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Journal of tribology :Transactions of the ASME |
Dépouillements
Ajouter le résultat dans votre panierOptimization of groove geometry for thrust air bearing to maximize bearing stiffness / Hiromu Hashimoto in Transactions of the ASME . Journal of tribology, Vol. 130 n°3 (Juillet 2008)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 11 p.
Titre : Optimization of groove geometry for thrust air bearing to maximize bearing stiffness Type de document : texte imprimé Auteurs : Hiromu Hashimoto, Auteur ; Masayuki Ochiai, Auteur Année de publication : 2008 Article en page(s) : 11 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Bearings Film thickness Geometry Stiffness Optimization Design Springs Résumé : Hydrodynamic gas film bearings are widely used for very-high-speed, lightly loaded rotating machinery. In the design of hydrodynamic gas film bearings, it is of cardinal importance to enhance the stiffness of gas films to minimize vibration due to external excitations. Among various types of hydrodynamic gas film thrust bearings, grooved bearings have an advantage of high stiffness and load-carrying capacity, but the stiffness of the bearings strongly depends on groove geometry. Therefore, when the groove geometry is suitably designed, it is expected to considerably improve the stability characteristics of the bearings. However, conventional bearing geometries are based on a fixed logarithmic spiral curve, and there is no literature on how to effectively change the groove geometry to drastically improve the bearing characteristics. In this paper, the entirely new optimum design methodology, in which the groove geometry can be flexibly changed by using the spline function, is presented to maximize the stiffness of gas films for grooved thrust bearings. The effectiveness of the methodology is experimentally verified. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468053 [article] Optimization of groove geometry for thrust air bearing to maximize bearing stiffness [texte imprimé] / Hiromu Hashimoto, Auteur ; Masayuki Ochiai, Auteur . - 2008 . - 11 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 11 p.
Mots-clés : Bearings Film thickness Geometry Stiffness Optimization Design Springs Résumé : Hydrodynamic gas film bearings are widely used for very-high-speed, lightly loaded rotating machinery. In the design of hydrodynamic gas film bearings, it is of cardinal importance to enhance the stiffness of gas films to minimize vibration due to external excitations. Among various types of hydrodynamic gas film thrust bearings, grooved bearings have an advantage of high stiffness and load-carrying capacity, but the stiffness of the bearings strongly depends on groove geometry. Therefore, when the groove geometry is suitably designed, it is expected to considerably improve the stability characteristics of the bearings. However, conventional bearing geometries are based on a fixed logarithmic spiral curve, and there is no literature on how to effectively change the groove geometry to drastically improve the bearing characteristics. In this paper, the entirely new optimum design methodology, in which the groove geometry can be flexibly changed by using the spline function, is presented to maximize the stiffness of gas films for grooved thrust bearings. The effectiveness of the methodology is experimentally verified. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468053
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 10 p.
Titre : The static performance analysis of foil journal bearings considering three-dimensional shape of the foil structure Type de document : texte imprimé Auteurs : Dong Hyun Lee, Auteur ; Young-Cheol Kim, Auteur ; Kyung-Woong Kim, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Stress Bearings Finite element analysis Deflection Film thickness Shapes Stiffness Pressure Thickness Journal bearings Résumé : To obtain the foil bearing characteristics, the fluid film pressure must be coupled with the elastic deformation of the foil structure. However, all of the structural models thus far have simplified the foil structure without consideration of its three-dimensional shape. In this study, a finite element foil structural model is proposed that takes into consideration the three-dimensional foil shape. Using the proposed model, the deflections of interconnected bumps are compared to those of separated bumps, and the minimum film thickness determined from the proposed structural models is compared to those of previous models. In addition, the effects of the top foil and bump foil thickness on the foil bearing static performance are evaluated. The results of the study show that the three-dimensional shape of the foil structure should be considered for accurate predictions of foil bearing performances and that too thin top foil or bump foil thickness may lead to a significant decrease in the load capacity. In addition, the foil stiffness variation does not increase the load capacity much under a simple foil structure. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468056 [article] The static performance analysis of foil journal bearings considering three-dimensional shape of the foil structure [texte imprimé] / Dong Hyun Lee, Auteur ; Young-Cheol Kim, Auteur ; Kyung-Woong Kim, Auteur . - 2008 . - 10 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 10 p.
Mots-clés : Stress Bearings Finite element analysis Deflection Film thickness Shapes Stiffness Pressure Thickness Journal bearings Résumé : To obtain the foil bearing characteristics, the fluid film pressure must be coupled with the elastic deformation of the foil structure. However, all of the structural models thus far have simplified the foil structure without consideration of its three-dimensional shape. In this study, a finite element foil structural model is proposed that takes into consideration the three-dimensional foil shape. Using the proposed model, the deflections of interconnected bumps are compared to those of separated bumps, and the minimum film thickness determined from the proposed structural models is compared to those of previous models. In addition, the effects of the top foil and bump foil thickness on the foil bearing static performance are evaluated. The results of the study show that the three-dimensional shape of the foil structure should be considered for accurate predictions of foil bearing performances and that too thin top foil or bump foil thickness may lead to a significant decrease in the load capacity. In addition, the foil stiffness variation does not increase the load capacity much under a simple foil structure. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468056
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 8 p.
