bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of fluid inertia on the dynamic coefficients and stability of journal bearings
Authors: Kakoty S. K. , Majumdar B. C.
Published: October 2002

In the analysis of hydrodynamic journal bearings the effect of fluid inertia is generally neglected in view of its negligible contribution compared with viscous forces. However, there is a necessity to evaluate its effect at moderate values of the modified Reynolds number. An attempt is made to study the effect of fluid inertia on the stability of journal bearing for a flow in the laminar regime, i.e. for a value of the modified Reynolds number of the order of one. A linear perturbation technique is used to find the dynamic characteristics and stability of a finite journal bearing.
Stability analysis of a rigid rotor on tilting-pad journal bearings
Authors: Guijosa J. M. M. , Feng Z. C.
Published: October 2002

Tilting-pad journal bearings are used in many rotating machinery applications. They are known to have superior performance in comparison with fixed geometry cylindrical bearings. Previous analysis by other investigators on the rotor stability has shown that the pad inertia is the main limiting factor on the bearing performance. In this paper, that analysis is extended to examine the bifurcation types that are associated with the loss of stability in order to gain insight into whether the linear stable regions are robust under finite perturbations. The effect of pad friction force on the rotor stability is also examined. Furthermore, the analysis is extended to bearings with four pads.
Elastohydrodynamic lubrication of a circular point contact for a compliant layered surface bonded to a rigid substrate Part 1: Theoretical formulation and numerical method
Authors: Jin Z. M.
Published: October 2002

A full numerical analysis of the elastohydrodynamic lubrication problem of a circular point contact involving a compliant layered surface firmly bonded to a rigid substrate is reported in the present study. The Reynolds equation has been solved simultaneously with the full elasticity equation for the layered bearing surface under entraining motion, using the Newton-Raphson method. The theoretical formulation and the numerical method are presented in the present paper (Part 1), together with the comparison of the predicted minimum and central film thickness between the present solution when the contact radius is much smaller than the layer thickness and the results for a semi-infinite solid reported in the literature.
Tribological behaviour of carbon-fibre-reinforced SiC matrix composites
Authors: Fournier P , Reynaud Ph , Platon F , Absi J
Published: October 2002

Reinforcement of monolithic ceramics by carbon fibres improves the tribological behaviour of ceramic materials. The lamellar graphite of carbon fibres can act as a natural third body, leading to low friction. The tribological behaviour of carbon-fibre (M40)-reinforced SiC matrix composites under different experimental conditions (velocity, load and temperature) is discussed in this paper. C-SiC composites are tested in sliding contact using a disc-on-disc tribometer. The results show that the behaviour of the contact is highly dependent on friction conditions. Friction transitions can occur during tests. The purpose of this paper is to identify the mechanisms which lead to these transitions. The main hypothesis concerns the mechanical and thermal fatigue phenomena. Under restrictive experimental conditions the C-SiC composites can be considered as self-lubricating materials. Self-lubricating conditions are experimentally given by a curve according to test temperature and pv parameter.
Grease soap particles passing through an elastohydrodynamic contact under side slip conditions
Authors: Eriksson P , Wikström V , Larsson R
Published: October 2002

In a previous investigation, grease thickener fibres were tracked as they passed through an elastohydrodynamic (EHD) contact in pure rolling using interferometry in a standard ball-and-disc apparatus. In order to capture single thickener fibres, a high-speed video camera was used.

Here, the experiments have been repeated introducing different amounts of side slip for different rolling speeds and a faster video camera capable of capturing 4500 frames/s. The contact was lubricated with a continuous supply of grease. Two greases, based on the same synthetic poly(α-olefin) but thickened with Li-12-OH and lithium complex soap respectively, were studied. It was observed that the thickener fibres were stretched both before entering the contact and as they passed through it. Fibres seem to avoid the minimum film thickness regions and, if they enter, the film is restored immediately after passage.
Lubricant thermal conductivity and heat capacity under high pressure
Authors: Larsson R , Andersson O
Published: October 2002

The thermal conductivity λ and the heat capacity per unit volume, ρ c p, have been measured for a number of common lubricating oils. The oils tested were paraffinic and naphthenic mineral oils and a 50/50 blend of these. Poly-α-olefin, polyglycol, Santotrac, ester and rapeseed oils have also been tested. The measurements, using the transient hot-wire method, were carried out under isothermal conditions over a pressure range from atmospheric to 1.1 GPa and at two temperatures, 295 and 380K (22 and 107 °C respectively).

The temperature had only a marginal effect on thermal conductivity; however, the thermal conductivity was doubled as the pressure was increased to 1 GPa. The heat capacity per unit volume was influenced by both the pressure and the temperature. Some of the lubricants solidified as the pressure increased and the transition from a fluid to a solid state could be detected in the measurements of ρ c p.

