Size Effect on the Behavior of Thermal Elastohydrodynamic Lubrication of Roller Pairs

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
Xiaoling Liu ◽  
Jinlei Cui ◽  
Peiran Yang
Keyword(s):  
Size Effect ◽  
Newtonian Fluid ◽  
Effective Viscosity ◽  
Numerical Solutions ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Load Parameter ◽  
Performance Results ◽  
Thermal Ehl ◽  
Strong Size Effect

In order to investigate the size effect on elastohydrodynamic lubrication (EHL) of roller pairs, complete numerical solutions for both the Newtonian fluid and the Eyring fluid thermal EHL problems of roller pairs under steady state conditions have been achieved. It can be seen that there is no size effect on the isothermal EHL performance; however, there is a very strong size effect on the thermal EHL performance. Results show that the term of shearing heat is the most important factor for the film temperature when the size of a contact changes. Comparison between the Newtonian solution and the Eyring solution has been made under some operating conditions. It is interesting to see that the effective viscosity of the Eyring fluid is nearly the same as that of the Newtonian fluid when the size of a contact is large enough. The non-Newtonian effect, therefore, can be ignored when the size of a contact is very large. It is equally interesting to see that the thermal effect can be ignored when the size of a contact is very small. In addition, the influence of the velocity parameter, the load parameter, and the slide-roll ratio on the lubricating performance for various sizes of contacts has been investigated.

Transient thermal elastohydrodynamic lubrication of point contacts subjected to normal vibration

2016 ◽  
Vol 68 (5) ◽  
pp. 536-547
Author(s):  
Jianjun Zhang ◽  
Qibo Ni ◽  
Jing Wang ◽  
Feng Guo
Keyword(s):  
Film Thickness ◽  
Newtonian Fluid ◽  
Normal Vibration ◽  
Numerical Solutions ◽  
Elastohydrodynamic Lubrication ◽  
Vibration Period ◽  
Content Type ◽  
Multi Level ◽  
Vertical Vibrations ◽  
Thermal Ehl

Purpose Vibration exists widely in all machineries working under high speed. The unpredictability of vibration and the change of the relative surface speed may result in difficulties in the elastohydrodynamic lubrication (EHL) analysis. By far, few studies on EHL relating to vibration have been published. The purpose of the present study is to investigate the effect of the vertical vibrations and the influence of temperature on the thermal EHL contacts. Design/methodology/approach The lubricant was assumed to be Newtonian fluid. The time-dependent numerical solutions were achieved instant after instant in each period of the vibration. At each instant, the pressure field was solved with a multi-level technique, the surface deformation was solved with a multi-level multi-integration method and the temperature filed was solved with a finite different scheme through a sweeping progress. The periodic error was checked at each end of the vibration period until the responses of pressure, film thickness and temperature were all periodic functions with the frequency of the roller’s vibrations. Findings The results reveal that normal vibration produces little drastic change of pressure, film thickness and temperature in EHL. Under some conditions, the vibrations of the roller can produce transient dimples within the contact conjunction. It is also showed that the lubrication in the same sliding is better than the opposite sliding. Research limitations/implications For the unpredictability of vibration, it is not easy to do the experiment to realize a real comparison with numerical results. The reach does not show any verification and consider the effect of non-Newtonian fluid. Originality/value The effect of the vertical vibrations on the thermal EHL point contact hast been studied. The effects of both the amplitude and the frequency on the predicted load-carrying capacity, minimum film thickness, center pressure and center temperature and the coefficient of friction were investigated. The role of the thermal effect was given.

Non-Newtonian Thermal Analyses of Point EHL Contacts Using the Eyring Model

2005 ◽  
Vol 127 (1) ◽  
pp. 70-81 ◽  
Author(s):  
Xiaoling Liu ◽  
Ming Jiang ◽  
Peiran Yang ◽  
Motohiro Kaneta
Keyword(s):  
Effective Viscosity ◽  
Numerical Solutions ◽  
Thermal Analyses ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Contact Problems ◽  
Point Contacts ◽  
Eyring Model ◽  
Thermal Ehl

