There is sufficient understanding of the rheology of traction in the viscous regime to make accurate calculations from measurable properties. It is no longer necessary to invoke fictitious viscosity or shear-thinning laws.

     Today, the inherent limits of high-temperature rolling bearing greases based on ester oil and containing polyurea as thickener are becoming more and more apparent, and this trend will continue in the future. While for rolling bearings in the automotive industry lifetime lubrication has been mandatory for many years, other branches of the machine building sector are now also requesting long-term or even lifetime lubrication. The new product concept presented in this article is to close the gap between high-temperature greases for up to 180^oC and the high-temperature greases based on perfluorinated polyethers and PTFE. Our experience so far has shown that these new greases are suitable for temperatures up to 220^oC. Grease life tests on FAG FE 9 and SKF ROF test rigs have demonstrated the greases' high level of performance.

     The present paper studies parametrically the flow patterns and pressure profiles inside of, and on the adjoining seals of a single hydrostatic pocket, characteristic component of hydrostatic journal bearings. The major focus is on the interaction between the effects of the shear flow (Couette) created by the rotation of an eccentric shaft and the pressure induced flow due to hydrostatic jet penetrating at the bottom of the pocket. The pocket is square in nature with a size of 17.8mm x 17.8mm footprint. Its bottom surface has a radial sliding capability, such that the depth of the pocket can be changed, without breaking pocket integrity. This construction allows the study and ensuing comparison of the influence of changes in clearance, jet strength and shaft angular velocity on the flow patterns, pressure profiles and the combined hydrostatic and hydrodynamic effects. The flow structure of the jet and its interaction with the flow in the pocket itself is visualized qualitatively using long distance microscopy (up to x400). The PIV system used herein is equipped with a digital video-camera and a pulsing laser (30mJ/pulse) with a repetition capability of up to 5000Hz.

     In this research, tribological properties of mineral, rapeseed, polyglycol oils and their mixtures were initially studied on a friction pilot stand (tribometer), a replica of a tribological wormgear transmission process. A "Steel ball bearing-three bronze surface" friction pair unit was used. A load of 216N at 0.5m/s was applied. The coefficients of friction, f, wear diameter scar, d_w, on bronze samples and viscosity index, VI on more than 50 oil samples in total were analyzed.
     Using mathematical modeling and simplex-centered optimization methods, optimum concentrations presented in the form of response surfaces on three-factor "composition – property" charts and polynomial equations describing the research parameters were obtained. The procedure includes the design and determination of permissible area and compromise search for viscosity index maximization with subsequent minimization of the other two parameters. Processing of experimental results, checking reproducibility, obtaining mathematical polynomial models describing the surfaces of response, checking the importance of regression factors, truncation of statistically insignificant equation coefficients, checking of the experimental results’ representation adequacy of the obtained equations using Fisher criterion were conducted at a 5% significance value.

     The objective of this paper is to present the analytical and numerical development leading to the simulation of a wavy thrust bearings. The analytical formulation is based on the application of the Reynolds equation to the geometry of two parallel circular plates with prescribed boundary conditions at their inner and outer circumferential edges. The upper plate is assumed to be rotating while the lower plate, which is wavy in geometry, is stationary. A numerical procedure based on the discretisation of the Reynolds equation yields a finite difference formulation that reduces the second order partial differential equation to a set of simultaneous algebraic equations. For a given loading condition, the equilibrium position of the rotating plate is evaluated using the Newton-Raphson search, by balancing the applied load with the force generated by the hydrodynamic fluid film resisting pressure. The stiffness of the bearing is then calculated using a numerical small perturbation procedure at the equilibrium position of the upper plate. Finally the transient motion of the journal is evaluated using a numerical integration scheme on the translational and angular acceleration parameters. General and specific conclusions are drawn based on these numerical results.

     Wire drawing experiments were performed under laboratory conditions using the hexagonal close packed metals cobalt and magnesium. It was experimentally shown that the material flow in the peripheral region controls the drawability of both metals at ambient temperature. Further, it became apparent that the roughness peak parameter R_z(DIN) was a reasonable measure to characterise the wire surface with regard to the drawability. R_z(DIN) < 2 micro m resulted in a successful drawing process. On the other hand, R_z(DIN) > 4 micro m led to shear crack formation and failure of the cobalt wires. Magnesium was less susceptible to surface roughness effects on shear crack formation than cobalt. Thicker lubricant films were tolerated and even needed.