Titre : A continuum description of dense granular lubrication flow Type de document : texte imprimé Auteurs : John Tichy, Auteur ; Yves Berthier, Auteur ; Ivan Iordanoff, Auteur Année de publication : 2008 Article en page(s) : 8 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Flow (Dynamics) Lubrication Particulate matter Shear (Mechanics) Equations Stress Gravity (Force) Force Engineering simulation Résumé : The present paper applies a recent continuum theory due to Aranson and Tsimring (2002, “Continuum Theory of Partially Fluidized Granular Flows ,” Phys. Rev. E, 65, p. 061303) for the dense granular flow of particles in sustained contact to lubrication flows. Such third body granular flow may apply to some solid lubrication mechanisms. The continuum theory is unique in that it addresses solidlike behavior and the transition to fully fluidized behavior. The continuum studies are complemented by a discrete particle dynamics model of Iordanoff (2005, “Numerical Study of a Thin Layer of Cohesive Particles Under Plane Shearing ,” Powder Technol., 159, pp. 46–54). Three problems are treated: (1) flow due to the gravity of a layer of granular material down an inclined plane, (2) simple shear flow of a layer confined between sliding parallel surfaces, and (3) lubrication flow of a layer confined between a curved surface and a sliding plane. The perspective of this paper is that a continuum model will be more useful than a discrete model in engineering design of solid lubrication systems for the foreseeable future. In the inclined plane problem, the discrete simulations are used to provide material property parameters to the continuum model. In the simple shear problem, for validation, predictions of the continuum model are compared to those of the discrete element computer simulations. Finally, the continuum theory is applied to a more complex lubrication flow. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468057 [article] A continuum description of dense granular lubrication flow [texte imprimé] / John Tichy, Auteur ; Yves Berthier, Auteur ; Ivan Iordanoff, Auteur . - 2008 . - 8 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 8 p.
Mots-clés : Flow (Dynamics) Lubrication Particulate matter Shear (Mechanics) Equations Stress Gravity (Force) Force Engineering simulation Résumé : The present paper applies a recent continuum theory due to Aranson and Tsimring (2002, “Continuum Theory of Partially Fluidized Granular Flows ,” Phys. Rev. E, 65, p. 061303) for the dense granular flow of particles in sustained contact to lubrication flows. Such third body granular flow may apply to some solid lubrication mechanisms. The continuum theory is unique in that it addresses solidlike behavior and the transition to fully fluidized behavior. The continuum studies are complemented by a discrete particle dynamics model of Iordanoff (2005, “Numerical Study of a Thin Layer of Cohesive Particles Under Plane Shearing ,” Powder Technol., 159, pp. 46–54). Three problems are treated: (1) flow due to the gravity of a layer of granular material down an inclined plane, (2) simple shear flow of a layer confined between sliding parallel surfaces, and (3) lubrication flow of a layer confined between a curved surface and a sliding plane. The perspective of this paper is that a continuum model will be more useful than a discrete model in engineering design of solid lubrication systems for the foreseeable future. In the inclined plane problem, the discrete simulations are used to provide material property parameters to the continuum model. In the simple shear problem, for validation, predictions of the continuum model are compared to those of the discrete element computer simulations. Finally, the continuum theory is applied to a more complex lubrication flow. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468057
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 9 p.
Titre : A model for contact and static friction of nominally flat rough surfaces under full stick contact condition Type de document : texte imprimé Auteurs : D. Cohen, Auteur ; Y. Kligerman, Auteur ; I. Etsion, Auteur Année de publication : 2008 Article en page(s) : 9 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Force Plasticity Friction Surface roughness Stress Stiction Junctions Equations Résumé : A model for elastic-plastic nominally flat contacting rough surfaces under combined normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of junction growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468059 [article] A model for contact and static friction of nominally flat rough surfaces under full stick contact condition [texte imprimé] / D. Cohen, Auteur ; Y. Kligerman, Auteur ; I. Etsion, Auteur . - 2008 . - 9 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 9 p.
Mots-clés : Force Plasticity Friction Surface roughness Stress Stiction Junctions Equations Résumé : A model for elastic-plastic nominally flat contacting rough surfaces under combined normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of junction growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468059
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 6 p.