The relationship between the thermodynamic properties and the pressure and temperature are described by two empirical equations. These equations can be used in thermal elastohydrodynamic analyses.
Lubricated seizure of mild steel observed by X-ray imaging
Authors: Chandrasekaran M , Batchelor A. W. , Loh N. L.
Published: October 2002

Observation of frictional contacts has always been a problem as the contact is normally hidden. In this work, an X-ray microscope has been used for in situ observation of frictional seizure, wear and interfacial features during the testing of mild steel specimens sliding against an Al alloy 6061 disc. This technique enables the interfacial features of the hidden contact to be observed. Seizure tests were conducted at different sliding speeds of 2, 4 and 5 m/s under lubricated conditions with plain mineral oil. The images obtained during the tests indicated that the X-ray attenuation along its path increased with sliding at isolated locations, due possibly to localized changes in path length or attenuation by the degraded mineral oil. The sliding speed was found to have a considerable impact on the degradation of the oil, which affected the seizure behaviour.
Prediction of oil-film thickness and shape in elliptical point contacts under combined rolling and sliding motion
Authors: Jalali-Vahid D , Rahnejat H , Gohar R , Jin Z. M.
Published: October 2002

The paper presents a numerical solution for elliptical point contact conjunctions under combined rolling and sliding motion. This condition is prevalent in many practical applications, such as rolling element bearings and conformal gears. An effective influence Newton-Raphson method is employed in local point distributed or global line distributed low-relaxation iterations. This method enables determination of the pressure distribution and film shape at high loads such as are encountered in many practical applications. Some of the numerical predictions have been validated against experimental results.
Surface roughness attenuation in line and point contacts
Authors: Hooke C. J. , Venner C. H.
Published: October 2002

Surface roughness effects in line and point elastohydrodynamically lubricated contacts are compared and it is shown that the underlying behaviours in both types of contact are identical. Long wavelength components of roughness are attenuated; short wavelength components pass through the conjunction unaltered. It is also shown that the roughness attenuation, plotted against a non-dimensional wavelength, follows almost identical curves in both cases.
Friction study of carbon-silicon carbide couples
Authors: Vantomme P , Deprez P , Placet A , Gaillot D
Published: October 2002

This experimental study concerns the tribological properties of different carbon-porous silicon carbide couples. A tribometer was used to determine the coefficients of static and dynamic friction of these couples of materials. The parameters able to influence the static and the dynamic friction coefficients such as the finish of the porous silicon carbide material, the quality of the carbon material, the normal load, the surroundings and the speed in the case of dynamic friction have been studied.
Establishing the effectiveness of a lubricant in the deep drawing process by means of prior loading duration variation
Authors: Ashbridge M. T. J. , Gilmour K. R. , Leacock A. G.
Published: October 2002

With the many different lubricants available for similar purposes today, the choice that the engineer must make is often based on arbitrary assumptions or confined to personal experience. In the present paper, the authors present a new technique of determining the suitability of potential lubricants for the deep drawing process. The technique is also applicable to many metal forming processes where lubricant selection is critical to the success of the operation.
Non-isothermal performance characteristics of fluidfilm mechanical face seals
Authors: Cicone T , Pascovici M. D. , Tournerie B
Published: October 2002

Published experimental data and results of numerical modelling have shown that in certain cases the temperature gradient along the radius of the sealing gap of mechanical face seals (MFSs) can be significant. As a consequence, isothermal calculation of seal performance characteristics can induce some errors. In a recent paper, Pascovici and Etsion investigated the accuracy of the steady state isoviscous solution of the Reynolds equation in an MFS with flat and aligned surfaces (parallel faces). The aim of the present paper is to continue the investigation to the more general case of a non-parallel film. Hence, an analytical non-isothermal solution of the Reynolds equation for an MFS with coning is developed. The solution, based on a simplified linear temperature distribution across the seal dam, allows the seal performance characteristics for inwardly convergent, externally pressurized seals to be calculated. A parametric study is performed in order to define the level of approximation made by the isoviscous solution. It is found that, for a practical range of seal operation conditions, the accuracy of the isoviscous solution is acceptable for the opening force, film stiffness and frictional torque. On the contrary, the isoviscous solution can lead to an important underestimation of the leakage for almost all practical cases. The errors depend on two variables representative of the film thickness and viscosity variation in the seal dam.
Studies of fly stiction
Authors: Zhao Z , Bhushan B
Published: October 2002

