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سال ۱۳۹۷ سال حمایت از کالای ایرانی گرامی باد

Friction

  1. Abstract

    To reduce harmful sulfur content in lubricant additives, making use of isosterism has been shown to be an effective strategy. When thiobenzothiazole compounds were used as templates, the exchange of sulfur atoms in the thiazole ring with oxygen atoms and NH groups produced twelve isosteres. Similarly, 2-benzothiazole- S-carboxylic acid esters were used as template molecules to produce six isosteres. About 30% of the isosteres exhibited a satisfactory deviation of ±5% relative to the template, ignoring the specific changes in the base oils, the differences in molecular structure, and the friction or wear properties. The template molecules and isosteres in triisodecyl trimellitate exhibited better tribological properties than in trimethylolpropane trioleate or bis(2- ethylhexyl) adipate. Comparative molecular field analysis (CoMFA)- and comparative molecular similarity index analysis (CoMSIA)-quantitative structure tribo-ability relationship (QSTR) models were employed to study the correlation of molecular structures between the base oils and additives. The models indicate that the higher the structural similarities of the base oils and additives are, the more synergetic the molecular force fields of the lubricating system are; the molecular force fields creating synergistic effects will improve tribological performance.

  2. Abstract

    The film forming condition may transit into thin film lubrication (TFL) at high speeds when it is under severe starvation. Central film thicknesses and film thickness profiles are obtained via a technique of relative optical interference intensity. These profiles show a critical film thickness lower than which the absolute values of the film thickness gradient against speed or time decrease. It is possible to be in the thin film lubrication mode under such conditions. The high speed flow drives the lubricant molecules to rearrange in TFL and critical film thickness higher than 100 nm is achieved. The viscosity is one of the main factors controlling the decreasing rate and the critical film thickness. This paper is designed to investigate the thin film lubrication behavior at high speeds.

  3. Abstract

    Polymer tribology is a fast growing area owing to increasing applications of polymers and polymer composites in industry, transportation, and many other areas of economy. Surface forces are very important for polymer contact, but the real origin of such forces has not been fully investigated. Strong adhesive interaction between polymers leads to an increase in the friction force, and hence, the asperities of the material may be removed to form wear particles or transfer layers on the counterface. The theory of polymer adhesion has not been completely elucidated yet and several models of adhesion have been proposed from the physical or chemical standpoints. This paper is focused on the research efforts on polymer adhesion with emphasis on adhesion mechanisms, which are very important in the analysis of polymer friction and wear.

  4. Abstract

    The combined effect of the use of carbon fiber and seawater and the molecular structure on the tribological behavior of various polymer materials under natural seawater lubrication was investigated. After the investigation, the wear morphology of the contact surface was observed by a laser scanning confocal microscope, and the texture of the wear scars and tracks were presented in 3D profiles. Moreover, the mechanism of mixed lubrication and wear resistance was analyzed. The results demonstrated that the friction coefficient of carbon fiber-reinforced polyetheretherketone (CFRPEEK) is the lowest and fluctuates at approximately 0.11. Moreover, the seven polymer materials in ascending order of friction coefficients are CFRPEEK, carbon fiber-reinforced polyamide-imide, polytetrafluoroethylene, polyoxymethylene, polyetheretherketone (PEEK), acrylonitrile butadiene styrene resin, and glass fiber–epoxy resin. More critically, the simultaneous incorporation of deposition, polymeric scrap, hydrophilic groups, and seawater resulted in a decrease in the friction and wear of polymer materials under seawater lubrication. This observation implies that a synergistic friction-reducing and wear-resistant effect exists between carbon fiber, seawater, and the molecular structure of PEEK. As a result, a highly effective polymer material was discovered, CFRPEEK, which has the lowest friction coefficient of 0.11 and lowest wear rate of 2 × 10–5 mm3·(N·m)−1 among the polymer materials; this validates the selection of dual friction pairs for seawater hydraulic components.

  5. Abstract

    Owing to the increasing demand for tribological brakes for space applications, the development of novel materials and advanced technologies is necessary. This paper presents the design, characterization, and realization of powder metallurgy processed metal-matrix friction materials intended for the above-mentioned tribological brakes. Selecting appropriate ingredients, which provides an effective way to tailor the properties of the friction material, is evolving as a strategy to meet the design requirements. The tribological behaviors of the friction material are experimentally investigated under different conditions, and special attention is focused on the vacuum tribology. Examinations and analyses of the friction surface and subsurface corroborate the wear mechanism. In addition, the erosion resistances of the friction material are evaluated by exposure tests of ultraviolet irradiation and atomic oxygen. Finally, present and potential space applications of the friction material are also introduced based on experimental studies.

