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It is necessary to develop an analytical solution in order to combine predictions with measured tribological parameters and fundamentally understand the mechanism of lubrication in a typical region of engine cycle, using tribometric studies. This paper deals with the development of such a representative approach. An analytical, rather than a numerical approach is expounded, as it is shown to suffice for the purpose of precise time-efficient predictions, which conform well to the measurements. The effect of surface topography, material and operating conditions are ascertained for the representative case of top compression ring—cylinder liner contact at the top dead centre reversal in transition from the compression to power stroke. Stainless steel uncoated surface used as press fit cylinder liners for niche original equipment manufacturer applications are compared with those furnished with a Nickel-Silicon Carbide wear-resistant coating of choice in high performance motorsport.

Triboconditioning is a mechanochemical surface finishing process developed for improving the tribological properties of mechanical components made of steel or cast iron. The process combines elements of extreme pressure mechanical burnishing of the component surface with a tribochemical deposition of a low-friction anti-wear film of tungsten disulphide (WS2). This allows one to produce, in a single finishing operation, a smoother surface with a significantly reduced coefficient of boundary friction and improved wear-resistance and load-carrying capacity. This study presents results of tribological rig tests carried out with valve train components and cylinder bores that underwent the triboconditioning treatment. The results show significant improvement in the tribological properties of triboconditioned components. The improvement is attributed to the formation of WS2 tribofilms at the component surface and a modified surface roughness profile with reduced core roughness (Rk) and peak height (Rpk). Elemental composition of the tribofilms generated by the triboconditioning process has been studied by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy the surface profile of the treated components has been studied using vertical scanning interferometry and the internal structure of the tribofilms has been studied with focused ion beam–transmission electron microscope technique. Copyright © 2013 John Wiley & Sons, Ltd.

The friction behaviour of five different gear oils in rolling–sliding and pure sliding contacts and how temperature influences their friction properties were investigated. It is found that increasing temperature decreases boundary friction with gear oils that contain friction modifiers while not for other gear oils, at all contact pressures investigated. In mixed lubrication region, temperature decreases friction at low contact pressures while increases friction at high contact pressures. The effect of slide–roll ratio on friction is significant in boundary lubrication region especially at higher temperature while less significant in mixed lubrication region at both low and high temperatures. The ranking of gear oils for friction in boundary and mixed lubrication regimes is similar both in rolling–sliding and pure sliding contacts, regardless of temperature. Copyright © 2013 John Wiley & Sons, Ltd.

Starches of varying chemical structures were esterified with anhydrides, formulated into dry film lubricants with the addition of canola oil, and its friction properties investigated. In the absence of canola, chemically modified starch displayed a very high coefficient of friction (COF). Addition of canola resulted in a sharp decrease in COF, which decreased with increasing [canola] until it attained a minimum and constant value that was independent of the further increase in [canola]. This observation was attributed to the adsorption of the canola oil onto starch due to H-bonding between the ester groups of the canola triglycerides and the free hydroxyl groups of starch. Analysis of the [canola] vs COF data using the Langmuir adsorption model showed stronger adsorption of canola to modified starch with a lower degree of substitution (DS). This was attributed to the availability of more free hydroxyl group adsorption sites on starches with lower DS than those with higher DS. Copyright © 2008 John Wiley & Sons, Ltd.

The boundary coefficient of friction (COF) of starch–oil composite dry film lubricants was investigated as a function of starch type (waxy vs. normal purified food grade corn starch), oil chemistry (hexadecane vs. oleic acid and various vegetable oils), and starch-to-oil ratio. Based on the results, a mechanism of starch–oil interaction in these composites was proposed. According to the proposed mechanism: (a) the oil in the composite is distributed between the bulk and the surface of the starch; and (b) the fraction of the oil trapped in the bulk and that adsorbed on the surface are related to each other by an equilibrium constant, and are functions of the total oil concentration in the composite. In line with the proposed mechanism, an adsorption model was used to quantify the free energy of adsorption (ΔGads) of the polar oils onto the starch surface. The analysis gave ΔGads values that were higher than those reported for the adsorption of the same polar oils onto steel surfaces. This result is consistent with the effect of the relative surface energies of steel and starch on the adsorption of polar oils. The adsorption property of the non-polar hexadecane relative to the polar oils was estimated by comparing their interfacial tensions with starch. The result showed a higher interfacial tension for hexadecane–starch than that for the polar oil–starch composites. This result predicts a relatively poorer compatibility with, and, hence, poorer adsorption of hexadecane onto starch leading to higher COF, as was observed in the friction measurements. Published in 2006 by John Wiley & Sons, Ltd.