A study of fly stiction caused after a head slider flew over a disk surface was conducted to understand the mechanisms responsible for high stiction. In this paper, laser-textured disks and three types of nanosliders (50 per cent of the standard size) were used. Friction/stiction was measured and the r. m.s. acoustic emission was recorded in both a short sweep test where the slider swept for periods of 1 h and a long-sweep test where the slider swept for periods of 6 days. The surface of the head slider after tests was analysed using optical microscopy, atomic force microscopy/frictional force microscopy and Raman spectroscopy. Results showed that, in the short sweep test, stiction was sensitive to environmental humidity. Stiction was low at low humidities and increased with increase in the humidity. In the long-sweep test, liquid droplets accumulated during flying were observed on the head slider surface. The vortex around the head slider was found to be responsible for the accumulation of liquid droplets. The droplets then migrated to the rail surface and led to fly stiction during the following start-up. Stiction was sensitive to these liquid droplets in addition to the humidity. Both negative and positive-pressure sliders could cause fly stiction. A lower flying height was found to be more susceptible to fly stiction. A disk with a fully bonded lubricant film lowered the stiction. Increasing the disk speed could increase the stiction of a negative-pressure slider whereas it lowered the stiction of a positive-pressure slider because of the effects of flying heights, lubricant spin-off and intensity of the vortex
Investigation of the ball-bearing temperature rise under an oil-air lubrication system
Authors: Jeng Y-R , Gao C-C
Published: October 2002

Ball-bearings are widely used on many high-speed rotating systems. However, heat generation and dynamic loading caused by high-speed operation have been the limiting factors for increasing the speed limit of many high-speed ball-bearing applications. Therefore, providing proper lubrication and preload to reduce heat generation effectively is a major task for high-speed ball-bearings.

Recently, oil-air lubrication has been used on high-speed ball-bearings because of precise oil quantity control and high cooling efficiency. However, the fluctuation in oil supply resulting from the periodic oil feeding is unfavourable. In this study, equipment for measuring the fluctuation in the oil supply was established. The operation parameters affecting the stability of the oil supply for an oil-air lubrication system were experimentally studied. A test rig for high-speed ball-bearings was also developed. Tests were conducted to study the effects of the preload, oil quantity, air flowrate and rotating speed on the bearing temperature rise. The operating conditions that provide a stable oil supply and low bearing temperature rise were established.
Dynamics of rotors supported on fluid-film bearings using neural networks
Authors: Rao M Ananda , Srinivas J
Published: October 2002

This paper deals with the determination of shaft centre response and oil-film forces of a rotating rotor-bearing assembly. The successive points in a long time history of the rotor-centre motion during a transient vibration period have been identified. Fluid-film forces are generally influenced by several design variables. The calculation of these forces is not straightforward because these equations of motion of the system contain non-linear terms. Initially the most influential parameters are identified. A supervised multi-layer neural network model is then trained with the input and output data using the back-propagation algorithm. The response characteristics and fluid-film forces are derived as the outputs of the neural network for different conditions of bearing parameters. The results are compared with the usual solution techniques.
Influence of ‘off-contact’ electric potential on frictional behaviour of an agate-brass (SiO2-Cu) rubbing couple
Authors: Jiang H , Wong P. L. , Meng Y
Published: October 2002

The effect of ‘off-contact’ electric potentials on the frictional behaviour of an agate-brass rubbing couple was investigated using a commercial pin-on-disc wear machine. The electric field was set to cover a large portion of the disc surface area but excluding the agate ball and brass contact. This is referred to as the ‘off-contact’ potential. A suspension of 1 wt % zinc stearate powder dispersed in de-ionized water was adopted as a lubricant in the experiments. Experimental results show that the coefficient of friction can be increased markedly by imposing a positive biased potential (disc with negative charge) when it exceeds a threshold value. For applying negative biased potentials, there are no obvious effects recorded. Furthermore, the amount of increase in the coefficient of friction by imposing a fixed potential decreases with an increase in the applied load and the sliding speed, but the decreasing rate gradually becomes smaller. Experimental results under a. c. potentials in the frequency range from 0.1 to 100000 Hz were also presented and no obvious changes in the coefficient of friction for an agate-brass rubbing couple were observed.
Design and development of a ball impact apparatus for the direct measurement of lubricant friction under high pressures and shear rates
Authors: Workel M. F. , Dowson D , Ehret P , Taylor C. M.
Published: October 2002

The development of a new ball impact apparatus for the measurement of the traction behaviour of solidified lubricants is described. The normal and tangential forces between an oily plate and an obliquely impacting ball were measured directly on two different forms of apparatus by means of piezoelectric transducers. From the measured forces the coefficient of friction during impact could be calculated. For one particular oil, Santotrac 50, a full set of results is given and these are shown to be in good agreement with values reported previously by others using different forms of experimental equipment.
The development and application of the spacer layer imaging method for measuring lubricant film thickness
Authors: Spikes H. A. , Cann P. M.
Published: October 2002