  6. Abstract

    Unlike most of the conventional ionic liquids (ILs) derived from non-renewable resources, five environmentally friendly ILs ([Ch][AA] ILs) derived from amino acids (AAs) and choline (Ch) were synthesized using biomaterials by a simple, green route: acid–base reaction of Ch and AAs. The thermal and corrosion properties, as well as viscosity, of the prepared ILs were examined. The results revealed that the anion structure of ILs plays a dominant role in their thermal and viscosity behavior. These ILs exhibited less corrosion toward copper, related to their halogen-, sulfur-, and phosphorus-free characteristics. The tribological behavior of the synthesized ILs was examined using a Schwingungs Reibung und Verschleiss tester, and the results indicated that these ILs exhibit good friction-reducing and anti-wear properties as lubricants for steel/steel contact. Results from energy-dispersive spectroscopy and X-ray photoelectron spectroscopy indicated that the good tribological properties of [Ch][AA] ILs are related to the formation of a physically adsorbed film on the metal surface during friction.

  7. Abstract

    The effect of galvanically induced potentials on the friction and wear behavior of a 1RK91 stainless steel regarding to tribocorrosion was investigated using an oscillating ball-on-disk tribometer equipped with an electrochemical cell. The aim of this investigation is to develop a water-based lubricant. Therefore 1 molar sodium chloride (NaCl) and 1% 1-ethyl-3-methylimidazolium chloride [C2mim][Cl] water solutions were used. Tribological performance at two galvanically induced potentials was compared with the non-polarized state: cathodic potential-coupling with pure aluminum- and anodic potential-coupling with pure copper. Frictional and electrochemical response was recorded during the tests. In addition, wear morphology and chemical composition of the steel were analyzed using scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively.

    The galvanically induced cathodic polarization of the stainless steel surface results in electrochemical corrosion protection and the formation of a tribolayer. Cations from the electrolyte (sodium Na+ and 1-ethyl-3-methylimidazolium [C2mim]+) interact and adhere on the surface. These chemical interactions lead to considerably reduced wear using 1 NaCl (86%) and 1% 1-ethyl-3-methylimidazolium chloride [C2mim][Cl] (74%) compared to the nonpolarized system. In addition, mechanical and corrosive part of wear was identified using this electrochemical technique. Therefore this method describes a promising method to develop water-based lubricants for technical applications.

  8. Abstract

    The process of a cluster-containing water jet impinging on a monocrystalline silicon substrate was studied by molecular dynamics simulation. The results show that as the standoff distance increases, the jet will gradually diverge. As a result, the solidified water film between the cluster and the substrate becomes “thicker” and “looser”. The “thicker” and “looser” water film will then consume more input energy to achieve complete solidification, resulting in the stress region and the high-pressure region of the silicon substrate under small standoff distances to be significantly larger than those under large standoff distances. Therefore, the degree of damage sustained by the substrate will first experience a small change and then decrease quickly as the standoff distance increases. In summary, the occurrence and maintenance of complete solidification of the confined water film between the cluster and the substrate plays a decisive role in the level of damage formation on the silicon substrate. These findings are helpful for exploring the mechanism of an abrasive water jet.

  9. Abstract

    In this study, the lubrication performance of the crank pin bearing in a marine two–stroke diesel engine is evaluated to investigate the adhesional failure on the crank pin bearing. A numerical algorithm for the lubrication analysis considering motion analysis of the crank pin system is developed. The film pressure and thickness for three clearances and three lubricant temperatures are calculated. The results show that the lubricant temperature has a higher effect on film thickness than clearance. In terms of the film parameter, the operating condition that can result in solid–solid contact is investigated. We also suggest the desirable operating conditions of clearance and lubricant temperature to prevent the solid–solid contact.

  10. Abstract

    The objective of this study was to investigate the grease-lubricated film-forming mechanisms in the finite line contact and to improve the grease-lubricated finite line contact’s film-forming capacity. An elastohydrodynamic lubrication (EHL) test rig with two interferometry microscopes, which could simultaneously monitor two different contact locations in the finite line contact, was constructed in order to study the influences of the grease thickener formulation on the film thickness and lubrication condition. By using the relative light intensity method, the thickness maps of the grease-lubricated film were calculated from the interferometer images captured by the two microscopes. The test results revealed that the grease thickener’s formulation had remarkable effects on film formation and the perturbation of film thickness. For the lithium-based grease, the film’s thickness near the two ends of the roller was prone to severe perturbation caused by the conglomeration of clumps that were hard to shear. For the aluminum-complex-based grease, the fibers tended to accumulate in the middle of the roller rather than at the two ends. The urea-based grease could be easily sheared into smaller particles. In addition to the straight-line profile rollers, the logarithmic profile rollers were tested and found to effectively enhance the axial grease flow, increase the axial shear stress, and thus shear more fibers into particles within the contact area.

