Roughness in rolling-sliding elastohydrodynamic lubricated contacts

A stiffness model for EHL contact on smooth/rough surfaces and its application in mesh stiffness calculation of the planetary gear set

Measurement of EHL temperature by thin film sensors – Thermal insulation effects

Part 1 of this paper [1] described how the behaviour of low amplitude, sinusoidal roughness in elastohydrodynamically lubricated (EHL) contacts could be characterized by three complex quantities: attenuation of original profile, amplitude of complementary wave and its wave number and decay rate. This second part outlines how these results can be used to estimate, rapidly, the clearances and pressures in any rough EHL contact. The method is applied to a number of contacts for which accurate experimental results are available and it is shown that the process gives close estimates of the clearance and pressure distributions where the amplitude of the attenuated roughness is less than 50 per cent of the clearance and good indication of the behaviour of rougher surfaces.

ABSTRACTThe paper is devoted to the development of an asymptotic approach to solution of the steady isothermal problem of elastohydrodynamic lubrication (EHL) for heavily loaded point contacts. It is shown that the whole contact region can be subdivided into three subregions: the central one that is adjacent to the other two regions occupied by the ends of the horseshoe‐shaped pressure/gap distribution zone. The central region, in turn, can be subdivided into the Hertzian region and its adjacent inlet and exit zones that, in turn, are adjacent to the inlet and exit boundaries of the contact, respectively. Moreover, in the central region, in the inlet and exit zones of heavily loaded point EHL contact, the EHL problem can be reduced to asymptotically valid equations identical to the ones obtained in the inlet and exit zones of heavily loaded line EHL contacts. The latter means that many of the well‐known properties of heavily loaded line EHL contacts are also valid for heavily loaded point EHL contacts. These asymptotically valid equations can be analysed and numerically solved based on the stable methods using a specific regularisation approach that were developed for lubricated line contacts. Cases of pre‐critical and over‐critical lubrication regimes are considered. The by‐product of this asymptotic analysis is an easy analytical derivation of formulas for the lubrication film thickness for pre‐critical and over‐critical lubrication regimes. The method is validated by the results of some experimental and numerical studies published by a number of researches. Copyright © 2013 John Wiley & Sons, Ltd.

The elastohydrodynamic lubrication (EHL) film thickness of polymer thickened oils in sliding point contact has been measured by optical interference method.Generally, the oil film thickness in EHD contact depends on three variables, i. e., viscosity, sliding speed, and load. The film thickness increases with increase in the bulk viscosity of the base oil and with increase in the sliding speed. The EHL film thickness decreases slightly as the load increases. However, the experimental data suggest that the EHL film thickness of polymer thickened oils is almost independent of bulk viscosity of the doped oils. It seems that the major portion of the polymer additives may be separated from the base oil at the oil inlet zone of EHL contact or the molecular degradation of polymer as a result of being sheared in the EHL contact.

PurposeThis paper aims to investigate the effects of inhomogeneities on the rolling contact fatigue (RCF) life in elastohydrodynamically lubricated (EHL) point contacts.Design/methodology/approachA numerical model for predicting the RCF life of inhomogeneous materials in EHL contacts was established by combining the EHL model and the inclusion model through the eigen-displacement and then connecting to the RCF life model through the subsurface stresses. Effects of the type, size, location and orientation of a single inhomogeneity and the distribution of multiple inhomogeneities on the RCF life were investigated.FindingsThe RCF life of a half-space containing manganese sulfide (MnS) inhomogeneity or the mixed inhomogeneity of aluminium oxide (Al2O3) and calcium oxide (CaO) was longer than that for the case of Al2O3inhomogeneity. For a single ellipsoidal MnS inhomogeneity, increases of its semi-axis length and decreases of its horizontal distance between the inhomogeneity and the contact center shortened the RCF life. Furthermore, the relationship between the depth of a single MnS inhomogeneity and the RCF life was found. For the half-space containing multiple inhomogeneitites, the RCF life decreased remarkably compared with the homogeneous half-space and showed discreteness.Originality/valueThis paper implements the prediction of the RCF life of inhomogeneous materials under EHL condition.

This article presents the results of a series of thermal elastohydrodynamic lubrication (EHL) analyses of a set of disc experiments carried out by Patching et al. The authors have previously calculated the heat partition at each load stage fromthe experimental data, and the present work seeks to compare the heat partition developed in a thermal EHL analysis of the lubricant film with that calculated from the experiments. These EHL analyses show that the heat partition depends on the non-Newtonian formulation used. Only when the dissipation takes place by wall slip occurring at the faster moving surface do the heat partition results approach those determined from the experimental results. It is concluded that this combination of experimental heat partition results with associated EHL analysis can prove to be a much more discerning test of rheological behaviour in EHL contacts than is provided by measurement of traction.