This paper reviews the historical development of optical interferometry as applied to the study of lubricant films. The technique was first applied to lubricated contacts in the 1960s, when it played an important role in the validation of the elastohydrodynamic theory of lubrication. Initially the method was not suited to the study of mixed and boundary lubrication because it could not measure film thicknesses of less than about 50 nm. In the 1970s, however, this limitation was partially overcome by the use of a spacer layer and this, coupled in the early 1990s with spectrometric analysis of the interfered light, enabled films down to just 1 nm thick to be measured in lubricated contacts, well within the boundary lubrication regime. Recently a number of workers have applied colorimetric image analysis to optical interference images to enable accurate three-dimensional maps of film distribution in lubricated contacts to be determined. This approach, coupled with the use of a spacer layer, has led to the spacer layer imaging method, which can map film thickness in boundary and mixed lubricated contact. Some recent applications of this technique are described.
Effects of slide-roll ratio and lubricant properties on elastohydrodynamic lubrication film thickness and traction
Authors: Lord J , Larsson R
Published: October 2002

With tribology research aimed at decreasing energy consumption, two factors are inherently in focus: lubricant film thickness and traction. These factors are effectively decoupled and depend on lubricant properties which are sometimes contradictory-favourable for one factor and disadvantageous for the other. The film thickness ought to be maximized to reduce the number of asperities in contact and thus wear, whilst the traction should be minimized in order to reduce energy losses. In this experimental investigation the tested lubricants were investigated to see whether they possess beneficial properties for forming thick lubricant films under severe operating conditions while maintaining low traction forces. This is done by experimentally studying the film thickness reduction due to thermal and rheological effects for a fully flooded electrohydrodynamic lubrication (EHL) contact. The base oils tested were a naphthenic mineral VG150, a synthetic poly-α-olefin VG68 and a synthetic ester VG46. It was found that the synthetic ester maintained a relatively thicker lubricant film during sliding than the poly-α-olefin and mineral oil. The film thickness reduction for the mineral oil was greater than for the poly-α-olefin.
An experimental/theoretical approach to modelling the viscous behaviour of liquid lubricants in elastohydrodynamic lubrication contacts
Authors: Fang N , Chang L , Johnson G. J. , Webster M. N. , Jackson A
Published: October 2002

This paper presents an experimental/theoretical approach to modelling the viscous behaviour of liquid lubricants under elastohydrodynamic lubrication (EHL) conditions. The main feature of the approach is that the rheological variables at a single point in the EHL contact are used rather than their global averages. The local rheological variables are calculated using first-principle theories in conjunction with experimental traction data. They are then curve fitted into an Eyring-based rheological model, and the model parameters are determined by minimizing the error vector associated with the curve-fitting procedures. The modelling approach is evaluated both theoretically and experimentally. The theoretical evaluation suggests that the method of modelling is meaningful for median to high-loading conditions of a Hertz peak pressure above 0.8 GPa. The experimental evaluation demonstrates that the approach may be used to study the rheological behaviour of synthetic lubricants with various molecular structures.
Thermal elastohydrodynamic analysis of circular contacts Part 2: Non-Newtonian model
Authors: Kim H. J. , Ehret P , Dowson D , Taylor C. M.
Published: October 2002

The numerical developments described in Part 1 are extended to incorporate the consideration of non-Newtonian effects, and fully coupled solutions of the thermal non-Newtonian elastohydrodynamic lubrication point contact problem are presented. The numerical findings are compared with a series of experimental results performed by Cann and Spikes with a steel-sapphire point contact in pure sliding conditions. Fair agreement with the experimental results is obtained in terms of surface temperature. Comparison of the results under identical conditions but with a steel-steel contact is also undertaken and shows that a steel-sapphire contact represents a good simulator of a steel-steel contact in terms of temperature and film thickness. The influence of the viscosity relationship is also considered and reveals that the Yasutomi et al. equation leads to only a marginal difference compared with the Roelands equation for the cases considered.
Prediction of lubricating film thickness in a ball-in-socket model with a soft lining representing human natural and artificial hip joints
Authors: Jalali-Vahid D , Jagatia M , Jin Z. M. , Dowson D
Published: October 2002

A simple ball-in-socket model was adopted in this study to analyse the lubrication problem of both natural hip joints and their artificial replacements. A compliant layered bearing surface was considered to represent articular cartilage as found in the natural synovial joint and also in the artificial hip replacement where an ultra-high molecular weight polyethylene (UHMWPE) acetabular cup was employed. The cup was assumed to be stationary while the ball was assumed to rotate at a steady angular velocity and under a constant load. A successful numerical method developed in a previous study by the present authors was used to solve the Reynolds equation in spherical coordinates, simultaneously in conjunction with the corresponding elasticity equation based upon the constrained column model. Numerical solutions thus obtained enabled general formulae to be fitted for both the minimum film thickness and the central film thickness, based upon the prediction from the equivalent ball-on-plane model and the half-contact angle. These formulae were then applied to predict the lubricating film thickness in both natural hip joints and their artificial replacements.
Archard wear and component geometry
Authors: Kauzlarich J. J. , Williams J. A.
Published: October 2002

