from static to boundary friction, to dynamic friction or to mixed-lubrication. Nonstandard macroscopic oscillatory tribometry as well as gliding experiments were carried out. A previous study showed that the surface and interfacial energies of PEEK, lubricant and steel can indicate trends in the tribological behavior. In the current study, these findings are confirmed for PA46 and a wider range of lubricants. It was shown that a reversal of the order of the work of spreading of two lubricants by switching from PEEK to PA46 as polymer component in the tribological system also resulted in a reversal of the coefficient of friction (COF) at low gliding velocities for these systems. The adhesion threshold of PA46 with the non-spreading lubricants water, glycerine, a water–glycerine mixture, ethylene glycol and poly-1-decene decreased with increasing solving tendency of the lubricants in contrast to the previous results for spreading lubricants for PEEK. Furthermore, the onset of forced wetting was studied for lubricants with different surface and interfacial energies and viscosities η. In general, a 1/η dependency was observed for the velocity which marks the onset of forced wetting. This agrees with theoretical models.
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Chong, William Woei Fong, Siti Hartini Hamdan, King Jye Wong i Suzana Yusup. "Modelling Transitions in Regimes of Lubrication for Rough Surface Contact". Lubricants 7, nr 9 (2.09.2019): 77. http://dx.doi.org/10.3390/lubricants7090077.
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Accurately predicting frictional performance of lubrication systems requires mathematical predictive tools with reliable lubricant shear-related input parameters, which might not be easily accessible. Therefore, the study proposes a semi-empirical framework to predict accurately the friction performance of lubricant systems operating across a wide range of lubricant regimes. The semi-analytical framework integrates laboratory-scale experimental measurements from a pin-on-disk tribometer with a unified numerical iterative scheme. The numerical scheme couples the effect of hydrodynamic pressure generated from the lubricant and interacting asperity pressure, essential along the mixed lubrication regime. The lubricant viscosity-pressure coefficient is determined using a free-volume approach, requiring only the lubricant viscosity-temperature relation as the input. The simulated rough surface contact shows transition in lubricant regimes, from the boundary to the elastohydrodynamic lubrication regime with increasing sliding velocity. Through correlation with pin-on-disk frictional measurements, the slope of the limiting shear stress-pressure relation γ and the pressure coefficient of boundary shear strength m for the studied engine lubricants are determined. Thus, the proposed approach presents an effective and robust semi-empirical framework to determine shear properties of fully-formulated engine lubricants. These parameters are essential for application in mathematical tools to predict more accurately the frictional performance of lubrication systems operating across a wide range of lubrication regimes.
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Nyberg, Erik, Dídac Llopart i Cervelló i Ichiro Minami. "Tribology in Space Robotic Actuators: Experimental Method for Evaluation and Analysis of Gearboxes". Aerospace 8, nr 3 (13.03.2021): 75. http://dx.doi.org/10.3390/aerospace8030075.
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Liquid lubricants are critical to enable long-life operation of high-performance machinery, such as geared actuators employed in robotics. In space applications, actuator gearboxes must operate in low temperatures, where liquid lubricants face inherent problems related to low temperature rheology. Heaters are relied upon to provide acceptable gearbox temperatures. Unfortunately, heating is energy-intense and does not scale well with increasing mechanism mass and performance. Effective boundary lubrication (BL), on the other hand, can minimize problems of low temperature rheology. BL relies on tribofilm formation over conventional fluid film separation. Effective space grade boundary lubricants can potentially allow for drastically reduced amounts of oil and the accompanying rheological problems. In this work, we describe the design of a methodology to evaluate and analyze tribology of actuator gearboxes operated under cryogenic oil-starved conditions in N2 atmosphere. The devised methodology enables research pertinent to space actuator tribology by accelerated testing and advanced analysis, as demonstrated by a lubricant candidate case study. Complementary microscopy techniques are discussed, and a novel methodology devised for gear internal microstructure analysis by X-ray microtomography (XMT) is presented.
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Holweger, Walter, Luigi Bobbio, Zhuoqiong Mo, Jörg Fliege, Bernd Goerlach i Barbara Simon. "A Computational Study on the Role of Lubricants under Boundary Lubrication". Lubricants 11, nr 2 (13.02.2023): 80. http://dx.doi.org/10.3390/lubricants11020080.
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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.
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Jackson, J. E., T. Gangjee i I. Haque. "Lubricant Modeling and Its Effect on Simulation of Material Forming". Journal of Engineering Materials and Technology 111, nr 1 (1.01.1989): 74–80. http://dx.doi.org/10.1115/1.3226436.
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Solid cylinder upsetting is analyzed using three different approaches for frictional boundary condition modeling. These are (1) constant shear friction factor, (2) experimentally measured frictional stresses, and (3) analytical models accounting for lubricant entrapment and redistribution. All three approaches are implemented in the CFORM finite element code. The error between the three approaches and actual experimental measurements of the material deformation and interfacial pressures is investigated. It is shown that the constant shear friction factor is more accurate for solid film lubricants than for liquid lubricants. However, the calculations indicate that if accurate prediction of near net shape forming processes is to become a reality, improvements need to be made in the characterization of frictional boundary conditions. New theoretical developments applicable to arbitrary shapes and more accurate than the constant shear friction factor approach are needed.
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Singh, Devendra, G. D. Thakre, L. N. Sivakumar Konathala i V. V. D. N. Prasad. "Friction Reduction Capabilities of Silicate Compounds Used in an Engine Lubricant on Worn Surfaces". Advances in Tribology 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/1901493.
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Effects of magnesium silicate and alumina dispersed in engine lubricant on friction, wear, and tribosurface characteristics are studied under boundary and mixed lubrication conditions. Magnesium silicate and alumina, henceforth called as friction reducing compounds (FRC), were dispersed in engine lubricant in very low concentration of 0.01% weight/volume. Four-ball wear test rig was used to assess friction coefficient and wear scar diameter of balls lubricated with and without FRC based engine lubricant. Scanning electron microscopy (SEM) equipped with Energy Dispersive X-ray (EDX) was used to analyse the tribosurface properties and elemental distributions on worn surfaces of the balls. Test results revealed that FRC based engine lubricant increases friction coefficient but marginally reduces wear scar diameter of new balls, whereas, test on the worn-out balls running on FRC based engine lubricants shows 46% reduction in friction coefficient compared to the new balls running on engine lubricants without FRC. Investigations on tribosurfaces with respect to morphology and elemental distribution showed the presence of Si and O elements in micropores of the worn surfaces of the balls, indicating role of FRC in friction coefficient reduction and antiwear properties. These FRC based engine lubricants may be used in the in-use engines.
