Dépouillements

Windage power loss modeling of a smooth rotor supported by homopolar active magnetic bearings / M. Saint Raymond in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 8 p. Titre : Windage power loss modeling of a smooth rotor supported by homopolar active magnetic bearings Type de document : texte imprimé Auteurs : M. Saint Raymond, Auteur ; M. E. Kasarda, Auteur ; P. E. Allaire, Auteur Année de publication : 2008 Article en page(s) : 8 p. Note générale : Tribology Langues : Anglais (eng) Résumé : Rotors supported by active magnetic bearings (AMBs) can spin at high surface speeds with relatively low power losses. This makes them particularly attractive for use in flywheels for energy storage in applications such as electric vehicles and uninterruptible power supplies. In order to optimize efficiency in these and other applications, the loss mechanisms associated with magnetic bearings and rotating machinery must be well understood. The primary parasitic loss mechanisms in an AMB include complex magnetic losses, due to eddy currents and hysteresis, and windage losses along the entire rotor in nonvacuum environments. In low-loss magnetic bearing designs, the windage loss component along the rotor can become dominant at high speeds, and the need for accurate windage models becomes even more critical. This study extends previous AMB power loss work by evaluating five different windage loss models using the experimental rundown data from the previous work. Each of the five windage models, along with standard models of eddy current and hysteresis losses, are used to reduce the rundown data into the associated power loss components. A comparison is then completed comparing the windage power loss component extracted through the rundown data reduction scheme to the associated analytical windage prediction in order to identify the most accurate model for calculating windage losses along a smooth rotor. Five empirical flat-plate drag coefficient models are implemented, four turbulent and one laminar. An empirical flat-plate turbulent boundary layer formula (referred to here as “Model 2”) developed by Prandtl and Schlichting displayed the best agreement between experimentally extracted and analytically predicted windage loss values. The most accurate model formula (Model 2) dictates that the frequency dependency of windage loss is both logarithmic and power based and represents the minimum error between experimentally extracted and analytically predicted losses of all models in the study of high-speed power losses in a smooth rotor supported in AMBs. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467996 [article] Windage power loss modeling of a smooth rotor supported by homopolar active magnetic bearings [texte imprimé] / M. Saint Raymond, Auteur ; M. E. Kasarda, Auteur ; P. E. Allaire, Auteur . - 2008 . - 8 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 8 p. Résumé : Rotors supported by active magnetic bearings (AMBs) can spin at high surface speeds with relatively low power losses. This makes them particularly attractive for use in flywheels for energy storage in applications such as electric vehicles and uninterruptible power supplies. In order to optimize efficiency in these and other applications, the loss mechanisms associated with magnetic bearings and rotating machinery must be well understood. The primary parasitic loss mechanisms in an AMB include complex magnetic losses, due to eddy currents and hysteresis, and windage losses along the entire rotor in nonvacuum environments. In low-loss magnetic bearing designs, the windage loss component along the rotor can become dominant at high speeds, and the need for accurate windage models becomes even more critical. This study extends previous AMB power loss work by evaluating five different windage loss models using the experimental rundown data from the previous work. Each of the five windage models, along with standard models of eddy current and hysteresis losses, are used to reduce the rundown data into the associated power loss components. A comparison is then completed comparing the windage power loss component extracted through the rundown data reduction scheme to the associated analytical windage prediction in order to identify the most accurate model for calculating windage losses along a smooth rotor. Five empirical flat-plate drag coefficient models are implemented, four turbulent and one laminar. An empirical flat-plate turbulent boundary layer formula (referred to here as “Model 2”) developed by Prandtl and Schlichting displayed the best agreement between experimentally extracted and analytically predicted windage loss values. The most accurate model formula (Model 2) dictates that the frequency dependency of windage loss is both logarithmic and power based and represents the minimum error between experimentally extracted and analytically predicted losses of all models in the study of high-speed power losses in a smooth rotor supported in AMBs. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467996

Dynamic analysis of rotor system with misaligned retainer bearings / Antti Kärkkäinen in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Titre : Dynamic analysis of rotor system with misaligned retainer bearings Type de document : texte imprimé Auteurs : Antti Kärkkäinen, Auteur ; Marlene Helfert, Auteur ; Beat Aeschlimann, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Résumé : Active magnetic bearings present a technology that has many advantages compared to traditional bearing concepts. Active magnetic bearings, however, require retainer bearings in order to prevent damages in the event of a component, power, or a control system failure. In the drop-down, when the rotor drops from the magnetic field on the retainer bearings, the design of the retainer bearings has a significant influence on the dynamic behavior of the rotor. In this study, the dynamics of an active magnetic bearing supported rotor during the drop on retainer bearings is studied employing a simulation model. The retainer bearings are modeled using a detailed ball bearing model while the flexibility of the rotor is described using the finite element method with component mode synthesis. The model is verified by comparing measurements carried out using an existing test rig and simulation results. In this study, the verified simulation model is employed studying the effect of misalignment of retainer bearings during the rotor drop-down on the retainer bearings. It is concluded in this study that the misalignment of the retainer bearings is harmful and can lead to whirling motion of the rotor. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467998 [article] Dynamic analysis of rotor system with misaligned retainer bearings [texte imprimé] / Antti Kärkkäinen, Auteur ; Marlene Helfert, Auteur ; Beat Aeschlimann, Auteur . - 2008 . - 10 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Résumé : Active magnetic bearings present a technology that has many advantages compared to traditional bearing concepts. Active magnetic bearings, however, require retainer bearings in order to prevent damages in the event of a component, power, or a control system failure. In the drop-down, when the rotor drops from the magnetic field on the retainer bearings, the design of the retainer bearings has a significant influence on the dynamic behavior of the rotor. In this study, the dynamics of an active magnetic bearing supported rotor during the drop on retainer bearings is studied employing a simulation model. The retainer bearings are modeled using a detailed ball bearing model while the flexibility of the rotor is described using the finite element method with component mode synthesis. The model is verified by comparing measurements carried out using an existing test rig and simulation results. In this study, the verified simulation model is employed studying the effect of misalignment of retainer bearings during the rotor drop-down on the retainer bearings. It is concluded in this study that the misalignment of the retainer bearings is harmful and can lead to whirling motion of the rotor. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467998

High-speed rotor with air bearings mounted on flexible supports / G. Belforte in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Titre : High-speed rotor with air bearings mounted on flexible supports : test bench and experimental results Type de document : texte imprimé Auteurs : G. Belforte, Auteur ; F. Colombo, Auteur ; T. Raparelli, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Rotor  Fourier  spectra Résumé : A test bench for rotors supported by air bearings floating on O-rings is designed in order to study the whirl phenomenon and characterize the stability threshold with damping elements mounted on bearings. The work includes a description of the test bench and some preliminary experimental results. A rotor of 1kg mass and 37mm diameter is rotated up to 75,000rpm by an air turbine machined on the rotor. Capacitance probes, placed in two radial planes, allow orbit scanning of both the rotor and the bushing at different rotating speeds and suitable load devices permit measurement of the static and dynamic stiffness of the rotor-bearing system. Curves of rotational response using rubber O-rings of three different materials are shown and compared. Also presented are the Fourier spectra of the signals for rotor displacement. The phenomenon of whirl instability is shown in terms of whirl frequency and orbit amplitudes of the rotor and bearings. The effects of both supply pressure and angular velocity on the stability threshold are shown. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468000 [article] High-speed rotor with air bearings mounted on flexible supports : test bench and experimental results [texte imprimé] / G. Belforte, Auteur ; F. Colombo, Auteur ; T. Raparelli, Auteur . - 2008 . - 7 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Mots-clés : Rotor  Fourier  spectra Résumé : A test bench for rotors supported by air bearings floating on O-rings is designed in order to study the whirl phenomenon and characterize the stability threshold with damping elements mounted on bearings. The work includes a description of the test bench and some preliminary experimental results. A rotor of 1kg mass and 37mm diameter is rotated up to 75,000rpm by an air turbine machined on the rotor. Capacitance probes, placed in two radial planes, allow orbit scanning of both the rotor and the bushing at different rotating speeds and suitable load devices permit measurement of the static and dynamic stiffness of the rotor-bearing system. Curves of rotational response using rubber O-rings of three different materials are shown and compared. Also presented are the Fourier spectra of the signals for rotor displacement. The phenomenon of whirl instability is shown in terms of whirl frequency and orbit amplitudes of the rotor and bearings. The effects of both supply pressure and angular velocity on the stability threshold are shown. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468000