The wear performance of tribological material pairs is commonly assessed by experimental investigations which make use of rigs incorporating a pin-on-disc geometry. The information so generated is conventionally interpreted in terms of a linear relation between wear volume, applied load and sliding distance in accord with the Archard wear equation. An appropriate material parameter is thus the so-called dimensional wear rate usually measured in mm3/N m. However, there are many practical situations in which, as components wear, the area of apparent contact changes so that, although the Archard relation may still be applicable on the microscale, the relation between either the macroscopic wear dimension, or the total wear volume, may be other than a linear function of sliding distance or load. The following examples are considered: a spherically ended pin sliding or rotating against a flat, a pair of crossed cylinders, a radially loaded journal bearing and a radially loaded spherical bearing. Data from the wear literature are examined in the light of the analyses presented.
Design functions for hydrodynamic bearings
Authors: Ståhl J , Jacobson B. O.
Published: October 2002

Designing hydrodynamic bearings usually requires a total numerical analysis of the pressure distribution and corresponding design quantities such as the load capacity, load position, oil flowrate, power loss, coefficient of friction and relative power loss. Another option is to determine the design quantities from design diagrams, which may give rise to inaccurate results, especially if interpolation between the curves is needed. Instead, it would have been better to have functions describing the design quantities.

The objective of this work is to determine curve-fitted functions describing each design quantity, by following a well-defined procedure. Three different kinds of geometry are analysed: rectangular tilting-pad thrust bearings, sector-shaped tilting-pad thrust bearings and journal bearings with two axial oil grooves. In addition, an optimum analysis is performed.

The approximate design functions obtained in this work show very good resemblance to the numerically calculated results, and they are valid for a wide range of the geometric parameters. The intention is to use the functions in programmable pocket calculators or implemented short computer programs, making them a very fast and accurate alternative to a complete numerical analysis in bearing design. Finally, the functions concerning the optimum analysis saves a large amount of time compared with a traditional analysis.
Bearing cage temperature measurement using radio telemetry
Authors: Joshi A , Marble S , Sadeghi F
Published: October 2002

Two different versions of a temperature telemeter were designed and developed for use in tribological environments and their usefulness as a condition-monitoring instrument for bearings is demonstrated. The first version is a battery-powered telemeter and it is designed to have extremely small size and mass, which are essential for application in rolling element bearings. The second version is a remotely powered design, which has similar features to that of the battery-powered telemeter but provides the advantage of an almost infinite life and even smaller size. The telemeters were installed on the cage of a tapered rolling element bearing and tests were conducted under normal and severe conditions to determine the feasibility of the cage temperature as a condition-monitoring parameter on a bearing. A finite element model of the cage was developed to study and compare with experimental results. The tests conducted indicate that the cage temperature demonstrates a very fast response to tribological changes such as interruption in lubrication supply, speed or torque variation and it is thus a good parameter for determining the temperature condition of a rolling element bearing.
The dynamic behaviour of a system that includes a rolling bearing
Authors: Wensing J. A. , van Nijen G. C.
Published: October 2002

To enable a reduction of cost and time-to-market, fast and accurate predictions are required of the dynamic characteristics of new products in the earliest stage of design. A growing number of these new products have rotating components, which are supported by rolling element bearings. Although ball and roller bearings have a significant and complex contribution to the dynamic behaviour of machinery, they are often subjected to rigorous assumptions in the case of modelling. At present many bearing models still fail to describe adequately the stiffness of the outer (and inner) rings and the actual stiffness and mass distribution of the connecting bearing housings, the time-dependent variations of the bearing stiffness (parametric excitation), the damping in the elastohydrodynamically lubricated contacts and the vibrations generated by form deviations. Therefore, a new method is presented, which accurately describes the time-dependent stiffness and mass properties of a rolling bearing application in an efficient way. The method enables a full transient analysis to study the effect of time dependent system properties, form deviations and mounting errors. Also the damping in ball and roller bearings is assessed, by comparing the results of advanced numerical simulations with experimental data. The new modelling method is used to investigate how damping and parametric excitation interact in a real bearing application. The increased level of accuracy that is obtained with the present method is elucidated by validation measurements.
Analysis of grease lubrication of a ball bearing using acoustic emission measurement
Authors: Miettinen J , Andersson P , Wikströ V
Published: October 2002

The behaviour of grease lubrication in a rolling bearing is less known than that of oil in the same type of tribological system. In recent years the research of grease lubrication has shown several features of the grease lubrication that differ from the classical elastohydrodynamic lubrication theory of oil lubrication, notably that starvation is more prominent under grease-lubricated conditions.

The goal of the present investigation was to clarify, by using a real bearing installation and realistic running conditions, how the fundamental properties of the lubricating grease influence the lubrication in a rolling bearing. The fundamental properties of the greases considered in the study were thickener concentration, base oil viscosity, base oil bleeding rate and consistency. Results obtained with grease lubrication were verified with pure oil lubrication.