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Ning, Lipu, Xianghui Meng i Youbai Xie. "Effects of lubricant shear thinning on the mixed lubrication of piston skirt-liner system". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 227, nr 7 (19.09.2012): 1585–98. http://dx.doi.org/10.1177/0954406212460610.
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A theoretical analysis is presented for the mixed lubrication of the piston skirt-liner system. The model is developed to consider the shear thinning effect of multigrade lubricant. The friction characteristics of the piston skirt-liner system for both monograde and multigrade lubricants are investigated. It is found that a decrease in the lubricant viscosity is effective in reducing the friction loss. However, the boundary friction at the expansion stroke will increase with low lubricant viscosity. Results in this study show a significant lubricant shear thinning effect on the piston skirt-liner system.
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Sajeeb, Ayamannil, i Perikinalil K. Rajendrakumar. "Tribological assessment of vegetable oil based CeO2/CuO hybrid nano-lubricant". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 234, nr 12 (16.01.2020): 1940–56. http://dx.doi.org/10.1177/1350650119899208.
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Vegetable oil based lubricants attract much attention nowadays due to their excellent boundary lubrication performance and biodegradability. Coconut oil is a vegetable oil with excellent lubricating properties which provides low friction coefficient and better oxidation stability. The purpose of this study is to investigate the performance of coconut oil based new hybrid CeO2/CuO nano-lubricant with various ratios of CeO2/CuO viz. 25/75, 50/50, and 75/25 at different concentrations (0.1, 0.25, 0.5, and 1.0 wt%). The rheological, thermal, thermo-gravimetric, and tribological evaluations were conducted for hybrid nano-lubricants and the results were compared with those of base oil (coconut oil) and nano-lubricants containing CeO2 and CuO nano-particles individually. A reduction of 15.7% in average friction coefficient and 23.4% in wear scar diameter was observed with the use of 0.25 wt% CeO2/CuO: 50/50 hybrid. Oil degradation studies and worn surface analyses after engine test were also done. The results showed that the surface enhancement is evidenced with the use of hybrid nano-lubricant.
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Gilmour, K. R., S. Paul i A. G. Leacock. "The Influence of Lubricant Film Thickness on Friction Coefficients During Slow Speed Deep Drawing Operations". Journal of Tribology 124, nr 4 (24.09.2002): 846–51. http://dx.doi.org/10.1115/1.1330732.
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During some deep drawing operations liquid lubricants are used under the blankholder to reduce friction coefficients. Under the clamping action of the blankholder, lubricants will be squeezed out resulting in a changing film thickness after the initial application of the blankholder load. A relationship between kinetic friction coefficient values and the loading duration of the blankholder can be observed from analysis of results recorded during simulative testing. By using a numerical model to combine empirical measurements, friction coefficients during boundary lubrication, lubricant film thickness with sheet surface topography data, it can be shown that the coefficient of friction can reliably be predicted for a given loading duration.
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Taylor, RI, N. Morgan, R. Mainwaring i T. Davenport. "How much mixed/boundary friction is there in an engine — and where is it?" Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 234, nr 10 (19.09.2019): 1563–79. http://dx.doi.org/10.1177/1350650119875316.
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Automotive engines are believed to operate predominantly in the hydrodynamic regime, as evidenced by the (1) the successful strategy of reducing lubricant viscosity to reduce engine friction and improve vehicle fuel consumption, and (2) for most engine operating conditions, direct measurements of engine friction (either motored or fired) find that engine friction increases with increasing engine speed. However, certain components in an engine are known to operate mainly in the mixed/boundary lubrication (e.g. the valve train) and other components (such as the piston rings) operate in the mixed/boundary regime for a portion of the time. In order to quantify the amount of mixed/boundary lubrication in an engine, and in the individual components of the engine, motored and fired friction tests have been carried out for a range of lubricants (of differing viscosity grade, and with/without friction modifier additives). A full discussion of the implications of this work, which includes the impact of fuel dilution and “running-in” is included with insights given into how the work reported here guides the development of future fuel-efficient engine lubricants.
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Anand, M., M. Hadfield, B. Thomas i R. Cantrill. "The depletion of ZDDP additives within marine lubricants and associated cylinder liner wear in RNLI lifeboat engines". Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 231, nr 1-2 (19.08.2016): 162–70. http://dx.doi.org/10.1177/1464420716663235.
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Previous work of authors indicated the wear of cylinder liners in marine engines of RNLI lifeboats due to the intense lubricant degradation identified by inductively coupled plasma and Fourier Transform Infrared spectroscopy techniques. In this paper, further analysis carried out to evaluate the effects of lubricant degradation on the actual cylinder liners installed in the Trent Class Lifeboat engines is presented. Surface characterisation of actual cylinder liner’s bore surface showed maximum wear near the top dead centre region compared to rest of the piston stroke. Wear in this region of the cylinder liner surface is controlled primarily by the protective film forming anti-wear additives in the lubricant which limit the direct surface contact between the piston rings and cylinder liner. The condition of zinc dialkyldithiophosphates anti-wear additives was analysed using the nuclear magnetic resonance spectroscopy. Tribology analysis was conducted to evaluate the tribological and boundary film forming performance of zinc dialkyldithiophosphates additives by simulating cylinder liner–piston ring contact near the top dead centre. To further understand the wear mechanisms of the cylinder liner, wear debris analysis (Analytical Ferrography) of lubricant samples was performed. Results revealed the depletion of phosphorus containing zinc dialkyldithiophosphates anti-wear additives as a function of the lubricant’s duty cycle within the marine engines and its effect on the tribological and boundary film forming performance of lubricants. Wear debris analysis showed the generation of ferrous debris potentially from the cylinder liners as a result of reduced anti-wear protection from the depleted zinc dialkyldithiophosphates additives during the tribological contact with piston rings and piston skirt region. These findings are useful to understand the lubricant degradation mechanisms which affect the functionality of cylinder liners, therefore allowing to plan the engine maintenance strategies.