Titre : Exact counting of random height features of product surfaces Type de document : texte imprimé Auteurs : M. A. Mohamed, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Surface roughness Waves Computation Fittings Stochastic processes Wavelength Spectra (Spectroscopy) Density Modeling Probability Résumé : Although many statistical parameters are readily derivable from the autocorrelation function, relevant computations make their acquisition infeasible if required for product surface roughness where such a function can only be expressed in its digital form. Presented is a semianalytical approach that significantly reduces numerical computations conventionally followed to obtain width-type statistics of surface topography from the height autocorrelation function (HACF). The approach is based on fitting the digital form of the HACF to an analytic damped cosine that can then be readily differentiated and integrated. The applicability and accuracy of the proposed approach are illustrated for sampled height data experimentally collected from real product surfaces. Comparison of results using both conventional and suggested approaches shows that analytic fitting of the HACF leads to a rich set of descriptive width-type statistics as accurate as but less time consuming than conventional numerical techniques. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468060 [article] Exact counting of random height features of product surfaces [texte imprimé] / M. A. Mohamed, Auteur . - 2008 . - 6 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 6 p.
Mots-clés : Surface roughness Waves Computation Fittings Stochastic processes Wavelength Spectra (Spectroscopy) Density Modeling Probability Résumé : Although many statistical parameters are readily derivable from the autocorrelation function, relevant computations make their acquisition infeasible if required for product surface roughness where such a function can only be expressed in its digital form. Presented is a semianalytical approach that significantly reduces numerical computations conventionally followed to obtain width-type statistics of surface topography from the height autocorrelation function (HACF). The approach is based on fitting the digital form of the HACF to an analytic damped cosine that can then be readily differentiated and integrated. The applicability and accuracy of the proposed approach are illustrated for sampled height data experimentally collected from real product surfaces. Comparison of results using both conventional and suggested approaches shows that analytic fitting of the HACF leads to a rich set of descriptive width-type statistics as accurate as but less time consuming than conventional numerical techniques. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468060
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 7 p.
Titre : Modeling of asperity collisions and their effects in a frictionless sliding contact of nominally flat metallic surfaces Type de document : texte imprimé Auteurs : L. Chang, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Collisions (Physics) Metal surfaces Modeling Stress Force Electrical resistance Equations Motion Résumé : The collision process of a pair of asperities on two opposing surfaces is modeled in frictionless sliding motion with an analytically traceable approach. Equations of a sufficiently general representation are derived for the contact force, the load-carrying capacity, and the motion resistance of the asperity collision. A system model of the contact of two nominally flat metallic surfaces is subsequently developed incorporating the effects of asperity microcontact collisions. Results of a general nature are presented of the load capacity and motion resistance of the contact system in sliding motion. The model and the results may provide a first-order approximation of the effects of the asperity collisions in a sliding contact system. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468061 [article] Modeling of asperity collisions and their effects in a frictionless sliding contact of nominally flat metallic surfaces [texte imprimé] / L. Chang, Auteur . - 2008 . - 7 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 7 p.
Mots-clés : Collisions (Physics) Metal surfaces Modeling Stress Force Electrical resistance Equations Motion Résumé : The collision process of a pair of asperities on two opposing surfaces is modeled in frictionless sliding motion with an analytically traceable approach. Equations of a sufficiently general representation are derived for the contact force, the load-carrying capacity, and the motion resistance of the asperity collision. A system model of the contact of two nominally flat metallic surfaces is subsequently developed incorporating the effects of asperity microcontact collisions. Results of a general nature are presented of the load capacity and motion resistance of the contact system in sliding motion. The model and the results may provide a first-order approximation of the effects of the asperity collisions in a sliding contact system. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468061
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 10 p.
Titre : Thermal study of the dry sliding contact with third body presence Type de document : texte imprimé Auteurs : David Richard, Auteur ; Ivan Iordanoff, Auteur ; Mathieu Renouf, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Heat Temperature Rheology Particulate matter Résumé : When the thermal aspect of sliding contacts is investigated, few models take into account the presence of a third body at the contact interface. Moreover, when the presence of the third body is considered, its rheology is neglected. For this reason, the thermal study of such contact configuration is not fully understood and relies on strong hypothesis or even important simplifications. To fill this lack of knowledge, a thermal model has been developed embedded in a discrete element scheme. Such investigations highlight the key role played by both thermal and mechanical properties of the contact elements. If the third body rheology can affect the localization of the heat generation leading to important thermal asymmetries, the diffusive nature of the first bodies can also strongly control the phenomenon and accentuate or diminish the initial differences of surfaces temperature for the contacting volumes. The goal of this paper is to bring information or complete existing theories (Blok, H. A., 1937, “Theoretical Study of Temperature Rise at Surface at Actual Contact Under Oilness Lubricating Conditions ,” I. Mech. E. Conf. Publ., 2, pp. 222–235;Ryhming, I. L., 1979, “On Temperature and Heat Source Distributions in Sliding Contact Problems ,” Acta Mech., 32, pp. 261–274;Dragon-Louiset, M., and Stolz, C., 1999, “Approche Thermodynamique des Phénomenès liés à l’Usure de Contact ,” Acad. Sci. Paris, C. R., 327, pp. 1275–1280) but also to bring a new point of view on the differences observed in the past between the numerical predictions and experimental measurements. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468062 [article] Thermal study of the dry sliding contact with third body presence [texte imprimé] / David Richard, Auteur ; Ivan Iordanoff, Auteur ; Mathieu Renouf, Auteur . - 2008 . - 10 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 10 p.
