Abstract
The knowledge of the film thickness values is very important in lubricated contacts to verify the lubrication conditions. Optical interferometry is one of the most used methodologies for film thickness and shape determination of Elastohydrodynamic‐lubricated contacts. An image processing programme has been developed for the analysis of white light interferograms. The programme, based on the analysis of the hue channel, has been developed in order to process big amounts of images, as often generated under transient conditions. The measurement range is currently limited to a maximum film thickness of 0.7 μm. The programme has been used for analysing several images recorded in tests carried out with a ball on disc contact under steady‐state as well as transient conditions for different velocities and slide‐to‐roll ratios. Under transient conditions, the entraining velocity is varied with a sinusoidal law for two different frequencies. The results obtained evidenced an asymmetric reduction of the film thickness when increasing the percentage of sliding, both for stationary and transient conditions. Under transient conditions with increasing test frequency, film thickness loops of increasing amplitude have been found that reduce their amplitude more when the ball is running faster than the disc. Squeeze and thermal effects can explain the results obtained.
Highlights
Film thickness measurements of Elastohydrodynamic (EHD) lubricated contacts are important to evaluate the lubrication regime
An image processing programme has been developed for the analysis of white light interferograms
It must be considered that machine elements are working mainly under transient conditions by means of changing radius of curvature, load, or speed
Summary
Film thickness measurements of Elastohydrodynamic (EHD) lubricated contacts are important to evaluate the lubrication regime. The authors investigated nonconformal lubricated contacts between steel balls and glass discs for different S under transient conditions [5, 6]. These previous works were more addressed to friction investigation and showed the need of further investigations and a better film thickness analysis. One recent method is based on the analysis of the RGB colour space [9], whereas the other method uses the HSV colour space [10] The latter image processing method first introduced by Marklund is used due to its greater simplicity and minor sensitivity to illumination conditions. The film thickness results obtained both under stationary and transient conditions for different S are presented and analysed
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