The analysis of grease lubrication in the present investigation is based on the relative differences in the pulse count rate of the acoustic emission (AE) generated by the running of the bearing. In order to make the correct decisions about the lubrication situation of a bearing, the fundamentals of the behaviour of grease lubrication in rolling bearings and its influence on the AE signal have to be known. Moreover, AE has proven to be a good tool to study grease lubrication in situ in a bearing. The results show that starvation of the lubrication situation increases with increasing thickener content and decreases with lowered base oil viscosity. This is in agreement with film thickness measurements made in ball-and-disc type equipment.
Effect of debris contamination on the fatigue life of roller bearings
Authors: Ai X
Published: October 2002

Debris-induced surface-initiated fatigue failure has been recognized as a major mode of failure for modern rolling element bearings. The important aspects essential for failure prediction are discussed. The discussion covers contaminant analysis, particle entrainment, surface indentation, stress concentration and debris life reduction. Quantitative relationships are provided. They constitute a set of useful tools for debris-life prediction of roller bearings.
Modified split Hopkinson pressure bar method for determination of the dilatation-pressure relationship of lubricants used in elastohydrodynamic lubrication
Authors: Åhrström B-O , Lindqvist S , Höglund E , Sundin K. G.
Published: October 2002

In theoretical calculations of film thickness, pressure distribution and friction in an elastohydrodynamically lubricated (EHL) conjunction it is necessary to model the physical/ mechanical behaviour of the lubricant. It is important to know, for example, the dilatation-pressure or the density-pressure relationship. In this paper a modified split Hopkinson pressure bar system for determination of the compressibility of oil is presented. It makes it possible to test oils under conditions similar to those found in real EHL contacts: loading duration in the range of 100–300 μs and pressures of almost 2 GPa. An empirical model has been suggested for mathematical description of the dilatation-pressure relation of the specific oils. A naphthenic mineral oil and a synthetic oil, 5P4E, have been tested under adiabatic conditions and at pressures up to 1.5 and 1.9 GPa respectively. The adiabatic results have been recalculated to isothermal conditions for comparison.
The efficiency and friction of plastic cylindrical gears Part 2: Influence of tooth geometry
Authors: Walton D , Cropper A. B. , Weale D. J. , Meuleman P Klein
Published: October 2002

In Part 1 the influences of materials and material combinations on the efficiency of plastic gears were investigated. In this paper, the effect of changes to plastic gear tooth geometry is investigated. Using a gear tooth form of standard proportions as the benchmark gear, gears were moulded to a number of different specifications. These changes in geometry included speed ratio, module, pressure angle, addendum, integer contact ratios and tip relief. Sensitivity to centre distance variations was investigated on the benchmark geometry. A helical gear was also tested for comparison with a spur gear of comparable specification. Using measured efficiencies, coefficients of friction were determined for a number of the gear geometries examined.
Application of analysis of variance to wet clutch engagement
Authors: Mansouri M , Khonsari M. M. , Holgerson M. H. , Aung W
Published: October 2002

Factorial design is applied to a wet clutch in automatic transmission in order to study and predict the effects of operating conditions on its engagement. The analysis relies on a series of experimental measurements and computer simulations to compute process responses. Included in the simulations are the drive torque, friction coefficient, system inertia, applied load, engagement time, developed energy, maximum brake torque, maximum power requirement and maximum temperature rise. Analysis of variance (ANOVA) is performed to quantify realistically the main and interaction effects of the system parameters on process responses.

ANOVA results are effectively compiled into charts complemented with prediction models, which could be used as a valuable tool to facilitate learning for a novice trainee and to allow a designer to evaluate quickly and effectively the effects of operating conditions on, and prediction of, performance parameters. The scope of this analysis tool, as applied to wet-clutch engagement, is not limited to operating conditions and could be extended to include materials selection, and to explore ideas not yet fully tested.
The high pressure rheology of some simple model hydrocarbons
Authors: Bair S
Published: October 2002

The variation in viscosity with pressure and shear rate is required for modelling of film thickness and traction in elastohydrodynamic contacts. Two examples are presented with supporting data for lubricants. Then, five well-characterized simple, low molecular weight hydrocarbon liquids are investigated in detail. The effect of structure on the pressure-viscosity response and non-Newtonian response is discussed. A favourable comparison can be made with non-equilibrium molecular dynamics simulations on squalane.
Dynamic behaviour of elastic engine main bearings: Theory and measurements
Authors: Moreau H , Maspeyrot P , Chomat-Delalex A. M. , Bonneau D , Frene J
Published: October 2002

The design of crankshaft bearings is carried out with software using many assumptions on the geometrical and operating bearing parameters. The calculation results are thus more or less close to reality according to the assumptions used. In order to know the level of accuracy of the theoretical results, it is necessary to compare these results with those obtained by experimentation.