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Nyberg, Erik, Christoph Schneidhofer, Lucia Pisarova, Nicole Dörr i Ichiro Minami. "Ionic Liquids as Performance Ingredients in Space Lubricants". Molecules 26, nr 4 (14.02.2021): 1013. http://dx.doi.org/10.3390/molecules26041013.
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Low vapor pressure and several other outstanding properties make room-temperature ionic liquids attractive candidates as lubricants for machine elements in space applications. Ensuring sufficient liquid lubricant supply under space conditions is challenging, and consequently, such tribological systems may operate in boundary lubrication conditions. Under such circumstances, effective lubrication requires the formation of adsorbed or chemically reacted boundary films to prevent excessive friction and wear. In this work, we evaluated hydrocarbon-mimicking ionic liquids, designated P-SiSO, as performance ingredients in multiply alkylated cyclopentane (MAC). The tribological properties under vacuum or various atmospheres (air, nitrogen, carbon dioxide) were measured and analyzed. Thermal vacuum outgassing and electric conductivity were meas- ured to evaluate ‘MAC & P-SiSO’ compatibility to the space environment, including the secondary effects of radiation. Heritage space lubricants—MAC and perfluoroalkyl polyethers (PFPE)—were employed as references. The results corroborate the beneficial lubricating performance of incorporating P-SiSO in MAC, under vacuum as well as under various atmospheres, and demonstrates the feasibility for use as a multifunctional additive in hydrocarbon base oils, for use in space exploration applications.
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Taylor, R. I. "Engine friction: The influence of lubricant rheology". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 211, nr 3 (1.03.1997): 235–46. http://dx.doi.org/10.1177/135065019721100306.
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The sensitivity of engine friction to lubricant viscometry has been determined for a modern fuelefficient engine, the Mercedes Benz M111 2.0 litre gasoline engine, under both cold starting and fully warmed-up conditions. The study has taken into account realistic lubricant viscometric parameters such as the lubricant viscosity variation with shear rate and temperature. Results are reported for the variation of engine friction with different monograde and multigrade lubricants, including the distribution of friction losses between valve train, piston assembly and bearings with the different lubricant types. The work also enabled estimates to be made of the proportion of hydrodynamic and boundary friction in the engine, since the vast majority of boundary lubrication occurs in the valve train. Knowledge of the ratio of boundary to hydrodynamic lubrication was found to be important since the two key lubricant parameters that can be varied are (a) viscosity and (b) the introduction of a friction modifier additive. The viscosity of the lubricant will affect the hydrodynamically lubricated parts of the engine whereas the presence of a friction modifier will reduce boundary friction in the engine. Brief comparisons are made of the lubricant sensitivity of the Mercedes Benz M111 engine with other important fuel-efficient engines (such as the Ford Sequence VI and Ford Sequence VIA engines).
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Kumar, Rajneesh, i Suresh Verma. "Effect of micropolar lubrication in non-circular hole-entry hybrid journal bearing with constant flow valve restrictor". Industrial Lubrication and Tribology 68, nr 6 (12.09.2016): 737–51. http://dx.doi.org/10.1108/ilt-07-2015-0097.
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Purpose In the present scenario of high-speed machines, the use of non-circular hole-entry bearing configuration, i.e. two-lobe, multi-lobe, lemon bore, etc., has becomes unavoidable, as the journal bearings with non-circular configurations provide better stability at high operating speed and heavy dynamic loading. Further, this research aims to show that the presence of micro particles in the lubricants greatly affects performance of the bearings, as their presence leads to non-Newtonian behaviors of the lubricant. Therefore, to consider the effect of these micro particles, the lubricant is modeled as a micropolar lubricant. The present work analyzes the effect of these micropolar lubricants on the performance of hole-entry circular and non-circular (two-lobe) hybrid journal bearings compensated with constant flow valve restrictor and compares with that of Newtonian lubricants. Design/methodology/approach The modified Reynolds equation governing the laminar flow of iso-viscous, incompressible micropolar lubricant in the clearance space of a journal bearing system has been solved using finite element method and appropriate boundary conditions. Further, a comparative analysis between circular and non-circular (two-lobe) hybrid journal bearing compensated with constant flow valve restrictor operating with Newtonian and micropolar lubricant has been presented. Findings The numerically simulated results reveal that the non-circular bearing configuration provides better performance vis-à-vis the circular bearing configuration. Further, the increase in the micropolar effect of the lubricant enhances the performance of circular and the non-circular bearing configurations compared with the Newtonian lubricant. Also, in the case of the non-circular bearing configuration with an offset factor (δ = 1.5), the bearing performance improved compared with (δ = 1.25). Originality/value Many research studies have been done in the area of non-circular hybrid journal bearing with Newtonian lubricants with different types of restrictors, but the non-circular hole-entry constant flow valve-compensated hybrid journal bearing operating with the micropolar lubricant has not been analyzed. Therefore, in the present work, an effort has been made to fill this research gap.
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Carre´, D. J., P. D. Fleischauer, C. G. Kalogeras i H. D. Marten. "Comparison of Lubricant Performance in an Oscillating Spacecraft Mechanism". Journal of Tribology 113, nr 2 (1.04.1991): 308–12. http://dx.doi.org/10.1115/1.2920621.
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A life test of lubricants for the R2 shaft bearings of a spacecraft oscillating scanner mechanism was performed under simulated orbital conditions. The lubricant originally used in the application, a chloroarylalkylsiloxane (CAS) oil, and a linear perfluoropolyalkylether (PFPE) oil failed in less than 2500 hr of operation. A poly-alpha-olefin (PAO) oil has been running for more than 11,000 hr without any indication of lubricant or system degradation. The performances of the oils are discussed in terms of the boundary lubrication conditions of the test.
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Loktev, V. M., i Yu G. Pogorelov. "Boundary friction on molecular lubricants: rolling mode?" Low Temperature Physics 30, nr 4 (kwiecień 2004): 317–20. http://dx.doi.org/10.1063/1.1705439.
