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1.
A Reynolds' equation, using Winer's viscoplastic model to express the non-Newtonian fluid property, is derived for line-contact EHL problems. The numerical solutions are obtained to the incorporated Reynolds', elasticity, and energy equations for pressure, film thickness, and temperature distribution between two surfaces simultaneously having rolling and sliding motions. The results are presented for thermal non-Newtonian lubrication, to observe the difference between Winer's equation and Trachman's expression on temperature distribution, pressure, and film thickness. The variation in friction coefficient with slip shear rate is in agreement with other experimental data.  相似文献   

2.
In this study, base fluid parameters for elastohydrodynamic lubrication (EHL) and friction analyses have been determined experimentally. The viscosity at atmospheric pressure, η0, the pressure‐viscosity index, α, and the EHL friction coefficient, γ, are important parameters in EHL theory and they are crucial in the selection of efficient lubricants for different applications. This investigation focuses on three important lubrication mechanisms: the capability of forming a separating lubricant film, the friction generated in a lubricated contact, and the height of pressure peaks, such as the outlet pressure spike and pressure ripple caused by surface roughness. The influence of different lubricant parameters on these three mechanisms is discussed. The value of α is measured in a Couette high‐pressure viscometer, and the value of γ is obtained from a jumping‐ball device. Other parameters discussed are temperature‐viscosity coefficient, β, bulk modulus, B0, thermal conductivity at atmospheric pressure, λ0, and heat capacity unit volume, ρcp0. A comparison between traditional mineral base oils and environmentally adapted oil based on rapeseed oil and synthetic esters contributes to the further understanding of the performance of these new materials in lubrication applications. It is shown that rapeseed oil and synthetic esters have good lubricating properties and are, in most cases, better than mineral oils.  相似文献   

3.
《Wear》1986,111(1):83-99
In this paper the lubrication of a rigid cylinder sliding or rolling on an elastomeric layer which is bonded to a rigid substrate is examined. Results are presented for central and minimum film thicknesses for the complete range of operating conditions and for a wide range of values of the ratio of the semicontact width-to-layer thickness.  相似文献   

4.
The Spacer Layer Imaging (SLIM) method has been used to investigate the influence of transverse roughness on the thickness and shape of elastohydrodynamic (EHD) films. The effects of entrainment speed and lubricant viscosity on film distribution are shown for three distinct asperity heights over a wide range of lambda ratio (ratio of lubricant film thickness, separating two contacting surfaces, to their combined RMS roughnesses). Subsequently, the behaviour of film distribution for a range of mixed rolling–sliding conditions is also studied for both thin and thick film conditions. This study provides an estimate of how and when transverse asperities decompress and an indication of conditions under which these asperities cease to affect lubricant film formation.  相似文献   

5.
The effect of a non-Newtonian oil (shear thinning) on the lubrication of a piston ring is theoretically investigated. A variation of shear strain rate with shear stress that is cubic in form is used to obtain a modified form of the Reynolds equation (dynamic) applicable to a run-in ring profile which is considered to be a double parabola with a central straight portion. Numerical solutions are obtained for the film thickness, pressure and frictional force over a complete stroke for the case of a constant load. Results presented in non-dimensional form show that the effect of pseudo plasticity is to reduce slightly the minimum film thickness, peak pressure ratio and friction coefficient.  相似文献   

6.
A.W. Bush  P.H. Skinner  R.D. Gibson 《Wear》1984,96(2):177-202
The effect of surface roughness on the load capacity and friction in bearings operating in the elastohydrodynamic regime is predicted. A perturbation expansion is used to expand the pressure in powers of e (the ratio of the standard deviation of the surface roughness to the central film thickness). Two-dimensional roughness on both bearing surfaces with arbitrary anisotropy is considered. It is shown how the leading-order effects of roughness are insensitive to the precise form of the surface autocorrelation function and depend only on the variance of the height distribution and a parameter which describes the extent and nature of the anisotropy.  相似文献   

7.
C.R. Gentle  A. Cameron 《Wear》1974,29(2):141-151
A study of rolling elastohydrodynamic point contact film thicknesses for indications of solidification revealed a method of apparently predicting the pour-points of glass-forming liquids. The variation of pour-point with pressure is investigated and compared with other estimates from longer time scale experiments. The method is examined in the light of this comparison and is found to be worthy of further work. Support is particularly gained from direct observation of a lubricant below its pour-point in an asymmetric entrapment.  相似文献   

8.
9.
Lin Tsann-Rong  Lin Jen-Fin 《Wear》1990,140(2):235-249
A new Reynolds equation, obtained by using the pseudoplastic model to express the non-newtonian fluid property, is derived for line contact elastohydrodynanic lubrication problems. The Reynolds equation results in a non-linear equation of high order which is derived by using an approximate method. The Newton-Raphson technique is utilized to solve the simultaneous system of modified Reynolds and elasticity equations. The results in this paper show that on increase in the coefficient of non-linearity, the pressure spike and film thickness decrease, and they approach a hertzian situation. With respect to the various loads and/or velocity values, the behaviours of the pressure spike and film thickness for non-newtonian fluids are almost the same as those of a newtonian fluid.  相似文献   

10.
The inertia effects in an externally pressurized bearing with a viscoelastic lubricant were considered using the methods of averaged inertia and of iteration. The inertia forces reduce the load-bearing capacity at a given flow rate. The effect of the elasticity of the liquid is to increase the pressure and the load-bearing capacity at any point. The effects of the elastic number S, the volume flow rate Q, the ratio σ of the inner radius of the bearing to the outer radius of the bearing and H = ha on the pressure and the loadbearing capacity are presented graphically. The results obtained by the two methods are in good agreement.  相似文献   