Mots-clés : Heat Temperature Rheology Particulate matter Résumé : When the thermal aspect of sliding contacts is investigated, few models take into account the presence of a third body at the contact interface. Moreover, when the presence of the third body is considered, its rheology is neglected. For this reason, the thermal study of such contact configuration is not fully understood and relies on strong hypothesis or even important simplifications. To fill this lack of knowledge, a thermal model has been developed embedded in a discrete element scheme. Such investigations highlight the key role played by both thermal and mechanical properties of the contact elements. If the third body rheology can affect the localization of the heat generation leading to important thermal asymmetries, the diffusive nature of the first bodies can also strongly control the phenomenon and accentuate or diminish the initial differences of surfaces temperature for the contacting volumes. The goal of this paper is to bring information or complete existing theories (Blok, H. A., 1937, “Theoretical Study of Temperature Rise at Surface at Actual Contact Under Oilness Lubricating Conditions ,” I. Mech. E. Conf. Publ., 2, pp. 222–235;Ryhming, I. L., 1979, “On Temperature and Heat Source Distributions in Sliding Contact Problems ,” Acta Mech., 32, pp. 261–274;Dragon-Louiset, M., and Stolz, C., 1999, “Approche Thermodynamique des Phénomenès liés à l’Usure de Contact ,” Acad. Sci. Paris, C. R., 327, pp. 1275–1280) but also to bring a new point of view on the differences observed in the past between the numerical predictions and experimental measurements. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468062
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 10 p.
Titre : Thermal study of the dry sliding contact with third body presence Type de document : texte imprimé Auteurs : David Richard, Auteur ; Ivan Iordanoff, Auteur ; Mathieu Renouf, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Heat Temperature Rheology Particulate matter Résumé : When the thermal aspect of sliding contacts is investigated, few models take into account the presence of a third body at the contact interface. Moreover, when the presence of the third body is considered, its rheology is neglected. For this reason, the thermal study of such contact configuration is not fully understood and relies on strong hypothesis or even important simplifications. To fill this lack of knowledge, a thermal model has been developed embedded in a discrete element scheme. Such investigations highlight the key role played by both thermal and mechanical properties of the contact elements. If the third body rheology can affect the localization of the heat generation leading to important thermal asymmetries, the diffusive nature of the first bodies can also strongly control the phenomenon and accentuate or diminish the initial differences of surfaces temperature for the contacting volumes. The goal of this paper is to bring information or complete existing theories (Blok, H. A., 1937, “Theoretical Study of Temperature Rise at Surface at Actual Contact Under Oilness Lubricating Conditions ,” I. Mech. E. Conf. Publ., 2, pp. 222–235;Ryhming, I. L., 1979, “On Temperature and Heat Source Distributions in Sliding Contact Problems ,” Acta Mech., 32, pp. 261–274;Dragon-Louiset, M., and Stolz, C., 1999, “Approche Thermodynamique des Phénomenès liés à l’Usure de Contact ,” Acad. Sci. Paris, C. R., 327, pp. 1275–1280) but also to bring a new point of view on the differences observed in the past between the numerical predictions and experimental measurements. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468062 [article] Thermal study of the dry sliding contact with third body presence [texte imprimé] / David Richard, Auteur ; Ivan Iordanoff, Auteur ; Mathieu Renouf, Auteur . - 2008 . - 10 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 10 p.
Mots-clés : Heat Temperature Rheology Particulate matter Résumé : When the thermal aspect of sliding contacts is investigated, few models take into account the presence of a third body at the contact interface. Moreover, when the presence of the third body is considered, its rheology is neglected. For this reason, the thermal study of such contact configuration is not fully understood and relies on strong hypothesis or even important simplifications. To fill this lack of knowledge, a thermal model has been developed embedded in a discrete element scheme. Such investigations highlight the key role played by both thermal and mechanical properties of the contact elements. If the third body rheology can affect the localization of the heat generation leading to important thermal asymmetries, the diffusive nature of the first bodies can also strongly control the phenomenon and accentuate or diminish the initial differences of surfaces temperature for the contacting volumes. The goal of this paper is to bring information or complete existing theories (Blok, H. A., 1937, “Theoretical Study of Temperature Rise at Surface at Actual Contact Under Oilness Lubricating Conditions ,” I. Mech. E. Conf. Publ., 2, pp. 222–235;Ryhming, I. L., 1979, “On Temperature and Heat Source Distributions in Sliding Contact Problems ,” Acta Mech., 32, pp. 261–274;Dragon-Louiset, M., and Stolz, C., 1999, “Approche Thermodynamique des Phénomenès liés à l’Usure de Contact ,” Acad. Sci. Paris, C. R., 327, pp. 1275–1280) but also to bring a new point of view on the differences observed in the past between the numerical predictions and experimental measurements. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468062
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 8 p.
