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Journal of tribology :Transactions of the ASME |
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Ajouter le résultat dans votre panierUnsteady flow and dynamic behavior of ultrashort lomakin gas bearings / C. J. Teo in Transactions of the ASME . Journal of tribology, Vol. 130 N°1 (Janvier 2008)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 9 p.
Titre : Unsteady flow and dynamic behavior of ultrashort lomakin gas bearings Type de document : texte imprimé Auteurs : C. J. Teo, Auteur ; Z. S. Spakovszky, Auteur ; S. A. Jacobson, Auteur Année de publication : 2008 Article en page(s) : 9 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Bearings Computational fluid dynamics Rotors Flow (Dynamics) Hydrostatics Unsteady flow Whirls Journal bearings Gas bearings Clearances (Engineering) Résumé : Ultrashort microscale high-speed gas bearings exhibit a whirl instability limit and dynamic behavior much different from conventional hydrostatic gas bearings. In particular, the design space for a stable high-speed operation is confined to a narrow region and involves a singular behavior. The previously developed ultrashort gas bearing theory (Liu (2005, “Hydrostatic Gas Journal Bearings for Micro-Turbomachinery ,” ASME J. Vibr. Acoust., 127(2), pp. 157–164)) assumed fully developed flow in the journal bearing gap. There is experimental evidence that this assumption might not be fully applicable for the relatively short flow-through times in such bearings. This has an impact on the estimation of whirl instability onset, bearing operability and power requirements. In this paper, unsteady flow effects in the bearing gap are investigated with the goal to quantify their impact on the bearing dynamic behavior. It is shown that although three-dimensional flow calculations in the ultrashort journal bearing are necessary to quantify the onset of whirl instability, the underlying mechanisms can be qualitatively described by the impulsive starting of a Couette flow. Using this description, two time scales are identified that govern the journal bearing dynamic behavior: the viscous diffusion time and the axial flow-through time. Based on this, a reduced frequency parameter is introduced that determines the development of the flow field in the journal bearing and, together with bearing force models, yields a criterion for whirl instability onset. Detailed three-dimensional computational fluid dynamics calculations of the journal bearing flow have been conducted to assess the criterion. A singular behavior in whirl ratio as a function of the reduced frequency parameter is observed, verifying the refined stability criterion. Using high-fidelity flow calculations, the effects of unsteady journal bearing flow on whirl instability limit and bearing power loss are quantified, and design guidelines and implications on gas bearing modeling are discussed. The stability criterion is experimentally validated demonstrating repeatable, stable high-speed operation of a novel microbearing test device at whirl ratios of 35. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467958 [article] Unsteady flow and dynamic behavior of ultrashort lomakin gas bearings [texte imprimé] / C. J. Teo, Auteur ; Z. S. Spakovszky, Auteur ; S. A. Jacobson, Auteur . - 2008 . - 9 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 9 p.
Mots-clés : Bearings Computational fluid dynamics Rotors Flow (Dynamics) Hydrostatics Unsteady flow Whirls Journal bearings Gas bearings Clearances (Engineering) Résumé : Ultrashort microscale high-speed gas bearings exhibit a whirl instability limit and dynamic behavior much different from conventional hydrostatic gas bearings. In particular, the design space for a stable high-speed operation is confined to a narrow region and involves a singular behavior. The previously developed ultrashort gas bearing theory (Liu (2005, “Hydrostatic Gas Journal Bearings for Micro-Turbomachinery ,” ASME J. Vibr. Acoust., 127(2), pp. 157–164)) assumed fully developed flow in the journal bearing gap. There is experimental evidence that this assumption might not be fully applicable for the relatively short flow-through times in such bearings. This has an impact on the estimation of whirl instability onset, bearing operability and power requirements. In this paper, unsteady flow effects in the bearing gap are investigated with the goal to quantify their impact on the bearing dynamic behavior. It is shown that although three-dimensional flow calculations in the ultrashort journal bearing are necessary to quantify the onset of whirl instability, the underlying mechanisms can be qualitatively described by the impulsive starting of a Couette flow. Using this description, two time scales are identified that govern the journal bearing dynamic behavior: the viscous diffusion time and the axial flow-through time. Based on this, a reduced frequency parameter is introduced that determines the development of the flow field in the journal bearing and, together with bearing force models, yields a criterion for whirl instability onset. Detailed three-dimensional computational fluid dynamics calculations of the journal bearing flow have been conducted to assess the criterion. A singular behavior in whirl ratio as a function of the reduced frequency parameter is observed, verifying the refined stability criterion. Using high-fidelity flow calculations, the effects of unsteady journal bearing flow on whirl instability limit and bearing power loss are quantified, and design guidelines and implications on gas bearing modeling are discussed. The stability criterion is experimentally validated demonstrating repeatable, stable high-speed operation of a novel microbearing test device at whirl ratios of 35. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467958
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 4 p.
Titre : Predicting air bearing contamination using air flow pattern analysis Type de document : texte imprimé Auteurs : Shuyu Zhang, Auteur ; Brian D. Strom, Auteur Année de publication : 2008 Article en page(s) : 4 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Flow (Dynamics) Particulate matter Air flow Contamination Bearings Disks Mechanisms Résumé : A new method is introduced for predicting particle and liquid droplet contamination on an air bearing surface. The method primarily relies on the analysis of flow patterns nearest the air bearing surface, restricted to two dimensions. In addition, a mathematical model for the vertical flow perpendicular to the disk surface adds clarity to the contamination mechanisms. The predictions compare well with contamination patterns observed in prototype disk drives. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467959 [article] Predicting air bearing contamination using air flow pattern analysis [texte imprimé] / Shuyu Zhang, Auteur ; Brian D. Strom, Auteur . - 2008 . - 4 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 4 p.
Mots-clés : Flow (Dynamics) Particulate matter Air flow Contamination Bearings Disks Mechanisms Résumé : A new method is introduced for predicting particle and liquid droplet contamination on an air bearing surface. The method primarily relies on the analysis of flow patterns nearest the air bearing surface, restricted to two dimensions. In addition, a mathematical model for the vertical flow perpendicular to the disk surface adds clarity to the contamination mechanisms. The predictions compare well with contamination patterns observed in prototype disk drives. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467959
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 9 p.
