EHL Modeling for Nonhomogeneous Materials: The Effect of Material Inclusions

2007 ◽  
Vol 129 (2) ◽  
pp. 256-273 ◽  
Author(s):  
Trevor S. Slack ◽  
Nihar Raje ◽  
Farshid Sadeghi ◽  
Gary Doll ◽  
Michael R. Hoeprich
Keyword(s):  
Film Thickness ◽  
Pressure Distribution ◽  
Fatigue Crack Initiation ◽  
Base Material ◽  
Elastohydrodynamic Lubrication ◽  
Elastic Half Space ◽  
Lubricant Film ◽  
Stress Concentrations ◽  
Rolling Element ◽  
Bearing Materials

Inclusions are common in bearing materials and are a primary site for subsurface fatigue crack initiation in rolling element bearings. This paper presents a new approach for computing the pressure, film thickness, and subsurface stresses in an elastohydrodynamic lubrication (EHL) contact when inclusions are present in the elastic half-space. The approach is based on using the discrete element method to determine the surface elastic deformation in the EHL film thickness equation. The model is validated through comparison with the smooth EHL line contact results generated using linear elasticity. Studies are then carried out to investigate the effects of size, location, orientation, and elastic properties of inclusions on the EHL pressure and film thickness profiles. Both inclusions that are stiffer than and/or softer than the base material are seen to have effects on the pressure distribution within the lubricant film and to give rise to stress concentrations. For inclusions that are stiffer than the base material (hard inclusions), the pressure distribution within the lubricant film behaves as though there is a bump on the surface, whereas for inclusions that are less stiff than the base material (soft inclusions), the pressure distribution behaves in a manner similar to that of a dented surface. Inclusions close to the surface cause significant changes in the contact stresses that are very significant considering the stress life relationship. For inclusions that are located deep within the surface, there is little change in the EHL pressure and film thickness.

scholarly journals Grease film thickness measurement in rolling bearing contacts

2020 ◽  
pp. 135065012096127
Author(s):  
Xingnan Zhang ◽  
Romeo Glovnea
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Rolling Bearing ◽  
Thickness Measurement ◽  
Lubricant Film ◽  
Rolling Element Bearings ◽  
Lubricant Film Thickness ◽  
Rolling Bearings ◽  
Rolling Element ◽  
Film Thickness Measurement

Rolling bearings are the second most used machine components. They work in what it is called elastohydrodynamic lubrication regime. The geometry of rolling element bearings makes the direct measurement of the lubricant film thickness a challenging task. Optical interferometry is widely used in laboratory conditions for studying elastohydrodynamic lubrication however it cannot be used directly in rolling element bearings thus the only suitable methods are electrical techniques. Of these, film thickness measurement based on electrical capacitance of the contacts has been used in the past by a number of authors. One of the limitations of the capacitance method, when used in rolling bearings, is that it cannot distinguish between the contacts of every rolling element and raceway on one hand and on the other between the inner and outer ring contacts. In the present study the authors used an original test rig which can measure the film thickness for only one ball and separately for the inner and outer rings of a radial ball bearing. This paper thus shows for the first-time results of the lubricant film thickness, at the inner and outer raceways, in grease lubricated rolling bearings.

Effects of out-of-contact lubricant channeling on friction and film thickness in starved elastohydrodynamic lubrication point contacts

2016 ◽  
Vol 231 (4) ◽  
pp. 432-440 ◽  
Author(s):  
Fadi Ali ◽  
Ivan Křupka ◽  
Martin Hartl
Keyword(s):  
Film Thickness ◽  
Digital Camera ◽  
Elastohydrodynamic Lubrication ◽  
Contact Condition ◽  
Friction Reduction ◽  
Rolling Element Bearings ◽  
Point Contacts ◽  
Practical Applications ◽  
Rolling Element ◽  
Ball On Disc

This study presents experimental results on the effect of out-of-contact lubricant channeling on the tribological performance of nonconformal contacts under starved lubrication. Channeling of lubricant was carried out by adding a slider with a limited slot for scraping the displaced lubricant on one of mating surfaces (ball). Thus, the scraped lubricant is forced to flow back into the depleted track through the limited slot resulting in robust replenishment. The measurements have been conducted using optical tribometer (ball-on-disc) equipped with a digital camera and torque sensor. The effect of lubricant channeling was compared to the original contact condition by means of measuring friction and film thickness. The results show that the out-of-contact lubricant channeling leads to a significant enhancement of film thickness and friction reduction under starved conditions. Indeed, the starved elastohydrodynamic lubrication contacts transformed to the fully flooded regime after introducing the flow reconditioning. Moreover, the film thickness decay over time, which is common with starved elastohydrodynamic lubrication contacts, has not been observed in the case of lubricant channeling. However, the beneficial effect of lubricant channeling diminishes as the original contact condition tends to the fully flooded regime. The results of this study can be easily implemented in practical applications such as radial and thrust rolling-element bearings.

