This paper concerns a study of the lubricant film formation and behavior of a point contact under non-steady state conditions. Transient Elastohydrodynamic (EHD) lubrication, where operating parameters such as speed and load vary over time,occurs in many machine elements including cams, gears and roller bearings. Therefore, an attention in last few years was focused on behavior and formation of a lubricant film in Elastohydrodynamic lubricated (EHL) contact under non-steady state conditions. The critical running sequences of EHL contacts include e.g. starting or halting of contact surfaces and also abrupt increases or decreases of surface speed and load. These cases can cause a rupture of a lubricant film and in consequence of this action also damage of contact surfaces. This study is devoted to the experimental research of the behavior of EHD films during reversal of entrainment in reciprocating motion. Moreover influence of surface tecturing on rolling contact fatigue life of rubbing surfaces was also studied. and Obsahuje seznam literatury
The aim of this study is to perform detail experimental mapping of the lubricating film thickness of bovine serum (BS) within the contact between an artificial metal or ceramic femoral head and a glass disc and analyze effect of proteins on the film formation. Mapping of the lubricating film of various concentrations of BS solutions was carried out using an optical test rig. Chromatic interferograms were recorded with a high-speed digital camera and evaluated with thin film colorimetric interferometry. The film thickness was studied as a function of both time and mean speed. The results showed that film thickness increases with time for both the metal and ceramic heads. Films formed at the end of measurements with the metal head were found to be typically in the range of 60-100 nm for all BS solutions and were independent on the amount of proteins in tested fluids. At the beginning of the speed measurements, BS of all concentrations forms a very thin film (1-2 nm) and its thickness increases with increasing mean speed. However, when the speed was decreased, the film thickness did not reduce but increased with decreasing speeeds that supports the findings of other researchers. Moreover, it was found that BS supply is sensitive parameter. When the lubricant reservoir below tested head was used then the measured central film thicknesses achieved values only about 20 nm, whereas when the tests were realized without the reservoir, measured central film thicknesses achieved higher values about 100 nm. For both types of the experiments, distribution of the film thickness within the contact zone is not homogeneous and two different film thickness regions can be found; thicker protein film and thinner base film that both increase with time and speed. and Obsahuje seznam literatury