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MARUI, Etsuo, Shinobu KATO i Akiyoshi KOBAYASHI. "Boundary lubrication ability of lubricants on slideways." Transactions of the Japan Society of Mechanical Engineers Series C 54, nr 508 (1988): 3065–72. http://dx.doi.org/10.1299/kikaic.54.3065.
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Gong, Xiao, i Lei Li. "Nanometer-Thick Ionic Liquids as Boundary Lubricants". Advanced Engineering Materials 20, nr 5 (15.11.2017): 1700617. http://dx.doi.org/10.1002/adem.201700617.
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Czarny, Ryszard. "THE EFFECT OF THE TYPE OF WALL MATERIAL AND GREASE COMPOSITION PAIRING ON SHEAR STRESSES IN BOUNDARY LAYER". Tribologia 284, nr 2 (30.04.2019): 27–36. http://dx.doi.org/10.5604/01.3001.0013.4146.
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The paper presents the results of research on the influence of fillers introduced into plastic greases on the rheological properties of the boundary layer of the resultant lubricant compositions. The fillers were PTFE and MoS2 powders. They are added to lubricants to improve their tribological properties; however, these fillers also affect the rheological properties of the composition. This affects the change of the shear stress value in the lubricant during its flow in the lubrication system. Knowledge of this value, especially during the flow of the lubricant composition in the boundary layer, has a significant impact on the operation of automated central lubrication systems in which these compositions can be used. Measurements were carried out by means of a rotary rheometer (Rheotest 2.1). Tests were performed on lithium and bentonite greases (without additives) as well as compositions of these greases containing various percentage of the fillers mentioned above. Test results showed that both the type of grease and the type of filler introduced into this grease affect the rheological properties in the boundary layer of the produced lubricating compositions.
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Hsu, S. M., R. Munro i M. C. Shen. "Wear in boundary lubrication". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 216, nr 6 (1.06.2002): 427–41. http://dx.doi.org/10.1243/135065002762355343.
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Wear is a complex subject. Wear studies under lubricated conditions can be classified into two categories: wear mechanisms study of the materials under ‘lubricated’ conditions, and the evaluation of the lubricant chemistry using the same materials. Much confusion exists in the literature because these two communities historically do not interact frequently to understand each other's views. In the 1980s, material science research was emphasized around the world. As a result, wear studies began to flourish, examining various new materials for potential applications in new technologies. Since new materials came in many different forms, a wide variety of wear test geometries and test methods were developed for solids, coatings and thin films. Many of the wear test methodologies were established under a ‘dry’ condition (without the use of liquid lubricants). In this paper, the dry condition will be used as a baseline to compare various wear phenomena under lubricated conditions. Within this context, wear test procedures, basic assumptions and associated data interpretations will be examined. Wear mechanisms under lubricated conditions will also be discussed. Finally the current state of modelling under lubricated wear conditions will be reviewed.
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Moreno, Karla J., María Teresa Hernández-Sierra, José E. Báez, Eloy Rodríguez-deLeón, Luis Daniel Aguilera-Camacho i J. Santos García-Miranda. "On the Tribological and Oxidation Study of Xanthophylls as Natural Additives in Castor Oil for Green Lubrication". Materials 14, nr 18 (19.09.2021): 5431. http://dx.doi.org/10.3390/ma14185431.
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The present study focuses on an introductory analysis of the use of three xanthophylls as additives for green lubricant applications. For this purpose, the additives were characterized by FTIR and 1H-NMR techniques, and the bio-lubricants were described by their physical properties. The effect of the natural compounds on the friction and wear properties of bio-lubricants were evaluated by sliding friction tests under boundary conditions, as confirmed by an analysis of the lubricating film thickness. The antioxidant capacity was analyzed by FTIR spectroscopy. It was observed better wear protection in castor oil with xanthophylls than without these additives. The wear rate was reduced up to 50% compared with neat oil. Lesser beneficial effects were appreciated in friction coefficient since it was increased 25%. The best contribution was observed with astaxanthin as an additive. In addition, a significant improvement in the oxidation of castor oil, complemented with this additive, was exhibited by FTIR analysis. It was found that xanthophylls could be employed as additives for totally biodegradable lubricant applications since they have better tribological and antioxidant behavior than current additives.
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Chen, Wei, Tobias Amann, Andreas Kailer i Jürgen Rühe. "Macroscopic Friction Studies of Alkylglucopyranosides as Additives for Water-Based Lubricants". Lubricants 8, nr 1 (16.01.2020): 11. http://dx.doi.org/10.3390/lubricants8010011.
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Water-based lubricants might become an interesting alternative to conventional oil-based lubricants and help to reduce wear as well as improve the energy efficiency of transport processes. Since pure water is generally a rather poor lubricant due to its low viscosity and corrosiveness, it must be tribologically optimized with suitable additives. Here, we study the friction behavior of alkyl glucopyranosides (AGPs) with varying lengths of the alkyl chain. Sliding experiments show that a significant reduction in the coefficient of friction compared to that of pure water is observed. The extent of friction reduction depends strongly on the concentration and on the shearing conditions. It is assumed that the low coefficients of friction are due to the ability of AGPs to form liquid crystalline phases with an ordered structure in the friction gap. Furthermore, the interaction of the AGPs with the surface forms a wear protection layer (boundary lubrication). The friction properties of the water-based system are compared to those of a conventional, mineral oil-based lubricant.
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Bell, J., A. A. Besong, J. L. Tipper, E. Ingham, B. M. Wroblewski, M. H. Stone i J. Fisher. "Influence of gelatin and bovine serum lubricants on ultra-high molecular weight polyethylene wear debris generated in in vitro simulations". Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine 214, nr 5 (1.05.2000): 513–18. http://dx.doi.org/10.1243/0954411001535543.
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Ultra-high molecular weight polyethylene (UHMWPE) wear debris induced osteolysis has a major role in the late aseptic loosening and ultimate failure of total hip replacements (THR). Clinically relevant in vitro simulations of wear are essential to predict the osteolytic potential of bearing surfaces in artificial hip joints. Newborn calf or bovine serum has been accepted as a boundary lubricant for such in vitro tests, but its biological stability has been questioned. This study compared the wear factors, number of wear particles and levels of microbial contamination produced in bovine serum and a gelatin-based lubricant. The wear factors produced by the two lubricants were not significantly different, however the wear debris morphology produced was substantially different. The bovine serum became contaminated with micro-organisms within 28 h, whereas the protein-based lubricant remained uncontaminated. The results showed that bovine serum was not a stable boundary lubricant. They also showed that although the wear factors for the two solutions were not significantly different, the protein-based lubricant was not a suitable alternative to bovine serum because the wear debris produced was not clinically relevant.