11.
A complete numerical solution for the thermal elastohydrodynamic lubrication (EHL) problem of a finite line contact between an infinite plane and an axially profiled cylindrical roller is obtained. The pressure profile and the film shape in the middle part of the roller are very different from those at the ends. However, the finite line contact results in the middle part of the roller are nearly the same as those of the corresponding infinite line contact. It is revealed that, in a finite line contact, the maximum pressure, the highest film temperature and the minimum film thickness all occur at the end regions of the roller. A comparison is made between isothermal and thermal solutions of a finite line contact. In addition, variations in the minimum film thickness, the maximum pressure and the highest temperature with the dimensionless velocity parameter, the slide/roll ratio and the radius of the end profiles of the roller are discussed.  相似文献   

12.
For the starved thermal elastohydrodynamic lubrication in elliptical contacts, a numerical solver based on the multi-grid technique was developed and numerical solutions were achieved. The influences of the thickness of oil-supply layer, elliptical ratio, entrainment velocity, slide-roll ratio, and the maximum Hertzian pressure on the lubrication behaviour were investigated. The thermal solutions were compared with isothermal solutions. The numerical results show that, for an oil-starved contact, the central and minimum film thicknesses predicted by both thermal and isothermal solutions change at the same trend as the thickness of the oil-supply layer increases. That is, as the thickness of the oil-supply layer increases, in the beginning both the central and minimum film thicknesses increase rapidly, however, their increasing rates become smaller gradually, at last, when the thickness of the oil-supply layer reaches a certain value, both the central and minimum film thicknesses almost stop increasing. Such situation was called a quasi-fully flooded state in this study. It has been found that the amount of the supplied oil for the quasi-fully flooded state differs with the elliptical ratio, and the maximum amount of the supplied oil is required by a circular contact.  相似文献   

13.
The elastohydrodynamic traction coefficients of two Chinese aviation lubricating oils were investigated for various loads, rolling velocities, and lubricant inlet temperatures using a self‐made test rig. Traction coefficient versus slide‐to‐roll ratio curves were generated. The concept of critical load varying with the lubricant temperature is proposed. This paper presents a new empirical formula for the dynamic performance design of high‐speed rolling bearings, that relates traction coefficient with normal load, rolling velocity, and lubricant inlet temperature. The coefficients of the formula may be computed by regression analysis of the experimental data. Two example calculations are presented. The predicted results from the formula agree well with experimental observations.  相似文献   

14.
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.  相似文献   

15.
The application of advanced multilevel techniques to the solution of the EHL line contact problem has resulted in a multilevel solver of complexity O(n In n). The reduction in computing time thus obtained enables the use of large numbers of nodes and allows detailed study of the pressure spike. Both occurrence and height of the spike as a function of the governing parameters were studied. The parameter range where a pressure spike can be expected, and the results of spike height calculations, are presented.  相似文献   

16.
In order to investigate thermal effect of tilting roller pairs, a numerical solution for TEHL of tilting roller pairs has been presented. Variations in the lubricating performance with tilting angle have been investigated. Comparison between thermal and isothermal solutions has been made. Effects of the end profile radius, the velocity, and the maximum Hertzian pressure have been discussed. Profile modification of the roller generatrix has been assumed. Results show that all of the highest temperature, the maximum pressure, and the minimum film thickness occur at the load-carrying end. Larger tilting angle results in more evident thermal effect.  相似文献   

17.
A numerical solution to the elastohydrodynamic lubrication (EHL) problem of two coated elastic bodies in line contact is introduced. The non‐Newtonian behavior of the lubricant is incorporated into EHL analysis using Eyring's nonlinear viscous model. The surface elastic deformations are computed from full elasticity analysis of layered elastic half‐space. The iterative Newton–Raphson technique is used in the numerical solution. Subsurface stresses are calculated using two different techniques, the numerical integral scheme based on Fourier transformation and the finite element method. The effects of surface coating (material and thickness) on the pressure profile and subsurface stresses are presented and discussed. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

18.
The coupled effects of surface roughness and flow rheology on elastohydrodynamic lubrication (EHL) circular contact problems are analyzed and discussed. The averaged type Reynolds equation utilizing the average flow model on the interactions between couple stress fluids and surface roughness, the elastic deformation equation, the viscosity–pressure and density–pressure relations equations, and the force balance equation are solved numerically by the multilevel multi-integration (MLMI) algorithm to calculate the pressure distributions and film thickness shapes. The results show that the transverse type roughness and standard deviation of composite roughness enhance the pressure and film thickness in the central contact region. Moreover, the longer the characteristic length of the couple stress fluids is, the smaller the pressure distribution is in the central contact region and the greater the film thickness is in all regions.  相似文献   

19.
We study the lubricated (wet) contact mechanics of a smooth hard cylinder sliding on a randomly rough nominally flat surface of a linear viscoelastic solid. We calculate the rolling and sliding friction, and study the transition from the boundary lubrication to the elasto-hydrodynamic lubrication regime. For the viscoelastic contact the minimum (average) separation does not monotonically increase with the sliding velocity, and the Stribeck curve exhibits new structures not shown for elastic solids.  相似文献   

20.
基于弹流知识的球轴承设计   总被引:1,自引:0,他引:1  
基于点接触弹流知识与赤兹接触理论,对球轴承设计参数沟道半径系数和滚动体直径与节圆直径的比进行了分析,结果表明,沟道半径系数对微型轴承其取值范围较大;对小的沟道半径系数,滚动体直径与节圆直径的比的大小对形成油膜的能力影响较小,并且最大接触压力随沟道半径系数的变化大,而随滚动体直径与节圆直径的比的变化不大。  相似文献   

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