This paper describes the experimental measurements and the theoretical calculations of oil-film thickness in a dynamically loaded crankshaft main bearing. Four eddy current gap sensors for each bearing are used to measure the oil-film thickness and to deduce the shaft trajectories. The elastohydrodynamic model considers the bearings, housing and crankshaft elastic deformations. The calculation process uses the finite element method and the Newton-Raphson method for the numerical analysis. Comparisons of the load effects and crankshaft speed are made between the experiment and the theory.
Analysis of lubrication and friction for a complete piston-ring pack with an improved oil availability model: Part 1: Circumferentially uniform film
Authors: Ma M-T , Sherrington I , Smith E H
Published: October 2002

The study of the tribological performance of piston rings plays an important role in piston assembly design. In this study, a comprehensive analysis of piston-ring pack lubrication has been developed. The model employs a flow-continuity algorithm and considers relative ring locations in the piston-ring pack as well as oil accumulation in front of the ring in determining the oil availability. The computer model is able to predict the effect that bore distortion and ring conformability have on piston-ring performance. (This influence is discussed in Part 2 of the paper). In this part of the paper (Part 1), the theoretical formulation of the model is briefly described. The model is verified through comparison of the calculated ring-liner film thicknesses with those measured experimentally by Hamilton and Moore on a diesel engine. Then some results, obtained under situations where film thicknesses are circumferentially uniform, are presented to simulate a piston-ring pack in a modern petrol engine as an example to demonstrate the capabilities of the model and to show the effects of some important factors on the performance characteristics of the ring pack. The authors have found that the model developed is a robust one which can be used to analyse the tribological performance of ring packs effectively in both circular and distorted cylinder bores of internal combustion (IC) engines.
Experimental study of ultrathin liquid lubrication film thickness at the molecular scale
Authors: Matsuoka H , Kato T
Published: October 2002

Ultrathin liquid lubrication film thicknesses at the molecular scale are measured by a new apparatus developed by the authors. Mica is used as the solid specimen and octamethylcyclotetrasiloxane (OMCTS), cyclohexane and n-hexadecane are used as liquid specimens. From experimental measurements, discretization of the lubrication film thickness is observed when the thickness is less than about 10 times the molecular diameter of the intervening liquid. Analysis of experimental data shows that the discretization of the lubrication film thickness is due to the solvation force. Dynamic measurements show that the solvation force is almost the same as the non-sliding case and is independent of the sliding speed of the solid surface.
Elastohydrodynamic lubrication of soft viscoelastic materials in line contact
Authors: Hooke C. J. , Huang P
Published: October 2002

The paper discusses the influence of viscoelasticity in elastohydrodynamic lubrication (EHL). It is shown that viscoelastic effects, particularly in soft materials such as rubber and polymers, may significantly affect the lubrication process. The variations of the pressure and film thickness with viscoelasticity are discussed, as is the internal energy loss in the material. Two effects are present. The first, controlled by the Deborah number based on the Hertz contact width, determines the width of the contact, the overall pressure distribution and the energy loss. The second, controlled by the Deborah number based on the entrainment length, largely determines the thickness of the entrained film and the minimum film thickness.
The design of lubricious oil-in-water emulsions
Authors: Ratoi-Salagean M , Spikes H , Hoogendoorn R
Published: October 2002

Oil-in-water emulsions, as used in metal working and fire-resistant hydraulic fluids, often show poor lubricating performance and one reason for this is their inability to form effective elastohydrodynamic films. This paper considers how the composition of an oil-in-water emulsion contributes to its lubricating properties.

A key factor in oil-in-water emulsion performance lies in the ability of the dispersed oil droplets to wet polar metal surfaces and thus promote full elastohydrodynamic lubrication, without starvation, up to high speeds. In this paper it is shown how this ability can be quantified in terms of measurable surface chemical parameters. Based on this work, three rules for designing lubricious oil-in-water emulsions are proposed. Where possible (a) the emulsifier concentration used should be just below its critical micelle concentration value, (b) the base oil should be polar and (c) the base oil should be viscous. The first two of these factors will promote oil-phase surface wetting while the third will ensure thick-film formation in the full elastohydrodynamic regime.
Effect of environment on drop-outs in rotary head—tape drives
Authors: Anderson R M , Bhushan B
Published: October 2002