  11. Abstract

    The objective of this work is to investigate the influence of contact pressure and sliding speed on the coefficient of friction and wear of an activated carbon-epoxy composite derived from palm kernel under dry sliding conditions. A wear mode map approach was employed to identify the transitions from mild to severe wear of the composite. The dry sliding test was executed by utilizing a ball-on-disc tribometer at different contact pressures and sliding speeds with a constant sliding distance and operating temperature. The results showed that, regardless of the sliding speed, the friction coefficient and wear rate of the composite increased drastically when a critical limit of contact pressure is exceeded. As for the sliding speed, both the friction coefficient and wear rate increased first and thereafter decreased at a higher speed of 500 rpm. A wear mode map is proposed to classify the boundary from mild to severe wear regimes. The predominant wear failures identified include micro-crack, fine grooves, debonding, delamination, debris, broken carbon, and fracture.

  12. Abstract

    The plant cuticle is a complex mixture of omnipresent, commonly monofunctional, fatty acid derivatives and taxon-specific, generally bifunctional, specialty compounds. This study explored expanded applications for these substances. Four types of plant cuticles were distilled from leaves and the resulting lipid mixtures were analyzed using gas chromatography-mass spectrometry. These were then used as additives for a synthetic ester lubricant. A reciprocating friction and wear testing machine was utilized to investigate the resulting tribological properties. The worn surfaces of the lower discs were observed and analyzed using optical microscopy and time-of-flight secondary ion mass spectrometry. The results reveal that cuticular waxes can modify the friction properties of the base oil. Furthermore, cuticular waxes demonstrate better performance when compared to the commercially available additive molybdenum dithiocarbamates. A protective adsorption film was identified as the reason for the improved friction reduction and anti-wear properties of the lubricant on the friction pair. This study provides a reference for the study of new types of non-sulfur, phosphorus, and other active element additives and demonstrates considerable potential for the economical utilization of plant leaf waxes.

  13. Abstract

    In this study, based on the classical Archard adhesion wear theory, a three-dimensional finite element model was established, with the aim of simulating the failure process of self-lubricating spherical plain bearings in the swinging wear condition. The results show that the self-lubricating spherical plain bearings go through two different stages during the wear process, namely, initial wear stage and stable wear stage. Because the large contact points wear out during the initial wear stage, the maximum contact pressure decreases as the test period increases. The relatively larger wear depth region shows elliptical distribution, and the maximum distribution appears in the central contact area. The wear depth reaches 0.974 mm after swinging 25,000 times. PTFE fibers, which possess a good friction performance but poor abrasion resistance, abundantly exist on the friction surfaces of the fabric liner. Consequently, the friction torque during the initial wear stage is slightly smaller than the friction torque during the stable wear stage; however, the wear rate during the initial wear stage is high. The reliability and effectiveness of the finite element model are verified by experiment. The developed finite element model can be used for the analysis of the wear mechanisms of bearings and the prediction of the service life of bearings.

  14. Abstract

    In the classical study of elastohydrodynamic lubrication (EHL) which does not employ real, measurable viscosity in analysis, the possibility of a glass transition has not been considered in many years. Indeed, the two rheological assumptions of classical EHL, the Newtonian inlet and the equivalence of a traction curve to a flow curve, would not have persisted so long had the pressure dependence of the viscosity been accurately stated. With the recent appearance of viscosity obtained from viscometers in EHL analysis, the possibility of a glass transition in the contact should be reexamined, especially for the fragile traction fluids. This article employs published data for a synthetic cycloaliphatic hydrocarbon to estimate the glass transition viscosity so that, when using real viscosities in EHL simulations, the state of the liquid may be assessed. Far into the glassy state the liquid should be treated as an elastic solid with a yield stress.

  15. Abstract

    This paper presents experimental rigs of the Research Centre for the Mechanics of Turbomachinery of the Department of Civil and Industrial Engineering of the University of Pisa. Most of them were designed and constructed to allow investigations of real machine components and to furnish more realistic results than basic tribological test rigs.

    Tilting pad journal bearings, as well as gears and complete gearboxes for advanced industrial applications, can be tested using the rigs described in the paper. A novel test rig with a power rating of approximately 1 MW allows investigations of the static and dynamic characteristics of high-performance tilting pad journal bearings for turbomachinery. A twin disc machine and closed loop gear test rig are used to investigate the different kinds of wear mechanisms occurring in gears. Functional and durability tests on planetary gearboxes for new turbo-fan engines could be performed using another novel large test rig. A circulating power configuration was adopted for most of the rigs so that only the power needed to cover the friction losses has to be supplied, while the circulating power can be more than 20 times higher. All the test rigs include very complex load applications and lubrication plants, as well as dedicated control and data acquisition systems.

