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Punit Kumar - One of the best experts on this subject based on the ideXlab platform.
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new Minimum Film Thickness formula for ehl rolling sliding line contacts considering shear thinning behavior
Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 2013Co-Authors: Parinam Anuradha, Punit KumarAbstract:Full EHL line contact simulations have been carried out to obtain a new Minimum Film Thickness formula pertaining to thin Film EHL line contacts for Carreau-type shear-thinning lubricants. The present analysis uses Doolittle’s free volume based viscosity model with Tait’s equation to describe the density–pressure relationship. The load parameter (W) used in the present simulations ranges from 2 × 10−5 to 5 × 10−4, while the piezo-viscous coefficient varies from 15 to 30 GPa −1 using different sets of Doolittle–Tait parameters. The curve-fitted values of Minimum Film Thickness are found to conform well with the corresponding simulated values. Further, the present equation is shown to accurately capture the effect of increased scale and load sensitivities due to shear-thinning behavior.
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new Minimum Film Thickness formula for ehl rolling sliding line contacts considering shear thinning behavior
Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 2013Co-Authors: Parinam Anuradha, Punit KumarAbstract:Full EHL line contact simulations have been carried out to obtain a new Minimum Film Thickness formula pertaining to thin Film EHL line contacts for Carreau-type shear-thinning lubricants. The pres...
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ehl line contact central and Minimum Film Thickness equations for lubricants with linear piezoviscous behavior
Tribology International, 2011Co-Authors: Parinam Anuradha, Punit KumarAbstract:Full EHL line contact simulations for smooth surfaces are carried out under fully flooded condition to obtain central and Minimum Film Thickness equations pertaining to lubricants with linear piezoviscous response. The present analysis is based upon the assumptions of isothermal condition and Newtonian fluid model. A major drop in the sensitivity of pressure viscosity coefficient (and hence, the material parameter G) is observed. The exponent of the speed parameter U is marginally smaller while that of load parameter is slightly increased. There is close agreement between the simulated and fitted Film Thickness values.
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ehl circular contact Film Thickness correction factor for shear thinning fluids
Journal of Tribology-transactions of The Asme, 2008Co-Authors: Punit Kumar, M M KhonsariAbstract:An extensive set of full elastohydrodynamic lubrication point contact simulations ha been used to develop correction factors to account for the effect of shear-thinning lubri cant behavior on the central and Minimum Film Thickness in circular contacts under pun rolling condition. T h e Film Thickness for a shear-thinning lubricant can be easily obtained by dividing the corresponding Newtonian Film Thickness by the appropriate correction factor. Comparisons of the Film Thickness values obtained using the correction factor have been matched with the published experimental results pertaining to shear-thinning lubricants with a variety of realistic flow and piezoviscous properties under a wide range of operating speed. The good agreement between them establishes the validity and ver satility of the correction factors developed in this paper.
M M Khonsari - One of the best experts on this subject based on the ideXlab platform.
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a study on the effect of starvation in mixed elastohydrodynamic lubrication
Tribology International, 2015Co-Authors: Mohammad Reza Masjedi, M M KhonsariAbstract:Abstract The effect of starvation in mixed elastohydrodynamic lubrication (EHL) regime is studied. Numerical simulations are conducted for both line and point (elliptical) contacts with the consideration of the surface roughness. The degree of starvation is linked directly to the reduction in the lubricant mass flow rate. Results are presented to gain insight on the influence of starvation on the Film Thickness as well as the interaction between the surface asperities. Extensive sets of simulation results are used to quantify the effect of starvation in the EHL of rough surfaces. Expressions are developed to predict the percentage of the load carried by the surface asperities (asperity load ratio) as well as the reduction of the central and Minimum Film Thickness in the starved mixed EHL.
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on the effect of surface roughness in point contact ehl formulas for Film Thickness and asperity load
Tribology International, 2015Co-Authors: Mohammad Reza Masjedi, M M KhonsariAbstract:Abstract Formulas are derived for predicting the central Film Thickness, Minimum Film Thickness, and the asperity load ratio in point-contact EHL of rough surfaces. The rough EHL model includes simultaneous solution to the modified Reynolds and surface deformation equations with the consideration of both bulk and asperity deformations. To include the effect of surface roughness, a statistically-based elasto-plastic asperity micro-contact model is utilized. Regression analyses based on the results from an extensive set of simulations are performed to obtain predictive expressions for the Film Thickness and the asperity load ratio. These formulas are of the form f(κ, W, U, G, σ ¯ , V), where the parameters represented are ellipticity, dimensionless load, speed, material, surface roughness and hardness, respectively. The results predicted using these formulas are in good agreement with wide range of data available in the literature.