Study of Direct Measuring of Lubricant Condition in Rolling Element Bearings With Microcomputer Technique

1990 ◽  
Vol 112 (1) ◽  
pp. 92-97 ◽  
Author(s):  
Dongchu Zhao
Keyword(s):  
Film Thickness ◽  
Strain Gage ◽  
Lubricant Film ◽  
Rolling Element Bearings ◽  
Main Program ◽  
Test Apparatus ◽  
Lubricant Film Thickness ◽  
Rolling Element ◽  
Lubricant Films ◽  
Flow Charts

A method for measuring the lubricant condition with strain gage in rolling element bearings and the instrument used are introduced. In order to illustrate the method and the instrument, the theory of measuring lubricant films in rolling element bearings using strain technique, test apparatus, microcomputer hardware as well as software, flow charts for the main program and subprograms, are first described in detail. In addition, the lubricant film thickness is measured for several different lubricants and results are compared with theoretical ones. It is demonstrated that using the method and the instrument introduced in this paper, one can measure the lubricant condition inside bearings very accurately.

Formation of Lubricant Film in Rotary Sealing Contacts: Part II—A New Measuring Principle for Lubricant Film Thickness

1992 ◽  
Vol 114 (2) ◽  
pp. 290-296 ◽  
Author(s):  
G. Poll ◽  
A. Gabelli
Keyword(s):  
Film Thickness ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Lip Seal ◽  
Tribological System ◽  
Lip Seals ◽  
Magnetite Particles ◽  
Rotary Speed ◽  
Fluid Film Thickness ◽  
Insight Into

The development of models for the elastohydrodynamic lubrication of rotary lip seals requires the measurement of the film thickness under a real seal. A new method has been developed for this purpose which is based on the use of lubricant oils in which magnetite particles are suspended (so-called magnetic fluids). A change in the fluid film thickness will create a change in the impedance of the coil of the measuring circuit, the magnetic flux of which is directed through the oil film of the contact area. The advantage of this technique is that minimal modifications have to be applied to the tribological system under examination. Initial measurements carried out with a model rubber lip seal provided new insight into the build-up of a lubricant film as a function of the rotary speed and allowed comparison with the results of a theoretical model for the analysis of lip seal lubrication developed in parallel.

Effect of changing geometrical characteristics for different shapes of a single ridge passing through elastohydrodynamic of point contacts

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Mohamed Abd Alsamieh
Keyword(s):  
Film Thickness ◽  
Pressure Distribution ◽  
Reynolds Equation ◽  
Point Contact ◽  
Elastohydrodynamic Lubrication ◽  
Point Contacts ◽  
Time Step ◽  
Content Type ◽  
Geometrical Characteristics ◽  
Different Shapes

Purpose The purpose of this paper is to study the behavior of a single ridge passing through elastohydrodynamic lubrication of point contacts problem for different ridge shapes and sizes, including flat-top, triangular and cosine wave pattern to get an optimal ridge profile. Design/methodology/approach The time-dependent Reynolds’ equation is solved using Newton–Raphson technique. Several shapes of surface feature are simulated and the film thickness and pressure distribution are obtained at every time step by simultaneous solution of the Reynolds’ equation and film thickness equation, including elastic deformation. Film thickness and pressure distribution are chosen to be the criteria in the comparisons. Findings The geometrical characteristics of the ridge play an important role in the formation of lubricant film thickness profile and the pressure distribution through the contact zone. To minimize wear, friction and fatigue life, an optimal ridge profile should have smooth shape with small ridge size. Obtained results are compared with other published numerical results and show a good agreement. Originality/value The study evaluates the performance of different surface features of a single ridge with different shapes and sizes passing through elastohydrodynamic of point contact problem in relation to film thickness and pressure profile.

Pressure Distribution Within EHD Point Contacts Based on Measured Film Thickness

Tribology ◽  
2006 ◽  
Author(s):  
Radek Poliscuk ◽  
Michal Vaverka ◽  
Martin Vrbka ◽  
Ivan Krupka ◽  
Martin Hartl
Keyword(s):  
Film Thickness ◽  
Numerical Solution ◽  
Pressure Distribution ◽  
Elastic Deformation ◽  
Contact Fatigue ◽  
Lubricant Film ◽  
Rolling Contact ◽  
Lubricant Film Thickness ◽  
Machine Elements ◽  
Lubricated Contact

Surface topography significantly influences the behavior of lubricated contacts between highly loaded machine elements. Most oil- or grease- lubricated machine elements such as gears, rolling bearings, cams and traction drives operate in mixed lubrication conditions and the lubricant film thickness is directly related to the main practical performance parameters such as function, wear, contact fatigue and scuffing. For determination wear and especially contact fatigue, the values and distribution of the pressure in rolling contact are required. The theoretical studies usually involve the numerical solution of pressure and film thickness in the contact, using some physical mathematical model built around the Reynolds equation to describe the flow and the theory of elastic deformation of semi-infinite bodies. Such calculations can be extremely time consuming, especially when lubricant films are very thin and/or contact load very high. This study is aimed at obtaining pressure distribution within lubricated contact from measured film thickness. Lubricant film thickness distribution within the whole concentrated contact is evaluated from chromatic interferograms by thin film colorimetric interferometry. Consequently, an elastic deformation is separated from the film thickness, geometry and mutual approach of the surfaces. Calculation of the pressure distribution is based on inverse elasticity theory. EHD lubricated contact with smooth surfaces of solids was first investigated. Calculated pressure, distributions were compared with data obtained from full numerical solution to check the accuracy. The approach was also applied to surfaces with dents and their influence on distribution of pressure in lubricant film.