    The rigs and related plants were designed and constructed through strong and fruitful collaborations between the university and some large and small–medium companies. Despite some limitations in the publication of the results as a result of the industrial sensitivity of the data, the synergy among these different actors was stimulating and fundamental for the realization of new advanced industrial applications.

  16. Abstract

    Wear is an important factor for failures of mechanical components. Current research on wear is mainly focused on experiments while the numerical simulation of wear is hardly used owing to the complexities of the wear process. Explaining the effect of friction on the wear process is important, as it will lead to a deeper understanding of the evolution of wear. This study proposed a numerical method to expound the wear process in the contact between an elastic cylinder and a half-space simulating the ring-block tester. There are two difficulties during the calculation; one is that the contact shapes vary with time, causing the pressure distribution to change simultaneously and the other is the integral equation for calculating the contact pressure under different worn shapes. In the present study, the wear rate was computed using Archard’s law and the wear process was calculated step by step until the specified total sliding distance was achieved. During each step of the calculation, the contact topography was updated. The simulation intuitively reproduced the contact state of change from line to surface contact throughout the wear process. Reasonable agreements on the changes of the wear scar, achieved from experiments and numerical simulations, were obtained.

  17. Abstract

    This study achieved water-based superlubricity with the lubrication of H3PO4 solution in vacuum (highest vacuum degree <10–4 torr) for the first time by performing a pre-running process in air before running in vacuum. The stable water-based superlubricity was sustainable in vacuum (0.02 torr) for 14 h until the test was stopped by the user for non-experimental factor. A further analysis suggested that the superlubricity may be attributed to the phosphoric acid–water network formed in air, which can efficiently lock water molecules in the liquid lubricating film even in vacuum owing to the strong hydrogen bond interaction. Such capability to lock water is strongly affected by the strength of hydrogen bond and environmental conditions. The realization of water-based superlubricity with H3PO4 solution in vacuum can lead to its application in space environment.

  18. Abstract

    A hybrid lubricant with improved thermal and tribological properties was developed by blending multiwalled carbon nanotubes (MWCNTs) with alumina-based nanoparticles into cutting fluid at fixed volumetric proportions (10:90). The hybrid cutting fluid was prepared in different volumetric concentrations (0.25, 0.75, and 1.25 vol%), and the tribological properties and contact angles were measured using pin-on-disc tribometry and goniometry, respectively. The study showed a reduction in wear and friction coefficient with increasing nanoparticle concentration. The cutting fluid performance was investigated using minimum quantity lubrication (MQL) in the turning of AISI 304 stainless steel. Regression models were developed for measuring the temperature and tool flank wear in terms of cutting speed, feed, depth of the cut, and nanoparticle concentration using response surface methodology. The developed hybrid nanolubricants significantly reduced the tool flank wear and nodal temperature by 11% and 27.36%, respectively, as compared to alumina-based lubricants.

  19. Abstract

    Hot pressed silicon carbide (SiC) composites prepared with 0, 10, 30 or 50 wt% tungsten carbide (WC) are subjected to dry sliding wear against WC-Co and steel ball. In particular an attempt has been made to answer the following important questions: (i) How does the load (from 5 to 20 N) effect sliding wear behaviour of SiC-ceramics against WC-Co and steel counterbodies? (ii) Is there any effect of WC content on friction and wear characteristics of SiC ceramics? (iii) Does the dominant material removal mechanism of SiC ceramics change with the addition of WC or counterbody? (iv) What is the influence of mechanical properties on the sliding wear? Experimental results indicated that coefficient of friction (COF) for the SiC ceramics varied between 0.66 and 0.33 with change in load and counterbodies. Wear volume for SiC ceramics found approximately 6−10 times more against WC-Co as compared against steel. Wear volume changes from 2.0 × 10–3 mm3 to 1.2 × 10–2 mm3 with change in counterbodies for SiC-(10, 30 or 50 wt%) WC composite at 20 N. SiC ceramics indicated abrasion and composites reveal tribochemical wear as major material removal mechanisms. Wear is influenced by the hardness of counterbody and fracture toughness of SiC-WC composites.

  20. Abstract

    The present paper is devoted to a theoretical analysis of sliding friction under the influence of in-plane oscillations perpendicular to the sliding direction. Contrary to previous studies of this mode of active control of friction, we consider the influence of the stiffness of the tribological contact in detail and show that the contact stiffness plays a central role for small oscillation amplitudes. In the present paper we consider the case of a displacement-controlled system, where the contact stiffness is small compared to the stiffness of the measuring system. It is shown that in this case the macroscopic coefficient of friction is a function of two dimensionless parameters—a dimensionless sliding velocity and dimensionless oscillation amplitude. In the limit of very large oscillation amplitudes, known solutions previously reported in the literature are reproduced. The region of small amplitudes is described for the first time in this paper.