Titre : A simplified one-dimensional thermal model for journal bearings Type de document : texte imprimé Auteurs : Daquan Liu, Auteur ; Wen Zhang, Auteur ; Tiesheng Zheng, Auteur Année de publication : 2008 Article en page(s) : 9 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Pressure Temperature Equations Journal bearings Bearings Boundary-value problems Temperature distribution Résumé : The variational approach, which is used to solve the Reynolds equation based on the assumption of constant temperature, is extended to the generalized Reynolds equation calculation. The direct solution method of the generalized Reynolds equation is presented, where the pressure of the nodal points and the cavitation zone boundary of the film can be determined without iterating. A simplified one-dimensional thermal model is built on the basis of the original two-dimensional thermal model. The model not only concerns the thermal effects of the lubricating film, but also offers a direct and rapid numerical algorithm for solving lubricating film temperature field. The numerical results of the temperature distributions for the one model are in good agreement with experiment, and less computing time is needed. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467960 [article] A simplified one-dimensional thermal model for journal bearings [texte imprimé] / Daquan Liu, Auteur ; Wen Zhang, Auteur ; Tiesheng Zheng, Auteur . - 2008 . - 9 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 9 p.
Mots-clés : Pressure Temperature Equations Journal bearings Bearings Boundary-value problems Temperature distribution Résumé : The variational approach, which is used to solve the Reynolds equation based on the assumption of constant temperature, is extended to the generalized Reynolds equation calculation. The direct solution method of the generalized Reynolds equation is presented, where the pressure of the nodal points and the cavitation zone boundary of the film can be determined without iterating. A simplified one-dimensional thermal model is built on the basis of the original two-dimensional thermal model. The model not only concerns the thermal effects of the lubricating film, but also offers a direct and rapid numerical algorithm for solving lubricating film temperature field. The numerical results of the temperature distributions for the one model are in good agreement with experiment, and less computing time is needed. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467960
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 20 p.
Titre : Numerical modeling of mixed lubrication and flash temperature in EHL elliptical contacts Type de document : texte imprimé Auteurs : Neelesh Deolalikar, Auteur ; Farshid Sadeghi, Auteur ; Sean Marble, Auteur Année de publication : 2008 Article en page(s) : 20 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Pressure Lubrication Temperature Lubricants Stress Friction Computer simulation Film thickness Heat Surface roughness Résumé : Highly loaded ball and rolling element bearings are often required to operate in the mixed elastohydrodynamic lubrication regime in which surface asperity contact occurs simultaneously during the lubrication process. Predicting performance (i.e., pressure, temperature) of components operating in this regime is important as the high asperity contact pressures can significantly reduce the fatigue life of the interacting components. In this study, a deterministic mixed lubrication model was developed to determine the pressure and temperature of mixed lubricated circular and elliptic contacts for measured and simulated surfaces operating under pure rolling and rolling/sliding condition. In this model, we simultaneously solve for lubricant and asperity contact pressures. The model allows investigation of the condition and transition from boundary to full-film lubrication. The variation of contact area and load ratios is examined for various velocities and slide-to-roll ratios. The mixed lubricated model is also used to predict the transient flash temperatures occurring in contacts due to asperity contact interactions and friction. In order to significantly reduce the computational efforts associated with surface deformation and temperature calculation, the fast Fourier transform algorithm is implemented. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467962 [article] Numerical modeling of mixed lubrication and flash temperature in EHL elliptical contacts [texte imprimé] / Neelesh Deolalikar, Auteur ; Farshid Sadeghi, Auteur ; Sean Marble, Auteur . - 2008 . - 20 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 20 p.
Mots-clés : Pressure Lubrication Temperature Lubricants Stress Friction Computer simulation Film thickness Heat Surface roughness Résumé : Highly loaded ball and rolling element bearings are often required to operate in the mixed elastohydrodynamic lubrication regime in which surface asperity contact occurs simultaneously during the lubrication process. Predicting performance (i.e., pressure, temperature) of components operating in this regime is important as the high asperity contact pressures can significantly reduce the fatigue life of the interacting components. In this study, a deterministic mixed lubrication model was developed to determine the pressure and temperature of mixed lubricated circular and elliptic contacts for measured and simulated surfaces operating under pure rolling and rolling/sliding condition. In this model, we simultaneously solve for lubricant and asperity contact pressures. The model allows investigation of the condition and transition from boundary to full-film lubrication. The variation of contact area and load ratios is examined for various velocities and slide-to-roll ratios. The mixed lubricated model is also used to predict the transient flash temperatures occurring in contacts due to asperity contact interactions and friction. In order to significantly reduce the computational efforts associated with surface deformation and temperature calculation, the fast Fourier transform algorithm is implemented. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467962
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 6 p.
Titre : A two-parameter function for nanoscale indentation measurement of near surface properties Type de document : texte imprimé Auteurs : K. Farhang, Auteur ; L. E. Seitzman, Auteur ; B. Feng, Auteur Année de publication : 2008 Article en page(s) : 6 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Nanoscale phenomena Surface properties Displacement Equations Errors Elasticity Functions Shapes Crystals Force measurement Résumé : A two-parameter function for estimation of projected area in instrumented indentation measurement is obtained to account for indenter tip imperfection. Imperfection near indenter tip is modeled using a spherical function and combined with a linear function describing the edge boundary of the indenter. Through an analytical fusion technique, the spherical and linear functions are combined into a single function with two unknown geometric parameters of tip radius of curvature and edge slope. Data from indentation measurement of force and displacement, using a Berkovich tip and single crystal alumina and silica samples, are implemented in the proposed area function yielding estimated values of Young’s modulus. Results were compared with that obtained from Oliver and Pharr technique for deep as well as shallow indentation regimes. The estimates for Young’s modulus were found to agree quite favorably. More importantly, in contrast to the Oliver–Pharr technique, the use of the two-parameter function resulted in a significantly more accurate estimation of Young’s modulus for shallow indentation depth of 0–50nm. The error in estimation of Young’s modulus was found to be within 10% for indentation depths of 25–50nm and within 20% for indentation depths of 0–25nm. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467964 [article] A two-parameter function for nanoscale indentation measurement of near surface properties [texte imprimé] / K. Farhang, Auteur ; L. E. Seitzman, Auteur ; B. Feng, Auteur . - 2008 . - 6 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 6 p.