A non-Newtonian numerical solution system for the thermal elastohydrodynamic lubrication (EHL) problems in point contacts has been developed. The Eyring rheology model has been used to describe the non-Newtonian flow of the lubricant. An effective viscosity has been defined for the Eyring fluid. The Newtonian solver can be applied easily to the non-Newtonian problems when the viscosity of the Newtonian fluid is replaced by the effective viscosity. A novel technique for the determination of the effective viscosity is proposed. Numerical solutions for the conventional point contact and normally crossing cylinders contact problems are presented and the effects of the entraining velocity, the load, the slide-roll ratio, and the characteristic shear stress of the Eyring fluid on the lubricating performance are discussed. The results indicate that the non-Newtonian thermal EHL theory predicts more realistic film temperatures and traction coefficients.

On the Theory of Thermal Elastohydrodynamic Lubrication at High Slide-Roll Ratios—Circular Glass-Steel Contact Solution at Opposite Sliding

2000 ◽  
Vol 123 (4) ◽  
pp. 816-821 ◽  
Author(s):  
Feng Guo ◽  
Peiran Yang ◽  
Shiyue Qu
Keyword(s):  
Steady State ◽  
Numerical Solution ◽  
Elastohydrodynamic Lubrication ◽  
Numerical Results ◽  
Operating Conditions ◽  
Theoretical Evidence ◽  
Thermal Ehl ◽  
Wedge Effect ◽  
Film Profile ◽  
Circular Contact

A full numerical solution for the thermal EHL problem in circular contact formed by steel-glass conjunctions with slide-roll ratios larger than 2 has been carried out. An anomalous film profile, which is similar to that reported by Kaneta et al. (1996), has been obtained. The numerical results by the authors, involving three basic kinds of film profiles, the kinematic conditions for the formation of dimples, and the variations of dimples and traction behavior with operating conditions, have been carefully compared with the experiments by Kaneta et al., and provided a sound theoretical evidence of the dimple phenomena under steady-state conditions. The present study indicates that the temperature-viscosity-wedge effect seems to be an essential mechanism for the dimple phenomena.

Progressive Mesh Densification Method for Numerical Solution of Mixed Elastohydrodynamic Lubrication

2015 ◽  
Vol 138 (2) ◽  
Author(s):  
Wei Pu ◽  
Jiaxu Wang ◽  
Dong Zhu
Keyword(s):  
Surface Roughness ◽  
Numerical Solution ◽  
Numerical Solutions ◽  
Initial Conditions ◽  
Solution Process ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Machined Surface ◽  
Progressive Mesh ◽  
Wide Range

Numerical solution of mixed elastohydrodynamic lubrication (EHL) is of great importance for the study of lubrication formation and breakdown, as well as surface failures of mechanical components. However, converged and accurate numerical solutions become more difficult, and solution process with a fixed single discretization mesh for the solution domain appears to be quite slow, especially when the lubricant films and surface contacts coexist with real-machined roughness involved. Also, the effect of computational mesh density is found to be more significant if the average film thickness is small. In the present study, a set of sample cases with and without machined surface roughness are analyzed through the progressive mesh densification (PMD) method, and the obtained results are compared with those from the direct iteration method with a single fixed mesh. Besides, more numerical analyses with and without surface roughness in a wide range of operating conditions are conducted to investigate the influence of different compound modes in order to optimize the PMD procedure. In addition, different initial conditions are used to study the effect of initial value on the behaviors of this transient solution. It is observed that, no matter with or without surface roughness considered, the PMD method is stable for transient mixed EHL problems and capable of significantly accelerating the EHL solution process while ensuring numerical accuracy.

Traction in Thermal Elastohydrodynamic Lubrication of Rough Surfaces

1992 ◽  
Vol 114 (1) ◽  
pp. 186-191 ◽  
Author(s):  
L. Chang
Keyword(s):  
Numerical Solutions ◽  
Rough Surfaces ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Wide Range ◽  
Line Contacts ◽  
Simulation Results

This paper studies the traction behavior of elastohydrodynamically lubricated line contacts between two rough surfaces. The study uses a thermal micro-elastohydrodynamic-lubrication (micro-EHL) model and obtains traction coefficients for a wide range of operating conditions and for film parameters as small as 1.50. The simulation results suggest that the traction is generally insensitive to the roughness structure and magnitude as long as the contact maintains a full EHL film. The results also indicate clearly that the lubricant squeeze induced by the motion and interaction of rough surfaces significantly affects the numerical solutions to thermal micro-elastohydrodynamic lubrication.