Titre : Fully coupled frictional contact using elastic halfspace theory Type de document : texte imprimé Auteurs : K. Willner, Auteur Année de publication : 2008 Article en page(s) : 8 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Pressure Deformation Friction Computer simulation Surface roughness Stress Displacement Tangential loading Mechanisms Force Résumé : The effect of dry metallic friction can be attributed to two major mechanisms: adhesion and ploughing. While ploughing is related to severe wear and degradation, adhesion can be connected to pure elastic deformations of the contacting bodies and is thus the predominant mechanism in a stable friction pair. The transmitted friction force is then proportional to the real area of contact. Therefore, a lot of effort has been put into the determination of the fraction of real area of contact under a given load. A broad spectrum of analytical and numerical models has been employed. However, it is quite common to employ the so-called Mindlin assumptions, where the contact area is determined by the normal load only, disregarding the influence of friction. In the subsequent tangential loading, usually the contact pressure distribution is kept fixed such that the coupling between the tangential and normal solutions is neglected. Here, a numerical solution scheme based on elastic halfspace theory for frictional contact problems is presented where full coupling between the normal and tangential tractions and displacements is taken into account. Several examples show the influence of the coupling effects, but also the limitations for the analysis of rough contacts. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468064 [article] Fully coupled frictional contact using elastic halfspace theory [texte imprimé] / K. Willner, Auteur . - 2008 . - 8 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 8 p.
Mots-clés : Pressure Deformation Friction Computer simulation Surface roughness Stress Displacement Tangential loading Mechanisms Force Résumé : The effect of dry metallic friction can be attributed to two major mechanisms: adhesion and ploughing. While ploughing is related to severe wear and degradation, adhesion can be connected to pure elastic deformations of the contacting bodies and is thus the predominant mechanism in a stable friction pair. The transmitted friction force is then proportional to the real area of contact. Therefore, a lot of effort has been put into the determination of the fraction of real area of contact under a given load. A broad spectrum of analytical and numerical models has been employed. However, it is quite common to employ the so-called Mindlin assumptions, where the contact area is determined by the normal load only, disregarding the influence of friction. In the subsequent tangential loading, usually the contact pressure distribution is kept fixed such that the coupling between the tangential and normal solutions is neglected. Here, a numerical solution scheme based on elastic halfspace theory for frictional contact problems is presented where full coupling between the normal and tangential tractions and displacements is taken into account. Several examples show the influence of the coupling effects, but also the limitations for the analysis of rough contacts. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468064
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 6 p.
Titre : Effect of stiff coatings on EHL film thickness in point contacts Type de document : texte imprimé Auteurs : Yuchuan Liu, Auteur ; Q. Jane Wang, Auteur ; Dong Zhu, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Coating processes Coatings Film thickness Thickness Lubrication Résumé : Coatings are widely used for interface performance enhancement and component life improvement, as well as for corrosion prevention and surface decoration. More and more mechanical components, especially those working under severe conditions, are coated with stiff (hard) thin coatings. However, the effects of coatings on lubrication characteristics, such as film thickness and friction, have not been well understood, and designing coating for optimal tribological performance is a grand challenge. In this paper, the influences of coating material properties and coating thickness on lubricant film thickness are investigated based on a point-contact isothermal elastohydrodynamic lubrication (EHL) model developed recently by the authors. The results present the trend of minimum film thickness variation as a function of coating thickness and elastic modulus under a wide range of working conditions. Curve fitting of numerical results indicates that the maximum increase in minimum film thickness, Imax, and the corresponding optimal dimensionless coating thickness, H2max, can be expressed in the following forms: Imax=0.769M0.0238R0.02972L0.1376exp(−0.0243ln2L) and H2max=0.049M0.4557R−0.17222L0.7611exp(−0.0504ln2M−0.0921ln2L). These formulas can be used to estimate the effect of coatings on film thickness for EHL applications. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468066 [article] Effect of stiff coatings on EHL film thickness in point contacts [texte imprimé] / Yuchuan Liu, Auteur ; Q. Jane Wang, Auteur ; Dong Zhu, Auteur . - 2008 . - 6 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 6 p.
Mots-clés : Coating processes Coatings Film thickness Thickness Lubrication Résumé : Coatings are widely used for interface performance enhancement and component life improvement, as well as for corrosion prevention and surface decoration. More and more mechanical components, especially those working under severe conditions, are coated with stiff (hard) thin coatings. However, the effects of coatings on lubrication characteristics, such as film thickness and friction, have not been well understood, and designing coating for optimal tribological performance is a grand challenge. In this paper, the influences of coating material properties and coating thickness on lubricant film thickness are investigated based on a point-contact isothermal elastohydrodynamic lubrication (EHL) model developed recently by the authors. The results present the trend of minimum film thickness variation as a function of coating thickness and elastic modulus under a wide range of working conditions. Curve fitting of numerical results indicates that the maximum increase in minimum film thickness, Imax, and the corresponding optimal dimensionless coating thickness, H2max, can be expressed in the following forms: Imax=0.769M0.0238R0.02972L0.1376exp(−0.0243ln2L) and H2max=0.049M0.4557R−0.17222L0.7611exp(−0.0504ln2M−0.0921ln2L). These formulas can be used to estimate the effect of coatings on film thickness for EHL applications. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468066
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 6 p.