Hexadecane is widely used as the model base oil to investigate both tribological effectiveness and tribochemical reaction mechanisms of various antiwear and extreme pressure additives. On the other hand, it is well known from existing references that hexadecane, similarly to hydrocarbon oils, oxidizes during the lubrication process of tribological systems. It has frequently been pointed out that carboxylic acids are formed which — reacting with rubbing surfaces — generate soaps. Most recent studies, however, demonstrate that the oxidation process under friction conditions is very complex and the major oxidation compounds from hexadecane under boundary friction conditions relate to other oxygenates than carboxylic acids. This paper aims to examine what types of surface compound are generated from the hexadecane lubricant in the friction contact zone. Tribological tests were performed on a ball-on-disc tribometer. The discs used were made from several materials (steel, aluminium, brass, bronze). Fourier transform infrared (FTIR) microspectrophotometry and techniques involving a scanning electron microscope equipped with an energy-dispersive spectrometer were used to analyse tribochemical reaction products formed on different substrates. Analytical results obtained clearly demonstrate a similar tribochemical reaction process operating on all the metals tested. The FTIR results obtained allowed new absorption bands to be discovered and accounted for. These absorption bands have been assigned to specific complex compounds. Copyright © 2006 John Wiley & Sons, Ltd.

Studies were conducted to investigate whether adsorption of amphiphiles from oil onto a degreased metal can be predicted from knowledge about adsorption of the amphiphiles at the oil-water interface. The surface of a degreased metal comprises oxides, hydroxides, and adsorbed water vapor, which form from the reaction of the metal with air and moisture. If the behaviors of amphiphiles at water-oil and metal-oil interfaces are similar, this information can be useful in the development of cheaper and quicker methods of estimating amphiphile adsorption properties on degreased metals. The amphiphiles used were safflower oil (SA) and jojoba oil (JO), both of which are plant-based oils, and methyl palmitate (MP). SA is a triester whereas JO and MP are monoesters. The interfacial tension of water-hexadecane was measured as a function of amphiphile concentration in hexadecane and used to estimate an interfacial-based free energy of adsorption, ΔGads. The resulting interfacial-based ΔGads values for SA were identical to those reported from friction-based adsorption isotherms. The corresponding values for the monoesters were within the range reported from friction-based adsorption isotherms.

Effective axle oils must efficiently transfer torque from the drive-train to the wheels, while maintaining low axle oil operating temperatures. Previous studies have shown that fluids, which form thicker elastohydrodynamic (EHD) films and have lower EHD friction, have higher torque transfer efficiencies (TE) and lower axle oil operating temperatures (OT). In general, oils with higher viscosities form thicker films and those with lower viscosities have lower EHD friction. Therefore, optimizing oil's rheological properties to maximize TE and minimize OT is difficult. In this paper, we examine two approaches to maintaining high TE while reducing OT. One approach is to minimize boundary friction since previous studies have shown that the boundary frictional properties of oils influence OT and not TE. A second approach is to more thoroughly examine the effect of rheology on film thickness and EHD friction. Film thickness and EHD friction are related to the high temperature high shear viscosity and pressure-viscosity coefficient of oils. We have found that oils with high pressureviscosity coefficients and low high temperature high shear viscosities will form thick films and have low EHD friction. This optimized combination of physical parameters, along with lowering the boundary friction coefficient of axle oils, results in oils with high TE and low OT. Copyright © 2006 John Wiley & Sons, Ltd.

The ability of a lubricating oil to reduce wear and prevent damage of interacting solids is a crucial factor controlling lubricant formulation. It is well known that friction produces local high temperatures. Many chemical reactions that are initiated by the friction process itself occur at much lower temperatures than those needed to provide the activation energy. Under boundary lubrication conditions, a clean surface exposed as a result of mechanical activity of the solid surface is extremely reactive, especially in the case of metals. This review mostly relates to the tribochemistry of aluminium, and discusses the tribological characteristics of alcohol- and amine-type liquids used as either additives or lubricants to lubricate aluminium and its alloys under boundary friction conditions. Although tribochemical reactions during sliding are perceived in various ways, here the emphasis is on the negative-ion-radical action mechanism (NIRAM) approach. This review addresses the question as to how present knowledge of tribochemistry can be applied to the elucidation of the mechanisms of action by which the boundary lubricant compounds considered reduce aluminium-on-aluminium, steel-on-aluminium, and aluminium-on-steel wear. Also, information and a discussion on the tribological behaviour of other additives and/or lubricants in relation to the friction and wear of aluminium and its alloys are presented. A concise review of the most recent work on the tribochemistry of selected fluorinated alcohols is also included.

