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Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication / R. S. Dwyer-Joyce in Transactions of the ASME . Journal of tribology, Vol. 133 N° 3 (Juillet 2011) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 133 N° 3 (Juillet 2011) . - 11 p. Titre : Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication Type de document : texte imprimé Auteurs : R. S. Dwyer-Joyce, Auteur ; T. Reddyhoff, Auteur ; Zhu, J., Auteur Année de publication : 2012 Article en page(s) : 11 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Elastic  moduli  Film  flow  Flow  separation  Flow  visualisation  Hydrodynamics  Liquid  films  Lubricating  oils  Rheology  Rough  surfaces  Ultrasonic  waves Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The reflection of ultrasound can be used to determine oil film thickness in elastohydrodynamic lubricated (EHL) contacts if the opposing surfaces are fully separated by the liquid layer. The proportion of the wave amplitude reflected depends on the stiffness of the liquid layer, which is a function of its bulk modulus and thickness. However, in many practical applications, boundary or mixed film lubrication is a common occurrence as the nominal thickness of the separating film is of a similar order to the height of the surface asperities. The reflection is then dependent on both the liquid contact and solid contact parts and the total interfacial stiffness is the controlling parameter. In this paper an investigation was carried to study the reflection of ultrasonic waves from the lubricated contact between a sliding steel ball and a flat steel disc when substantial solid contact occurs. To interpret the ultrasonic reflection results, a mixed regime model for a circular point contact was established. The liquid film stiffness was calculated by using a predicted film thickness and a bulk modulus estimated from published rheological models of lubricants under high pressure. Solid contact stiffness was predicted using a statistical rough surface contact model. Under all operating conditions, the prediction of fluid stiffness was found to be much greater than the solid contact stiffness. The total stiffness predicted by the model showed good agreement with experimental measurements for kinematic cases. The model was used to separate the stiffness contributions from the asperity contact part and lubricant layer part from the experimental data. For contact pressures ranging from 0.42 to 0.84 GPa and sliding speed from zero to 2 m/s, the film thickness was found to vary from 0.01 to 0.8 µm, and the proportion of the load supported by asperity contact varied from 50% to 0%. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Ultrasonic measurement for film thickness and solid contact in elastohydrodynamic lubrication [texte imprimé] / R. S. Dwyer-Joyce, Auteur ; T. Reddyhoff, Auteur ; Zhu, J., Auteur . - 2012 . - 11 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 133 N° 3 (Juillet 2011) . - 11 p. Mots-clés : Elastic  moduli  Film  flow  Flow  separation  Flow  visualisation  Hydrodynamics  Liquid  films  Lubricating  oils  Rheology  Rough  surfaces  Ultrasonic  waves Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : The reflection of ultrasound can be used to determine oil film thickness in elastohydrodynamic lubricated (EHL) contacts if the opposing surfaces are fully separated by the liquid layer. The proportion of the wave amplitude reflected depends on the stiffness of the liquid layer, which is a function of its bulk modulus and thickness. However, in many practical applications, boundary or mixed film lubrication is a common occurrence as the nominal thickness of the separating film is of a similar order to the height of the surface asperities. The reflection is then dependent on both the liquid contact and solid contact parts and the total interfacial stiffness is the controlling parameter. In this paper an investigation was carried to study the reflection of ultrasonic waves from the lubricated contact between a sliding steel ball and a flat steel disc when substantial solid contact occurs. To interpret the ultrasonic reflection results, a mixed regime model for a circular point contact was established. The liquid film stiffness was calculated by using a predicted film thickness and a bulk modulus estimated from published rheological models of lubricants under high pressure. Solid contact stiffness was predicted using a statistical rough surface contact model. Under all operating conditions, the prediction of fluid stiffness was found to be much greater than the solid contact stiffness. The total stiffness predicted by the model showed good agreement with experimental measurements for kinematic cases. The model was used to separate the stiffness contributions from the asperity contact part and lubricant layer part from the experimental data. For contact pressures ranging from 0.42 to 0.84 GPa and sliding speed from zero to 2 m/s, the film thickness was found to vary from 0.01 to 0.8 µm, and the proportion of the load supported by asperity contact varied from 50% to 0%. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]