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Placek, D. G., i T. Freiheit. "Progress in Vapor Phase Lubrication Technology". Journal of Engineering for Gas Turbines and Power 115, nr 4 (1.10.1993): 700–705. http://dx.doi.org/10.1115/1.2906762.
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Improving the efficiency of engine performance will require the design of systems with higher operating temperatures and pressures. These conditions will stress traditional lubricants beyond their current performance capabilities, and require the development of improved methods for friction and wear reduction. The most revolutionary approach to high-temperature lubrication is the concept of vapor phase delivery. An ashless organic compound can be vaporized by the heat of the operating engine or a carrier gas, and introduced into the ring zone of the cylinder. The vapor condenses or chemically binds with the piston ring or cylinder wall, and provides boundary lubrication. A minute amount of lubricant is constantly introduced in order to maintain a lubricating film. Each stroke of the piston shears off a portion of the lubricant layer, but condensing vapor continually replaces the surface film. Lubricant contributions to exhaust emissions are expected to be lower than those currently resulting from liquid lubricants. Vapor phase lubrication is an emerging concept that may be the key to the development of a commercial low heat rejection engine with improved energy efficiency and reduced emissions. The Department of Energy continues to fund research at a variety of industrial and academic institutions. Basic concepts and recent developments in the field of vapor phase lubrication will be reviewed.
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Waltman, Robert J., Connie Wiita i Roberto Valsecchi. "Perfluoropolyether Boundary Lubricants Based on the Star Architecture". Tribology Online 13, nr 5 (15.12.2018): 262–74. http://dx.doi.org/10.2474/trol.13.262.
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Lu, Renguo, Masaya Morimoto, Hiroshi Tani, Norio Tagawa i Shinji Koganezawa. "Tribological Properties of Alkyldiphenylethers in Boundary Lubrication". Lubricants 7, nr 12 (10.12.2019): 112. http://dx.doi.org/10.3390/lubricants7120112.
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Lubricants that are used in miniaturized moving mechanical components generally serve under severe conditions, such as high temperature, high speed, and high load. Although alkyldiphenylethers (ADEs) are used as base oils for high-temperature greases, their tribological properties remain unclear. This study investigated the influence of the alkyl chains on the tribological properties of ADEs. Longer and more attached alkyl chains decreased the friction coefficient of ADEs under both reciprocating and continuous sliding conditions. Wear was found to be independent of the alkyl chain under reciprocating sliding conditions due to abrasion being caused by debris that was not readily removed. ADEs showed good anti-wear properties when used as either a lubricant or an additive under continuous sliding conditions. Much smoother surfaces in the friction track were observed in comparison to poly-α-olefin. Fourier-Transform infrared spectroscopy analysis suggested that the ether groups were attracted to the worn steel surface, phenyl groups became consequently perpendicular, and the attached alkyl chains repelled other substances and prevented further wear of the surface. Moreover, ADEs showed a high adaptability with traditional additives.
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Lince, Jeffrey R. "Effective Application of Solid Lubricants in Spacecraft Mechanisms". Lubricants 8, nr 7 (10.07.2020): 74. http://dx.doi.org/10.3390/lubricants8070074.
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Solid lubricants, antiwear coatings, and self-lubricating composites are used in applications on spacecraft where oils and greases cannot be used because of the need to avoid lubricant volatility/migration, and where the application requires significant temperature variation, accelerated testing, higher electrical conductivity, or operation in boundary conditions. The purpose of this review is to provide spacecraft designers with tools that can aid in the effective use of solid-based tribological materials, both to increase their usage, and to reduce anomalies. The various tribological material formulations are described, including how their materials, physical, and chemical properties affect their performance. Included are typical solid lubricants like PTFE and bonded or sputter-deposited MoS2, as well as low shear metal coatings, hard coatings, and composite materials (including bulk composites and nanocomposite coatings). Guidance is given on how to develop mechanisms that meet performance requirements, but also how to optimize robustness, so that success is achieved even under unforeseen circumstances. Examples of successful applications are given, as well as how to avoid potential pitfalls, and what the future of solid tribological materials may hold.
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Hills, B. A. "Graphite-like lubrication of mesothelium by oligolamellar pleural surfactant". Journal of Applied Physiology 73, nr 3 (1.09.1992): 1034–39. http://dx.doi.org/10.1152/jappl.1992.73.3.1034.
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Six studies have been completed to reevaluate pleural surfactant as a possible boundary lubricant in mesothelial sliding. It is capable of remarkable antiwear action, giving a mean scar diameter on a standard “four-ball test” comparable to the best commercially available lubricants and reducing friction to values anticipated from lamellated solid lubricants such as graphite. Pleural surfaces displayed appreciable hydrophobicity, which was almost eliminated by rinsing with a lipid solvent from which phospholipid was recovered and quantified. These quantities indicated that equivalent of 7.3 adsorbed monolayers of surface-active phospholipid, which was in general agreement with the number of layers of a graphite-like surface coating visualized by electron microscopy by use of a novel fixation procedure that avoids conventional aldehydes known to destroy hydrophobic surfaces. Graphite-like (dry) lubrication by adsorbed surface-active phospholipid is discussed as an excellent lubrication system available wherever the distribution of fluid allows the pleura to make contact.
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Ismakov, R. A., V. G. Konesev, F. N. Yangirov, G. L. Gaymaletdinova i A. R. Yahin. "Research of the kinetics of thickness of the boundary layers of lubricating materials applied to drilling technology". SOCAR Proceedings, nr 2 (30.06.2021): 115–20. http://dx.doi.org/10.5510/ogp20210200502.