Scuffing performance of a hard coating under EHL conditions at sliding speeds up to 16m∕s and contact pressures up to 2.0GPa / R. W. Snidle in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Titre : Scuffing performance of a hard coating under EHL conditions at sliding speeds up to 16m∕s and contact pressures up to 2.0GPa Type de document : texte imprimé Auteurs : R. W. Snidle, Auteur ; A. K. Dhulipalla, Auteur ; H. P. Evans, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Résumé : Scuffing experiments were conducted using 76mm diameter disks both with and without a metal-containing, carbon-based hard coating. The operating conditions in the experiments were severe with sliding speeds up to 16m∕s and maximum Hertzian contact pressures up to 2.0GPa. The disks were of alloy steel, which was case carburized and hardened followed by axial grinding. Four different surface conditions were investigated as follows: ground/uncoated, ground/coated, superfinished/uncoated, and superfinished/coated. Experiments were also carried out in which ground/coated disks were run against ground/uncoated disks. The results of the experiments show that the addition of the hard coating to the ground disks significantly improved both their scuffing resistance and frictional behavior, but the coating was less effective in producing an improvement in the durability and friction of the superfinished disks. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468002 [article] Scuffing performance of a hard coating under EHL conditions at sliding speeds up to 16m∕s and contact pressures up to 2.0GPa [texte imprimé] / R. W. Snidle, Auteur ; A. K. Dhulipalla, Auteur ; H. P. Evans, Auteur . - 2008 . - 10 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Résumé : Scuffing experiments were conducted using 76mm diameter disks both with and without a metal-containing, carbon-based hard coating. The operating conditions in the experiments were severe with sliding speeds up to 16m∕s and maximum Hertzian contact pressures up to 2.0GPa. The disks were of alloy steel, which was case carburized and hardened followed by axial grinding. Four different surface conditions were investigated as follows: ground/uncoated, ground/coated, superfinished/uncoated, and superfinished/coated. Experiments were also carried out in which ground/coated disks were run against ground/uncoated disks. The results of the experiments show that the addition of the hard coating to the ground disks significantly improved both their scuffing resistance and frictional behavior, but the coating was less effective in producing an improvement in the durability and friction of the superfinished disks. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468002

Experimental investigation on the stick-slip phenomenon in granular collision lubrication / Karim N. Elkholy in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Titre : Experimental investigation on the stick-slip phenomenon in granular collision lubrication Type de document : texte imprimé Auteurs : Karim N. Elkholy, Auteur ; M. M. Khonsari, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Stick-slip  phenomenon  Granular  collision  lubrification Résumé : An investigation on the nature of stick-slip associated with granular materials sheared between two parallel disks within the context of granular lubrication is presented. Experiments are carried out in an annular shear cell apparatus to demonstrate the effect of the stick-slip on the friction coefficient. Results are presented for the friction coefficient and the displacement as a function of the rotational speed and the applied load. The results reveal the occurrence of stick-slip at low speed and provided further evidence for the formation of granular lift between two disks undergoing sliding motion. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468004 [article] Experimental investigation on the stick-slip phenomenon in granular collision lubrication [texte imprimé] / Karim N. Elkholy, Auteur ; M. M. Khonsari, Auteur . - 2008 . - 7 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Mots-clés : Stick-slip  phenomenon  Granular  collision  lubrification Résumé : An investigation on the nature of stick-slip associated with granular materials sheared between two parallel disks within the context of granular lubrication is presented. Experiments are carried out in an annular shear cell apparatus to demonstrate the effect of the stick-slip on the friction coefficient. Results are presented for the friction coefficient and the displacement as a function of the rotational speed and the applied load. The results reveal the occurrence of stick-slip at low speed and provided further evidence for the formation of granular lift between two disks undergoing sliding motion. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468004

Study of the effect of type (Cu, Ti and Cu, Mo) electrospark coatings on friction in pin-on-disk testing / Antoszewski Bogdan in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Titre : Study of the effect of type (Cu, Ti and Cu, Mo) electrospark coatings on friction in pin-on-disk testing Type de document : texte imprimé Auteurs : Antoszewski Bogdan, Auteur ; Levi, Emil, Auteur ; Audy Jaromír, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Résumé : Recent advances in the commercial exploitation of electrospark coatings have focused on improving surface roughness by depositing Ti, Mo, V, or W over an interlayer of Cu, Sn, Pb, or Cd on the top of a tool steel material. This paper presents results of a systematic pin-on-disk experimental study of different type bilayer coatings (Cu–Sn/bronze, bottom layer; Ti and Mo, top layer) deposited on a Type 45 steel. The results are discussed in terms of friction coefficients obtained under different dry-friction conditions (speeds ranging from 0.3m∕sto0.8m∕s, and pressures ranging from 10Nto40N). An additional focus is on scuffling resistance of faces in friction, microhardness and surface roughness of coated items, and the competitive advantage of using advanced surface coatings. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468005 [article] Study of the effect of type (Cu, Ti and Cu, Mo) electrospark coatings on friction in pin-on-disk testing [texte imprimé] / Antoszewski Bogdan, Auteur ; Levi, Emil, Auteur ; Audy Jaromír, Auteur . - 2008 . - 6 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Résumé : Recent advances in the commercial exploitation of electrospark coatings have focused on improving surface roughness by depositing Ti, Mo, V, or W over an interlayer of Cu, Sn, Pb, or Cd on the top of a tool steel material. This paper presents results of a systematic pin-on-disk experimental study of different type bilayer coatings (Cu–Sn/bronze, bottom layer; Ti and Mo, top layer) deposited on a Type 45 steel. The results are discussed in terms of friction coefficients obtained under different dry-friction conditions (speeds ranging from 0.3m∕sto0.8m∕s, and pressures ranging from 10Nto40N). An additional focus is on scuffling resistance of faces in friction, microhardness and surface roughness of coated items, and the competitive advantage of using advanced surface coatings. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468005

Experimental study of adhesive static friction in a spherical elastic-plastic contact / A. Ovcharenko in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Titre : Experimental study of adhesive static friction in a spherical elastic-plastic contact Type de document : texte imprimé Auteurs : A. Ovcharenko, Auteur ; G. Halperin, Auteur ; I. Etsion, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Deformable  sphereAdhesive  static  friction Résumé : The elastic-plastic contact between a deformable sphere and a rigid flat during presliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. Different behavior of the static friction is observed in the elastic and in the elastic-plastic regimes of sphere deformation. It is found that at low normal loads, the static friction coefficient depends on the normal load in breach of the classical laws of friction. The presliding displacement is found to be less than 5% of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468006 [article] Experimental study of adhesive static friction in a spherical elastic-plastic contact [texte imprimé] / A. Ovcharenko, Auteur ; G. Halperin, Auteur ; I. Etsion, Auteur . - 2008 . - 6 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Mots-clés : Deformable  sphereAdhesive  static  friction Résumé : The elastic-plastic contact between a deformable sphere and a rigid flat during presliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. Different behavior of the static friction is observed in the elastic and in the elastic-plastic regimes of sphere deformation. It is found that at low normal loads, the static friction coefficient depends on the normal load in breach of the classical laws of friction. The presliding displacement is found to be less than 5% of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468006

Three-dimensional rough surface contact model for anisotropic materials / Ling He in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Titre : Three-dimensional rough surface contact model for anisotropic materials Type de document : texte imprimé Auteurs : Ling He, Auteur ; Timothy C. Ovaert, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Three-dimensional  rough  surface  Anisotropic  materials Résumé : By applying the line integral of Barnett–Lothe tensors on oblique planes, the three-dimensional rough surface contact problem for a semi-infinite anisotropic elastic half-plane in contact with a rough rigid sphere is formulated. The conjugate gradient technique of analytical continuation was employed to determine the contact parameters. The general solutions due to varying degrees of anisotropy and mechanical boundary conditions are obtained, and examples with fiber-reinforced composites are presented. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468007 [article] Three-dimensional rough surface contact model for anisotropic materials [texte imprimé] / Ling He, Auteur ; Timothy C. Ovaert, Auteur . - 2008 . - 6 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Mots-clés : Three-dimensional  rough  surface  Anisotropic  materials Résumé : By applying the line integral of Barnett–Lothe tensors on oblique planes, the three-dimensional rough surface contact problem for a semi-infinite anisotropic elastic half-plane in contact with a rough rigid sphere is formulated. The conjugate gradient technique of analytical continuation was employed to determine the contact parameters. The general solutions due to varying degrees of anisotropy and mechanical boundary conditions are obtained, and examples with fiber-reinforced composites are presented. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468007