A Three-Dimensional Model of Line-Contact Elastohydrodynamic Lubrication for Heterogeneous Materials with Inclusions

2016 ◽  
Vol 08 (02) ◽  
pp. 1650014 ◽  
Author(s):  
Kun Zhou ◽  
Qingbing Dong
Keyword(s):  
Film Thickness ◽  
Half Space ◽  
Surface Deformation ◽  
Three Dimensional ◽  
Elastohydrodynamic Lubrication ◽  
Lubricant Film ◽  
Line Contact ◽  
Lubricant Film Thickness ◽  
Equivalent Inclusion Method ◽  
Surface Contact

This paper develops a three-dimensional (3D) model for a heterogeneous half-space with inclusions distributed periodically beneath its surface subject to elastohydrodynamic lubrication (EHL) line-contact applied by a cylindrical loading body. The model takes into account the interactions between the loading body, the fluid lubricant and the heterogeneous half-space. In the absence of subsurface inclusions, the surface contact pressure distribution, the half-space surface deformation and the lubricant film thickness profile are obtained through solving a unified Reynolds equation system. The inclusions are homogenized according to Eshelby’s equivalent inclusion method (EIM) with unknown eigenstrains to be determined. The disturbed half-space surface deformations induced by the subsurface inclusions or eigenstrains are iteratively introduced into the lubricant film thickness until the surface deformation finally converges. Both time-independent smooth surface contact and time-dependent rough surface contact are considered for the lubricated contact problem.

Study on Photoelastic Method for Measuring Elastohydrodynamic Lubrication Pressure in Line Contact

2013 ◽  
Vol 281 ◽  
pp. 329-334
Author(s):  
Jun He ◽  
Huang Ping ◽  
Qian Qian Yang
Keyword(s):  
Film Thickness ◽  
Pressure Distribution ◽  
Reynolds Equation ◽  
Friction Pair ◽  
Elastohydrodynamic Lubrication ◽  
Ccd Camera ◽  
Measuring System ◽  
Line Contact ◽  
Basic Equations ◽  
Plastic Disk

In the present paper, a new method for measuring elastohydrodynamic lubrication (EHL) pressure in line contact is proposed, which is based on the photoelastic technique. The pressure distribution of EHL film and the inner stresses in the friction pairs are fundamental issues to carry out EHL research. The film thickness, pressure and temperature have been successfully obtained with solving the basic equations such as Reynolds equation and energy equation simultaneously or separately, with numerical model of EHL problem. The film thickness can be also measured with the optical interference technique. However, the pressure measurement is still a problem which has not been well solved yet, so as the inner stresses inside the friction pairs. With the experimental mechanics, the photoelastic technique is a possible method to be used for measuring the pressure distribution of EHL film and inner friction pair in the line contact. Therefore, A flat plastic disk and a steel roller compose the frictional pairs of the photoelastic pressure measuring rig with combining the monochromatic LED light source, polarizer CCD camera and stereomicroscope to form the whole pressure measuring system of the line contact EHL. The experimental results with the rig display the typical features of EHL pressure. This shows that the method is feasible to be used for measuring the pressure of EHL film and the inner stresses of the friction pairs in the line contact.

Non-Newtonian behaviour in elastohydrodynamic lubrication

1974 ◽  
Vol 337 (1608) ◽  
pp. 101-121 ◽  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Film Thickness ◽  
Pressure Distribution ◽  
Critical Stress ◽  
Elastohydrodynamic Lubrication ◽  
Critical Factor ◽  
Molecular Size ◽  
High Speeds ◽  
Oil Films

The relation between shear stress and shear rate has been determined for elastohydrodynamic oil films. At low values the rate of shear is directly proportional to the shear stress, but at higher values the shear rate increases more rapidly than the stress. It is shown that the critical factor is the magnitude of the shear stress, not the shear rate, and that this critical magnitude depends upon the pressure and the molecular size. Above the critical stress, in the non-Newtonian region, the shape of the curve relating the stress to the rate of shear depends upon the distribution of the sizes of the molecules in the oil. It is shown that in elastohydrodynamic conditions the limits of Newtonian behaviour are frequently exceeded and that this is liable to influence the pressure distribution, the magnitude of the traction, the generation of heat, and, at high speeds, the value of the film thickness.

Sign in / Sign up

Export Citation Format

Share Document