Influence des indentations sur la durée de vie des roulements

Les lubrifiants contiennent des particules qui sont `a la fois initialement présentes dans le lubrifiant et dans le mécanisme (fabrication, stockage)générées durant le rodage, par usure ou corrosionou bien issues de sources externes. Les particules détériorent les surfaces en créant des indents lorsqu\u27elles sont piégées dans les contacts. Ces indents augmentent le risque de rupture par fatigue en induisant des perturbations de pression et de contraintes. Ce travail est basé sur une étude des contacts indentés secs et lubrifiés (EHD). L\u27équation de Reynolds en fluide Newtonien est utilisée. Les techniques mutigrilles et multi-intégration sont employées. L\u27objectif de ce travail est de proposer un modèle de prédiction des perturbations des champs de pression et de contraintes, et finalement un modèle de réduction de durée de vie des contacts indentés en fonction de la géométrie des indents et des conditions de contact

Influence of indentations on rolling bearing life

All lubricants contain particles. These particles are both initially present in the lubricant and mechanisms (manufacturing process, storage ); generated during running-in, through wear and corrosion; or come from external sources. These particles damage the surfaces, creating indents when they are squashed in the contact. These indents increase the fatigue failure risk inducing pressure and stress perturbations. This work is based on a dry and lubricated (EHL) contact study. The Reynolds equation for Newtonian fluids is used. Multigrid and multi-integration techniques are used to limit computing time. The aim is to predict pressure and stress distribution perturbations, and finally to predict the life reduction of indented contacts as a function of the indent geometry and the operating conditions.Les lubrifiants contiennent des particules qui sont à la fois initialement présentes dans le lubrifiant et dans le mécanisme (fabrication, stockage ) ; générées durant le rodage, par usure ou corrosion ; ou bien issues de sources externes. Les particules détériorent les surfaces en créant des indents lorsqu'elles sont piégées dans les contacts. Ces indents augmentent le risque de rupture par fatigue en induisant des perturbations de pression et de contraintes. Ce travail est basé sur une étude des contacts indentés secs et lubrifiés (EHD). L'équation de Reynolds en fluide Newtonien est utilisée. Les techniques mutigrilles et multi-intégration sont employées. L'objectif de ce travail est de proposer un modèle de prédiction des perturbations des champs de pression et de contraintes, et finalement un modèle de réduction de durée de vie des contacts indentés en fonction de la géométrie des indents et des conditions de contact

Geometric Starvation of a One-Dimensional Parabolic Profile

International audienceThis paper proposes closed form solutions that describe the film thickness in a one-dimensional parabolic hydrodynamic contact as a function of the operating conditions and geometry: radius of curvature and length. For large slider lengths, the classical film thickness formula are found: linear increasing film thickness with Sommerfeld number. However, for small lengths (and certain operating conditions) the film thickness decreases with the Sommerfeld number, as is the case for starvation due to a limited lubricant supply. A modified Sommerfeld number is proposed that allows for a unique description of the film thickness in the fully flooded and starved regime. Finally, a simple curve-fitted solution is proposed covering the film thickness evolution from the fully flooded to the starved regime

Hydrodynamic force and moment in pure rolling lubricated contacts. Part 2: point contacts

International audienceHydrodynamic rolling force and moments in point contact have been studied in detail using isoviscousrigid (IVR) and elastohydrodynamic (EHL) models. Using fully flooded assumptions, curve-fitted relationships are given for calculating the IVR and EHL hydrodynamic rolling forces. Both are proportional (or almost proportional in the IVR case) to 2a, the Hertzian contact length being perpendicular to the rolling direction, and are also functions of the dimensionless speed parameter. A single curve-fitted relationship has been derived to cover the full range of operating conditions with a smooth transition from IVR to EHL regime of lubrication. The results obtained are slightly higher than those previously published (the ratio being of the order of 1.5 for usual operating conditions). Point contact and line contact (with a contact length L being equal to the point contact length 2a) hydrodynamic rolling forces have also been compared. The point contact forces are about 26 per cent larger than those obtained using line contact relationship (published in part 1) because of a larger domain of integration in the lateral direction. By limiting the width of the integration domain to L (roller length or ball diameter), the effect of 2a/ L on the hydrodynamic rolling force has been studied, leading to the derivation of a truncation factor C. As the load increases, 2a increases and the truncation factor decreases until reaching a limit when ellipse truncation starts because 2a/ L is equal to or larger than one. Using the truncation factor and limiting the 2a/ L ratio to one, it was found that point contact and line contact hydrodynamic forces are the same within a few per cent. A single point contact relationship can therefore be suggested, covering the IVR to EHL operating conditions with a smooth transition between these lubrication regimes, and also a smooth transition from point contact to line contact as the load increases and contact ellipse truncation occurs. Finally, calculations of power losses due to the Poiseuille flow in the rolling direction x and in the perpendicular direction z show that the power loss in the z direction is usually very small for wide elliptical contacts and that most of the power is dissipated in the inlet and outlet, with a 26 per cent contribution of the integration domain defined out the range -a < z < a. This result is in line with the truncation factor defined previously

