"A best film thickness model in using interferometry in finding the pressure-viscosity coefficient alpha of a fluid"

With ever increasing power densities, the so-called pressure-viscosity coefficient alpha of fluids is becoming more and more important. An example is the high pressure viscosity of diesel fuel with common rail systems, where maximum pressures will soon reach 0.3 GPa (3,000 bars). At the occasion of the 3rd Arnold Tross Colloquium (2007) a new method was introduced to employ very accurate film thickness measurement results in determining the pressure-viscosity coefficient of an arbitrary fluid. In this method, the most recent film thickness model, and the believed most accurate one to date, was used: the Moes (2000) central film thickness formula for elliptical EHL (elastohydro-dynamically lubricated) contacts. The measurements are carried out on commonly used interferometric devices and is a cheap alternative to high pressure viscometers. Back in 2007, it was assumed that the Moes model would yield the best results. But many models have been developed, and which one really is the best? In this presentation 11 models are compared with calibration measurements. The unknown pressure-viscosity value is matched in such a way that its value minimizes the least squared error sum for the calculated film thickness with the measured values. The range of investigations was limited to 1.5 < L < 7 for the reference lubricant. The Moes model is the best one at very small film thickness values. The Moes model is the most versatile and general one available, but in the range of the measurements it lacks the accuracy of the Chittenden approximation. The Chittenden et al. model turned out to be superior in the full range of the measurements. The validity of the Chittenden formula transcends the area where it was originally designed for. It is recommended to perform film thickness measurements for fluids with high L values, as traction fluids, and check whether the conclusions still hold

Die Elastohydrodynamik : Geschichte und Neuentwicklungen

Deze paper geeft een overzicht gegeven van de geschiedenis, de resultaten en de doelstellingen van het onderzoek op het gebied van de elastohydrodynamica. De fysica van elastohydrodynamisch (EHD) gesmeerd contact wordt besproken, wat resulteert in benaderende formules voor filmdikte en wrijving. Met deze gedetailleerde inleiding, waarin veel verwijzingen naar de internationale literatuur zijn opgenomen, zou de ontwerper in staat moeten zijn om zelf de EHD-condities van het glijdend contact te schatten.Geïnspireerd door de praktijk hebben veel onderzoekers geprobeerd de dikte van de smeerfilm en de wrijving voor zwaar belaste gesmeerde contacten (tandwielen) te berekenen. Rond 1950 werd een zeer scherpe drukpiek in de smeerfilm theoretisch voorspeld. Dit kon pas in het begin van de jaren zeventig experimenteel worden bewezen met behulp van microsensoren uit de dunne-filmtechnologie. Door experimenten in de jaren '60 werd ook vastgesteld dat de wrijving in het contactpunt niet-Newtons moet zijn. Ongeveer een decennium later werden niet-Newtonse vloeistofmodellen ontwikkeld. Met behulp van nieuwe numerieke technieken werd goede vooruitgang geboekt op het gebied van theoretische ontwikkelingen. Op het gebied van de meettechniek hebben zich in de afgelopen 20 jaar echter nauwelijks nieuwe principiële ontwikkelingen voorgedaan. Hier zijn nieuwe meettechnieken nodig die nu nog niet bestaan.Ondanks dit werk zijn veel problemen nog niet opgelost. Enkele van de huidige onderzoeksdoelstellingen worden hier behandeld. Het belangrijkste doel van deze bijdrage blijft echter de toepassing van de resultaten in de werktuigbouwkunde

Regimes of traction in concentrated contact lubrication

This contribution discusses different regimes of EHD lubrication from a film thickness formation point of view, and tries to reconciliate this with recent theories on EHD traction, as published by Bair and Winer

A new concept in rotary shaft seal lubrication : viscoelastohydrodynamic (VEHD) lubrication

In practice rotary shaft seals will experience a small-amplitude dynamic excitation. It is shown that under periodic excitation circumferentially nonuniform clearances develop due to viscous seal material behaviour. The nearby fluid will fill these gaps, so entrainment and squeeze effects can develop fluid pressures, which are sufficiently high to overcome the radial preload. Viscous seal properties are essential in this type of EHD lubrication. Hence it is designated viscoelastohydrodynamic (VEHD) lubrication. At present, this lubrication concept is the only macrohydrodynamic theory that explains the existence of a consistent circumferentially nonuniform film geometry of appreciable dimensions. Moreover, calculated values of film thickness and friction are in agreement with experimental data

Elastohydrodynamic film thickness and temperature measurements in dynamically loaded concentrated contacts : eccentric cam-flat follower

This paper describes some results of local film thickness and temperature measurements in an eccentric cam-flat follower contact by means of miniature vapour deposited thin layer transducers. Complex transducer patterns can be realized by employing photolithography, allowing local measurements in axial direction. A full film will develop at relatively low speeds. At high speeds chemical reaction layer formation starts. Film thickness and temperature at both sides of the contact differed appreciably, thus invalidating the assumption of line contact. Under high loads and misalignment a constriction in the film thickness, typically for EHD contacts, appears at the heavy load side. Only after supporting the follower on a self-aligning elastic hinge, a line contact condition could be attained. Temperature variations of the follower surface were found to be moderate. The transducers worked well and have a satisfying life expectancy