On the Behavior of Friction in Lubricated Point Contact With Provision for Surface Roughness

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
H. Sojoudi ◽  
M. M. Khonsari
Keyword(s):  
Surface Roughness ◽  
Friction Coefficient ◽  
Numerical Solutions ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Hydrodynamic Pressure ◽  
Operating Conditions ◽  
Asperity Contact ◽  
Type Curve ◽  
Lift Off

This paper presents a simple approach to predict the behavior of friction coefficient in the sliding lubricated point contact. Based on the load-sharing concept, the total applied load is supported by the combination of hydrodynamic film and asperity contact. The asperity contact load is determined in terms of maximum Hertzian pressure in the point contact while the fluid hydrodynamic pressure is calculated through adapting the available numerical solutions of elastohydrodynamic lubrication (EHL) film thickness formula for smooth surfaces. The simulations presented cover the entire lubrication regime including full-film EHL, mixed-lubrication, and boundary-lubrication. The results of friction, when plotted as a function of the sum velocity, result in the familiar Stribeck-type curve. The simulations are verified by comparing the results with published experimental data. A parametric study is conducted to investigate the influence of operating condition on the behavior of friction coefficient. A series of simulations is performed under various operating conditions to explore the behavior of lift-off speed. An equation is proposed to predict the lift-off speed in sliding lubricated point contact, which takes into account the surface roughness.

The Influence of the Operating Conditions on the Lubrication Regimes of Ball Screws

2013 ◽  
Vol 371 ◽  
pp. 581-585
Author(s):  
George Constantin Puiu ◽  
Vasile Puiu
Keyword(s):  
Numerical Solutions ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Operating Conditions ◽  
Ball Screw ◽  
Minimum Thickness ◽  
Lubrication Regimes ◽  
Lubrication Regime ◽  
Ball Screw Drive ◽  
Ellipticity Parameter

In point contact related applications (ball bearings, ball-screws) the minimum and the central film thickness of lubricant have a particular importance. The literature presents various numerical solutions to determine these parameters in the case of elliptical contacts [1-4]. Most of them refer to the fully developed elastohydrodynamic lubrication regime (EHD). Hamrock [5] proposes four different lubrication regimes depending on the size and importance of two physical phenomena that occur in contact: elastic deformation of the bodies in contact under a given load and lubricant viscosity variation of contact pressure. These four lubrication regimes have specific relations for calculating the two parameters. Also, Hamrock [5] develops a methodology for identifying the lubrication regime in a point contact, depending on three dimensionless parameters: the ellipticity parameter; the viscosity parameter; the elasticity parameter. According to the viscosity and elasticity parameters, for each value of the ellipticity parameter a map of lubrication regimes can be built. These parameters are influenced by the materials and geometry of the bodies in contact and operating conditions. By using the methodology [5] a comprehensive analysis regarding the lubrication regimes in contacts between balls and races of a ball screw drive has been done. Thus, a complex program to draw lubrication regimes maps, starting from an imposed geometry and from given operating conditions, has been developed. The developed maps have revealed the different lubrication regimes that can occur in contacts between the balls and races on the screw and nut. It was also revealed, for a given type of screw, which are the load and speed limits that allow transition from an isoviscous-rigid regime of lubrication (IVR) / hydrodynamic (HD) to an elastohydrodynamic lubrication regime (EHD). For each lubrication regime, relations were used for calculating the appropriate minimum thickness of lubricant film, hence the major importance of accurate knowledge of lubrication regime.