     The surface and bulk of injection moulded spur gears made of glass fibres reinforced polyamide internally lubricated with polytetrafluoroethylene PTFE have been characterised before and after wear testing on a gear test rig. The use of irradiated PTFE proved to be essential to obtain the best wear behaviour. The evolution of surface morphology across testing time allowed to visualise the formation and breaking of a film layer between the two running gears. This film, formed through the melting of the polymers at the surface, plays an important role in polymer tribology in reducing the dry wear. In long lasting tests, the film is not only observed around the pitch line, but everywhere at the worn tooth surface. Generated wear debris could be parts of the film, broken through high shear and abrasive effect of fibre fragments, as confirmed by thermogravimetric and elemental analysis. The conclusions could be extended to various polyamide based composite gears. Running dissimilar materials against each other showed that the film is formed from the bulk of the gear. Therefore the film formation does not involve material transfer from one surface to its counterpart.

     Functionally graded metal matrix composites (FGMMCs) are novel materials attractive for aircraft and automotive tribological components. A superior combination of surface and bulk mechanical properties may be pointed as one of the main advantages of this new material concept. In particular, through an adequate control of the ceramic particles distribution from the surface down to the core of the component, the wear resistance may be improved at the surface while global toughness is preserved. In this work, the tribological behaviour of a Al-9%Si alloy reinforced with SiC particles processed by gravity and centrifugal casting is compared. Wear tests were performed using the pin-on-disc configuration, the composite being the disc while pins were built in cast iron. Sliding speed (0.5-1.5ms^-1) and disc temperature (22-300oC) were the main variables considered in the tests. Results suggest that formation of adherent iron-rich tribolayers in tests carried-out at room temperature is the main mechanism leading to an improvement of the wear resistance. For v=0.5ms^-1 , this effect is enhanced in the material obtained by centrifugal casting in which the surface area fraction of particles is higher. Temperature (externally applied or due to frictional heating) degrades the tribological performance of the reinforced materials, promoting transfer of aluminium from the disc to the cast iron counterface.

     In statically indeterminate rotor bearing systems involving hydrodynamic bearings, the relative lateral alignment of the bearing housings, i.e. the system configuration state, has a significant influence on the system stability and its vibration behaviour. This paper deals with a general identification procedure for determining the configuration state of any statically indeterminate system with hydrodynamic bearings. The technique is illustrated via numerical experiments using a fictitious four bearing system; and utilises the knowledge of the relative motion of the flexible rotors in their respective housing and of the absolute motion of the flexibly supported bearing housings, information which is now frequently available in existing turbomachinery installations. It is shown that acceptable configuration state identification is obtained even with 5% measurement uncertainty, here simulated by truncating all numerical 'measurements' to two significant digits. Since 5% measurement uncertainty is attainable with present measurement instrumentation, the identification technique is expected to be practically realisable.

     The extension viscosity increases for five examined greases above an individually different border area of the rate of extension. The maximum of the extension length could be measured. The formed fibres obtain substantial higher stretch almost close to the extension rate at which the extension viscosity starts to increase. It is suggested that there is a relation between the normal stress in shear tests and the tendency to form long fibres by drag.

     This paper examines the role of lubrication in mixed friction which is understood as a sum of different friction regimes from liquid to unlubricating. In this case, the friction zone is modeled by a two-demensional non-linear porous medium and the equations of the liquid filtration theory are used for describing the lubricant flow, the equations being modified since the rough surfaces forming the "porous medium" displace relative to each other. The lubricant flow model through rough friction surfaces is a new on in the theory of sliding friction.

     During scratching of a viscoelastic surface with a rigid tip, the geometry of the contact changes with the sliding speed and temperature. The apparent friction is the ratio of the tangential load, which is necessary to generate the relative motion, to the applied normal load. An apparent friction model is presented here and used to analyse the experimental friction coefficient of a polymer and the effects of the asymmetry of the contact area. The true friction might also depend on the sliding speed (contact time) and temperature.