A full-system approach of the elastohydrodynamic line/point contact problem / W. Habchi in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Titre : A full-system approach of the elastohydrodynamic line/point contact problem Type de document : texte imprimé Auteurs : W. Habchi, Auteur ; D. Eyheramendy, Auteur ; P. Vergne, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Résumé : The solution of the elastohydrodynamic lubrication (EHL) problem involves the simultaneous resolution of the hydrodynamic (Reynolds equation) and elastic problems (elastic deformation of the contacting surfaces). Up to now, most of the numerical works dealing with the modeling of the isothermal EHL problem were based on a weak coupling resolution of the Reynolds and elasticity equations (semi-system approach). The latter were solved separately using iterative schemes and a finite difference discretization. Very few authors attempted to solve the problem in a fully coupled way, thus solving both equations simultaneously (full-system approach). These attempts suffered from a major drawback which is the almost full Jacobian matrix of the nonlinear system of equations. This work presents a new approach for solving the fully coupled isothermal elastohydrodynamic problem using a finite element discretization of the corresponding equations. The use of the finite element method allows the use of variable unstructured meshing and different types of elements within the same model which leads to a reduced size of the problem. The nonlinear system of equations is solved using a Newton procedure which provides faster convergence rates. Suitable stabilization techniques are used to extend the solution to the case of highly loaded contacts. The complexity is the same as for classical algorithms, but an improved convergence rate, a reduced size of the problem and a sparse Jacobian matrix are obtained. Thus, the computational effort, time and memory usage are considerably reduced. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468009 [article] A full-system approach of the elastohydrodynamic line/point contact problem [texte imprimé] / W. Habchi, Auteur ; D. Eyheramendy, Auteur ; P. Vergne, Auteur . - 2008 . - 10 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Résumé : The solution of the elastohydrodynamic lubrication (EHL) problem involves the simultaneous resolution of the hydrodynamic (Reynolds equation) and elastic problems (elastic deformation of the contacting surfaces). Up to now, most of the numerical works dealing with the modeling of the isothermal EHL problem were based on a weak coupling resolution of the Reynolds and elasticity equations (semi-system approach). The latter were solved separately using iterative schemes and a finite difference discretization. Very few authors attempted to solve the problem in a fully coupled way, thus solving both equations simultaneously (full-system approach). These attempts suffered from a major drawback which is the almost full Jacobian matrix of the nonlinear system of equations. This work presents a new approach for solving the fully coupled isothermal elastohydrodynamic problem using a finite element discretization of the corresponding equations. The use of the finite element method allows the use of variable unstructured meshing and different types of elements within the same model which leads to a reduced size of the problem. The nonlinear system of equations is solved using a Newton procedure which provides faster convergence rates. Suitable stabilization techniques are used to extend the solution to the case of highly loaded contacts. The complexity is the same as for classical algorithms, but an improved convergence rate, a reduced size of the problem and a sparse Jacobian matrix are obtained. Thus, the computational effort, time and memory usage are considerably reduced. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468009

The Shear-Thinning Elastohydrodynamic Film Thickness of a Two-Component Mixture / Yuchuan Liu in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Titre : The Shear-Thinning Elastohydrodynamic Film Thickness of a Two-Component Mixture Type de document : texte imprimé Auteurs : Yuchuan Liu, Auteur ; Q. Jane Wang, Auteur ; Ivan Krupka, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Résumé : Lubricant base oils are often blends of different molecular weight cuts to arrive at a specified ambient pressure viscosity and, to improve the temperature-viscosity behavior or to simply increase the viscosity, viscosity-modifying polymer additives are often added to the base oil. This paper investigates the effect of mixture rheology on elastohydrodynamic lubrication (EHL) film thickness using EHL contact measurements and a full numerical analysis for three synthetic lubricants including two single-component lubricants PAO650 and PAO100 and a mixture of these. The pressure and shear dependences of the viscosity of these lubricants were measured with high-pressure viscometers; viscosities were not adjusted to fit experiment. The point contact film thicknesses for these lubricants in pure rolling were measured using a thin-film colorimetric interferometry apparatus. Numerical simulations based on the measured rheology show very good agreement with the measurements of film thickness while the Newtonian prediction is up to twice the measurement. These results validate the use of realistic shear-thinning and pressure-viscosity models, which originate from viscosity measurements. It is conceivable that simulation may provide a means to “engineer” lubricants with the optimum balance of film thickness and friction through intelligent mixing of components. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468010 [article] The Shear-Thinning Elastohydrodynamic Film Thickness of a Two-Component Mixture [texte imprimé] / Yuchuan Liu, Auteur ; Q. Jane Wang, Auteur ; Ivan Krupka, Auteur . - 2008 . - 7 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Résumé : Lubricant base oils are often blends of different molecular weight cuts to arrive at a specified ambient pressure viscosity and, to improve the temperature-viscosity behavior or to simply increase the viscosity, viscosity-modifying polymer additives are often added to the base oil. This paper investigates the effect of mixture rheology on elastohydrodynamic lubrication (EHL) film thickness using EHL contact measurements and a full numerical analysis for three synthetic lubricants including two single-component lubricants PAO650 and PAO100 and a mixture of these. The pressure and shear dependences of the viscosity of these lubricants were measured with high-pressure viscometers; viscosities were not adjusted to fit experiment. The point contact film thicknesses for these lubricants in pure rolling were measured using a thin-film colorimetric interferometry apparatus. Numerical simulations based on the measured rheology show very good agreement with the measurements of film thickness while the Newtonian prediction is up to twice the measurement. These results validate the use of realistic shear-thinning and pressure-viscosity models, which originate from viscosity measurements. It is conceivable that simulation may provide a means to “engineer” lubricants with the optimum balance of film thickness and friction through intelligent mixing of components. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468010

Performance of spur gears considering surface roughness and shear thinning lubricant / S. Akbarzadeh in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 8 p. Titre : Performance of spur gears considering surface roughness and shear thinning lubricant Type de document : texte imprimé Auteurs : S. Akbarzadeh, Auteur ; M. M. Khonsari, Auteur Année de publication : 2008 Article en page(s) : 8 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Spur  gears  Roughless Résumé : A model is developed for predicting the performance of spur gears with provision for surface roughness. For each point along the line of action, the contact of pinion and gear is replaced by that of two cylinders. The radii of cylinders, transmitted load, and contact stress are calculated, and lubricant film thickness is obtained using the load-sharing concept of Johnson (1972, “A Simple Theory of Asperity Contact in Elastohydrodynamic Lubrication ,” Wear, 19, pp. 91–108) To validate the analysis, the predicted film thickness and the friction coefficient are compared to published theoretical and experimental data. The model is capable of predicting the performance of gears with non-Newtonian lubricants—such as that of shear thinning lubricants—often used in gears. For this purpose, a correction factor for shear thinning film thickness introduced by Bair (2005, “Shear Thinning Correction for Rolling/Sliding Electrohydrodynamic Film Thickness ,” Proc. Inst. Mech. Eng., Part J: J. Eng. Tribol., 219, pp. 1–6) has been employed. The results of a series of simulations presenting the effect of surface roughness on the friction coefficient are presented and discussed. The results help to establish the lubrication regime along the line of action of spur gears. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468011 [article] Performance of spur gears considering surface roughness and shear thinning lubricant [texte imprimé] / S. Akbarzadeh, Auteur ; M. M. Khonsari, Auteur . - 2008 . - 8 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 8 p. Mots-clés : Spur  gears  Roughless Résumé : A model is developed for predicting the performance of spur gears with provision for surface roughness. For each point along the line of action, the contact of pinion and gear is replaced by that of two cylinders. The radii of cylinders, transmitted load, and contact stress are calculated, and lubricant film thickness is obtained using the load-sharing concept of Johnson (1972, “A Simple Theory of Asperity Contact in Elastohydrodynamic Lubrication ,” Wear, 19, pp. 91–108) To validate the analysis, the predicted film thickness and the friction coefficient are compared to published theoretical and experimental data. The model is capable of predicting the performance of gears with non-Newtonian lubricants—such as that of shear thinning lubricants—often used in gears. For this purpose, a correction factor for shear thinning film thickness introduced by Bair (2005, “Shear Thinning Correction for Rolling/Sliding Electrohydrodynamic Film Thickness ,” Proc. Inst. Mech. Eng., Part J: J. Eng. Tribol., 219, pp. 1–6) has been employed. The results of a series of simulations presenting the effect of surface roughness on the friction coefficient are presented and discussed. The results help to establish the lubrication regime along the line of action of spur gears. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468011