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Improving the operational properties of lubricants increases the service life of the mechanisms and increase the durability of rubbing joints, which has a positive effect on the indicators of technical and economic efficiency and equipment safety. Therefore, great attention in tribology is paid to the analysis of the state of friction units in technology and the assessment of their resource characteristics, which makes it possible to increase their service life. The research aim is to study the general provisions on lubricants and lubricants, as well as the features of the boundary layers formation on friction surfaces and the observed patterns. Calculations of the boundary layers thickness using lubricating reagents at different energetic loading of the friction pair were carried out as applied to the roller bearing of a roller cone bit in the medium of cylinder oil 52 and DPS grease. The proposed research methodology made it possible to in-crease the efficiency and effectiveness of the means development for improving the tribotech-nical properties of drilling lubricants.
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Zahid, Rehan, Masjuki Hj. Hassan, Abdullah Alabdulkarem, Mahendra Varman, Md Abul Kalam, Riaz Ahmad Mufti, Nurin Wahidah Mohd Zulkifli i in. "Tribological characteristics comparison of formulated palm trimethylolpropane ester and polyalphaolefin for cam/tappet interface of direct acting valve train system". Industrial Lubrication and Tribology 70, nr 5 (9.07.2018): 888–901. http://dx.doi.org/10.1108/ilt-06-2017-0156.
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Purpose There is a continuous drive in automotive sector to shift from conventional lubricants to environmental friendly ones without adversely affecting critical tribological performance parameters. Because of their favorable tribological properties, chemically modified vegetable oils such as palm trimethylolpropane ester (TMP) are one of the potential candidates for the said role. To prove the suitability of TMP for applications involving boundary-lubrication regime such as cam/tappet interface of direct acting valve train system, a logical step forward is to investigate their compatibility with conventional lubricant additives. Design/methodology/approach In this study, extreme pressure and tribological characteristics of TMP, formulated with glycerol mono-oleate (GMO), molybdenum dithiocarbamate (MoDTC) and zinc dialkyldithiophosphate (ZDDP), has been investigated using four-ball wear tester and valve train test rig. For comparison, additive-free and formulated versions of polyalphaolefin (PAO) were used as reference. Moreover, various surface characterization techniques were deployed to investigate mechanisms responsible for a particular tribological behavior. Findings In additive-free form, TMP demonstrated better extreme pressure characteristics compared to PAO and lubricant additives which are actually optimized for conventional base-oils such as PAO, are also proved to be compatible with TMP to some extent, especially ZDDP. During cylinder head tests, additive-free TMP proved to be more effective compared to PAO in reducing friction of cam/tappet interface, but opposite behavior was seen when formulated lubricants were used. Therefore, there is a need to synthesize specialized friction modifiers, anti-wear and extreme pressure additives for TMP before using it as engine lubricant base-oil. Originality/value In this study, additive-free and formulated versions of bio-lubricant are tested for cam/tappet interface of direct acting valve train system of commercial passenger car diesel engine for the very test time. Another important aspect of this research was comparison of important tribological performance parameters (friction torque, wear, rotational speed of tappet) of TMP-based lubricants with conventional lubricant base oil, that is, PAO and its formulated version.
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Feng, R., K. T. Ramesh i A. S. Douglas. "An Analytical and Computational Investigation of High-Rate Rheometry". Journal of Tribology 118, nr 3 (1.07.1996): 601–7. http://dx.doi.org/10.1115/1.2831579.
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This paper examines a class of experimental techniques used to develop constitutive models for lubricants, by simulating the shearing of a thin lubricant layer while accounting for transient phenomena. The complete transient thermal problem with fully nonlinear constitutive relations is solved, and heat conduction is accounted for both in the lubricant layer and into the walls. Numerical simulations are used to examine the shear stress history, the velocity profile, and the temperature profile as functions of time. As a particular example, the high-rate torsional Kolsky bar rheometer (Feng and Ramesh, 1993) is simulated. The computations indicate that the Kolsky bar experiments, which are able to examine the time-histories of the stresses and of the motion, can he used to obtain material properties for lubricants at high shear rates. A full numerical analysis may be required to properly interpret some of the data available from the Kolsky bar experiments, since at longer times (greater than that associated with the peak shear stress) the thermal softening may dominate the response and the velocity field may become strongly inhomogeneous. The numerical simulations are performed using both rate-dependent and limiting stress constitutive laws, and the effects of the layer thickness and the rise time of the relative velocities are examined. The simulations show that the film thickness and the rise time of the relative velocities can have strong effects on the character of the solution when the transient phenomena are included in the analysis. The computations also demonstrate that highly inhomogeneous and even localized flows may occur within rheometers as a result of transient effects. The development of these flows depends on the layer thickness, the rise-time of the boundary velocity, the thermal boundary conditions, and the constitutive behavior of the lubricant.
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Ortega-Álvarez, Ricardo, Guillermo E. Aguilar-Cortés, María T. Hernández-Sierra, Luis D. Aguilera-Camacho, J. S. García-Miranda i Karla J. Moreno. "Physical and rheological investigation of vegetable oils and their effect as lubricants in mechanical components". MRS Advances 4, nr 59-60 (2019): 3291–97. http://dx.doi.org/10.1557/adv.2019.407.
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ABSTRACTThe aim of this investigation was to study castor, canola, and sesame vegetable oils in order to evaluate their potential use as lubricants in steel mechanical components. For this purpose, densities of each oil were evaluated using the pycnometer method, as well as their dynamic viscosities through a Brookfield DV-II rotational viscometer. Both properties were evaluated at temperatures of 25, 40 and 100 °C. Additionally, viscosity indexes were determined according to ASTM D 2270. These rheological properties were used to estimate the lubrication regime considering parameters of real contact conditions in mechanical components. Friction and wear analyses were carried out to investigate the behaviour of the vegetable oil as lubricants. Such tests were carried out at room temperature on a CSM tribometer with pin-on-disk configuration by using castor, canola and sesame oils as lubricants. AISI 4140 hardened steel against AISI 100Cr6 steel pin was used as a mechanical component. From the rheological study, it was observed that canola and sesame oils behave as dilatant fluids at the evaluated temperatures, while castor oil behaves like a Newtonian fluid at 25 and 40 °C. Castor oil showed the highest density value among oils studied, but it also exhibited the lowest value of viscosity index (271). Contrarily, sesame oil was the least dense, but it exhibited the highest viscosity index (545). On the other hand, the lubrication regime study showed that by using castor oil as a lubricant in the mechanical component (4140/100Cr6), the system worked in a mixed lubrication regime while by using canola and sesame oils the system operated in boundary lubrication conditions. Finally, the kinetic friction coefficients were different for each lubricant obtaining the lowest value with castor oil while the highest value of friction coefficient was exhibited by the sesame oil lubricant.
