Elasto-hydrodynamic friction changes on steel surfaces arising from the modified surface energy of the steel due to additive boundary films

Published on Dec 1, 2021in Tribology International4.872
· DOI :10.1016/J.TRIBOINT.2021.107203
M. Polajnar5
Estimated H-index: 5
(University of Ljubljana),
Benoit Thiebaut14
Estimated H-index: 14
+ 1 AuthorsMitjan Kalin40
Estimated H-index: 40
(University of Ljubljana)
Source
Abstract
Abstract null null The effect of three different film-forming additives mixed in PAO oil on the elasto-hydrodynamic (EHD) friction was investigated and compared to cases with the base oil only. When the boundary films were formed on the surfaces, the organic friction modifier (OFM) decreased the EHL friction by up to 8.7%, the ionic liquid (IL) decreased it by up to 6.4%, while the polymeric organic friction modifier (pOFM) increased it by up to 4.2%. In contrast, if the boundary films were not formed, the EHL friction remained the same as with the base oils only. The oils’ surface tension and viscosity were analysed at 25 °C and 100 °C as potential influencing effects, and the most important parameter for friction changes was found to be the surface energy. The mechanism behind this EHL friction reduction is, therefore, the effect of the boundary films on the poor oil-surface wetting and the consequent boundary slip. This study confirms the poor wetting arising from additive boundary-film formation as a relevant EHL friction-reduction mechanism. This observation is similar to that observed previously for surface coatings, thus suggesting that the boundary films of the surface-energy-reducing additives is a parameter with the potential to reduce the EHL friction.
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References67
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#2Maja Kus (University of Ljubljana)H-Index: 3
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#1Maja Kus (University of Ljubljana)H-Index: 3
#2Mitjan Kalin (University of Ljubljana)H-Index: 40
Abstract The effect of additives, their type and structure on the wetting of oil has received little attention so far and is thus poorly understood. This is despite the fact that a number of additives are present in every lubricating oil. Here, we report on the influence of the addition of some simple organic friction modifiers, namely, fatty acids, amides, alcohols and amines, on the static and dynamic (i.e., the advancing and receding contact angles, and the contact-angle hysteresis) wetting o...
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#1Lars Bobach (Otto-von-Guericke University Magdeburg)H-Index: 6
#2Dirk Bartel (Otto-von-Guericke University Magdeburg)H-Index: 13
Last. Holger Ziegele (BMW)H-Index: 4
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This work evaluates the influence of DLC coatings on the frictional behaviour of lubricated line contacts in the fluid friction regime. Experiments on a twin-disc machine showed a significant reduction in friction using DLC coated discs instead of uncoated ones. The experimental results are compared by calculations using a three-dimensional thermal elastohydrodynamic simulation model. According to the calculations, the lower heat conductivity of DLC coatings is the main reason for the reduction ...
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#1M. Polajnar (University of Ljubljana)H-Index: 5
#2Mitjan Kalin (University of Ljubljana)H-Index: 40
In this paper, we show how the slide-to-roll ratio (SRR), the contact kinematics and the surface energy all have important effects on the elastohydrodynamic friction. As reported previously, diamond-like-carbon (DLC) contacts of the type DLC/DLC provide the lowest coefficient of friction, in particular those DLC materials with the lowest surface energies (three different DLC coatings were used in this study). A friction reduction of up to 48 %, compared to a steel/steel contact, was obtained. A ...
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#1Hugh Spikes (ICL: Imperial College London)H-Index: 76
The need for energy efficiency is leading to the growing use of additives that reduce friction in thin film boundary and mixed lubrication conditions. Several classes of such friction modifier additive exist, the main ones being organic friction modifiers, functionalised polymers, soluble organo-molybdenum additives and dispersed nanoparticles. All work in different ways. This paper reviews these four main types of lubricant friction modifier additive and outlines their history, research and the...
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#1L. Guo (CityU: City University of Hong Kong)H-Index: 7
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#1Z. Fu (SZU: Shenzhen University)H-Index: 1
#2P.L. Wong (CityU: City University of Hong Kong)H-Index: 20
Last. F. Guo (QUT: Qingdao Technological University)H-Index: 9
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The study aimed to determine the formation of an adsorption film at elastohydrodynamic lubricated (EHL) contacts and its effects on EHL film shape and friction. Experiments were conducted on an optical EHL test rig with surfaces of different surface energies. A new type of “abnormal” EHL film shape characterized with three dimples in the inlet of the contact was obtained in pure ball sliding experiments with long-chain polybutene. The adsorption layer was inferred to be the main cause for the “t...
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#1Hugh Spikes (ICL: Imperial College London)H-Index: 76
#2Zhang Jie (ICL: Imperial College London)H-Index: 1
There is currently considerable debate concerning the most appropriate rheological model to describe the behaviour of lubricant films in rolling–sliding, elastohydrodynamic contacts. This is an important issue since an accurate model is required to predict friction in such contacts. This paper reviews the origins of this debate, which primarily concerns a divergence of views between researchers using high pressure, high shear rate viscometry and those concerned with the measurement and analysis ...
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#1Aleks Ponjavic (ICL: Imperial College London)H-Index: 13
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The effect of interfacial slip on the friction and film thickness in an elastohydrodynamic (EHD) contact was directly evaluated. Experiments showed that the film thickness and friction decrease upon the application of an oleophobic coating given a sufficient pressure, as opposed to bare glass. Direct measurements of the slip velocity enabled the determination of a power law relationship between pressure and slip length. This implied the existence of spatial heterogeneity of the flow in the tribo...
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