Mots-clés : Nanoscale phenomena Surface properties Displacement Equations Errors Elasticity Functions Shapes Crystals Force measurement Résumé : A two-parameter function for estimation of projected area in instrumented indentation measurement is obtained to account for indenter tip imperfection. Imperfection near indenter tip is modeled using a spherical function and combined with a linear function describing the edge boundary of the indenter. Through an analytical fusion technique, the spherical and linear functions are combined into a single function with two unknown geometric parameters of tip radius of curvature and edge slope. Data from indentation measurement of force and displacement, using a Berkovich tip and single crystal alumina and silica samples, are implemented in the proposed area function yielding estimated values of Young’s modulus. Results were compared with that obtained from Oliver and Pharr technique for deep as well as shallow indentation regimes. The estimates for Young’s modulus were found to agree quite favorably. More importantly, in contrast to the Oliver–Pharr technique, the use of the two-parameter function resulted in a significantly more accurate estimation of Young’s modulus for shallow indentation depth of 0–50nm. The error in estimation of Young’s modulus was found to be within 10% for indentation depths of 25–50nm and within 20% for indentation depths of 0–25nm. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467964
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 11 p.
Titre : Numerical analysis on dynamic coefficients of self-acting gas-lubricated tilting-pad journal bearings Type de document : texte imprimé Auteurs : Yang Lihua, Auteur ; Qi Shemiao, Auteur ; Yu Lie, Auteur Année de publication : 2008 Article en page(s) : 11 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Bearings Damping Numerical analysis Gas bearings Stiffness Journal bearings Inertia (Mechanics) Résumé : Although gas-lubricated tilting-pad bearings are widely used in high-speed turbomachinery, the theoretical prediction of the dynamic characteristics of tilting-pad gas bearings is also a very difficult problem because of its structural complexity. Several approaches have been proposed to solve this problem such as the pad assembly method and the small perturbation method. A numerical method by combining the partial derivative method with the equivalent coefficient method is presented in this paper to evaluate the dynamic stiffness and damping coefficients of self-acting tilting-pad gas bearing. The dynamic coefficients with the pads fixed and with the pads perturbation are, respectively, obtained for a typical self-acting tilting-pad gas bearing by using the proposed method to mainly explain the dependency of the bearing dynamic coefficients on the perturbation frequency. For bearings with the pads perturbation, the cross-coupling stiffness and damping coefficients are almost negligible compared with the direct ones. At lower perturbation frequency, the stiffness coefficients increase, while the damping coefficients decrease with an increasing frequency. The higher perturbation frequencies have very little effects on the bearing dynamic coefficients. Dynamic stiffness coefficients approach to the constant and damping coefficients to zero. However, with the pads fixed, in a low range of frequency, the absolute values of cross-coupling stiffness coefficients decrease with frequency. Furthermore, the cross-coupling coefficients are not negligible compared with the direct ones. In addition, the effects of pad inertia on dynamic coefficients are studied and compared with the results of pad inertia neglected. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467966 [article] Numerical analysis on dynamic coefficients of self-acting gas-lubricated tilting-pad journal bearings [texte imprimé] / Yang Lihua, Auteur ; Qi Shemiao, Auteur ; Yu Lie, Auteur . - 2008 . - 11 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 11 p.
Mots-clés : Bearings Damping Numerical analysis Gas bearings Stiffness Journal bearings Inertia (Mechanics) Résumé : Although gas-lubricated tilting-pad bearings are widely used in high-speed turbomachinery, the theoretical prediction of the dynamic characteristics of tilting-pad gas bearings is also a very difficult problem because of its structural complexity. Several approaches have been proposed to solve this problem such as the pad assembly method and the small perturbation method. A numerical method by combining the partial derivative method with the equivalent coefficient method is presented in this paper to evaluate the dynamic stiffness and damping coefficients of self-acting tilting-pad gas bearing. The dynamic coefficients with the pads fixed and with the pads perturbation are, respectively, obtained for a typical self-acting tilting-pad gas bearing by using the proposed method to mainly explain the dependency of the bearing dynamic coefficients on the perturbation frequency. For bearings with the pads perturbation, the cross-coupling stiffness and damping coefficients are almost negligible compared with the direct ones. At lower perturbation frequency, the stiffness coefficients increase, while the damping coefficients decrease with an increasing frequency. The higher perturbation frequencies have very little effects on the bearing dynamic coefficients. Dynamic stiffness coefficients approach to the constant and damping coefficients to zero. However, with the pads fixed, in a low range of frequency, the absolute values of cross-coupling stiffness coefficients decrease with frequency. Furthermore, the cross-coupling coefficients are not negligible compared with the direct ones. In addition, the effects of pad inertia on dynamic coefficients are studied and compared with the results of pad inertia neglected. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467966
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 11 p.