Numerical analysis of thermoelastohydrodynamic behavior of elastomer radial lip seals / A. Maoui in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 9 p. Titre : Numerical analysis of thermoelastohydrodynamic behavior of elastomer radial lip seals Type de document : texte imprimé Auteurs : A. Maoui, Auteur ; M. Hajjam, Auteur ; D. Bonneau, Auteur Année de publication : 2008 Article en page(s) : 9 p. Note générale : Tribology Langues : Anglais (eng) Résumé : This work is a numerical analysis of the thermal effect on the elastohydrodynamic behavior of elastomer radial lip seals. Two thermal approaches are considered, a local approach that determines the distribution of temperature in the contact zone and a simplified global approach that considers a mean temperature of fluid film. In addition, the thermoelastic behavior of the lip surface is taken into account with a relationship between Young’s modulus and the mean temperature of the lip surface. It is shown that the local temperature of the contact zone increases sensitively according to the shaft speed. Moreover, all operating characteristics such as film thickness and power loss are significantly influenced by the local temperature effect. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468014 [article] Numerical analysis of thermoelastohydrodynamic behavior of elastomer radial lip seals [texte imprimé] / A. Maoui, Auteur ; M. Hajjam, Auteur ; D. Bonneau, Auteur . - 2008 . - 9 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 9 p. Résumé : This work is a numerical analysis of the thermal effect on the elastohydrodynamic behavior of elastomer radial lip seals. Two thermal approaches are considered, a local approach that determines the distribution of temperature in the contact zone and a simplified global approach that considers a mean temperature of fluid film. In addition, the thermoelastic behavior of the lip surface is taken into account with a relationship between Young’s modulus and the mean temperature of the lip surface. It is shown that the local temperature of the contact zone increases sensitively according to the shaft speed. Moreover, all operating characteristics such as film thickness and power loss are significantly influenced by the local temperature effect. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468014

Interaction of asperities on opposing surfaces in thin film, mixed elastohydrodynamic lubrication / Jian W. Choo in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Titre : Interaction of asperities on opposing surfaces in thin film, mixed elastohydrodynamic lubrication Type de document : texte imprimé Auteurs : Jian W. Choo, Auteur ; Andrew V. Olver, Auteur ; Hugh A. Spikes, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Résumé : A novel experimental method has been developed to investigate how model asperities, on opposing surfaces in an elastohydrodynamic (EHD) contact, interact to influence the lubricant film distribution. This technique allows direct measurements of lubricant film thickness during asperity-asperity collision. A surface having a single transverse ridge asperity was rubbed against a second surface having three different roughness features, a transverse ridge, multiple transverse ridges, and an array of hemispherical bumps to study the resultant micro-EHD films. This work reveals how the film thickness is greatly reduced when the peaks of opposing asperities coincide, and how asperities can combine to cause a larger volume of lubricant to be entrapped at their leading edges. The new technique described shows considerable promise for the study of mixed lubrication. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468016 [article] Interaction of asperities on opposing surfaces in thin film, mixed elastohydrodynamic lubrication [texte imprimé] / Jian W. Choo, Auteur ; Andrew V. Olver, Auteur ; Hugh A. Spikes, Auteur . - 2008 . - 10 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Résumé : A novel experimental method has been developed to investigate how model asperities, on opposing surfaces in an elastohydrodynamic (EHD) contact, interact to influence the lubricant film distribution. This technique allows direct measurements of lubricant film thickness during asperity-asperity collision. A surface having a single transverse ridge asperity was rubbed against a second surface having three different roughness features, a transverse ridge, multiple transverse ridges, and an array of hemispherical bumps to study the resultant micro-EHD films. This work reveals how the film thickness is greatly reduced when the peaks of opposing asperities coincide, and how asperities can combine to cause a larger volume of lubricant to be entrapped at their leading edges. The new technique described shows considerable promise for the study of mixed lubrication. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468016

Observations of acoustic emission under conditions of varying specific film thickness for meshing spur and helical gears / R. I. Raja Hamzah in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 12 p. Titre : Observations of acoustic emission under conditions of varying specific film thickness for meshing spur and helical gears Type de document : texte imprimé Auteurs : R. I. Raja Hamzah, Auteur ; Khamis R. Al-Balushi, Auteur ; D. Mba, Auteur Année de publication : 2008 Article en page(s) : 12 p. Note générale : Tribology Langues : Anglais (eng) Résumé : This paper presents experimental findings on the generation of acoustic emission (AE) from operational spur and helical gears as a function of specific film thickness (λ). The latter was varied while the gears were operating by spraying liquid nitrogen onto the rotating gear wheel over a range of load and speed conditions. It was observed that the level of AE activity was dependent on the specific film thickness (λ) and consequently the level asperity contact. The presented finding on both spur and helical gears is the first known attempt at correlating friction, film thickness, and gear operating conditions with AE. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468018 [article] Observations of acoustic emission under conditions of varying specific film thickness for meshing spur and helical gears [texte imprimé] / R. I. Raja Hamzah, Auteur ; Khamis R. Al-Balushi, Auteur ; D. Mba, Auteur . - 2008 . - 12 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 12 p. Résumé : This paper presents experimental findings on the generation of acoustic emission (AE) from operational spur and helical gears as a function of specific film thickness (λ). The latter was varied while the gears were operating by spraying liquid nitrogen onto the rotating gear wheel over a range of load and speed conditions. It was observed that the level of AE activity was dependent on the specific film thickness (λ) and consequently the level asperity contact. The presented finding on both spur and helical gears is the first known attempt at correlating friction, film thickness, and gear operating conditions with AE. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468018

A Markovian finishing process / M. A. Mohamed in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 5 p. Titre : A Markovian finishing process Type de document : texte imprimé Auteurs : M. A. Mohamed, Auteur Année de publication : 2008 Article en page(s) : 5 p. Note générale : Tribology Langues : Anglais (eng) Résumé : Addressed is the mechanism of finishing processes for a workpiece surface using hard abrasive tools such as grinding, abrasive paper, and filing. The mechanism is intended to monitor the gradual changes of the workpiece surface state roughness as the tool is applied for several strokes. Based on a number of common features, the present study simulates each rubbing stroke as a Markov process, and each set of several strokes as a Markov chain. In the simulating model, the discrete probabilistic properties of a specific tool abrasive surface can be expressed in terms of a corresponding Markov matrix operator. Thus, the tool action after one rubbing stroke is obtained via a matrix mapping from a given state roughness to a subsequent state roughness of the workpiece surface. Although the suggested model is capable to handle a comprehensive finishing mechanism, the study focuses on the simple case of zero feeding using a hard abrasive tool, in which the Markov matrix shrinks to a special triangular form. Main findings show that major aspects of the tool surface are transferred to the stepwise roughness state of the workpiece immediately after the first stroke. In addition, regardless of the initial roughness state of the workpiece surface, whether with flat or randomly distributed heights, the ultimate state roughness is unique and definitely features the theoretical case of a plain flat surface. However, this theoretical case is infeasible since it can only be reached after infinite number of strokes. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468020 [article] A Markovian finishing process [texte imprimé] / M. A. Mohamed, Auteur . - 2008 . - 5 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 5 p. Résumé : Addressed is the mechanism of finishing processes for a workpiece surface using hard abrasive tools such as grinding, abrasive paper, and filing. The mechanism is intended to monitor the gradual changes of the workpiece surface state roughness as the tool is applied for several strokes. Based on a number of common features, the present study simulates each rubbing stroke as a Markov process, and each set of several strokes as a Markov chain. In the simulating model, the discrete probabilistic properties of a specific tool abrasive surface can be expressed in terms of a corresponding Markov matrix operator. Thus, the tool action after one rubbing stroke is obtained via a matrix mapping from a given state roughness to a subsequent state roughness of the workpiece surface. Although the suggested model is capable to handle a comprehensive finishing mechanism, the study focuses on the simple case of zero feeding using a hard abrasive tool, in which the Markov matrix shrinks to a special triangular form. Main findings show that major aspects of the tool surface are transferred to the stepwise roughness state of the workpiece immediately after the first stroke. In addition, regardless of the initial roughness state of the workpiece surface, whether with flat or randomly distributed heights, the ultimate state roughness is unique and definitely features the theoretical case of a plain flat surface. However, this theoretical case is infeasible since it can only be reached after infinite number of strokes. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468020