The behaviour of a range of model and commercial friction modifiers (FMs) has been evaluated under elastohydrodynamic (EHD) and boundary lubrication conditions. Using a series of long-chain carboxylic acids, it has been shown that measured boundary friction coefficients (BFCs) decrease with increasing chain length, unsaturation level, temperature, and concentration. Base oil polarity was found to have no effect under these conditions. Commercial oleate esters in synthetic base fluids gave lower BFCs than nitrogen-containing compounds under the same conditions. This difference was observed over a range of concentrations and temperatures. The friction performance of formulated oils under mixed and full-film EHD conditions was found to be dependent on FM, base oil, and detergent type. Under boundary conditions, friction was found to vary with FM type, but the effect of changing the base oil and the detergent system was negligible.

A theoretical analysis is presented of the mixed lubrication of a piston ring pack. The analysis comprises Patir and Cheng's average flow model and Greenwood and Tripp's asperity interaction model, and is developed to consider the shear thinning effect of a non-Newtonian fluid, multigrade lubricant. The friction characteristics of the piston ring pack 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, although this increases the boundary friction at the beginning of the expansion stroke. The friction characteristics are markedly affected by the shear thinning effect when multigrade lubricants are used.

This paper reviews selected phenomena related to the boundary friction process. The central thrust is on triboemission, defined as emission of electrons, charged particles, photons, etc., under conditions of boundary friction and/or surface damage caused by fracture processes. Low-energy electrons are one of the most important particle components in triboemission. Accordingly, the triboemission process is of particular significance for (i) the boundary friction process as such, and (ii) the tribochemistry of the boundary lubrication process. This review considers all the major issues of triboemission and related phenomena/processes. It is shown that, in the boundary lubrication regime with hydrocarbon lubricants, charge intensities decrease with an increase in lubricant molecular weight. The paper also includes some recent information concerning research on triboemission along with a newly developed apparatus.

Boundary friction between two crossed nylon 6,6 fibers has been reduced up to 6× by grafting polymeric lubricants to the surface. A modified adhesion model of friction, accommodating multiple materials on the surface, explains the variation in the friction coefficient with the molecular weight of the lubricant. The friction coefficient is proportional to the fraction of the surface covered by the grafted chain, represented by πR G 2 /A, where A is the surface area per graft site, and R G is the radius of gyration of the lubricant. It is also shown that for larger the grafted chains, the appropriate surface area fraction depends on πR G 2 /3A. It is argued that if R G of the grafted lubricant is larger than half the distance between graft sites, the next nearest graft site is used due to steric blocking of the nearest graft site.

An arbitrary Lagrangian-Eulerian model is described for the prediction of metal flow in a steady-state forming process. The formulation is shown to be capable of dealing with free surface and boundary friction; the coupling with thermal effects is also considered. The numerical techniques are based on the finite elements for spatial discretization of the momentum equation and on an explicit integration scheme for discretization relative to time. The mass and energy equations are integrated by a finite-volume method. Details on the application to an orthogonal cutting process are given in the final Section of the paper.

A linear model of lubricant-related engine friction was developed. Based on lubrication fundamentals, the technique is comprised of three simple bench tests that respectively operate under thick fluid-film hydrodynamic lubrication, elastohydrodynamic lubrication, and boundary lubrication. With adequate configuration and appropriate test conditions, these bench tests are seen to simulate major friction losses in a typical internal combustion engine. Lubricant characteristics obtained in the bench tests were combined using SAS linear regression and correlated to ASTM Five-Car and Sequence VI engine tests. The linear model gave an excellent prediction of engine data. It further showed that hydrodynamic friction losses dominate lubricant-related engine friction, followed by boundary friction losses, and elastohydrodynamic or mixed friction losses. This simple, reliable, and inexpensive technique can be used as a research tool to study friction characteristics of crankcase lubricants and to develop superior fuel-efficient engine oils. Major findings from this study can be summarised as follows: 1 The linear model predicts that 5 to 6% fuel economy improvement over the industry high reference oil HR-4 is achievable with today's motor oil technology 2 Hydrodynamic friction losses in both ‘thick' and ’thin' fluid-film lubrication account for 63% of total friction losses caused by the engine oil while boundary friction losses amount to 37%. 3 Friction losses in the elastohydrodynamic (EHD) engine are significant, up to 22% of total friction losses. This, combined with the fact that EHD film thickness is the most significant parameter in the linear model, suggests that pressure effects (ie, high-temperature/high-shear/high-pressure viscosity, pressure-viscosity coefficients) are important. 4 Increasing fuel economy improvement is in general in the order: SAE 10W–40 < SAE 10W–30 < SAE 5W–30, providing that base stock and additive systems are unchanged.