By assuming the contact geometry in elastohydrodynamic lubrication (EHL) to be that of an infinitely long contact with given nominal film thickness and mean pressure and considering the elastic displacements of the separate components of the initial roughness, it is possible to extend the Greenwood and Johnson analysis for sinusoidal pressure to any two-dimensional roughness. For typical EHL pressures the viscosity effects are negligible, so the Reynolds equation can be linearized and solved analytically; the solution provides a criterion to relate the amplitudes of the undeformed and deformed roughness to the wavelength, and shows that roughness with a short wavelength is likely to persist after deformation. The linearization of the Reynolds equation is extended to the transient case and it is found that the complete solution is made of two separate parts: the particular integral (steady state solution) and the complementary function (which depends on the entry of the partly deformed roughness into the Hertzian zone).

A mixture model suitable for studying the thermal effect on elastohydrodynamic lubrication (EHL) of emulsions is proposed. The maximum temperature rise occurs at the emulsion layer because sliding occurs mainly in the emulsion layer to generate shear heating, and it increases with increasing oil concentration, slide-to-roll ratio, mean speed, and load. The rise in surface temperature of the rollers decreases with the increase in the adsorbed layer’s thickness at the entrance. This result indicates that the adsorbed layers insulate the heat flux across the film, so that the surface temperature becomes cooler with a greater thickness of the adsorbed layer.

A CFD-FEM based partitioned fluid structure interaction model to investigate surface cracks in elastohydrodynamic lubricated line contacts

In this article, the problem of predicting the film thickness in so-called narrow or slender elliptic contacts is revisited. In particular, the variation of the minimum film and central film thickness and their ratio with load and ellipticity are studied. It is shown that the minimum film tends to decrease linearly with increasing ellipticity. The central film thickness, until a certain threshold, decreases very slowly, and then decreases linearly too, with a slope independent of the Hertzian pressure. The ratio central to minimum film thickness is not a constant and varies strongly with ellipticity and load conditions. In this article, it is shown that the ratio of central to minimum film thickness is a linear function of a single nondimensional parameter which has the physical meaning of the ratio of the length of the inlet pressure sweep to the relative width of the contact. Results for narrow contacts published in the engineering literature when represented as a function of this parameter exhibit the same trend. The behaviour is the consequence of the same unifying mechanism that, in the last decade, was discovered to determine aspects of behaviour in elasto-hydrodynamically lubricated (EHL) contacts under time varying conditions, such as surface waviness deformation. For these problems, the single parameter dependence facilitated the development of simple engineering tools (e.g. to predict the roughness deformation). The observation in this article that the ratio central to minimum film thickness is also governed by this parameter opens new perspectives to develop a simple computational engineering tool to predict central and minimum film thickness in EHL contacts.

For industrial roller or bush chains, the bush swings relative to the pin at working condition. If proper lubrication is maintained, an elastohydrodynamic lubrication contact is formed between the pin and the bush. In this study, a custom-made pin was used to replace the steel ball of a ball-disk test rig and optical interferometric experiments were carried out to study the effect of pin generatrix on the lubrication performance. The effects of generatrix shape, stroke length and oil supply condition on the lubrication state were explored. It is found that the change of the generatrix has an important influence on the oil film thickness, especially under rare oil supply condition.

Experimental study of elastohydrodynamic lubrication behaviour under single oil droplet supply

Elastohydrodynamic lubrication line contact of piezoelectric materials

This paper describes a comprehensive model of Elastohydrodynamic piston lubrication, incorporated the crown lands into solution domain to characterize the effect of crown-liner interactions on piston motion. Elastohydrodynamic Lubrication (EHL) analysis of a piston skirt-liner conjunction is in general a useful methodology for design analysis of pistons. The diameters of piston crown lands are much less than those of skirt and liner for typical piston designs. Therefore crown lands normally do not interact with liner under usual operating conditions and hence most of the researchers exclude crown lands from the EHL analysis and mainly focus on piston skirt. However, under some of the engine operating conditions piston crown lands play important role in the secondary dynamics and tribology aspects of pistons. During the thermodynamic cycle when piston is hot and cylinder liner is relatively colder, piston thermal expansion leads to crown-liner interaction, which necessitates EHL, asperity contact and wear considerations of piston crown along with piston skirt. The simulation methodology for piston EHL analysis uses a mass-conserving algorithm for the finite volume method solution of Reynolds equation, which is coupled to elasticity relations and Greenwood-Tripp asperity contact model. Elrod’s mass conserving algorithm enables to model and analyze partially lubricated piston-liner interface by the input of oil supply and moreover rigorously handles cavitated zones, and takes into account piston ring grooves, piston cut-outs and unlubricated areas due to piston geometry. Results are presented from parametric studies that show comparisons between the analyses of the models with piston skirt lubrication only and piston lubrication, which incorporates the crown lands to the EHL domain.