The effect of cementite size and morphology on the abrasive wear behavior of UHC steel / Niyazi Ozdemir in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 5 p. Titre : The effect of cementite size and morphology on the abrasive wear behavior of UHC steel Type de document : texte imprimé Auteurs : Niyazi Ozdemir, Auteur ; Furkan Sarsilmaz, Auteur ; Nuri Orhan, Auteur Année de publication : 2008 Article en page(s) : 5 p. Note générale : Tribology Langues : Anglais (eng) Résumé : In this study, the abrasive wear behavior of a grain refined hypereutectoid carbon steel containing 1.2% C, 4% Al, 0.20% Mo, and 0.1% Ti was investigated experimentally. Thermal cycles were applied to all specimens about ten times to obtain a fine-grained structure and to gain more softness structures, such as spheroidized cementite for these steels. After every thermal cycle, the microstructures of specimens were examined by scanning electron microscopy to determine the transformation mechanism of structure. Microstructure analyses showed that size of cementite decreased as a function of heat treatment cycle. With the increase of heat treatment cycle, the grain size of cementite in all specimens started to decrease. As a consequence, these cementite islands transformed to spherical cementite having an average grain size of 5μm. In addition, the wear test results indicated a correspondence between wear rate and thermal cycling. However, the hardness values decreased with increasing heat treatment cycle. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468021 [article] The effect of cementite size and morphology on the abrasive wear behavior of UHC steel [texte imprimé] / Niyazi Ozdemir, Auteur ; Furkan Sarsilmaz, Auteur ; Nuri Orhan, Auteur . - 2008 . - 5 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 5 p. Résumé : In this study, the abrasive wear behavior of a grain refined hypereutectoid carbon steel containing 1.2% C, 4% Al, 0.20% Mo, and 0.1% Ti was investigated experimentally. Thermal cycles were applied to all specimens about ten times to obtain a fine-grained structure and to gain more softness structures, such as spheroidized cementite for these steels. After every thermal cycle, the microstructures of specimens were examined by scanning electron microscopy to determine the transformation mechanism of structure. Microstructure analyses showed that size of cementite decreased as a function of heat treatment cycle. With the increase of heat treatment cycle, the grain size of cementite in all specimens started to decrease. As a consequence, these cementite islands transformed to spherical cementite having an average grain size of 5μm. In addition, the wear test results indicated a correspondence between wear rate and thermal cycling. However, the hardness values decreased with increasing heat treatment cycle. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468021

Comparison of interfacial forces during post-chemical-mechanical-polishing cleaning / Dedy Ng in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 5 p. Titre : Comparison of interfacial forces during post-chemical-mechanical-polishing cleaning Type de document : texte imprimé Auteurs : Dedy Ng, Auteur ; Hong Liang, Auteur Année de publication : 2008 Article en page(s) : 5 p. Note générale : Tribology Langues : Anglais (eng) Résumé : This research investigates the interfacial forces involved in tribological interactions while removing nanosized particles during post-chemical-mechanical polishing cleaning. Surface and interfacial forces are discussed to understand the particle adhesion and subsequent removal through physical and chemical interactions. Approaches include theoretical analysis combined with experimental study. The theoretical analysis was focused on the forces that exist between particles and a substrate. Surface interaction consideration includes applied pressure, frictional force, and hydrodynamic drag. The polishing experiments were carried out on silicon wafers with SiO2 slurry. Cleaning experiments were performed in de-ionized water using a polyvinyl acetal brush to remove particles from a hydrophilic-silicon surface. The fluid-drag force was found to affect the lubricating behavior of cleaning through changing material properties. Values of interfacial forces and their effects on cleaning were discussed along with a lubricating model system. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468024 [article] Comparison of interfacial forces during post-chemical-mechanical-polishing cleaning [texte imprimé] / Dedy Ng, Auteur ; Hong Liang, Auteur . - 2008 . - 5 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 5 p. Résumé : This research investigates the interfacial forces involved in tribological interactions while removing nanosized particles during post-chemical-mechanical polishing cleaning. Surface and interfacial forces are discussed to understand the particle adhesion and subsequent removal through physical and chemical interactions. Approaches include theoretical analysis combined with experimental study. The theoretical analysis was focused on the forces that exist between particles and a substrate. Surface interaction consideration includes applied pressure, frictional force, and hydrodynamic drag. The polishing experiments were carried out on silicon wafers with SiO2 slurry. Cleaning experiments were performed in de-ionized water using a polyvinyl acetal brush to remove particles from a hydrophilic-silicon surface. The fluid-drag force was found to affect the lubricating behavior of cleaning through changing material properties. Values of interfacial forces and their effects on cleaning were discussed along with a lubricating model system. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468024

Pressure buildup mechanism in a textured inlet of a hydrodynamic contact / Samuel Cupillard in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Titre : Pressure buildup mechanism in a textured inlet of a hydrodynamic contact Type de document : texte imprimé Auteurs : Samuel Cupillard, Auteur ; Cervantes, Michel J., Auteur ; Sergei Glavatskih, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Résumé : A flow analysis is carried out for an inclined slider bearing with the aim of showing the governing mechanism at conditions where an optimum in load carrying capacity is achieved. The effects of surface texture on pressure buildup and load carrying capacity are explained for a textured slider bearing geometry. Numerical simulations are performed for laminar, steady, and isothermal flows. The energy transferred to the fluid from the moving wall is converted into pressure in the initial part of the converging contact and into losses in the second part. The convergence ratio can be increased, in order to get the greatest pressure gradient, until the limiting value where flow recirculation begins to occur. The texture appears to achieve its maximum efficiency when its depth is such that the velocity profile is stretched at its maximum extent without incurring incoming recirculating flow. The wall profile shape controlling the velocity profile can be optimized for many hydrodynamic contacts. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468026 [article] Pressure buildup mechanism in a textured inlet of a hydrodynamic contact [texte imprimé] / Samuel Cupillard, Auteur ; Cervantes, Michel J., Auteur ; Sergei Glavatskih, Auteur . - 2008 . - 10 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Résumé : A flow analysis is carried out for an inclined slider bearing with the aim of showing the governing mechanism at conditions where an optimum in load carrying capacity is achieved. The effects of surface texture on pressure buildup and load carrying capacity are explained for a textured slider bearing geometry. Numerical simulations are performed for laminar, steady, and isothermal flows. The energy transferred to the fluid from the moving wall is converted into pressure in the initial part of the converging contact and into losses in the second part. The convergence ratio can be increased, in order to get the greatest pressure gradient, until the limiting value where flow recirculation begins to occur. The texture appears to achieve its maximum efficiency when its depth is such that the velocity profile is stretched at its maximum extent without incurring incoming recirculating flow. The wall profile shape controlling the velocity profile can be optimized for many hydrodynamic contacts. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468026