Testing lubricants for fuel economy is a significant part of the drive for energy conservation. Generally, the small differences in fuel economy between lubricants make measurements inherently uncertain. Furthermore, precise engine tests for assessment of energy efficiency are expensive and time consuming. There has been a need, therefore, for the development of an effective laboratory screening technique to assess the energy efficiency of engine oils. With this objective in view, a new test technique consisting of two different tests has been developed for measuring lubricant-related fuel economy. Fuel economy through the use of engine oil is achieved by reducing boundary friction and viscous friction. Whereas reduction in boundary friction is obtained through the use of friction modifiers in engine oil, viscous friction is reduced through the use of low viscosity oils and by multigrading. The efficacy of action of friction modifiers in reducing boundary friction has been assessed with a SRV-Oscillating Friction and Wear Tester, using point and piston ring/liner segment contact. For the measurement of viscous friction, an attempt has been made to find out the reduction in viscous friction by using low viscosity oils and multigrade oils on a SAE No. 2 Machine, with all-steel clutch plates.

A phenomenological rate and state-variable friction law for the continuous sliding under lubricated and dry conditions, asit occurs in metal forming processes, is presented in this paper. The contact model is developed within the framework ofcontinuum thermodynamics of irreversible processes with internal variables and for large strains assuming the contact area asa material surface. The model reproduces the experimental boundary friction map obtained by Luengo et al [1]. Fil: Luege, Mariela. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Estructuras "Ing. Arturo M. Guzmán"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina Fil: Luccioni, Bibiana Maria. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Instituto de Estructuras "Ing. Arturo M. Guzmán"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán; Argentina

Technische Universitat Braunschweig, Institute of Dynamics and Vibrations, Schleinitzstrase 20, 38106 BraunschweigNowadays a common material for journal bearings is PEEK (Polyetheretherketon) which is increasingly used under boundaryfriction. A Cellular Automaton model is developed to describe the boundary layer dynamics of PEEK and its compositePEEK6 sliding against a steel surface. Whereas PEEK is a homogeneous synthetic material, PEEK6 contains also carbonfibres for stability and fillers working as solid lubricants. The automaton shows a representative area of the real surface.The processes in the interface are described by a set of rules based on physical assumptions and measurements. Based onthese rules the simulations show the dependency of friction and wear on the load spectrum. The discrete simulation allows toobserve the topographic development of the PEEK and PEEK6 surface as well as the build-up of a transfer film on the steelsurface.

The steel/steel boundary friction properties of soybean oil (SBO) and high-oleic soybean oil (HOSBO) are compared. HOSBO is significantly more saturated than SBO and more oxidatively stable. Changes in degree of unsaturation affect lateral interactions of adsorbate molecules, which in turn affects their adsorption and, hence, their boundary lubrication properties. To investigate this possibility, the free energies of adsorption (∆G ads ) of SBO, HOSBO, and methyl laurate (ML) were determined from the analysis of friction-derived adsorp- tion isotherms using the Langmuir and Temkin adsorption mod- els. The results showed a stronger adsorption for the vegetable oils than for ML, an indication of multiple interactions between the ester groups of the triglycerides and the steel surface. The result also showed no difference in the ∆G ads values of SBO and HOSBO obtained using either the Langmuir or Temkin models. This was interpreted as an indication of the lack of appreciable net lateral interaction between triglyceride adsorbates. Paper no. J9858 in JAOCS 79, 53-58 (January 2002).

This paper is concerned with the effect of material properties, boundary friction, and inertia on the flow and strain patterns in material undergoing large plane strain compression. Experimental results are presented for both the rapid compression of Plasticine and the quasi-static compression of aluminium. In addition, a finite element code for rigid-plastic material behaviour is discussed, and approximate procedures are described for both in-plane and platen friction. Provision in the code was also made for strain hardening and strain rate sensitive material properties, and inertia effects. Comparison of the finite element and experimental results showed good agreement. Finite element calculations revealed that in-plane friction had a very significant effect on the strain patterns observed in the Plasticine experiments. Finite element calculations also showed that strain hardening was of fundamental importance in determining the strain patterns that were observed to occur in the quasi-static compression of aluminium.