Following the pioneer work of Ertel-Grubin and Dowson and Higgingson, the field of elastohydrodynamic lubrication (EHL) has witnessed a remarkable increase in new developments, notably the incorporation into the analysis of roughness and other surface features (micro-EHL). This article describes the application of new developments in micro-EHL in the deduction of simple analytical formulations that might describe, in a better way, the lubrication of rolling bearings and the effects on life ratings. In this context the lubrication quality factors κ (used in rolling bearing technology) and Λ (generally applied in machine design) are critically compared and discussed. It is found that the commonly used average roughness, R q, is not quite able to properly account for the surface topography effect when the detailed micro-EHL response of the surface has to be accounted for. To this effect, the whole surface micro-geometry needs to be retained in the evaluation. A calculation methodology suitable for this type of analysis is proposed and used in a parametric evaluation of standard bearing surfaces.

This paper reports on a theoretical study on the fluid-assisted surface cracking in lubricated rolling-sliding contact. An analytical 2D model, validated by the CFD simulations, is developed to describe the transient process of lubricant seepage into a surface-breaking crack during the contact loading. The fluid-crack interaction is studied by FE calculations.

Only few studies have been published on EHD contacts that experienced simultaneously rolling, sliding and spinning motions. This paper describes a new test rig especially designed to simulate such operating conditions while imposing normal load and speeds as those found in real life mechanisms. Then, experimental results are presented and discussed.

A numerical model designed to simulate a moving line contact of two rough layered bodies is presented. Fourier transforms are used to obtain fundamental solutions to relevant differential equations and then these solutions are used as kernel functions in a numerical scheme designed to provide a full thermomechanical solution for real layered contacts. The model assumes steady state heat transfer and predicts contact pressures and deformations, contact temperature rise, and resulting thermal stresses. The heat division between the contacting components is fully accounted for, as are the interactions between the mechanical and thermal displacements. Some results are presented to illustrate the potential importance of a full thermomechanical analysis as compared to a purely mechanical one as well as to demonstrate the influence of coating properties and surface roughness structure on the contact temperatures.

Particle denting, and contamination marks found on bearing raceways, can induce stress concentrations and facilitate surface initiated fatigue. The lubricant film developed at the dent and related local surface stresses are also significant to the crack initiation mechanism. In this article, a new methodology is presented to link the micro-EHL film and related local stresses to the fatigue life of rolling bearings. The applied methodology is based on Fourier analysis of the harmonic components of the surface microgeometry to predict stresses and induced lubricant film. The application of this method to actual bearing surfaces is discussed and analyzed in relation to some existing microcontact EHL solutions. A global evaluation of the use of the method to rolling bearings dynamic load ratings is also carried out. A comparison between experimentally obtained rolling bearing life and lives predicted using the present theory indicate the global ability of the model to describe the effect of the lubrication quality on the life expectancy of rolling contacts. From this analysis, an assessment of some typical equations used in rolling bearing dynamic ratings is carried out. It is found that the degree of lubrication of the rolling contact and the cleanliness conditions of the oil are indeed significant to the prediction of the life expectancy of the bearing.

Established metallographic methods of determining the cleanliness of bearing steels with respect to micro-inclusions, such as ASTM E 45, are capable of differentiating poor quality melts from good quality melts. However, as steelmaker capabilities improve, with increasing numbers being able to consistently produce good quality melts, the established methods of cleanliness assessment are unable to differentiate between melts. These established methods, which give single figure ratings based on both the size and number of inclusions, are extremely difficult to use in predicting the performance of a bearing component under conditions of rolling contact fatigue. In this work, the method of Extreme Value Analysis (EVA) is used to characterize the inclusion population of five different steel melts of known and varying quality. A link between the EVA distribution and the measured bearing life, performed on material with a low reduction ratio, is also presented.

A recently developed thermo-mechanical model was used to study the temperature distribution in a sliding contact of a cylinder and a coated real rough surface. The model conducts a full thermo-mechanical analysis of the contact including the interactions between the thermal and elastic displacements and full heat division. Following a brief description of the numerical model, results are presented to illustrate the thermo-mechanical effects of various contact parameters, coating properties and surface roughness structure.Copyright © 2006 by ASME

The need for rapid development of high efficiency jet engines and other mechanical systems has forced the pace of development of simulation tools so that the detailed behavior of the rolling element bearings can be simulated. This includes modeling of the motions, the exchanged forces, and heat between all the bearing components, i.e. rings, cage and rolling elements. The computer program BEAST is a multi-body computer program with sophisticated and robust modeling of the tribological contacts in the bearing where the exchange of forces between the bearing components takes place.