     In a self-sealing journal bearing with spiral grooves, the bearing gap is not actually fully filled with lubricant. Specially at the seal interfaces, the so-called free boundary between the lubricant and ambient air is formed. A free boundary does not only influence the load-capacity and stability of a bearing, more importantly, it affects the bearing dynamic sealing capability. In this paper, an analytical model and numerical procedure is developed to investigate the free boundary of a journal bearing with spiral grooves. The simulation results are discussed on how the bearing parameters may affect free boundary and its impact on the bearing leakage. The approach establishes a base for precise calculation of performance parameters and optimization design of a journal bearing with spiral grooves in HDD.

     The nucleation mechanisms and early stages of four types of catastrophic wear (cw), which can be identified as adhesion-initiated (ai) are considered. Close connections are established: a) between two low-energy types of AICW and a disclination mode of plastic deformation and between two high-energy types of AICW and an amorphous mode of plastic deformation, b) between the incidence of either type of low-energy aicw and the hardness of an AICW seed domain relative to that of the friction surfaces, and c) between the onset of AICW and a competitive stripping and reformation of interlayers. Hypothesis on generation and transfer of energy and heat at microlevel (in process of movement of dislocations and disclinations) is developed as a base of amorphous deformation. Attention is drawn to a need for further consideration of terminology in this field.

     An overview of micro-tribological events, including micro-adhesion, micro-hysteresis and micro-lubrication is presented in this paper. The link between micro-lubrication and elastohydrodynamics is inseparable, but it appears that elastomer properties have diminishing importance as the scale of texture reduces. In the limit, micro-hysteresis effects give way to micro-adhesion, the latter depending critically on the harshness of micro-texture. Lubricant entrainment over asperity peaks is a function primarily of macro-texture, in particular the slope of such asperities and the void volume created by the macro-texture. This void volume acts as minute lubricant reservoirs which supply the entrainment mechanism and ultimately oppose the adhesion-generating harshness effect. There has been a limited investigation as reported in the literature of the macro-tribology of elastomeric contacts, but very little in the case of micro-events. This is surprising in view of the crucial relevance of such phenomena to an understanding of sliding seals, rubber mounts and tyre friction.

     A method to determine elastohydrodynamic film thickness in helical gears is developed by combining the Dowson-Higginson EHD formulation with helical gear geometry and kinematics. Comparisons are made to traditional gear film thickness models. This analysis is then used to characterize film thickness and lambda ratio in automotive planetary gearset. Methods to measure surface roughness in fine pitch gears are described.

     Wear as a surface loss of material resulting from friction is considered in connection with various factors affecting a tribosystem. It is shown that debris formed at friction can be a source of valuable information on the wear mechanism and mode. The shape, texture and color of particles can be used for wear analysis. Methods of image recognition are used in order to solve the problem of debris analysis and classification for further use as a database being a part of integrated monitoring service. The concept of wear monitoring and its main purposes are considered in the context of providing non-failure, long-term operation at optimum friction performance of a tribosystem. Wear monitoring tools based on the analysis of debris accumulation in lubricated machinery are reviewed.

     Hydrodynamic journal bearings are essential components of high speed machinery. Under severe operating conditions, manufacturing defects or thermal distortions may induce running problems such as misalignment. The aim of this paper is to present a realistic numerical model in order to predict the misaligned plain journal bearing performance under steady-state conditions. Therefore, a three-dimensional thermohydrodynamic (THD) analysis has been developed and the predictions obtained with the proposed numerical model are validated by comparison with measurements carried out on our test device.

     The model for the FEM based calculation of flow factors of operation media in immovable seals is proposed. The model is developed for the real 3D surface analysis.

     We propose a model for mixed lubrication between parallel surfaces. We first analyze the microgeometry. We determine a statistical distribution for asperity height and radius. Drawing upon these geometric parameters we identify the main mechanism available on a given asperity where from we deduce the individual normal and friction forces. The five possible mechanisms are iso- or piezo-viscous hydrodynamic, elastohydrodynamic, elastoplastic and full plastic. By association of the results obtained for each asperity, we derive the mechanical behaviour for the entire contact. Several numerical applications are proposed. Theoretical results show the influence of the main contact parameters. They strongly agree with experimental results and theoretically confirm the master curve obtained by plotting the evolution of the friction coefficient versus the _ parameter with respect to a given pair of materials and their microgeometry.