The effect of environment on the drop-out performance of magnetic tapes in a rotary head-tape drive was studied. A capacitance probe, mounted on the rotating upper drum and positioned to measure tangential deflection of the head, was used to measure friction force. This technique, in conjunction with the measurement of head signal amplitude, was used to investigate the effect of environment on drop-outs. Streaming mode tests were conducted with two brands of S-VHS tapes at various combinations of temperature (6-38 °C) and relative humidity (10-80% RH). From the experiments, it was found that the propensity for intermittent drop-outs increases in a low relative humidity environment. A low relative humidity environment increases the propensity for debris to persist over the head gap and create a loss in the head signal. High temperature further increases the propensity for drop-outs in a low relative humidity environment. The propensity for intermittent drop-outs is reduced by increasing the relative humidity, changing magnetic tapes and to some extent by lowering the temperature of the environment. It was also determined that variability in the quality of magnetic tapes has a significant impact on the number of intermittent and permanent drop-outs encountered during playback.
Location of an acoustic emission source in a radially loaded deep groove ball-bearing
Authors: Nélias D , Yoshioka T
Published: October 2002

This paper describes a deep groove ball-bearing analysis which has been developed to simulate acoustic emission occurring during ball-bearing operation. The computer simulation is useful to clarify experimental research on rolling contact fatigue initiation using the acoustic emission technique. Results show the ability of the method to detect and to locate a subsurface defect, due to rolling contact fatigue, before the rolling bearing failure occurs. The subsurface defect can be accurately located within the inner ring of a deep groove ball-bearing operating under radial load.
Aspects of thrust cone tribology: Part 1: Effects of slide to roll ratio on surface failure mechanisms in twin-disc tests
Authors: Kelly D. A. , Barnes C. G. , Rudd L. M.
Published: October 2002

This paper describes mineral oil lubricated twin-disc tests with nominal point or line contact at rolling (mean surface) speeds in the range 3-23 m/s and slide-roll ratios in the range 15-80 per cent. The results identify a regime in the sliding/rolling speed domain in which failure of EN36A (750 DPN) and EN24U (350 DPN) is predominantly by scuffing preceded by running-in, which delays scuffing to relatively severe operating conditions. At speed combinations above the identified regime, the steels fail by scuffing in, or close to, mixed lubrication conditions with little or no running-in, so that the conventional failure criterion based on a film thickness to r.m.s. surface roughness value of three is appropriate. At speed combinations below the identified regime, load intensity becomes sufficient so that general plastic deformation intervenes before failure by scuffing can occur and a shakedown-based criterion becomes appropriate. Observations of contact frequency variations suggest that with steel surfaces at 650 and 750 DPN running-in is produced by rubbing of asperity tips and that with steel surfaces at 350 and 450 DPN it is produced by hydrodynamic ripple pressures. For the latter materials at low slide-roll ratios, macro- and micropitting are likely concomitants of plastic deformation.
Aspects of thrust cone tribology: Part 2: Surface failure in thrust cones and the influence of rolling and sliding speeds in concentrated contacts
Authors: Rudd L. M. , Barnes C. G. , Kelly D. A.
Published: October 2002

This paper outlines relevant aspects of the operation of thrust cones and describes salient features of an unexpected form of failure encountered in small-scale thrust cone simulation tests. Interpretation of the thrust cone simulation test results in the light of related twin-disc tests at the relevant low slide-roll ratio leads to two conclusions. Rather than scuffing, the limiting surface failure mechanism in small-scale thrust cone tests was general plastic deformation with cold pressure welding promoted by the lack of support at the cone edges and the prolate epicycloidal path followed by the contact. The limiting surface failure mechanism in full-scale thrust cone bearings, which have markedly lower curvature and higher rolling speed than used in small-scale simulation tests, was predicted to be scuffing delayed to relatively severe operating conditions by prior running-in. Further development of the insights gained from the related twin-disc work results in two recommendations. Future work should be directed to assessing the surface modification that follows transition from EHL to mixed lubrication and redefining the conditions in which transition to micro-EHL occurs in order to quantify the potential enhancement of scuffing resistance offered by controlled running-in. It should also concentrate on evaluating the combined effects of microgeometry conducive to lubricant film formation and material properties resistant to weld formation in order to obviate the difficulty of assigning a representative value to the operating friction coefficient that is common to a number of proposed failure criteria.
Land friction effects in the meshing of timing belts
Authors: Childs T. H. C. , Hojjati M. H. , Kohno M , Nakamura T
Published: October 2002

It is observed experimentally that local peaks occur in the tangential component of the force on a pulley pitch when a timing belt seats at entry to a driving pulley and unseats at exit from a driven pulley. In this paper it is shown that these peaks are caused by forces acting between the belt and pulley lands. It is further shown experimentally, in tests on nominally 9.525 mm pitch belts running on 19-tooth pulleys, that the direction of sliding of a belt land over a pulley land can differ in seating conditions from the direction in fully meshed contact expected from the pitch difference between the pulley and belt. A theory to predict the direction of sliding is developed that combines the constraints of synchronous motion with velocity differentials between the belt cord and land surface that depend on the belt radius. The theory almost agrees with experiments. It needs measurements of belt cord extension stiffness, belt land radial compliance and bending stiffness and belt land shear compliance. Data on all these quantities have been obtained and are presented: the belt land properties are very anisotropic.