Titre : Transient elastohydrodynamic lubrication of hip joint implants Type de document : texte imprimé Auteurs : Fengcai Wang, Auteur ; Zhongmin Jin, Auteur Année de publication : 2008 Article en page(s) : 11 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Lubrication Stress Bearings Elastohydrodynamic lubrication Motion Lubricants Viscosity Metals Pressure Résumé : A general transient elastohydrodynamic lubrication model was developed for artificial hip joint implants, particularly in which the three-dimensional time-dependent physiological load and motion components experienced during walking conditions were considered in the theoretical formulation, although only a predominantly vertical load combined with a flexion-extension motion was actually solved. A nominal ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup in both simplified and anatomical positions. An appropriate spherical coordinate system and the corresponding mesh grids were used in the general transient lubrication model. Additionally, an equivalent discrete spherical convolution model and the corresponding spherical fast Fourier transform technique were employed to facilitate the evaluation of elastic deformation of spherical bearing surfaces in hip joint implants. The general lubrication model was subsequently applied to investigate the transient lubrication performance of a typical metal-on-metal hip joint implant. The effects of both cup inclination angles in either anatomical or horizontally simplified positions and different lubricant viscosities on the transient elastohydrodynamic lubrication were analyzed under the predominant components of vertically dynamic loading and flexion-extension motion. It was found that the general lubrication model and the numerical methodology were efficient for the transient elastohydrodynamic lubrication analysis during walking condition in hip joint implants. Furthermore, the significant effect of squeeze-film action on maintaining and enhancing the total thin film thickness formation was discussed for the transient lubrication study of the typical hip joint implant. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467967 [article] Transient elastohydrodynamic lubrication of hip joint implants [texte imprimé] / Fengcai Wang, Auteur ; Zhongmin Jin, Auteur . - 2008 . - 11 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 11 p.
Mots-clés : Lubrication Stress Bearings Elastohydrodynamic lubrication Motion Lubricants Viscosity Metals Pressure Résumé : A general transient elastohydrodynamic lubrication model was developed for artificial hip joint implants, particularly in which the three-dimensional time-dependent physiological load and motion components experienced during walking conditions were considered in the theoretical formulation, although only a predominantly vertical load combined with a flexion-extension motion was actually solved. A nominal ball-in-socket configuration was adopted to represent the articulation between the femoral head and the acetabular cup in both simplified and anatomical positions. An appropriate spherical coordinate system and the corresponding mesh grids were used in the general transient lubrication model. Additionally, an equivalent discrete spherical convolution model and the corresponding spherical fast Fourier transform technique were employed to facilitate the evaluation of elastic deformation of spherical bearing surfaces in hip joint implants. The general lubrication model was subsequently applied to investigate the transient lubrication performance of a typical metal-on-metal hip joint implant. The effects of both cup inclination angles in either anatomical or horizontally simplified positions and different lubricant viscosities on the transient elastohydrodynamic lubrication were analyzed under the predominant components of vertically dynamic loading and flexion-extension motion. It was found that the general lubrication model and the numerical methodology were efficient for the transient elastohydrodynamic lubrication analysis during walking condition in hip joint implants. Furthermore, the significant effect of squeeze-film action on maintaining and enhancing the total thin film thickness formation was discussed for the transient lubrication study of the typical hip joint implant. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467967
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 4 p.
Titre : Simulating the air bearing pressure and flying height in a humid environment Type de document : texte imprimé Auteurs : Shuyu Zhang, Auteur ; Brian Strom, Auteur ; Sung-Chang Lee, Auteur Année de publication : 2008 Article en page(s) : 4 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Pressure Temperature Water vapor Bearings Vapor pressure Force Résumé : For a hard disk drive operating in a humid environment, the water vapor in the slider’s air bearing is typically compressed beyond its saturation vapor pressure, causing the vapor to condense. Consequently, the air bearing pressure decreases and the slider’s flying attitude adjusts to balance the forces from the suspension. A method for calculating this air bearing response to humid air is presented. Using two air bearing designs, several test cases are analyzed to illustrate the air bearing response for various temperatures and humidity levels. The calculated flying heights agree with those measured in commercial hard disk drives. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467969 [article] Simulating the air bearing pressure and flying height in a humid environment [texte imprimé] / Shuyu Zhang, Auteur ; Brian Strom, Auteur ; Sung-Chang Lee, Auteur . - 2008 . - 4 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 4 p.
Mots-clés : Pressure Temperature Water vapor Bearings Vapor pressure Force Résumé : For a hard disk drive operating in a humid environment, the water vapor in the slider’s air bearing is typically compressed beyond its saturation vapor pressure, causing the vapor to condense. Consequently, the air bearing pressure decreases and the slider’s flying attitude adjusts to balance the forces from the suspension. A method for calculating this air bearing response to humid air is presented. Using two air bearing designs, several test cases are analyzed to illustrate the air bearing response for various temperatures and humidity levels. The calculated flying heights agree with those measured in commercial hard disk drives. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467969
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 9 p.
Titre : Reducing friction in tilting-pad bearings by the use of enclosed recesses Type de document : texte imprimé Auteurs : Niels Heinrichson, Auteur ; Ilmar Ferreira Santos, Auteur Année de publication : 2008 Article en page(s) : 9 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Friction Bearings High pressure (Physics) Film thickness Design Résumé : A three-dimensional thermoelastohydrodynamic model is applied to the analysis of tilting-pad bearings with spherical pivots and equipped with deep recesses in the high-pressure regions. A potential for a 10–20% reduction in the friction loss compared to conventional plain bearing pads is documented. Design suggestions minimizing the power loss are given for various length-to-width ratios. The tilting angle in the sliding direction is more sensitive to correct positioning of the pivot point than conventional bearing pads. Improving the performance by equipping a tilting-pad bearing with a deep recess therefore requires accurate analysis and design of the bearing. Similarly, a high sensitivity perpendicular to the sliding direction suggests that this method of reducing friction is more feasible when using line pivots or spring beds than when using spherical pivots for controlling the tilting angle. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467971 [article] Reducing friction in tilting-pad bearings by the use of enclosed recesses [texte imprimé] / Niels Heinrichson, Auteur ; Ilmar Ferreira Santos, Auteur . - 2008 . - 9 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 9 p.
Mots-clés : Friction Bearings High pressure (Physics) Film thickness Design Résumé : A three-dimensional thermoelastohydrodynamic model is applied to the analysis of tilting-pad bearings with spherical pivots and equipped with deep recesses in the high-pressure regions. A potential for a 10–20% reduction in the friction loss compared to conventional plain bearing pads is documented. Design suggestions minimizing the power loss are given for various length-to-width ratios. The tilting angle in the sliding direction is more sensitive to correct positioning of the pivot point than conventional bearing pads. Improving the performance by equipping a tilting-pad bearing with a deep recess therefore requires accurate analysis and design of the bearing. Similarly, a high sensitivity perpendicular to the sliding direction suggests that this method of reducing friction is more feasible when using line pivots or spring beds than when using spherical pivots for controlling the tilting angle. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1467971
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 8 p.
