Radek Poliščuk

Thin Film Colorimetric Interferometry

Measurement technique for the study of very thin lubrication films down to one nanometer in a point contact between a steel ball and a transparent disc is used to explore the relationship between central and minimum film thickness and rolling speed at the interface between elastohydrodynamic and boundary lubrication for a series of lubricating fluids. This technique based on the colorimetric interferometry combines powerful film thickness mapping capabilities with high accuracy. It was confirmed that both hexadecane and mineral base oil obey the linear relationship between log central and minimum film thickness and log rolling speed predicted by elastohydrodynamic theory down to approximately one nanometer. Conversely, squalane and additive-treated mineral base oil showed film thickness enhancement at slow speeds caused by boundary layers formation within the lubricant film. Obtained experimental data was used for the determination of pressure-viscosity coefficients of test fluids. The measurement technique also enabled us to produce information about the influence of boundary layers on film thickness shape. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

An Automatic System for Real-Time Evaluation of EHD Film Thickness and Shape Based on the Colorimetric Interferometry

This paper presents an automatic system for the real-time evaluation of elastohydrodynamic (EHD) film thickness and shape that incorporates an advanced experimental apparatus controlled by a computer with an extensive interferogram processing software. This software coordinates the data acquisition and instrument control and also provides real-time data processing and displaying. Film thickness evaluation technique based on the colorimetric interferometry successfully overcomes limitations of conventional optical interferometry. Colorimetric interferometry combining conventional chromatic interferometry with image processing and differential colorimetry gives instantaneous detailed information on EHD film thickness and shape for various regimes. This approach makes it possible to determine film thickness in the range of 1 to 800 nm with a resolution of about 1 nm. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in Toronto, Ontario, Canada, Octob...

Experimental Study of Central and Minimum Elastohydrodynamic Film Thickness by Colorimetric Interferometry Technique

Recently developed colorimetric interferometry technique was used for the study of both minimum and central film thicknesses for a wide range of operating parameters. Over 300 film thickness maps were obtained for the combination of four values of the materials parameter G, five values of the load parameter W and many values of the speed parameter U. The use of a spacer layer extended the range of film thickness measurement down to 5 nm. An excellent agreement was found between experimental values and data obtained from numerical solution presented by Venner and ten Napel, especially for thin lubrication films. An increase in a speed exponent with increasing material parameter G was observed for both central and minimum film thicknesses. The minimum film thickness and, thereby, the ratio between central and minimum film thickness was confirmed to be of a stronger dependence on material and load dimensionless parameters than Hamrock and Dowson equations predict. Presented at the 54th Annual Meeting Las Vegas, Nevada May 23–27, 1999

Thin film lubrication study by colorimetric interferometry

Recently, we reported two novel experimental techniques for the determination of elastohydrodynamic lubricant film thickness and shape in model contacts based on colorimetric interferometry. This approach successfully overcomes two major limitations of conventional optical interferometry – accuracy and resolution. This paper presents the next stage in the development of these two techniques. The use of spacer layer has enabled to extend the film thickness measurement range down to several nanometers so that the relationship between the central and minimum film thickness and rolling speed in the very thin film thickness regime could be studied. The measurement techniques also produced information about film thickness profiles across lubricated contact and three-dimensional maps of film thickness.

Computer-aided chromatic interferometry

Abstract This paper demonstrates that it is possible to produce an effective measurement technique based on the combination of chromatic interferometry and computer graphics. Such a technique can be very useful for thin film measurement. A computer-aided system for the reconstruction of a thin fluid film shape from chromatic interference colours is presented conceptually and the parts of the system are demonstrated. The interference colour evaluation technique is based on the idea of replacing human eye by a simple differential colorimeter realised by computer program.

Effect of surface dents on contact pressure in elastohydrodynamic contacts

Abstract Nowadays film thickness measurement techniques can provide precise data for the detailed studies of the behaviour of lubricated contacts including transient operational conditions. Contact pressure is in relation with deformation of rubbing surfaces, which can be derived from experimentally evaluated film thickness. Even though the pressure distribution evaluated from measured film thickness is very sensitive to its accuracy, this approach represents a powerful tool for elastohydrodynamic pressure determination; thanks to the relative wide availability of film thickness measurement techniques. Chromatic interferograms can be captured within a few microseconds so that this approach seems to be promising in obtaining relevant pressure data even within non-smooth lubricated contacts. This article presents the results of the effort to extend the applicability of the pressure-film thickness evaluation approach to the non-smooth surfaces. It was found that the main problem is to obtain the film thickness distribution within the whole contact including the inside portion of the deep surface features (e.g. dents). That is why the combination of film thickness data and undeformed dent topography was suggested to overcome these limitations. This approach was validated through the comparison with numerical solution using dented surface and was tested on selected dented contacts operated under thin film and very thin film lubrication conditions.

Pressure Distribution Within EHD Point Contacts Based on Measured Film Thickness

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.Copyright

Differential Colorimetry: A tool for the analysis of fluid film lubrication

In the field of elastohydrodynamic (bearing, gears, etc.) or aerodynamic (hard disks, tape recorders, etc.) lubrication, optical interferometry is the most popular method for film thickness measurement. In 1994, for the first time an image analysis method allowing the automatic treatment of the interferograms was presented. Since then, various teams published numerous literature on this subject. This work aims to sum up the improvements realised. Various methods are described and analysed, then different applications in lubrication ensuing from these works are evoked. They show that image analysis associated to differential colorimetry allows not only to obtain results of better quality and of greater user-friendliness, but that this technique opens a field of studies impossible or difficult to achieve until then. At last, two tendencies are outlined for the near future: differential colorimetry seems to be a very promising tool for the understanding of the mixed lubrication regime and for the in situ study of lubricant behaviour under pressure.

Image Processing Methods Applied in Mapping of Lubrication Parameters

Simple image processing approaches, like advanced palette fitting and convolution filters, can effectively replace traditional numerical methods in study of ball bearings. Two innovative experimental methods for mapping of tribological parameters in elastohydrodynamically lubricated contacts were developed, based on combination of optical tribometer (used for view into simulated rolling bearing) and software processing of chromatic interferograms. The lubricant shape reconstruction uses optimized colorimetric analysis (Thin Film Colorimetric Interferometry, TFCI), while the fast contact pressure mapping method is based on Inverse Elasticity Theory (IET) and convolution.

Effect of Surface Texturing on Lubrication Film Formation within Non-Conformal Contacts

The paper is focused on the influence of surface texturing in non-conformal contacts on lubricant film thickness, contact pressure and rolling contact fatigue (RCF). Both the possible negative and positive effects of surface texturing are considered. The lubricant film thickness was measured using experimental apparatus based on thin film colorimetric interferometry, where the contact is realized between steel ball and glass disc. The RCF test rig consists of two discs loaded and running against roller specimen. The test results show that shallow micro-dents could be considered as beneficial to improve RCF of machine parts under mixed lubrication.