Titre : Cavitation erosion mechanism based on analysis of erosion particles Type de document : texte imprimé Auteurs : A. Abouel-Kasem, Auteur ; S. M. Ahmed, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Particulate matter Cavitation erosion Erosion Mechanisms Fatigue Résumé : The mechanism of cavitation erosion is investigated in detail through observations of the removed particles from pure aluminum (Al-99.999). The particles removed during the incubation stage have distinctive characteristics compared to those removed in the subsequent stages. These characteristics are distinguished by lamellae structure, foldness, waviness, large size as well as one of the particle surfaces appeared to be part of the original face of the specimen. Therefore, these characteristics can be used as a monitor for early detection of cavitation erosion in closed systems. Systematic observations of disloged particles and eroded surface morphology show that the dominant failure mode in cavitation erosion is fatigue. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468069 [article] Cavitation erosion mechanism based on analysis of erosion particles [texte imprimé] / A. Abouel-Kasem, Auteur ; S. M. Ahmed, Auteur . - 2008 . - 6 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 6 p.
Mots-clés : Particulate matter Cavitation erosion Erosion Mechanisms Fatigue Résumé : The mechanism of cavitation erosion is investigated in detail through observations of the removed particles from pure aluminum (Al-99.999). The particles removed during the incubation stage have distinctive characteristics compared to those removed in the subsequent stages. These characteristics are distinguished by lamellae structure, foldness, waviness, large size as well as one of the particle surfaces appeared to be part of the original face of the specimen. Therefore, these characteristics can be used as a monitor for early detection of cavitation erosion in closed systems. Systematic observations of disloged particles and eroded surface morphology show that the dominant failure mode in cavitation erosion is fatigue. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468069
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 12 p.
Titre : Modified Reynolds equation for aerostatic porous radial bearings with quadratic forchheimer pressure-flow assumption Type de document : texte imprimé Auteurs : Rodrigo Nicoletti, Auteur ; Zilda C. Silveira, Auteur ; Benedito M. Purquerio, Auteur Année de publication : 2008 Article en page(s) : 12 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Pressure Flow (Dynamics) Porous materials Bearings Equations Stress Stiffness Résumé : Aerostatic porous bearings are becoming important elements in precision machines due to their inherent characteristics. The mathematical modeling of such bearings depends on the pressure-flow assumptions that are adopted for the flow in the porous medium. In this work, one proposes a nondimensional modified Reynolds equations based on the quadratic Forchheimer assumption. In this quadratic approach, the nondimensional parameter Φ strongly affects the bearing load capacity, by defining the nonlinearity level of the system. For values of Φ>10, the results obtained with the modified Reynolds equation with quadratic Forchheimer assumption tend to those obtained with the linear Darcy model, thus showing that this is a more robust and global approach of the problem, and can be used for both pressure-flow assumptions (linear and quadratic). The threshold between linear and quadratic assumptions is numerically investigated for a bronze sintered porous bearing, and the effects of bearing geometry are discussed. Numerical results show that Φ strongly affects the bearing loading capacity and stiffness coefficients. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468072 [article] Modified Reynolds equation for aerostatic porous radial bearings with quadratic forchheimer pressure-flow assumption [texte imprimé] / Rodrigo Nicoletti, Auteur ; Zilda C. Silveira, Auteur ; Benedito M. Purquerio, Auteur . - 2008 . - 12 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 12 p.
Mots-clés : Pressure Flow (Dynamics) Porous materials Bearings Equations Stress Stiffness Résumé : Aerostatic porous bearings are becoming important elements in precision machines due to their inherent characteristics. The mathematical modeling of such bearings depends on the pressure-flow assumptions that are adopted for the flow in the porous medium. In this work, one proposes a nondimensional modified Reynolds equations based on the quadratic Forchheimer assumption. In this quadratic approach, the nondimensional parameter Φ strongly affects the bearing load capacity, by defining the nonlinearity level of the system. For values of Φ>10, the results obtained with the modified Reynolds equation with quadratic Forchheimer assumption tend to those obtained with the linear Darcy model, thus showing that this is a more robust and global approach of the problem, and can be used for both pressure-flow assumptions (linear and quadratic). The threshold between linear and quadratic assumptions is numerically investigated for a bronze sintered porous bearing, and the effects of bearing geometry are discussed. Numerical results show that Φ strongly affects the bearing loading capacity and stiffness coefficients. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468072
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 5 p.