An experimental study of oil-lubricated journal bearings undergoing oscillatory motion / Xiaobin Lu in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Titre : An experimental study of oil-lubricated journal bearings undergoing oscillatory motion Type de document : texte imprimé Auteurs : Xiaobin Lu, Auteur ; M. M. Khonsari, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Oil-lubricated  journal  Oscillatory  motion Résumé : A distinctive behavior of an oil-lubricated journal bearing undergoing oscillatory motion is the evolution of friction hysteresis as it traverses from boundary, to mixed, and to hydrodynamic regime. In this paper, the results of a series of experiments are reported to examine the effects of load, with or without oil, oil type, oil inlet temperature, and oscillating frequency on the friction hysteresis. Three types of hysteresis loop were found. The inertia of the lubricant flow contributes to the friction hysteresis. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468028 [article] An experimental study of oil-lubricated journal bearings undergoing oscillatory motion [texte imprimé] / Xiaobin Lu, Auteur ; M. M. Khonsari, Auteur . - 2008 . - 7 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Mots-clés : Oil-lubricated  journal  Oscillatory  motion Résumé : A distinctive behavior of an oil-lubricated journal bearing undergoing oscillatory motion is the evolution of friction hysteresis as it traverses from boundary, to mixed, and to hydrodynamic regime. In this paper, the results of a series of experiments are reported to examine the effects of load, with or without oil, oil type, oil inlet temperature, and oscillating frequency on the friction hysteresis. Three types of hysteresis loop were found. The inertia of the lubricant flow contributes to the friction hysteresis. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468028

Rolling stream trails / Coda H. Pan in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 11 p. Titre : Rolling stream trails : an alternative cavitation analysis Type de document : texte imprimé Auteurs : Coda H. Pan, Auteur ; Tae Ho Kim, Auteur ; Joseph J. Rencis, Auteur Année de publication : 2008 Article en page(s) : 11 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Rolling  stream  trail  Cavitation  analysis Résumé : The rolling stream trail (RST) model introduces a new formulation of cavitation analysis of an eccentric journal bearing; it is presented as a preferred foundation for cavitation analysis of a journal bearing to replace Floberg’s streamer hypothesis that had been adopted by many investigators in recent past. Based on a careful reinterpretation of published experimental photographic data, noting the blunt-nosed shape of the interspersing space that separates adjacent wetting outlines at the rupture boundary, it stipulates a 3D flow structure for transition from the filled fluid film (FFF) to a cross-void fluid transportation process. The transition starts as a two-component composite rupture front and becomes an adhered film (AF) that is masked by rolled-on stream trails, which are drawn from the rupture front. The AF moves with the journal surface across the void to feed the FFF at the formation boundary. Upon averaged across a full period of the rupture front, Olsson’s equation for flow continuity relative to a moving cavitation boundary yields a moving speed of the rupture front that is proportional to the reciprocal of the width fraction of the wet pockets multiplied into the FFF pressure gradient. For all nonvanishing width fraction of the wet pockets, both rupture and formation boundaries move with finite speeds. RST is an initial value time-dependent problem that deals with both the FFF and AF that are joined at rupture and formation boundaries. The initial fluid content in the void span is bracketed between a dry void and a freshly cavitated wet void. As time progresses, transportation of AF across the void space and boundary motions form a coupled evolution process. Formulas for the boundary motions indicate that the formation boundary would become stationary simultaneously as the rupture boundary approaches the Swift–Stieber condition. For implementation of RST analysis, analytic functions originally derived by Sommerfeld in his classical paper are employed to construct FFF pressure profile and subsequently to calculate boundary speeds. Precision and robustness achieved in this approach assure viability of RST cavitation analysis. Results include temporal evolution profiles of the FFF pressure and the cavitation boundary trajectories. Basic concepts and mathematical formulation of RST are applicable to 2D problems. A scheme to include squeeze film motion is outlined. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468031 [article] Rolling stream trails : an alternative cavitation analysis [texte imprimé] / Coda H. Pan, Auteur ; Tae Ho Kim, Auteur ; Joseph J. Rencis, Auteur . - 2008 . - 11 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 11 p. Mots-clés : Rolling  stream  trail  Cavitation  analysis Résumé : The rolling stream trail (RST) model introduces a new formulation of cavitation analysis of an eccentric journal bearing; it is presented as a preferred foundation for cavitation analysis of a journal bearing to replace Floberg’s streamer hypothesis that had been adopted by many investigators in recent past. Based on a careful reinterpretation of published experimental photographic data, noting the blunt-nosed shape of the interspersing space that separates adjacent wetting outlines at the rupture boundary, it stipulates a 3D flow structure for transition from the filled fluid film (FFF) to a cross-void fluid transportation process. The transition starts as a two-component composite rupture front and becomes an adhered film (AF) that is masked by rolled-on stream trails, which are drawn from the rupture front. The AF moves with the journal surface across the void to feed the FFF at the formation boundary. Upon averaged across a full period of the rupture front, Olsson’s equation for flow continuity relative to a moving cavitation boundary yields a moving speed of the rupture front that is proportional to the reciprocal of the width fraction of the wet pockets multiplied into the FFF pressure gradient. For all nonvanishing width fraction of the wet pockets, both rupture and formation boundaries move with finite speeds. RST is an initial value time-dependent problem that deals with both the FFF and AF that are joined at rupture and formation boundaries. The initial fluid content in the void span is bracketed between a dry void and a freshly cavitated wet void. As time progresses, transportation of AF across the void space and boundary motions form a coupled evolution process. Formulas for the boundary motions indicate that the formation boundary would become stationary simultaneously as the rupture boundary approaches the Swift–Stieber condition. For implementation of RST analysis, analytic functions originally derived by Sommerfeld in his classical paper are employed to construct FFF pressure profile and subsequently to calculate boundary speeds. Precision and robustness achieved in this approach assure viability of RST cavitation analysis. Results include temporal evolution profiles of the FFF pressure and the cavitation boundary trajectories. Basic concepts and mathematical formulation of RST are applicable to 2D problems. A scheme to include squeeze film motion is outlined. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468031

Performance of graphite and boron-nitride-silicone based lubricants and associated lubrication mechanisms in warm forging of aluminum / Gracious Ngaile in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Titre : Performance of graphite and boron-nitride-silicone based lubricants and associated lubrication mechanisms in warm forging of aluminum Type de document : texte imprimé Auteurs : Gracious Ngaile, Auteur ; Frank Botz, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Water/oil-graphite  emulsions  Graphite-based  lubricants  Boron-nitride-silicone  lubricants Résumé : Although water/oil-graphite emulsions are widely used in warm forging processes, they carry environmental concerns. In an attempt to replace graphite-based lubricants in warm forging of aluminum alloys, two variants of boron-nitride-silicone lubricants were formulated. The two variants were made by dispersing boron nitride powder in polydimethyl siloxane oil at concentrations of 1% and 8%. The formulated lubricants were initially tested for their thermal degradation characteristics using a thermogravimetric analyzer and compared to the thermal degradation behavior of graphite and silicone oil lubricants. Ring compression tests were then carried out at 260°C and 370°C. Boron-nitride-silicone lubricant variants did not show significant difference in performance as die temperature was increased from 260°Cto370°C. This is in contrast to graphite, which performed much better at 260°C than at 370°C, due to thermal oxidation. On the other hand, silicone oil exhibited the worst performance at 260°C and the best performance at 370°C. In both boron nitride lubricant variants, the polydimethyl siloxane facilitated hydrostatic/hydrodynamic lubrication at 260°C, with boron nitride acting as a barrier film that reduced friction. However, the lubrication mechanisms changed at 370°C, where the depolymerization of polydimethyl siloxane led to formation of silica due to thermal oxidation. Silica, together with boron nitride, acted as a film barrier with low shear strength. The dual lubrication mechanisms make boron-nitride-silicone lubricants suitable for a wide range of aluminum forging temperatures. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468033 [article] Performance of graphite and boron-nitride-silicone based lubricants and associated lubrication mechanisms in warm forging of aluminum [texte imprimé] / Gracious Ngaile, Auteur ; Frank Botz, Auteur . - 2008 . - 7 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Mots-clés : Water/oil-graphite  emulsions  Graphite-based  lubricants  Boron-nitride-silicone  lubricants Résumé : Although water/oil-graphite emulsions are widely used in warm forging processes, they carry environmental concerns. In an attempt to replace graphite-based lubricants in warm forging of aluminum alloys, two variants of boron-nitride-silicone lubricants were formulated. The two variants were made by dispersing boron nitride powder in polydimethyl siloxane oil at concentrations of 1% and 8%. The formulated lubricants were initially tested for their thermal degradation characteristics using a thermogravimetric analyzer and compared to the thermal degradation behavior of graphite and silicone oil lubricants. Ring compression tests were then carried out at 260°C and 370°C. Boron-nitride-silicone lubricant variants did not show significant difference in performance as die temperature was increased from 260°Cto370°C. This is in contrast to graphite, which performed much better at 260°C than at 370°C, due to thermal oxidation. On the other hand, silicone oil exhibited the worst performance at 260°C and the best performance at 370°C. In both boron nitride lubricant variants, the polydimethyl siloxane facilitated hydrostatic/hydrodynamic lubrication at 260°C, with boron nitride acting as a barrier film that reduced friction. However, the lubrication mechanisms changed at 370°C, where the depolymerization of polydimethyl siloxane led to formation of silica due to thermal oxidation. Silica, together with boron nitride, acted as a film barrier with low shear strength. The dual lubrication mechanisms make boron-nitride-silicone lubricants suitable for a wide range of aluminum forging temperatures. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468033