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Film Thickness and asperity load formulas for line contact elastohydrodynamic lubrication with provision for surface roughness
Journal of Tribology-transactions of The Asme, 2012Co-Authors: Mohammad Reza Masjedi, M M KhonsariAbstract:Three formulas are derived for predicting the central and the Minimum Film Thickness as well as the asperity load ratio in line-contact EHL with provision for surface roughness. These expressions are based on the simultaneous solution to the modified Reynolds equation and surface deformation with consideration of elastic, plastic and elasto-plastic deformation of the surface asperities. The formulas cover a wide range of input and they are of the form f(W, U, G, r, V), where the parameters represented are dimensionless load, speed, material, surface roughness and hardness, respectively. [DOI: 10.1115/1.4005514]
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ehl circular contact Film Thickness correction factor for shear thinning fluids
Journal of Tribology-transactions of The Asme, 2008Co-Authors: Punit Kumar, M M KhonsariAbstract:An extensive set of full elastohydrodynamic lubrication point contact simulations ha been used to develop correction factors to account for the effect of shear-thinning lubri cant behavior on the central and Minimum Film Thickness in circular contacts under pun rolling condition. T h e Film Thickness for a shear-thinning lubricant can be easily obtained by dividing the corresponding Newtonian Film Thickness by the appropriate correction factor. Comparisons of the Film Thickness values obtained using the correction factor have been matched with the published experimental results pertaining to shear-thinning lubricants with a variety of realistic flow and piezoviscous properties under a wide range of operating speed. The good agreement between them establishes the validity and ver satility of the correction factors developed in this paper.
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correction factor formula to predict the central and Minimum Film Thickness for shear thinning fluids in ehl
Journal of Tribology-transactions of The Asme, 2008Co-Authors: J Y Jang, M M Khonsari, Scott BairAbstract: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.
Leiming Gao - One of the best experts on this subject based on the ideXlab platform.
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a 3d transient elastohydrodynamic lubrication hip implant model to compare ultra high molecular weight polyethylene with more compliant polycarbonate polyurethane acetabular cups
Journal of The Mechanical Behavior of Biomedical Materials, 2021Co-Authors: Audrey C Ford, Zikai Hua, Stephen J Ferguson, Lisa A Pruitt, Leiming GaoAbstract:Wear remains a significant challenge in the design of orthopedic implants such as total hip replacements. Early elastohydrodynamic lubrication modeling has predicted thicker lubrication Films in hip replacement designs with compliant polycarbonate polyurethane (PCU) bearing materials compared to stiffer materials like ultra-high molecular weight polyethylene (UHMWPE). The predicted thicker lubrication Films suggest improved friction and wear performance. However, when compared to the model predictions, experimental wear studies showed mixed results. The mismatch between the model and experimental results may lie in the simplifying assumptions of the early models such as: steady state conditions, one dimensional rotation and loading, and high viscosities. This study applies a 3D-transient elastohydrodynamic model based on an ISO standard gait cycle to better understand the interaction between material stiffness and Film Thickness in total hip arthroplasty material couples. Similar to previous, simplified models, we show that the average and central Film Thickness of PCU (∼0.4μm) is higher than that of UHMWPE (∼0.2μm). However, in the 3D-transient model, the Film Thickness distribution was largely asymmetric and the Minimum Film Thickness occurred outside of the central axis. Although the overall Film Thickness of PCU was higher than UHMWPE, the Minimum Film Thickness of PCU was lower than UHMPWE for the majority of the gait cycle. The Minimum Film Thickness of PCU also had a larger range throughout the gait cycle. Both materials were found to be operating between boundary and mixed lubrication regimes. This 3D-transient model reveals a more nuanced interaction between bearing material stiffness and Film Thickness that supports the mixed results found in experimental wear studies of PCU hip implant designs.
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a numerical study of non newtonian transient elastohydrodynamic lubrication of metal on metal hip prostheses
Tribology International, 2016Co-Authors: Leiming Gao, D. Dowson, R W HewsonAbstract:This paper presents a comprehensive numerical study of transient non-Newtonian elastohydrodynamic lubrication of metal-on-metal hip prosthesis subjected to two different gait cycles. The shear-thinning property of the synovial fluid was found to have a significant effect on the lubricating Film, in terms of both the magnitude and location of the Minimum Film Thickness, and more generally the Film Thickness distribution. A range of clearances between the acetabular cup and femoral head was investigated and the shear-thinning effect was more pronounced in the hip replacements with smaller clearances.