     This paper presents results of investigating the influence of technical processes of forming surface layers of selected frictional pairs for minimization of their wear. As a friction pair frictional composite - metal was chosen, where technical processes (diffusion of nitriding type) concerned the metallic element - cast iron. Applied technical processes brought a positive effect in the form of total wear reduction of the frictional composite and the metal as well as an increased value of friction coefficient.

     In a sheet metal working process, products or half products are manufactured from a flat sheet of metal. The friction between the material and the tools influences the process by modifying the strain distribution. From a numerical point of view, a constant Coulomb coefficient is commonly used in FEM simulations to model the frictional behaviour of contacting solids. However, this coefficient varies in time and space with many parameters. We present here a new control of the flat die test friction device which allows the determination of the static coefficient of friction. Experimental results are given for hot dipped galvanised steel sheets. We also propose a local friction law based partly on experimental results. FEM simulations are carried out for an axisymmetric stamping operation using the defined friction law. We compare the computed sheet thickness related to a local or global coefficient of friction. A localised influence of the local model is found on the punch nose that underlines the higher friction coefficient in this zone.

     Total joint arthroplasty is probably the most effective treatment for severe degenerative bone diseases such as osteo-arthritis. There has been renewed interest in the use of hard bearings, particularly the metal-on-metal combination for hip joint replacements due to the osteolysis problem associated with current metal-on-polyethylene prostheses. The potential for full fluid film lubrication has been shown to exist during part of the walking cycle in these hard bearing joints. In this study, theoretical and numerical analyses were carried out to characterise the loading and velocity and the corresponding lubrication regime in a typical metal-on-metal hip joint replacement tested in a free pendulum machine. It was shown that the loading in the joint remains relatively constant throughout the duration of swing. The maximum angular velocity achieved under frictionless conditions with an initial angular displacement of 5^o, was found to be about 0.387 rad/s, corresponding to a sliding velocity of 5.412 mm/s for a femoral head radius of 14mm. The lubricating film thickness due to the entraining action is only 0.011 micro m, which implies at best a mixed lubrication regime is experienced for the metal-on-metal hip joint tested in a pendulum machine with an average surface roughness of about 0.01 micro m. Under squeeze-film motion, the lubricating film thickness decreases to only about 0.01 micro m after the first few swings, assuming an initial separation between the head and the cup by the radial clearance. The theoretical predictions are consistent with experimental observations reported in literature. The lubrication regime under more realistic walking conditions cannot be deduced in the pendulum machine, largely due to the inappropriate loading and velocity conditions experienced in the pendulum.

     Recent studies have shown that a full fluid film lubrication regime can be developed in artificial knee joint replacements under simulated steady-state walking conditions by employing a thin compliant bearing surface with an elastic modulus similar to that of natural articular cartilage (Unsworth et al., 1988); Auger et al., 1993). The compliant bearing surface is usually bonded to a relatively stiff substrate in order to provide the structure support. Due to the abrupt change in stiffness, high interfacial shear strain is developed between the compliant layer and the stiff substrate and de-bonding usually occurs. The de-bonding problem can be expected to be alleviated to a certain extent by using functionally graded materials with variable stiffness. The purpose of this study was to analyze the contact mechanics of these functionally graded materials, with particular reference to knee prostheses. The finite element method was used to predict the contact parameters including the predicted contact pressure at the bearing surfaces and the interfacial shear strain between the compliant layer and the polymeric substrate.

     Based on a first-order perturbation solution in a modified Reynolds number an analysis is presented to determine the effect of the inertial forces of an isothermal gas lubricant film on pressure distribution and other parameters of a bearing with curvilinear surfaces. The corrections to the pressure distribution are found to be small, but noticeable. It is also found that these corrections in the case of only rotational inertia forces are significant. Numerical results for thrust bearings with a constant film thickness are given in graphical form.

     The effects of centrifugal inertia forces on the pressure distribution in a curvilinear thrust bearing lubricated by a generalized second grade fluid of power-law type are examined. The examples of flows in the bearings modelled by two disks and two concentric spheres are considered. The results obtained show that fluid inertia forces have significant effects on the pressure distributions.