Titre : Effects of couple stress on elastohydrodynamic lubrication at impact loading Type de document : texte imprimé Auteurs : Hsiao-Ming Chu, Auteur ; Wang-Long Li, Auteur ; Yuh-Ping Chang, Auteur Année de publication : 2008 Article en page(s) : 8 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Pressure Viscosity Lubricants Stress Elastohydrodynamic lubrication Fluids Film thickness Force Motion Deformation Résumé : In this paper, pure squeeze elastohydrodynamic lubrication motion of circular contacts with couple stress lubricant is explored at impact loading. On the basis of microcontinuum theory, the transient modified Reynolds equation is derived. Then it is solved simultaneously with the elasticity deformation equation and ball motion equation, thus obtaining the transient pressure profiles, film shapes, normal squeeze velocities, and accelerations. The simulation results reveal that the effect of the couple stress is equivalent to enhancing the lubricant viscosity, which would also enlarge the damper effect. Therefore, as the characteristic length of the couple stress fluid increases, the pressure spike and the dimple form earlier, the maximum pressure and the film thickness increase, and the diameter of the dimple, the rebounding velocity, the maximum value of the relative impact force, and the acceleration decrease. Furthermore, the fact that the contact central pressure for a ball impacting and rebounding from a lubricated surface reached two peaks during the total impact period is proved numerically in this analysis. As the effect of couple stress increases, the first and second peaks form earlier; as the total impact time decreases, the pressure of the first peak increases and that of the second peak decreases. Moreover, the phase shift between the time of the peak value of the squeeze acceleration and the zero value of the squeeze velocity increases with increasing the characteristic length of the couple stress fluid. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467973 [article] Effects of couple stress on elastohydrodynamic lubrication at impact loading [texte imprimé] / Hsiao-Ming Chu, Auteur ; Wang-Long Li, Auteur ; Yuh-Ping Chang, Auteur . - 2008 . - 8 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 8 p.
Mots-clés : Pressure Viscosity Lubricants Stress Elastohydrodynamic lubrication Fluids Film thickness Force Motion Deformation Résumé : In this paper, pure squeeze elastohydrodynamic lubrication motion of circular contacts with couple stress lubricant is explored at impact loading. On the basis of microcontinuum theory, the transient modified Reynolds equation is derived. Then it is solved simultaneously with the elasticity deformation equation and ball motion equation, thus obtaining the transient pressure profiles, film shapes, normal squeeze velocities, and accelerations. The simulation results reveal that the effect of the couple stress is equivalent to enhancing the lubricant viscosity, which would also enlarge the damper effect. Therefore, as the characteristic length of the couple stress fluid increases, the pressure spike and the dimple form earlier, the maximum pressure and the film thickness increase, and the diameter of the dimple, the rebounding velocity, the maximum value of the relative impact force, and the acceleration decrease. Furthermore, the fact that the contact central pressure for a ball impacting and rebounding from a lubricated surface reached two peaks during the total impact period is proved numerically in this analysis. As the effect of couple stress increases, the first and second peaks form earlier; as the total impact time decreases, the pressure of the first peak increases and that of the second peak decreases. Moreover, the phase shift between the time of the peak value of the squeeze acceleration and the zero value of the squeeze velocity increases with increasing the characteristic length of the couple stress fluid. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467973
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 10 p.
Titre : A numerical model for life scatter in rolling element bearings Type de document : texte imprimé Auteurs : Nihar Raje, Auteur ; Farshid Sadeghi, Auteur ; Richard G. Rateick, Auteur Année de publication : 2008 Article en page(s) : 10 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Computer simulation Stress Shear (Mechanics) Electromagnetic scattering Fatigue Bearings Fatigue cracks Fatigue life Rolling bearings Weibull distribution Résumé : Fatigue lives of rolling element bearings exhibit a wide scatter due to the statistical nature of the mechanisms responsible for the bearing failure process. Life models that account for this dispersion are empirical in nature and do not provide insights into the physical mechanisms that lead to this scatter. One of the primary reasons for dispersion in lives is the inhomogeneous nature of the bearing material. Here, a new approach based on a discrete material representation is presented that simulates this inherent material randomness. In this investigation, two levels of randomness are considered: (1) the topological randomness due to geometric variability in the material microstructure and (2) the material property randomness due to nonuniform distribution of properties throughout the material. The effect of these variations on the subsurface stress field in Hertzian line contacts is studied. Fatigue life is formulated as a function of a critical stress quantity and its corresponding depth, following a similar approach to the Lundberg–Palmgren theory. However, instead of explicitly assuming a Weibull distribution of fatigue lives, the life distribution is obtained as an outcome of numerical simulations. A new critical stress quantity is introduced that considers shear stress acting along internal material planes of weakness. It is found that there is a scatter in the magnitude as well as depth of occurrence of this critical stress quantity, which leads to a scatter in computed fatigue lives. Further, the range of depths within which the critical stress quantity occurs is found to be consistent with experimental observations of fatigue cracks. The life distributions obtained from the numerical simulations are found to follow a two-parameter Weibull distribution closely. The L10 life and the Weibull slope decrease when a nonuniform distribution of elastic modulus is assumed throughout the material. The introduction of internal flaws in the material significantly reduces the L10 life and the Weibull slope. However, it is found that the Weibull slope reaches a limiting value beyond a certain concentration of flaws. This limiting value is close to that predicted by the Lundberg–Palmgren theory. Weibull slopes obtained through the numerical simulations range from 1.29 to 3.36 and are within experimentally observed values for bearing steels. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467974 [article] A numerical model for life scatter in rolling element bearings [texte imprimé] / Nihar Raje, Auteur ; Farshid Sadeghi, Auteur ; Richard G. Rateick, Auteur . - 2008 . - 10 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 10 p.