Titre : Experimental research on tribological properties of Mn0.78Zn0.22Fe2O4 magnetic fluids Type de document : texte imprimé Auteurs : Wang Li-jun, Auteur ; Guo Chu-wen, Auteur ; Ryuichiro Yamane, Auteur Année de publication : 2008 Article en page(s) : 5 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Tribology Friction Wear Particulate matter Magnetic fluids Nanoparticles Turbines Lubricating oils Résumé : The synthesis and application of nanometer-sized particles have received considerable attention in recent years because of their different physical and chemical properties from those of the bulk materials or individual molecules; however, few experimental investigations on the tribological properties of lubricating oils with and without nanoferromagnetic particles have been performed. This work investigates the tribological properties of Mn0.78Zn0.22Fe2O4 nanoferromagnetic as additive in 46# turbine oil using a four-ball friction and wear tester. It is shown that the 46# turbine oil containing Mn0.78Zn0.22Fe2O4 nanoparticles has much better friction reduction and antiwear abilities than the base oil. The 46# turbine oil doped with 6wt%Mn0.78Zn0.22Fe2O4 nanoparticles show the best tribological properties among the tested oil samples, and PB value is increased by 26%, and the decreasing percentage of wear scar diameter is 25.45% compared to base oil. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468074 [article] Experimental research on tribological properties of Mn0.78Zn0.22Fe2O4 magnetic fluids [texte imprimé] / Wang Li-jun, Auteur ; Guo Chu-wen, Auteur ; Ryuichiro Yamane, Auteur . - 2008 . - 5 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 5 p.
Mots-clés : Tribology Friction Wear Particulate matter Magnetic fluids Nanoparticles Turbines Lubricating oils Résumé : The synthesis and application of nanometer-sized particles have received considerable attention in recent years because of their different physical and chemical properties from those of the bulk materials or individual molecules; however, few experimental investigations on the tribological properties of lubricating oils with and without nanoferromagnetic particles have been performed. This work investigates the tribological properties of Mn0.78Zn0.22Fe2O4 nanoferromagnetic as additive in 46# turbine oil using a four-ball friction and wear tester. It is shown that the 46# turbine oil containing Mn0.78Zn0.22Fe2O4 nanoparticles has much better friction reduction and antiwear abilities than the base oil. The 46# turbine oil doped with 6wt%Mn0.78Zn0.22Fe2O4 nanoparticles show the best tribological properties among the tested oil samples, and PB value is increased by 26%, and the decreasing percentage of wear scar diameter is 25.45% compared to base oil. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468074
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008)
Titre : Friction behavior of poly (vinyl alcohol) gel against stainless steel ball in different lubricant media Type de document : texte imprimé Auteurs : Yu-Song Pan, Auteur ; Dang-Sheng Xiong, Auteur ; Xiao-Lin Chen, Auteur Année de publication : 2008 Note générale : Tibology Langues : Anglais (eng) Mots-clés : Stress Ethanol Hydrogels Stainless steel Friction Lubrication Lubricants Water Résumé : The effects of different variables on the friction coefficient of poly(vinyl alcohol) (PVA) hydrogel and stainless steel ball counterpart were investigated by a ball-on-plate friction and wear tester. Factors included lubrication condition, sliding speed, diameter of stainless steel ball, and load. It is shown that the free water in PVA hydrogel has a good lubrication on the friction counterpart. The friction coefficients have little difference between dry and lubricated conditions during the initial test stage. With the time prolonged, friction coefficient of PVA hydrogel under dry condition sharply increased within a short time. Friction coefficient decreased with increasing sliding speed and diameter of stainless steel ball. The decrease in the friction coefficient in bovine serum was 55.38% while the sliding speed increased from 45rpmto225rpm. The friction coefficient increased as the load increased, and the effect was more conspicuous at low load region. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468076 [article] Friction behavior of poly (vinyl alcohol) gel against stainless steel ball in different lubricant media [texte imprimé] / Yu-Song Pan, Auteur ; Dang-Sheng Xiong, Auteur ; Xiao-Lin Chen, Auteur . - 2008.
Tibology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008)
Mots-clés : Stress Ethanol Hydrogels Stainless steel Friction Lubrication Lubricants Water Résumé : The effects of different variables on the friction coefficient of poly(vinyl alcohol) (PVA) hydrogel and stainless steel ball counterpart were investigated by a ball-on-plate friction and wear tester. Factors included lubrication condition, sliding speed, diameter of stainless steel ball, and load. It is shown that the free water in PVA hydrogel has a good lubrication on the friction counterpart. The friction coefficients have little difference between dry and lubricated conditions during the initial test stage. With the time prolonged, friction coefficient of PVA hydrogel under dry condition sharply increased within a short time. Friction coefficient decreased with increasing sliding speed and diameter of stainless steel ball. The decrease in the friction coefficient in bovine serum was 55.38% while the sliding speed increased from 45rpmto225rpm. The friction coefficient increased as the load increased, and the effect was more conspicuous at low load region. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468076
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 7 p.
