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Indents perturb the pressure and stress distribution and increase the failure risk of rolling element bearings. A numerical study of the pressure perturbation is proposed. An existing dry contact model is extended to account for the indent shoulder influence and the pressure collapse in deeper indents. Moreover, results for pure rolling lubricated contacts are presented. Finally; the ellipticity influence is studied for both dry and lubricated contacts. Keywords: indentation, contamination, pollution, fatigue, rolling bearing life

This paper focuses on the lubrication behavior of starved elliptical Elasto-HydroDynamic (EHD) contacts. Starvation is governed by the amount of lubricant available in the inlet region and can result in much thinner films than occurring under fully flooded conditions. Therefore, it would be desirable to be able to predict the onset and severity of starvation and to be able to relate film reduction directly to the operating conditions and lubricant properties. The aim of this work is to explore the influence of these parameters on starvation. A combined modeling and experimental approach has been employed. The numerical model has been developed from an earlier circular contact study [1]. In this model the amount and distribution of the lubricant in the inlet region determines the onset of starvation and predicts the film decay in the contact. Numerical simulations for a uniform layer on the surface show that a single parameter, characteristic of the inlet length of the contact in the fully flooded regime, determines the starved behavior. Film thickness measurements under starved conditions were performed to validate this theory. For a circular contact excellent agreement was found. In theory the same mechanism applies to elliptic contacts, however, the behavior is more complicated. [DOI: 10.1115/1.1631020]

In ElastoHydrodynamic Lubrication (EHL), transient processes are much more common than stationary ones. Predicting the film thickness under steady state conditions has become straight forward. Using numerical methods, the effect of transient conditions on the film thickness profile can be computed. However, those analyses are very time consuming even using advanced numerical techniques. As such, they are inadequate for industrial applications as design and development. This paper shows that under certain assumptions, an approximate formula of the transient film thickness profile can be derived under transient operating conditions. The variations can occur in the geometry, the load or the hydrodynamic velocity. The theory can handle all variations separately, or even a combination of several parameters varying simultaneously. The analytical approximation obtained is rather good apart from the constriction at the contact edge(s). This approach can be applied to any set of time dependent conditions (load, speed, geometry). As an example an EHL contact is studied in which reversal of the entrainment velocity occurs. [DOI: 10.1115/1.1454105]

Using a dry point contact model, a parametric study of the peak pressure due to a dent was performed. The parameters varied were the dent depth and diameter. The numerical analysis was complemented by an analytical analysis. Using the elastic body hypothesis, the study of the dented contact shows that various configurations can occur. Introducing the parameters SC1, a dimensionless pressure parameter and SC2, a dimensionless dent geometry parameter, the pressure peak in all these configurations can be represented in a single graph. [DOI: 10.1115/1.1396345]

The lubrication with oil-in-water emulsions is usually supposed to be governed by the oil phase being concentrated in a reservoir that supplies the contact. In this paper, another lubrication process in an elastohydrodynamic ball/disc contact is presented. It is found that above a critical entrainment speed a thick film grows in the contact with time and reaches a limiting thickness. Viscous adherent boundary layers are formed and observed on both the surfaces. Pressure and speed are required for the film build-up. An additional sliding speed at constant entrainment speed induces a shearing at the interface between the boundary layers and the substrate that depends on the nature of the contacting surface. It is shown that these high viscosity boundary films ensure a starved lubrication. The modelling of the starvation process allows us to evaluate the viscosity of these boundary layers and their mean supply rate to the contact. A fine analysis of this latter parameter shows that the lubricating film results from the equilibrium between the flow rate of lubricating particles in the inlet zone and the amount of particles that cannot stay in the contact between two passages which strongly depends on the entrainment speed. A classical adsorption process does not seem responsible for the anchorage of the boundary films to the surfaces. The adherence of the films is explained by an approach based on electric interactions between ionic surfactants and the oxidized metallic surfaces according to the position of their isoelectric point compared to the pH of the emulsion. [DOI: 10.1115/1.1398549]

Due to technological pressures the lubricant film thickness in EHD contacts has decreased over the years and will continue to do so for the foreseeable future. On the other hand, financial constraints cause the surface roughness in these contacts to decrease very slowly, or might even cause an increase. As a result, the ratio of film thickness to composite roughness will continue to decrease. The question that remains to be answered is to what extent this decrease will affect the contact performance. A third development makes this question even more acute, the request of increased reliability. As a consequence, the problem of the detailed understanding of the elastohydrodynamic lubrication with rough surfaces is as urgent as ever. Recent work has shown that the features inside the contact deform, and that the level of deformation is a function of the wavelength of the feature and the contact operating conditions, including slip. This last aspect of the problem, which has not been addressed previously, forms the central topic of the current paper. Instead of studying the deformation of a real roughness profile, the deformation of its sinusoidal Fourier components is investigated.

This paper presents a numerical study of the effects of inlet supply starvation on film thickness in EHL point contacts. Generally this problem is treated using the position of the inlet meniscus as the governing parameter; however, it is difficult to measure this in real applications. Thus, in this paper an alternative approach is adopted whereby the amount of oil present on the surfaces is used to define the degree of starvation. It is this property which determines both meniscus position and film thickness reduction. The effect of subsequent overrollings on film thickness decay can also be evaluated. In the simplest case a constant lubricant inlet film thickness in the Y direction is assumed and the film thickness distribution is computed as a function of the oil available. This yields an equation predicting the film thickness reduction, with respect to the fully flooded value, from the amount of lubricant initially available on the surface, as a function of the number of overrollings n. However, the constant inlet film thickness does not give a realistic description of starvation for all conditions. Some experimental studies show that the combination of side flow and replenishment action can generate large differences in local oil supply and that the side reservoirs play an important role in this replenishment mechanism. Thus the contact centre can be fully starved whilst the contact sides remain well lubricated. In these cases, a complete analysis with a realistic inlet distribution has been carried out and the numerical results agree well with experimental findings.

This paper investigates in detail the influence of two different surface topographies on the pressure distribution and film thickness profile of a highly loaded (maximum Hertzian pressure 2 GPa) line contact as a function of the slide to roll ratio. To accomplish this the transient Reynolds equation is solved both in space and time. The first feature under investigation is localized, a so-called indentation, the second one is global: waviness. The observed lack of synchronism in the extremes of pressure and film thickness is explained theoretically by analyzing the Reynolds equation. The minimum and average film thickness values in case of waviness are analyzed as a function of the slide to roll ratio, amplitude, and wavelength. Depending on the slide to roll ratio, the transient solutions may differ significantly from their stationary counterparts. In such cases, therefore, a transient analysis cannot be avoided.