Mots-clés : Computer simulation Stress Shear (Mechanics) Electromagnetic scattering Fatigue Bearings Fatigue cracks Fatigue life Rolling bearings Weibull distribution Résumé : Fatigue lives of rolling element bearings exhibit a wide scatter due to the statistical nature of the mechanisms responsible for the bearing failure process. Life models that account for this dispersion are empirical in nature and do not provide insights into the physical mechanisms that lead to this scatter. One of the primary reasons for dispersion in lives is the inhomogeneous nature of the bearing material. Here, a new approach based on a discrete material representation is presented that simulates this inherent material randomness. In this investigation, two levels of randomness are considered: (1) the topological randomness due to geometric variability in the material microstructure and (2) the material property randomness due to nonuniform distribution of properties throughout the material. The effect of these variations on the subsurface stress field in Hertzian line contacts is studied. Fatigue life is formulated as a function of a critical stress quantity and its corresponding depth, following a similar approach to the Lundberg–Palmgren theory. However, instead of explicitly assuming a Weibull distribution of fatigue lives, the life distribution is obtained as an outcome of numerical simulations. A new critical stress quantity is introduced that considers shear stress acting along internal material planes of weakness. It is found that there is a scatter in the magnitude as well as depth of occurrence of this critical stress quantity, which leads to a scatter in computed fatigue lives. Further, the range of depths within which the critical stress quantity occurs is found to be consistent with experimental observations of fatigue cracks. The life distributions obtained from the numerical simulations are found to follow a two-parameter Weibull distribution closely. The L10 life and the Weibull slope decrease when a nonuniform distribution of elastic modulus is assumed throughout the material. The introduction of internal flaws in the material significantly reduces the L10 life and the Weibull slope. However, it is found that the Weibull slope reaches a limiting value beyond a certain concentration of flaws. This limiting value is close to that predicted by the Lundberg–Palmgren theory. Weibull slopes obtained through the numerical simulations range from 1.29 to 3.36 and are within experimentally observed values for bearing steels. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467974
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 13 p.
Titre : A numerical solution for quasistatic viscoelastic frictional contact problems Type de document : texte imprimé Auteurs : Fatin F. Mahmoud, Auteur ; Ahmed G. El-Shafei, Auteur ; Amal E. Al-Shorbagy, Auteur Année de publication : 2008 Article en page(s) : 13 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Force Creep Friction Viscoelastic materials Relaxation (Physics) Stress Displacement Equations Stiffness Equilibrium (Physics) Résumé : The tribological aspects of contact are greatly affected by the friction throughout the contact interface. Generally, contact of deformable bodies is a nonlinear problem. Introduction of the friction with its irreversible character makes the contact problem more difficult. Furthermore, when one or more of the contacting bodies is made of a viscoelastic material, the problem becomes more complicated. A nonlinear time-dependent contact problem is addressed. The objective of the present work is to develop a computational procedure capable of handling quasistatic viscoelastic frictional contact problems. The contact problem as a convex programming model is solved by using an adaptive incremental procedure. The contact constraints are incorporated into the model by using the Lagrange multiplier method. In addition, a local-nonlinear nonclassical friction model is adopted to model the friction at the contact interface. This eliminates the difficulties that arise with the application of the classical Coulomb’s law. On the other hand, the Wiechert model, as an effective model capable of describing both creep and relaxation phenomena, is adopted to simulate the linear behavior of viscoelastic materials. The resulting constitutive integral equations are linearized; therefore, complications that arise during the integration of these equations, especially with contact problems, are avoided. Two examples are presented to demonstrate the applicability of the proposed method. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467977 [article] A numerical solution for quasistatic viscoelastic frictional contact problems [texte imprimé] / Fatin F. Mahmoud, Auteur ; Ahmed G. El-Shafei, Auteur ; Amal E. Al-Shorbagy, Auteur . - 2008 . - 13 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 13 p.
Mots-clés : Force Creep Friction Viscoelastic materials Relaxation (Physics) Stress Displacement Equations Stiffness Equilibrium (Physics) Résumé : The tribological aspects of contact are greatly affected by the friction throughout the contact interface. Generally, contact of deformable bodies is a nonlinear problem. Introduction of the friction with its irreversible character makes the contact problem more difficult. Furthermore, when one or more of the contacting bodies is made of a viscoelastic material, the problem becomes more complicated. A nonlinear time-dependent contact problem is addressed. The objective of the present work is to develop a computational procedure capable of handling quasistatic viscoelastic frictional contact problems. The contact problem as a convex programming model is solved by using an adaptive incremental procedure. The contact constraints are incorporated into the model by using the Lagrange multiplier method. In addition, a local-nonlinear nonclassical friction model is adopted to model the friction at the contact interface. This eliminates the difficulties that arise with the application of the classical Coulomb’s law. On the other hand, the Wiechert model, as an effective model capable of describing both creep and relaxation phenomena, is adopted to simulate the linear behavior of viscoelastic materials. The resulting constitutive integral equations are linearized; therefore, complications that arise during the integration of these equations, especially with contact problems, are avoided. Two examples are presented to demonstrate the applicability of the proposed method. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467977
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 8 p.