Titre : Numerical model of a tandem reciprocating hydraulic rod seal Type de document : texte imprimé Auteurs : Bo Yang, Auteur ; Richard F. Salant, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Fluid mechanics Deformation Computer simulation Surface roughness Sealing (Process) Contact mechanics Steady state Leakage Pressure Fluids Résumé : A numerical model of a tandem reciprocating hydraulic rod seal, consisting of two elastomeric U cup seals, has been constructed. It is applicable to cases in which the stroke length is significantly larger than the seal width. The model consists of coupled steady state fluid mechanics, deformation mechanics, and contact mechanics analyses, with an iterative computational procedure. The behaviors of the two seals are coupled through the pressure∕density in the interseal region and through flow continuity. Results for a typical tandem seal are compared to those of a single seal and a double lip seal. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468077 [article] Numerical model of a tandem reciprocating hydraulic rod seal [texte imprimé] / Bo Yang, Auteur ; Richard F. Salant, Auteur . - 2008 . - 7 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 7 p.
Mots-clés : Fluid mechanics Deformation Computer simulation Surface roughness Sealing (Process) Contact mechanics Steady state Leakage Pressure Fluids Résumé : A numerical model of a tandem reciprocating hydraulic rod seal, consisting of two elastomeric U cup seals, has been constructed. It is applicable to cases in which the stroke length is significantly larger than the seal width. The model consists of coupled steady state fluid mechanics, deformation mechanics, and contact mechanics analyses, with an iterative computational procedure. The behaviors of the two seals are coupled through the pressure∕density in the interseal region and through flow continuity. Results for a typical tandem seal are compared to those of a single seal and a double lip seal. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468077
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 5 p.
Titre : Investigation of tribological behavior of Al–Si alloy against steel lubricated with ionic liquids of 1-diethylphosphonyl-n-propyl-3- alkylimidazolium tetrafluoroborate Type de document : texte imprimé Auteurs : Zonggang Mu, Auteur ; Xiaoxuan Wang, Auteur ; Shuxiang Zhang, Auteur Année de publication : 2008 Article en page(s) : 5 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Tribology Friction Wear Aluminum Steel Aluminum alloys Lubricants Silicon alloys Temperature Bearings Résumé : A series of room temperature ionic liquids bearing with phosphonyl groups on the imidazolium cations, namely, 1-(3′-O,O-diethylphosphonyl-n-propyl)-3-alkylimidazolium tetrafluoroborate, were prepared and their physical properties were determined. They were also evaluated as promising lubricants for the contacts of aluminum on steel by using a SRV test rig. The tribological test results show that the synthetic ionic liquids exhibit better friction-reducing and antiwear abilities than the unsubstituted ionic liquid of 1-ethyl-3-hexylimidazolium tetrafluoroborate (coded as L206) and phosphazene (X-1P). Both the anions and the side substitutes attached to the imidazolium cations affect the tribological performance of lubricants. The scanning electron microscopy, energy-dispersive x-ray analysis, and x-ray photoelectron spectroscopy analyses of the worn surfaces show that complicated tribochemical reactions are involved in the sliding process. The anion decomposition and chemical adsorption of cation took place on the worn surface of aluminum alloy during the sliding process. As a result of the generation of boundary lubrication films which are composed of metal fluorides, B2O3, BN, nitrogen oxide, and FePO4 help to effectively reduce the friction and wear of the contacts. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468080 [article] Investigation of tribological behavior of Al–Si alloy against steel lubricated with ionic liquids of 1-diethylphosphonyl-n-propyl-3- alkylimidazolium tetrafluoroborate [texte imprimé] / Zonggang Mu, Auteur ; Xiaoxuan Wang, Auteur ; Shuxiang Zhang, Auteur . - 2008 . - 5 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 5 p.
Mots-clés : Tribology Friction Wear Aluminum Steel Aluminum alloys Lubricants Silicon alloys Temperature Bearings Résumé : A series of room temperature ionic liquids bearing with phosphonyl groups on the imidazolium cations, namely, 1-(3′-O,O-diethylphosphonyl-n-propyl)-3-alkylimidazolium tetrafluoroborate, were prepared and their physical properties were determined. They were also evaluated as promising lubricants for the contacts of aluminum on steel by using a SRV test rig. The tribological test results show that the synthetic ionic liquids exhibit better friction-reducing and antiwear abilities than the unsubstituted ionic liquid of 1-ethyl-3-hexylimidazolium tetrafluoroborate (coded as L206) and phosphazene (X-1P). Both the anions and the side substitutes attached to the imidazolium cations affect the tribological performance of lubricants. The scanning electron microscopy, energy-dispersive x-ray analysis, and x-ray photoelectron spectroscopy analyses of the worn surfaces show that complicated tribochemical reactions are involved in the sliding process. The anion decomposition and chemical adsorption of cation took place on the worn surface of aluminum alloy during the sliding process. As a result of the generation of boundary lubrication films which are composed of metal fluorides, B2O3, BN, nitrogen oxide, and FePO4 help to effectively reduce the friction and wear of the contacts. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468080
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