Parinam Anuradha - One of the best experts on this subject based on the ideXlab platform.
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new Minimum Film Thickness formula for ehl rolling sliding line contacts considering shear thinning behavior
Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 2013Co-Authors: Parinam Anuradha, Punit KumarAbstract:Full EHL line contact simulations have been carried out to obtain a new Minimum Film Thickness formula pertaining to thin Film EHL line contacts for Carreau-type shear-thinning lubricants. The present analysis uses Doolittle’s free volume based viscosity model with Tait’s equation to describe the density–pressure relationship. The load parameter (W) used in the present simulations ranges from 2 × 10−5 to 5 × 10−4, while the piezo-viscous coefficient varies from 15 to 30 GPa −1 using different sets of Doolittle–Tait parameters. The curve-fitted values of Minimum Film Thickness are found to conform well with the corresponding simulated values. Further, the present equation is shown to accurately capture the effect of increased scale and load sensitivities due to shear-thinning behavior.
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new Minimum Film Thickness formula for ehl rolling sliding line contacts considering shear thinning behavior
Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 2013Co-Authors: Parinam Anuradha, Punit KumarAbstract:Full EHL line contact simulations have been carried out to obtain a new Minimum Film Thickness formula pertaining to thin Film EHL line contacts for Carreau-type shear-thinning lubricants. The pres...
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ehl line contact central and Minimum Film Thickness equations for lubricants with linear piezoviscous behavior
Tribology International, 2011Co-Authors: Parinam Anuradha, Punit KumarAbstract:Full EHL line contact simulations for smooth surfaces are carried out under fully flooded condition to obtain central and Minimum Film Thickness equations pertaining to lubricants with linear piezoviscous response. The present analysis is based upon the assumptions of isothermal condition and Newtonian fluid model. A major drop in the sensitivity of pressure viscosity coefficient (and hence, the material parameter G) is observed. The exponent of the speed parameter U is marginally smaller while that of load parameter is slightly increased. There is close agreement between the simulated and fitted Film Thickness values.
C J Hooke - One of the best experts on this subject based on the ideXlab platform.
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considerations in the design of partially hydrostatic slipper bearings
Tribology International, 1997Co-Authors: E Koc, C J HookeAbstract:The purpose of this study is to examine the design of hydrostatically balanced bearings as used in the slippers of high pressure axial piston pumps, and to outline a design procedure whereby the slipper behaviour, Minimum Film Thickness and loss of high pressure fluid can be estimated. It is shown that for successful operation the slippers need to have small amounts of non-flatness on the running surfaces. In addition, good agreement between the measured and calculated Film Thickness is demonstrated.
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the Minimum Film Thickness in lubricated line contacts during a reversal of entrainment general solution and the development of a design chart
Proceedings of the Institution of Mechanical Engineers Part J: Journal of Engineering Tribology, 1994Co-Authors: C J HookeAbstract:In most line contacts the load, effective radius of curvature and entraining velocity change with time. Generally this is ignored when calculating the Film Thickness and a quasi-steady solution is ...
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the Minimum Film Thickness in line contacts during reversal of entrainment
Journal of Tribology-transactions of The Asme, 1993Co-Authors: C J HookeAbstract:In contacts, such as cams, non-involute gears and shaft seals, where the direction of entrainment reverses during the operating cycle, the Minimum Film Thickness is typically found just after the reversal. This paper shows that this Minimum Film Thickness is determined by the rate of change of the entraining velocity and by the fluid and surface properties. For line contacts, four regimes of lubrication are found-as for the steady-state situation-and expressions for the Film Thickness in each regime are developed
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the Minimum Film Thickness in lubricated line contacts during a reversal of entrainment isoviscous behaviour
Proceedings of the Institution of Mechanical Engineers Part C: Journal of Mechanical Engineering Science, 1992Co-Authors: C J HookeAbstract:In many line contacts the operating conditions, such as load, entrainment velocity and contact radii, vary with time. Generally, the results from standard elastohydrodynamic lubrication theory, derived for constant conditions, can be used to obtain a quasi-steady prediction of Film Thickness that is sufficiently accurate for design purposes. An important exception to this is where the entrainment direction changes because, under those conditions, the quasi-steady approach predicts that there will be no clearance between the surfaces while in practice a residual Film will persist.A previous paper showed that the Minimum Film Thickness during entrainment reversal depends primarily on the rate of change of entrainment velocity. Limit expressions for the Minimum clearance in the four regimes of lubrication were obtained. The present paper is part of a programme to develop a Minimum Film Thickness chart for entrainment reversal and deals with the transition between the rigid-piezoviscous and the elastic-piezov...