A Circular Non-Newtonian Fluid Model: Part I—Used in Elastohydrodynamic Lubrication

1990 ◽  
Vol 112 (3) ◽  
pp. 486-495 ◽  
Author(s):  
Rong-Tsong Lee ◽  
B. J. Hamrock
Keyword(s):  
Shear Strength ◽  
Newtonian Fluid ◽  
Reynolds Equation ◽  
Fluid Model ◽  
Elastohydrodynamic Lubrication ◽  
Pressure Profile ◽  
Load Parameter ◽  
Viscosity Term ◽  
Pure Rolling ◽  
The Coefficient Of Friction

A circular non-Newtonian fluid model associated with the limiting shear strength was considered. Using this model a modified Reynolds equation was developed which is almost the same as the classical Reynolds equation except for the viscosity term. Results show that the calculation of the central and minimum film thicknesses from the classical Reynolds equation is still valid for pure rolling conditions. The effects on performance of dimensionless load parameter, dimensionless speed parameter, slide/roll ratio, different oils, the limiting shear strength proportionality constant were studied. Such parameters as the pressure profile, the film shape, the coefficient of friction, the dimensionless shear stress at surface a, and the velocitiy contour in the conjunction were considered.

A New Method for Eyring Shear-Thinning Models in Elliptical Contacts Thermal Elastohydrodynamic Lubrication

2018 ◽  
Vol 140 (5) ◽  
Author(s):  
Xiaoling Liu ◽  
Mingming Ma ◽  
Peiran Yang ◽  
Feng Guo
Keyword(s):  
Shear Stress ◽  
Strain Rate ◽  
Shear Strain ◽  
Effective Viscosity ◽  
Elastohydrodynamic Lubrication ◽  
Shear Thinning ◽  
New Method ◽  
Shear Strain Rate ◽  
Thermal Ehl ◽  
Shear Thinning Fluid

A new method for solving the shear stress and the effective viscosity of Eyring shear-thinning fluid in thermal elastohydrodynamic lubrication (EHL) was proposed and applied to two models. Model 1 is the thermal EHL model with one-direction velocity, and model 2 is the spinning thermal EHL model in which the velocity varies with coordinates. Comparisons between the new and the existing method were carried out. Results show that only replacing the shear strain rate of model 1 with that of model 2, the shear stress and the effective viscosity of model 2 for Eyring shear-thinning fluid can be obtained. For model 1, results obtained with the two methods are the same. The new method can be qualified and applied into model 2. It is proved that the new method has higher efficiency for shear-thinning fluid than the existing method. Therefore, the new method is more efficient and can be used for spinning Eyring shear-thinning thermal EHL.

On the Stribeck Curves for Lubricated Counterformal Contacts of Rough Surfaces

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Dong Zhu ◽  
Jiaxu Wang ◽  
Q. Jane Wang
Keyword(s):  
Film Thickness ◽  
Numerical Solutions ◽  
Rough Surfaces ◽  
Elastohydrodynamic Lubrication ◽  
Real Data ◽  
Operating Conditions ◽  
Stribeck Curve ◽  
Flash Temperature ◽  
Wide Range ◽  
Stribeck Curves

The “Stribeck curve” is a well-known concept, describing the frictional behavior of a lubricated interface during the transition from boundary and mixed lubrication up to full-film hydrodynamic/elastohydrodynamic lubrication. It can be found in nearly every tribology textbook/handbook and many articles and technical papers. However, the majority of the published Stribeck curves are only conceptual without real data from either experiments or numerical solutions. The limited number of published ones with real data is often incomplete, covering only a portion of the entire transition. This is because generating a complete Stribeck curve requires experimental or numerical results in an extremely wide range of operating conditions, which has been a great challenge. Also, numerically calculating a Stribeck curve requires a unified model with robust algorithms that is capable of handling the entire spectrum of lubrication status. In the present study, numerical solutions in counterformal contacts of rough surfaces are obtained by using the unified deterministic mixed elastohydrodynamic lubrication (EHL) model recently developed. Stribeck curves are plotted in a wide range of speed and lubricant film thickness based on the simulation results with various types of contact geometry using machined rough surfaces of different orientations. Surface flash temperature is also analyzed during the friction calculation considering the mutual dependence between friction and interfacial temperature. Obtained results show that in lubricated concentrated contacts, friction continuously decreases as speed and film thickness increase even in the full-film regime until extremely high speeds are reached. This is mainly due to the reduction of lubricant limiting shear stress caused by flash temperature rise. The results also reveal that contact ellipticity and roughness orientation have limited influence on frictional behaviors, especially in the full-film and boundary lubrication regimes.

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