Titre : Analyses of the long-term performance and tribological behavior of an axial piston pump using diamondlike-carbon-coated piston shoes and biodegradable oil Type de document : texte imprimé Auteurs : M. Kalin, Auteur ; F. Majdic, Auteur ; J. Vižintin, Auteur Année de publication : 2008 Article en page(s) : 8 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Tribology Wear Steel Carbon Pumps Oxidation Pistons Temperature Stress Petroleum Résumé : This work reports on the performance enhancement of a real-scale hydraulic system consisting of diamondlike-carbon (DLC)-coated components in combination with biodegradable oil in long-term experiments under conditions simulating those in an actual application. The performance of a hydraulic axial piston pump with DLC-coated piston shoes was evaluated in a newly designed, dedicated hydraulic test system using fully formulated biodegradable, synthetic ester oil. For comparison, an equal but separated hydraulic system with a conventional commercial pump and stainless-steel shoe surfaces was tested. The tests were run at 85% of the maximum pump load and an oil temperature of around 80°C for a period of 2000h, which corresponds to more than 1yr of continuous 8h∕day operation in an application. A major abrupt oxidation-induced degradation of the oil did not occur in either system; however, the oil from the system comprising the DLC-coated shoes showed noticeably and consistently better results. The wear of the DLC-coated shoes, especially during the running in, was much lower than that in the conventional steel system. Only minor polishing wear was observed on the DLC shoe’s sliding surfaces during the test period, while on the steel shoe’s surfaces, many scratches were found and some erosion of the edges was detected. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467979 [article] Analyses of the long-term performance and tribological behavior of an axial piston pump using diamondlike-carbon-coated piston shoes and biodegradable oil [texte imprimé] / M. Kalin, Auteur ; F. Majdic, Auteur ; J. Vižintin, Auteur . - 2008 . - 8 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 8 p.
Mots-clés : Tribology Wear Steel Carbon Pumps Oxidation Pistons Temperature Stress Petroleum Résumé : This work reports on the performance enhancement of a real-scale hydraulic system consisting of diamondlike-carbon (DLC)-coated components in combination with biodegradable oil in long-term experiments under conditions simulating those in an actual application. The performance of a hydraulic axial piston pump with DLC-coated piston shoes was evaluated in a newly designed, dedicated hydraulic test system using fully formulated biodegradable, synthetic ester oil. For comparison, an equal but separated hydraulic system with a conventional commercial pump and stainless-steel shoe surfaces was tested. The tests were run at 85% of the maximum pump load and an oil temperature of around 80°C for a period of 2000h, which corresponds to more than 1yr of continuous 8h∕day operation in an application. A major abrupt oxidation-induced degradation of the oil did not occur in either system; however, the oil from the system comprising the DLC-coated shoes showed noticeably and consistently better results. The wear of the DLC-coated shoes, especially during the running in, was much lower than that in the conventional steel system. Only minor polishing wear was observed on the DLC shoe’s sliding surfaces during the test period, while on the steel shoe’s surfaces, many scratches were found and some erosion of the edges was detected. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467979
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 5 p.
Titre : On elastic interaction of nominally flat rough surfaces Type de document : texte imprimé Auteurs : A. Sepehri, Auteur ; K. Farhang, Auteur Année de publication : 2008 Article en page(s) : 5 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Force Separation (Technology) Surface roughness Stress Optimization Approximation Equations Errors Résumé : A hybrid interactive/optimization technique is used to derive in approximate closed-form equations relating contact load to mean plane separation. Equations governing Hertz contact for the interaction of surface asperities are considered in which asperity shoulder-to-shoulder contact results in normal and tangential components of force. The normal component of asperity force is summed statistically to find total normal force between the two surfaces. The tangential force over a half-plane corresponding to a select direction is found accounting for the directionality of the tangential component of asperity forces. Two sets of approximate equations are found for each of the normal and half-plane tangential force components. The simplest forms of the approximate equations achieve accuracy to within 5% error, while other forms yield approximation error within 0.2%. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467980 [article] On elastic interaction of nominally flat rough surfaces [texte imprimé] / A. Sepehri, Auteur ; K. Farhang, Auteur . - 2008 . - 5 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 5 p.
Mots-clés : Force Separation (Technology) Surface roughness Stress Optimization Approximation Equations Errors Résumé : A hybrid interactive/optimization technique is used to derive in approximate closed-form equations relating contact load to mean plane separation. Equations governing Hertz contact for the interaction of surface asperities are considered in which asperity shoulder-to-shoulder contact results in normal and tangential components of force. The normal component of asperity force is summed statistically to find total normal force between the two surfaces. The tangential force over a half-plane corresponding to a select direction is found accounting for the directionality of the tangential component of asperity forces. Two sets of approximate equations are found for each of the normal and half-plane tangential force components. The simplest forms of the approximate equations achieve accuracy to within 5% error, while other forms yield approximation error within 0.2%. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467980
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 7 p.
Titre : Contact force and frictional heating due to “large” particles in the head disk interface Type de document : texte imprimé Auteurs : Xinjiang Shen, Auteur ; David B. Bogy, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Particulate matter Bearings Disks Heating Force Temperature Friction Résumé : Particles in the head disk interface may cause large contact forces acting on the slider as well as thermal asperities in the read/write signal. This is especially true for the close spacing required for 1Tbit/in.2. In this paper, a three-body contact model is employed to study the effects of a particle entrapped between a slider and a disk. A criterion for determining a particle’s movement pattern is proposed. The study of particles in the head disk interface shows that large particles are likely to slide between the slider and disk interface, and the particles going through the trailing pad of an air bearing slider cause severe contact forces on the slider and generate large heat sources. The frictional heating study shows that the temperature around the magnetoresistive head increases to about 5°C for a single 200nm particle passing through the trailing pad of the slider. The effects of the particle size, disk material, and friction coefficient are also studied. It is found that the disk and slider materials and the frictional coefficient between the materials largely affect the contact force acting on the slider by an entrapped particle as well as the temperature rise at its contact region. It is also found that the friction coefficient largely affects a particle’s movement pattern in the head disk interface. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467983 [article] Contact force and frictional heating due to “large” particles in the head disk interface [texte imprimé] / Xinjiang Shen, Auteur ; David B. Bogy, Auteur . - 2008 . - 7 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 7 p.