Free surface thin layer flow on bearing raceways / M. T. van Zoelen in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Titre : Free surface thin layer flow on bearing raceways Type de document : texte imprimé Auteurs : M. T. van Zoelen, Auteur ; C. H. Venner,, Auteur ; P. M. Lugt, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Layer  flow  Bearing  raceway Résumé : In this paper, the effects of rotation on the distribution of a layer of oil on a bearing raceway are analyzed in relation to the geometry of the raceway. The research is motivated by the need to understand the behavior of grease lubricated bearings. Some specific aspects of grease lubrication can be understood by approximating the contact as a starved lubricated elastohydrodynamic lubrication contact. In such a contact, the shape and thickness of the inlet layer of oil, supplied to the contact on the running track, are of crucial importance to the film formation and contact performance. Small changes in the distribution of lubricant on the rolling track, as a result of reflow or redistribution, may have a large (local) effect on the film thickness inside the contact. Starting from the Navier–Stokes equations, the free surface thin layer flow equation for axisymmetric rotating surfaces is derived. For the case of bearing applications, it is shown that a simple quasilinear equation can be derived for the layer thickness, as a function of location and time, which can be solved analytically. Experiments have been carried out, measuring the changes of a layer of oil on rotating raceways in time in relation to the rotational speed and the raceway geometry. It is shown that the simplified model accurately predicts the thin layer flow, except in a region near the outflow boundary, where the effect of the boundary condition on the layer shape is crucial. This is further illustrated by results of numerical simulations. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468035 [article] Free surface thin layer flow on bearing raceways [texte imprimé] / M. T. van Zoelen, Auteur ; C. H. Venner,, Auteur ; P. M. Lugt, Auteur . - 2008 . - 10 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 10 p. Mots-clés : Layer  flow  Bearing  raceway Résumé : In this paper, the effects of rotation on the distribution of a layer of oil on a bearing raceway are analyzed in relation to the geometry of the raceway. The research is motivated by the need to understand the behavior of grease lubricated bearings. Some specific aspects of grease lubrication can be understood by approximating the contact as a starved lubricated elastohydrodynamic lubrication contact. In such a contact, the shape and thickness of the inlet layer of oil, supplied to the contact on the running track, are of crucial importance to the film formation and contact performance. Small changes in the distribution of lubricant on the rolling track, as a result of reflow or redistribution, may have a large (local) effect on the film thickness inside the contact. Starting from the Navier–Stokes equations, the free surface thin layer flow equation for axisymmetric rotating surfaces is derived. For the case of bearing applications, it is shown that a simple quasilinear equation can be derived for the layer thickness, as a function of location and time, which can be solved analytically. Experiments have been carried out, measuring the changes of a layer of oil on rotating raceways in time in relation to the rotational speed and the raceway geometry. It is shown that the simplified model accurately predicts the thin layer flow, except in a region near the outflow boundary, where the effect of the boundary condition on the layer shape is crucial. This is further illustrated by results of numerical simulations. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468035

Investigation of contact stiffness and contact damping for magnetic storage head-disk interfaces / Xi Shi in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 9 p. Titre : Investigation of contact stiffness and contact damping for magnetic storage head-disk interfaces Type de document : texte imprimé Auteurs : Xi Shi, Auteur ; Andreas A. Polycarpou, Auteur Année de publication : 2008 Article en page(s) : 9 p. Note générale : Tribology Langues : Anglais (eng) Résumé : As the areal density of magnetic disk storage continues to increase and head-disk spacing decreases, contact between the recording slider and the rotating media becomes imminent. In order to predict contact forces, fly-height modulations, and off-track motions, dynamic models are typically used. A critical element of these models is the contact stiffness and damping arising from the interfacial interaction between the slider and the disk. In this paper, we review different models for predicting contact stiffness based on roughness and layered media and then we report experimental data of both contact stiffness and contact damping of typical head-disk interfaces. It is found that the contact stiffness models (based on roughness alone) overpredict the contact stiffness of actual head-disk interfaces by as much as an order of magnitude. Also, it is found that the contact damping ratio is typically few percent and its behavior is substrate dependent. In addition, the effects of a molecularly thin lubricant and humidity on contact stiffness and damping were experimentally investigated and no significant effects were found. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468038 [article] Investigation of contact stiffness and contact damping for magnetic storage head-disk interfaces [texte imprimé] / Xi Shi, Auteur ; Andreas A. Polycarpou, Auteur . - 2008 . - 9 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 9 p. Résumé : As the areal density of magnetic disk storage continues to increase and head-disk spacing decreases, contact between the recording slider and the rotating media becomes imminent. In order to predict contact forces, fly-height modulations, and off-track motions, dynamic models are typically used. A critical element of these models is the contact stiffness and damping arising from the interfacial interaction between the slider and the disk. In this paper, we review different models for predicting contact stiffness based on roughness and layered media and then we report experimental data of both contact stiffness and contact damping of typical head-disk interfaces. It is found that the contact stiffness models (based on roughness alone) overpredict the contact stiffness of actual head-disk interfaces by as much as an order of magnitude. Also, it is found that the contact damping ratio is typically few percent and its behavior is substrate dependent. In addition, the effects of a molecularly thin lubricant and humidity on contact stiffness and damping were experimentally investigated and no significant effects were found. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468038

Characterization of thermally actuated pole tip protrusion for head-media spacing adjustment in hard disk drives / Sung-Chang Lee in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Titre : Characterization of thermally actuated pole tip protrusion for head-media spacing adjustment in hard disk drives Type de document : texte imprimé Auteurs : Sung-Chang Lee, Auteur ; Brian D. Strom, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Thermomechanically  actuated  pole  tip  Hard  disk  drive Résumé : The effect of thermomechanically actuated pole tip protrusion on adhesive forces is characterized through model and experiment. The roughness of a thermomechanically actuated region is characterized by atomic force microscopy. Using the extracted roughness parameters and estimated apparent area associated with thermal actuation, the intermolecular forces at the head-disk interface (HDI) are calculated using the ISBL (improved sub-boundary lubrication) code. Both roughness and nominal area of contact are found to be significant factors determining adhesive forces. The adhesive forces for various HDI designs—including thermal actuation—are also characterized experimentally in situ using commercial hard disk drive samples. The experimental results are found to be consistent with the model calculations and imply certain advantages for thermally actuated HDI designs. However, the experiments also raise concerns regarding the field application of the technology. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468039 [article] Characterization of thermally actuated pole tip protrusion for head-media spacing adjustment in hard disk drives [texte imprimé] / Sung-Chang Lee, Auteur ; Brian D. Strom, Auteur . - 2008 . - 6 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Mots-clés : Thermomechanically  actuated  pole  tip  Hard  disk  drive Résumé : The effect of thermomechanically actuated pole tip protrusion on adhesive forces is characterized through model and experiment. The roughness of a thermomechanically actuated region is characterized by atomic force microscopy. Using the extracted roughness parameters and estimated apparent area associated with thermal actuation, the intermolecular forces at the head-disk interface (HDI) are calculated using the ISBL (improved sub-boundary lubrication) code. Both roughness and nominal area of contact are found to be significant factors determining adhesive forces. The adhesive forces for various HDI designs—including thermal actuation—are also characterized experimentally in situ using commercial hard disk drive samples. The experimental results are found to be consistent with the model calculations and imply certain advantages for thermally actuated HDI designs. However, the experiments also raise concerns regarding the field application of the technology. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468039