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Mocny, Piotr, i Harm-Anton Klok. "Tribology of surface-grafted polymer brushes". Molecular Systems Design & Engineering 1, nr 2 (2016): 141–54. http://dx.doi.org/10.1039/c5me00010f.
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Болотов, Александр Николаевич, Ольга Олеговна Новикова i Владислав Викторович Новиков. "SILICONE MAGNETIC NANOFLUIDS ADAPTED FOR THE CONDITIONS OF BOUNDARY FRICTION". Physical and Chemical Aspects of the Study of Clusters, Nanostructures and Nanomaterials, nr 12() (15.12.2020): 546–56. http://dx.doi.org/10.26456/pcascnn/2020.12.546.
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Известные в настоящее время магнитные смазочные наножидкости имеют недостаточно хорошие триботехнические характеристики при эксплуатации в режиме граничного трения. Предложен способ адаптации для граничного трения магнитных силоксановых наножидкостей, путем модификации их состава химически активными антифрикционными, противоизносными и противозадирными присадками. Создан ряд смазочных композиций магнитных наножидкости на основе полиэтилсилоксана ПЭС-5. Поведенные экспериментальные исследования показали, что наиболее значительное улучшение антифрикционных и противоизносных свойств наножидкостей достигается при введении в их структуру хлорсодержащих присадок Совол и 3Н2ТЭ. Добавление в наножидкость антиокислительной присадки ДФ-11, фторсодержащей присадки ЭО-1, металлоплакирующего соединения МКФ-18 не привело к значимому улучшению антифрикционных свойств. Установлено, что магнитные наножидкости с модифицирующими присадками, по трибосвойствам сопоставимы с традиционными немагнитными жидкими смазочными материалами и превосходят пластичные смазки на основе полиэтилсилоксана. Разработанные композиции на основе силоксановых наножидкостей, будут востребованы для смазывания подшипников качения и скольжения, зубчатых передач, контактных уплотнений, которые функционируют при низких и повышенных температурах в газовой среде или в условиях вакуума. Наиболее успешно они могут применяться в вакуумной и космической технике, для магнитных трибоузлов, где возможна только однократная заправка ограниченным объемом смазочного материала. Currently known magnetic lubricant nanofluids have insufficiently good tribological characteristics when operating in the boundary friction mode. An adaptation method is proposed for the boundary friction of magnetic siloxane nanofluids by modifying their composition with chemically active antifriction, antiwear and extreme pressure additives. A number of lubricating compositions of magnetic nanofluids based on polyethylsiloxane PES-5 have been created. Conducted experimental studies have shown that the most significant improvement in the antifriction and antiwear properties of nanofluids is achieved with the introduction of Sovol and 3N2TE chlorine additives into their structure. Adding to the nanofluid the antioxidant additive DF-11, the fluorine-containing additive EO-1, the metal-plating compound MKF-18 did not lead to a significant improvement in the antifriction properties. It has been established that magnetic nanofluids with modifying additives are comparable in tribological properties with traditional non-magnetic liquid lubricants and are superior to plastic lubricants based on polyethylsiloxane. The developed compositions based on siloxane nanofluids will be in demand for lubrication of rolling and sliding bearings, gears, contact seals, which operate at low and elevated temperatures in a gas environment or in a vacuum. Most successfully, they can be used in vacuum and space technology, for magnetic frictional units, where only one refueling with a limited amount of lubricant is possible.
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Black, A. J., E. M. Kopalinsky i P. L. B. Oxley. "Metallic Sliding Friction under Boundary Lubricated Conditions: A New Method for Measuring the Appropriate Shear Strength of Lubricants". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 208, nr 4 (grudzień 1994): 281–89. http://dx.doi.org/10.1243/pime_proc_1994_208_383_02.
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An experimental method is described for measuring the shear strength of lubricants for conditions similar to those encountered at the interfaces of contacting asperities in metallic sliding friction. Results are given for a number of lubricants including commercially available motor oils. The significance of the results is discussed.
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Bewsher, Stephen Richard, M. Leighton, Mahdi Mohammadpour, Homer Rahnejat, Guenter Offner i Oliver Knaus. "Atomic force microscopic measurement of a used cylinder liner for prediction of boundary friction". Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 233, nr 7 (16.08.2018): 1879–89. http://dx.doi.org/10.1177/0954407018792143.
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Accurate simulation performs a crucial role in the design and development of new modern internal combustion engines. In the case of piston rings, simulations are used to effectively predict generated friction and power loss of proposed designs. These are consequences of viscous shear of a thin lubricant film, likewise boundary friction caused by direct interaction of piston rings with the cylinder liner/bore surface. The most commonly used model for determining boundary friction is that of Greenwood and Tripp. The model requires the pressure coefficient of boundary shear strength of asperities from the softer of the contacting surfaces as an input. This parameter needs to be measured. The paper describes the process of measurement using an Atomic Force Microscope (AFM), both for a dry surface and that wetted by the presence of a lubricant layer. For realistic results, the investigated specimen is a used, tested engine cylinder liner where boundary active lubricant additives are bonded to its surface as well as combustion products. This approach is as opposed to the previously reported works using new flat surfaces with base oil or partially formulated lubricants and has not been previously reported in the literature. The results show that for used cylinder liners, the measured boundary shear strength of asperities varies according to location along the stroke. Results are reported for the top dead centre, mid-stroke and bottom dead centre locations. The measurements are subsequently used with two-dimensional Reynolds solution for a top compression ring-liner contact, where it is found that accurate localised predictions of generated friction and power loss can be made instead of the usual average value approach reported in the literature.
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Leighton, M., T. Nicholls, M. De la Cruz, R. Rahmani i H. Rahnejat. "Combined lubricant–surface system perspective: Multi-scale numerical–experimental investigation". Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 231, nr 7 (12.12.2016): 910–24. http://dx.doi.org/10.1177/1350650116683784.