A commercial CFD code has been applied to model lubricant flow behaviour within 2D and 3D linear pad bearings having closed pockets or recesses. The study indicates that the presence of closed pockets can result in a significant reduction in bearing friction coefficient. At high convergence ratios, no cavitation is predicted within the pockets. This means that suitably-positioned pockets in the high-pressure region of the bearing result in a much greater reduction in local shear stress than in local pressure, so that there is an overall reduction in friction coefficient. At low convergence ratios, cavitation occurs in the inlet to the pockets so that each pocket acts an effectively-independent step bearing. This results in the overall bearing supporting a higher load and thus having lower friction coefficient than is the case without pockets.

The paper employs a rough-surface numerical elastic contact method designed to analyze Hertzian elastic contact effects of surface coatings. In particular the paper explores the differences in the surface contact mechanics and the resulting sub-surface stresses experienced over a range of differing coating material-properties, thickness, and machined roughness levels in a quantitative manner. The effect of a range of surface roughness properties and in particular root mean square roughness (σ) and correlation length β*, on the magnitude and depth of maximum shear stresses in the layer under individual asperities is investigated. This is done for a hard and stiff, and also for a soft and compliant coating, and for two coating thicknesses in each case. The results suggest that the magnitude of the local shear stress increases with increasing ratio σ/β* approximately linearly. The depth of the maximum local shear stress is found to correlate best with β*, however a further clear trend is observed between this depth and the number of profile peaks. The depth also shows a relation to the ratio σ/β* but the correlation in this case is weaker with significant deviations. Neither the magnitude nor the depth of shear stresses shows any significant trend in relation to the roughness (σ) alone. The tensile stresses at the interface, and the subsequent potential for delamination, are also investigated and found to be significant. Approximate correlation between the magnitude of interface tensile stress and root mean square roughness is achieved, but no clear trend in relation to correlation length is evident.

A rolling element bearing comprises an inner ring and an outer ring which are each provided with a raceway, and a series of rolling elements which are in contact with the raceways of each ring. A lubricant film is provided in the contacts between the rolling elements and the raceways, which film forms a lubricant meniscus at the inlet side of each contact. In the bearing starved lubrication conditions prevail. The surface of each rolling element has minute recesses filled with a lubricant quantity, said recesses being flattened in the contact area defined by the contact between the rolling elements and the rings and thereby releasing lubricant at the inlet side of each contact resulting in a displacement of the meniscus further away from said contact. This meniscus displacement results in an increased lubricant film thickness in each contact area, thus improving the lubricating conditions in the bearing.

The damage caused by debris particles in concentrated contacts has been studied extensively in the past, both theoretically and experimentally. Most of the theoretical studies, in which the damage on the surfaces was calculated in the form of dents, were performed isothermally. It is known that sliding asperity contacts, which resemble third body contacts, reach high local temperatures that can affect local material properties which, in turn, will affect the way damage is generated on the surfaces of machine elements. In the present work the heat transfer of lubricated, rolling/sliding line contacts in the presence of a ductile spherical particle is modeled. The particle is assumed to be significantly softer than the counterfaces that squash it. The local flash temperatures due to the combined sliding and squashing of a debris particle are calculated. It is found that high temperatures caused from small and soft particles are rather the rule than the exception.

During the passage of a debris particle through an EHD contact, mechanical stresses due to particle compression and thermal stresses due to particle frictional heating produce a thermoelastic/plastic stress field, which governs the way a possible damage is generated. In the present paper, the complete three-dimensional solution of the thermoelastic distortion of surfaces due to the compression of a soft, ductile debris particle in an EHD line contact is presented both theoretically and through a realistic example. It is found that thermal stresses increase the likelihood of yielding and produce a characteristic "omega" shaped thermoelastic displacement. The important outcome of this work is the construction of a map which shows the critical particle size to cause damage (plastic deformations) in combination with operational parameters as the lubricant film thickness and relative sliding velocity of the contact.

Particles present as contamination in a lubricant are known to increase the wear of components in rolling bearings. This wear leads to deterioration in running accuracy and vibration levels, which results in early replacement. Experiments have been conducted to investigate the nature and mechanism of the damage caused by hard particles (harder than either counterface) to bearing surfaces. Initially considering single particle scratching between two surfaces subject to sliding and rolling using a test rig to create a single elastohydrodynamic contact (Ball on Cylinder). The nature of an individual scratch is examined and then compared to the results from a test with more realistic concentrations of particles. The results suggest that particle wear may often involve a more complex process than pure abrasion.