Influence of indentations on rolling bearing life

Les lubrifiants contiennent des particules qui sont \a la fois initialement présentes dans le lubrifiant et dans le mécanisme (fabrication, stockage ); générées durant le rodage, par usure ou corrosion; ou bien issues de sources externes. Les particules détériorent les surfaces en créant des indents lorsqu'elles sont piégées dans les contacts. Ces indents augmentent le risque de rupture par fatigue en induisant des perturbations de pression et de contraintes. Ce travail est basé sur une étude des contacts indentés secs et lubrifiés (EHD). L'équation de Reynolds en fluide Newtonien est utilisée. Les techniques mutigrilles et multi-intégration sont employées. L'objectif de ce travail est de proposer un modèle de prédiction des perturbations des champs de pression et de contraintes, et finalement un modèle de réduction de durée de vie des contacts indentés en fonction de la géométrie des indents et des conditions de contact.All lubricants contain particles. These particles are both initially present in the lubricant and mechanisms (manufacturing process, storage ); generated during running-in, through wear and corrosion; or come from external sources. These particles damage the surfaces, creating indents when they are squashed in the contact. These indents increase the fatigue failure risk inducing pressure and stress perturbations. This work is based on a dry and lubricated (EHL) contact study. The Reynolds equation for Newtonian fluids is used. Multigrid and multi-integration techniques are used to limit computing time. The aim is to predict pressure and stress distribution perturbations, and finally to predict the life reduction of indented contacts as a function of the indent geometry and the operating conditions.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Influence des indentations sur la durée de vie des roulements

All lubricants contain particles. These particles are both initially present in the lubricant and mechanisms (manufacturing process, storage ); generated during running-in, through wear and corrosion; or come from external sources. These particles damage the surfaces, creating indents when they are squashed in the contact. These indents increase the fatigue failure risk inducing pressure and stress perturbations. This work is based on a dry and lubricated (EHL) contact study. The Reynolds equation for Newtonian fluids is used. Multigrid and multi-integration techniques are used to limit computing time. The aim is to predict pressure and stress distribution perturbations, and finally to predict the life reduction of indented contacts as a function of the indent geometry and the operating conditions.Les lubrifiants contiennent des particules qui sont \a la fois initialement présentes dans le lubrifiant et dans le mécanisme (fabrication, stockage ); générées durant le rodage, par usure ou corrosion; ou bien issues de sources externes. Les particules détériorent les surfaces en créant des indents lorsqu'elles sont piégées dans les contacts. Ces indents augmentent le risque de rupture par fatigue en induisant des perturbations de pression et de contraintes. Ce travail est basé sur une étude des contacts indentés secs et lubrifiés (EHD). L'équation de Reynolds en fluide Newtonien est utilisée. Les techniques mutigrilles et multi-intégration sont employées. L'objectif de ce travail est de proposer un modèle de prédiction des perturbations des champs de pression et de contraintes, et finalement un modèle de réduction de durée de vie des contacts indentés en fonction de la géométrie des indents et des conditions de contact.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocSudocFranceF

Cross hatched texture influence on the load carrying capacity of oil control rings

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Load carrying capacity and friction in starved hydrodynamically lubricated circular contacts

International audienceThe current work studies the evolution of the load carrying capacity and friction forces as a function of the level of starvation for spherical hydrodynamically lubricated contacts. Unfortunately, the parabolic approximation of the geometry cannot be applied, as it leads to infinite friction forces for the fully flooded case. Thus, this work uses the complete spherical geometry but this introduces an additional parameter " which is the ratio between the minimum film thickness h 0 and the radius R. Two viscous forces are distinguished: the Couette term associated with sliding and the Poiseuille term generated by the pressure gradient. The load and friction forces are computed numerically as a function of the geometry and the level of starvation. Finally, some simple curve fitted equations are given for load and friction as a function of the degree of starvation A and the ratio "

Professor Duncan Dowson, a source of inspiration

International audienceThe current paper highlights the contribution of the Dowson and Higginson work to numerical line contact elastohydrodynamic lubrication film thickness prediction and the Hamrock and Dowson contribution to the film thickness prediction in elliptical contacts. This paper shows that, even by today’s standards, both the numerical pressure and film thickness results and the curve-fitted film thickness predictions are very accurate. As for the elliptical results, the authors show that the original predictions remain surprisingly accurate for moderately elliptical contact. For very long elliptical contacts, their prediction does not tend to a line contact asymptote. This paper then concludes that the predicted pressure spikes by Dowson, Higginson, and Hamrock are correct in shape and amplitude, at least near pure rolling conditions

Contact pressure of indented wide elliptical contacts: Dry and lubricated cases

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