Mots-clés : Particulate matter Bearings Disks Heating Force Temperature Friction Résumé : Particles in the head disk interface may cause large contact forces acting on the slider as well as thermal asperities in the read/write signal. This is especially true for the close spacing required for 1Tbit/in.2. In this paper, a three-body contact model is employed to study the effects of a particle entrapped between a slider and a disk. A criterion for determining a particle’s movement pattern is proposed. The study of particles in the head disk interface shows that large particles are likely to slide between the slider and disk interface, and the particles going through the trailing pad of an air bearing slider cause severe contact forces on the slider and generate large heat sources. The frictional heating study shows that the temperature around the magnetoresistive head increases to about 5°C for a single 200nm particle passing through the trailing pad of the slider. The effects of the particle size, disk material, and friction coefficient are also studied. It is found that the disk and slider materials and the frictional coefficient between the materials largely affect the contact force acting on the slider by an entrapped particle as well as the temperature rise at its contact region. It is also found that the friction coefficient largely affects a particle’s movement pattern in the head disk interface. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467983
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 15 p.
Titre : Thermo-mechanical model for Mmoving layered rough surface contacts Type de document : texte imprimé Auteurs : A. Kadiric, Auteur ; R. S. Sayles, Auteur ; E. Ioannides, Auteur Année de publication : 2008 Article en page(s) : 15 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Heat Temperature Surface roughness Coatings Pressure Coating processes Steady state Functions Résumé : A numerical model designed to simulate a moving line contact of two rough layered bodies is presented. Fourier transforms are used to obtain fundamental solutions to relevant differential equations and then these solutions are used as kernel functions in a numerical scheme designed to provide a full thermomechanical solution for real layered contacts. The model assumes steady state heat transfer and predicts contact pressures and deformations, contact temperature rise, and resulting thermal stresses. The heat division between the contacting components is fully accounted for, as are the interactions between the mechanical and thermal displacements. Some results are presented to illustrate the potential importance of a full thermomechanical analysis as compared to a purely mechanical one as well as to demonstrate the influence of coating properties and surface roughness structure on the contact temperatures. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467985 [article] Thermo-mechanical model for Mmoving layered rough surface contacts [texte imprimé] / A. Kadiric, Auteur ; R. S. Sayles, Auteur ; E. Ioannides, Auteur . - 2008 . - 15 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 15 p.
Mots-clés : Heat Temperature Surface roughness Coatings Pressure Coating processes Steady state Functions Résumé : A numerical model designed to simulate a moving line contact of two rough layered bodies is presented. Fourier transforms are used to obtain fundamental solutions to relevant differential equations and then these solutions are used as kernel functions in a numerical scheme designed to provide a full thermomechanical solution for real layered contacts. The model assumes steady state heat transfer and predicts contact pressures and deformations, contact temperature rise, and resulting thermal stresses. The heat division between the contacting components is fully accounted for, as are the interactions between the mechanical and thermal displacements. Some results are presented to illustrate the potential importance of a full thermomechanical analysis as compared to a purely mechanical one as well as to demonstrate the influence of coating properties and surface roughness structure on the contact temperatures. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467985
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 7 p.
Titre : Bearing signature analysis as a medium for fault detection : a review Type de document : texte imprimé Auteurs : M. S. Patil, Auteur ; Jose Mathew, Auteur ; P. K. Rajendrakumar, Auteur Année de publication : 2008 Article en page(s) : 7 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Bearings Vibration Flaw detection Rolling bearings Signals Product quality Résumé : Rolling element bearings find widespread domestic and industrial application. Defects in bearing unless detected in time may lead to malfunctioning of the machinery. Different methods are used for detection and diagnosis of the bearing defects. This paper is intended as a tutorial overview of bearing vibration signature analysis as a medium for fault detection. An explanation for the causes for the defects is discussed. Vibration measurement in both time domain and frequency domain is presented. Recent trends in research on the detection of the defects in bearings have been included. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467988 [article] Bearing signature analysis as a medium for fault detection : a review [texte imprimé] / M. S. Patil, Auteur ; Jose Mathew, Auteur ; P. K. Rajendrakumar, Auteur . - 2008 . - 7 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 7 p.
Mots-clés : Bearings Vibration Flaw detection Rolling bearings Signals Product quality Résumé : Rolling element bearings find widespread domestic and industrial application. Defects in bearing unless detected in time may lead to malfunctioning of the machinery. Different methods are used for detection and diagnosis of the bearing defects. This paper is intended as a tutorial overview of bearing vibration signature analysis as a medium for fault detection. An explanation for the causes for the defects is discussed. Vibration measurement in both time domain and frequency domain is presented. Recent trends in research on the detection of the defects in bearings have been included. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467988
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 4 p.
Titre : Influence of solid body temperature on the thermal EHL behavior in circular contacts Type de document : texte imprimé Auteurs : Xiaoling Liu, Auteur ; Peiran Yang, Auteur Année de publication : 2008 Article en page(s) : 4 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Temperature Solids Résumé : In order to investigate the influence of the body temperature of contacting solids on the lubrication performance of machine components, such as gears and roller bearings, a full numerical solution for the thermal elastohydrodynamic lubrication (EHL) problem in circular contacts under steady state has been achieved. The analysis assumed that the body temperature is different from the temperature of the supplied lubricating oil. The effects of the body temperature, the slide-roll ratio, and the velocity parameter have been discussed. Results show that if the entrainment velocity is not very high, the solid body temperature plays a dominant role in the EHL behavior; however, the influence of the body temperature decreases as the entrainment velocity increases. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467990 [article] Influence of solid body temperature on the thermal EHL behavior in circular contacts [texte imprimé] / Xiaoling Liu, Auteur ; Peiran Yang, Auteur . - 2008 . - 4 p.
Tribology
Langues : Anglais (eng)
in Transactions of the ASME . Journal of tribology > Vol. 130 N°1 (Janvier 2008) . - 4 p.
Mots-clés : Temperature Solids Résumé : In order to investigate the influence of the body temperature of contacting solids on the lubrication performance of machine components, such as gears and roller bearings, a full numerical solution for the thermal elastohydrodynamic lubrication (EHL) problem in circular contacts under steady state has been achieved. The analysis assumed that the body temperature is different from the temperature of the supplied lubricating oil. The effects of the body temperature, the slide-roll ratio, and the velocity parameter have been discussed. Results show that if the entrainment velocity is not very high, the solid body temperature plays a dominant role in the EHL behavior; however, the influence of the body temperature decreases as the entrainment velocity increases. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleid=1467990
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