Quantification of the surface morphology of lubricant films with polar end groups using molecular dynamics simulation / Susumu Ogata in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 9 p. Titre : Quantification of the surface morphology of lubricant films with polar end groups using molecular dynamics simulation : periodic changes in morphology depending on film thickness Type de document : texte imprimé Auteurs : Susumu Ogata, Auteur ; Hedong Zhang, Auteur ; Kenji Fukuzawa, Auteur Année de publication : 2008 Article en page(s) : 9 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Lubrifiant  films  Molecular  dynamic  simulation Résumé : Using a coarse-grained molecular dynamics simulation based on the bead-spring polymer model, we reproduced the film distribution of molecularly thin lubricant films with polar end groups coated on the disk surface and quantified the film-surface morphology using a molecular-probe scanning method. We found that the film-surface morphology changed periodically with increasing film thickness. The monolayer of a polar lubricant that entirely covers the solid surface provides a flat lubricant surface by exposing its nonpolar backbone outside of the monolayer. By increasing film thickness, the end beads aggregate to make clusters, and bulges form on the lubricant surface, accompanying an increase in surface roughness. The bulges continue to grow even though the averaged film thickness reaches or exceeds the bilayer thickness. With further increases in film thickness, the clusters start to be uniformly distributed in the lateral direction to clearly form a third layer. As for the formation of fourth and fifth layers, the process is basically the same as that for the second and third layers. Through our calculations of the intermolecular potential field and the intermolecular force field, these values are found to change periodically and are synchronized with the formation of molecule aggregations, which explains the mechanism of forming the layered structure that is inherent to a polar lubricant. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468041 [article] Quantification of the surface morphology of lubricant films with polar end groups using molecular dynamics simulation : periodic changes in morphology depending on film thickness [texte imprimé] / Susumu Ogata, Auteur ; Hedong Zhang, Auteur ; Kenji Fukuzawa, Auteur . - 2008 . - 9 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 9 p. Mots-clés : Lubrifiant  films  Molecular  dynamic  simulation Résumé : Using a coarse-grained molecular dynamics simulation based on the bead-spring polymer model, we reproduced the film distribution of molecularly thin lubricant films with polar end groups coated on the disk surface and quantified the film-surface morphology using a molecular-probe scanning method. We found that the film-surface morphology changed periodically with increasing film thickness. The monolayer of a polar lubricant that entirely covers the solid surface provides a flat lubricant surface by exposing its nonpolar backbone outside of the monolayer. By increasing film thickness, the end beads aggregate to make clusters, and bulges form on the lubricant surface, accompanying an increase in surface roughness. The bulges continue to grow even though the averaged film thickness reaches or exceeds the bilayer thickness. With further increases in film thickness, the clusters start to be uniformly distributed in the lateral direction to clearly form a third layer. As for the formation of fourth and fifth layers, the process is basically the same as that for the second and third layers. Through our calculations of the intermolecular potential field and the intermolecular force field, these values are found to change periodically and are synchronized with the formation of molecule aggregations, which explains the mechanism of forming the layered structure that is inherent to a polar lubricant. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468041

Correction factor formula to predict the central and minimum film thickness for shear-thinning fluids in EHL / J. Y. Jang in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 4 p. Titre : Correction factor formula to predict the central and minimum film thickness for shear-thinning fluids in EHL Type de document : texte imprimé Auteurs : J. Y. Jang, Auteur ; M. M. Khonsari, Auteur ; Scott Bair, Auteur Année de publication : 2008 Article en page(s) : 4 p. Note générale : Tribology Langues : Anglais (eng) En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468043 [article] Correction factor formula to predict the central and minimum film thickness for shear-thinning fluids in EHL [texte imprimé] / J. Y. Jang, Auteur ; M. M. Khonsari, Auteur ; Scott Bair, Auteur . - 2008 . - 4 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 4 p. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468043

Influence of surface parameters on the elastoplastic contact behavior of fractal-regular surfaces / K. Willner in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Titre : Influence of surface parameters on the elastoplastic contact behavior of fractal-regular surfaces Type de document : texte imprimé Auteurs : K. Willner, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Elastoplastic  contacts  Fractal-regular  surface Résumé : In a recent paper (2004, “Elasto-Plastic Normal Contact of Three-Dimensional Fractal Surfaces Using Halfspace Theory ,” J. Tribol., 126, pp. 28–33) the author developed a halfspace model for the elasto-plastic normal contact of rough surfaces. This model is now used to study the influence of intrinsic surface parameters on constitutive contact laws, such as load-gap relation and load-area relation, for a specific type of surface topography known as fractal-regular surfaces. Numerical investigations show that the fractal dimension has only minor influence on the load-gap relationship, which is mostly determined by the dimensionless ratio between the transition length and the rms values of the height data. Due to the fractal nature of the surfaces at the small wavelength limit, initial deformation will always be in the plastic range. The load-area relation becomes then completely independent of the geometric surface parameters and is determined by material properties alone, at least if the predicted plastic deformation occurs at a length scale larger than the atomic scale. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468044 [article] Influence of surface parameters on the elastoplastic contact behavior of fractal-regular surfaces [texte imprimé] / K. Willner, Auteur . - 2008 . - 6 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 6 p. Mots-clés : Elastoplastic  contacts  Fractal-regular  surface Résumé : In a recent paper (2004, “Elasto-Plastic Normal Contact of Three-Dimensional Fractal Surfaces Using Halfspace Theory ,” J. Tribol., 126, pp. 28–33) the author developed a halfspace model for the elasto-plastic normal contact of rough surfaces. This model is now used to study the influence of intrinsic surface parameters on constitutive contact laws, such as load-gap relation and load-area relation, for a specific type of surface topography known as fractal-regular surfaces. Numerical investigations show that the fractal dimension has only minor influence on the load-gap relationship, which is mostly determined by the dimensionless ratio between the transition length and the rms values of the height data. Due to the fractal nature of the surfaces at the small wavelength limit, initial deformation will always be in the plastic range. The load-area relation becomes then completely independent of the geometric surface parameters and is determined by material properties alone, at least if the predicted plastic deformation occurs at a length scale larger than the atomic scale. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468044

Thermal and starvation effects on the minimum film thickness in inlet zone in cold rolling / P. Singh in Transactions of the ASME . Journal of tribology, Vol. 130 n°2 (Mars/Avril 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Titre : Thermal and starvation effects on the minimum film thickness in inlet zone in cold rolling Type de document : texte imprimé Auteurs : P. Singh, Auteur ; R. K. Pandey, Auteur ; Nath, Y., Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Minimum  film  thickness  Roll-strip  interface  Inlet  zone Résumé : The main objective of this research is to analyze the variation of minimum film thickness in the inlet zone of roll-strip interface by incorporating starvation and viscous shear heating effects at high rolling speeds (5–20m∕s), reduction ratios (0.05–0.20), and slip values (varying up to 20%). An additional objective of this paper is to develop empirical relations for predictions of minimum film thicknesses (both isothermal and thermal) and maximum film temperature rise in the inlet zone of the lubricated roll strip contact as functions of roll-speed, reduction ratio, material parameter, slip, and starvation parameter. An efficient numerical method based on Lobatto quadrature technique is adopted for rigorous analysis of the present problem. The results reveal that the existence of starvation seems to be beneficial in terms of reduction in maximum film temperature rise as well as reduction in quantity of oil required for lubrication provided thin continuous film exists at the contact. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468047 [article] Thermal and starvation effects on the minimum film thickness in inlet zone in cold rolling [texte imprimé] / P. Singh, Auteur ; R. K. Pandey, Auteur ; Nath, Y., Auteur . - 2008 . - 7 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°2 (Mars/Avril 2008) . - 7 p. Mots-clés : Minimum  film  thickness  Roll-strip  interface  Inlet  zone Résumé : The main objective of this research is to analyze the variation of minimum film thickness in the inlet zone of roll-strip interface by incorporating starvation and viscous shear heating effects at high rolling speeds (5–20m∕s), reduction ratios (0.05–0.20), and slip values (varying up to 20%). An additional objective of this paper is to develop empirical relations for predictions of minimum film thicknesses (both isothermal and thermal) and maximum film temperature rise in the inlet zone of the lubricated roll strip contact as functions of roll-speed, reduction ratio, material parameter, slip, and starvation parameter. An efficient numerical method based on Lobatto quadrature technique is adopted for rigorous analysis of the present problem. The results reveal that the existence of starvation seems to be beneficial in terms of reduction in maximum film temperature rise as well as reduction in quantity of oil required for lubrication provided thin continuous film exists at the contact. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1468047

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