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Frictional losses are one of the main causes of reduced energy efficiency in all machines and mechanisms. In particular, there is mounting pressure upon manufacturers of all forms of vehicle to comply with increasingly stringent legislation and directives with regard to harmful emissions. Therefore, reduction of friction has become an imperative issue. The traditional approach of dealing with surface material and lubricant formulation in isolation has been replaced by a lubricant–surface system approach. This paper presents multi-scale experimentation from nano/meso-scale lateral force microscopy of ultra-thin surface adsorbed films through to micro-scale precision sliding tribometry to investigate lubricant–surface friction optimisation within the mixed regime of lubrication, using lubricants with different organic and inorganic friction modifying species. These affect the parameters of the system, commonly used as input to models for mixed and boundary regimes of lubrication. Therefore, the precise measurement of these parameters at different physical scales is important. The study also makes use of detailed numerical predictions at micro-scale through combined solution of the average Reynolds equation as well as interaction of wetted asperities in mixed and boundary regimes of lubrication. Good agreement is found between the predictions and measurements at micro-scale tribometric interactions. Furthermore, the same trends are observed in testing across the physical scales.
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Mu, Liwen, Yijun Shi, Xiaojing Guo, Tuo Ji, Long Chen, Ruixia Yuan, Logan Brisbin, Huaiyuan Wang i Jiahua Zhu. "Non-corrosive green lubricants: strengthened lignin–[choline][amino acid] ionic liquids interaction via reciprocal hydrogen bonding". RSC Advances 5, nr 81 (2015): 66067–72. http://dx.doi.org/10.1039/c5ra11093a.
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Bliznyuk, Valery N., Mark P. Everson i Vladimir V. Tsukruk. "Nanotribological Properties of Organic Boundary Lubricants: Langmuir Films Versus Self-Assembled Monolayers". Journal of Tribology 120, nr 3 (1.07.1998): 489–95. http://dx.doi.org/10.1115/1.2834577.
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Frictional characteristics of several types of boundary lubricants were tested using scanning probe microscopy (SPM). These include Langmuir monolayers of stearic acids (STA), their cadmium salts (STCd), self-assembling monolayers (SAMs) of alkylchlorsilanes, and complexes of STA with rigid naphthoylene benzimidazole (x-NBI) fragments. We observed that a Langmuir monolayer deposited on a silicon surface had a very low friction coefficient against a silicon nitride tip (about 0.01–0.05) but also low mechanical stability. SAMs were found to be much more stable but had the drawback of growth in the friction coefficient at high sliding velocities. Composite NBI/STA monolayers were much more stable and were not damaged by the highest normal load applied. The frictional behavior of different monolayers was analyzed in relation to their structural organization (the type of tethering to the surface and packing density). We introduced a figure of merit (FOM) parameter which allowed comparison of frictional properties of very different lubricant materials to those of the supporting substrate. For Langmuir monolayers the FOM increased strongly with surface packing density whereas for SAMs and x-NBI/STA complexes it possessed a maximum at surface densities in the range 3.5–4.5 molecules per nm2. Because of the possibility of tailoring the surface packing density of aliphatic tails in the complexes, they are a promising alternative to both LB films and SAMs. For such composite monolayers, the surface packing density can be optimized to give a desired frictional behavior.
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Nemyrovskyi, Ya B., I. V. Shepelenko, E. K. Posviatenko, M. I. Chernovol i F. Y. Zlatopolskiy. "Creation of progressive hole processing processes based on the study of contact phenomena during deforming broaching and finishing antifriction non-abrasive treatment in various technological environments". Problems of Tribology 27, nr 1/103 (27.03.2022): 14–25. http://dx.doi.org/10.31891/2079-1372-2022-103-1-14-25.
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This work is devoted to the creation of progressive technological processes for processing holes. The relevance of studying this issue is substantiated, technological environments (TE) used in these operations are listed. The purpose of the work performed is to study the influence of TE on contact phenomena and quality parameters of the treated surface during deformation broaching (DB) and finishing antifriction non-abrasive processing (FANT) and the creation on this basis of new technological processes to obtain parts with improved performance. New methods have been developed for studying contact interaction in the case of DB using solid lubricants, as well as for modeling the FANT process. The conditions for the use of liquid lubricants in the DB are described. It has been established that, when them applied, the altitudinal roughness parameters decrease and the surface layer hardens to a considerable depth. It is shown that the use of solid lubricants in DB is mandatory when processing products from hard-to-work materials and alloys. When them applied, significant plastic deformations of the hole can be made. In this case, the surface layer of the workpiece is little different from the original. The change in the altitude parameters of the rough layer, as well as contact pressures using solid lubricants, was studied. Peculiarities of contact phenomena in the case of DB using solid lubricants are revealed. For this case, a functional relationship has been established between the altitude parameters of roughness and the relative contact pressure. An analytical dependence is proposed for their calculation. The boundary conditions for its application are determined. Formation FANT also occurs when using the TE. It was established that solid lubricants during FANT perform a dual function, namely, technological, like solid lubricant during processing, and operational - improve the quality parameters of the processed parts. The combination of DB and FANT operations allows us to develop a new technological process for processing holes of parts such as bushings and sleeves. This process consists in the use of DB as a roughing and finishing operations, and FANT as a finishing operation, which allows to improve the quality indicators of the machined part
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Buckholz, R. H. "Cavitation Boundary Shapes for Submerged Short Journal Bearings Using Newtonian Lubricants". Journal of Applied Mechanics 52, nr 4 (1.12.1985): 771–76. http://dx.doi.org/10.1115/1.3169144.
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Cavitation boundary shapes for submerged short journal bearings are investigated in this study. In this analysis, the Reynolds lubrication equation is approximated by using the bearing slenderness ratio as a small parameter. The slenderness ratio appears explicitly in the Reynolds lubrication equation. The lubrication equation is solved subjected to the boundary condition of a subambient value for the cavitation pressure and the additional Reynolds’ free-surface boundary condition along the unknown cavitation boundary. The Ocvirk short bearing solution is shown to fail near the leading edge of the cavitation region, and a matched asymptotic theory is used to determine the shape and location of this cavitated region. Cavitation bubble location and size are shown to depend on bearing aspect ratio, journal eccentricity, and cavitation pressure. Finally the present journal bearing analysis is limited to those cases where the cavitation region has a large axial extent.