Abstract
Film thickness is the most important parameter of a lubricated contact. Its evaluation in a cam-follower contact is not easy due to the continuous variations of speed, load and geometry during the camshaft rotation. In this work, experimental apparatus with a system for film thickness and shape estimation using optical interferometry, is described. The basic principles of the interferometric techniques and the color spaces used to describe the color components of the fringes of the interference images are reported. Programs for calibration and image analysis, previously developed for point contacts, have been improved and specifically modified for line contacts. The essential steps of the calibration procedure are illustrated. Some experimental interference images obtained with both Hertzian and elastohydrodynamic lubricated cam-follower line contacts are analyzed. The results show program is capable of being used in very different conditions. The methodology developed seems to be promising for a quasi-automatic analysis of large numbers of interference images recorded during camshaft rotation.
Highlights
It is well known that film thickness is one of the most important quantities to be determined for a lubricated contact
In order to obtain an evaluation thethickness film thickness starting from the interferograms, a procedure must first be carried out to relate the component to the distance between the two bodies calibration procedure must first be carried out to relate the H component to the distance between the two bodies contact.ofThe purpose of imageiscalibration is toand findoffset scale factors and offset factors that can to berelate in contact
In order to give give an idea idea of the the different images that can be elaborated by the theprogram, program,some some to an of different images that by the program, some images recorded at some particular points during the rotation of the same cam used for images recorded recordedatat some particular points during the rotation of the same used forthethe images some particular points during the rotation of the same cam usedcam for the calibration, calibration, shown in
Summary
It is well known that film thickness is one of the most important quantities to be determined for a lubricated contact. Engineering methods used for the assessment of film thickness from which a lubrication regime can be determined are often based on numerical and empirical formulations obtained by experimental tests conducted in stationary conditions. Non-conformal contacts such as those occurring in gears and cams, are characterized by rapid variations of speed, load and geometry. In these cases, experimental results are difficult to obtain and steady-state numerical solutions can lead to over or underestimation of the film thickness. Very complex numerical models of the lubricated contacts are available—considering for instance mixed lubrication conditions, thermal effects and transient conditions—real contacts remain difficult to simulate and experimental studies are important
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