M. Polajnar
University of Ljubljana
Specific surface energyOpticsDiamond-like carbonViscosityFriction modifierCeramicWettingWork (thermodynamics)Surface forceWetting transitionComposite materialTribologyNanotechnologyMechanism (engineering)LubricationMetallurgyMaterials scienceSurface energyBreakupDuctile ironGraphiteSynthetic oilLubricantBrakePolarWear resistanceCoefficient of frictionFriction reductionHydrogen contentDlc coatingBrake padKinematicsSlip (materials science)Sessile drop techniqueDopingContact angleSurface tension
6Publications
5H-index
296Citations
Publications 8
Newest
#1M. Polajnar (University of Ljubljana)H-Index: 5
#2Benoit ThiebautH-Index: 11
Last. Mitjan Kalin (University of Ljubljana)H-Index: 38
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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 ...
Source
#1Mitjan Kalin (University of Ljubljana)H-Index: 38
#2M. Polajnar (University of Ljubljana)H-Index: 5
Last. Franc Majdič (University of Ljubljana)H-Index: 6
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1 CitationsSource
#1M. Polajnar (University of Ljubljana)H-Index: 5
#2Benjamin Bizjan (University of Ljubljana)H-Index: 9
Last. Mitjan Kalin (University of Ljubljana)H-Index: 38
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High-speed optical imaging is introduced as a visualization method to investigate the film-flow properties of liquids with different surface tensions and viscosities (water, poly-alpha-olefin oil, and glycerol) over free rotating surfaces with different surface energies and polarities (steel, and two different diamond-like-carbon - DLC coatings, i.e. DLC, and F-DLC). It was found that the polar surface energy strongly influences the structural dynamics of the liquid film's flow and the film's sl...
1 CitationsSource
#1M. Polajnar (University of Ljubljana)H-Index: 5
#2Mitjan Kalin (University of Ljubljana)H-Index: 38
Last. A. Botor-ProbierzH-Index: 1
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Abstract Due to its wear resistance, functionally graded ductile iron (FGDI) is a potential material for automotive brake pads. In this investigation it was studied (i) under well controlled sliding conditions in a typical tribological model-test to show in detail the mechanism behind improved wear resistance, namely the “property on-demand” functionality in the sub-surface zone and (ii) in a validation experiment on a disc-brake machine that mimic realistic brake-contact conditions, at various ...
20 CitationsSource
#1M. Polajnar (University of Ljubljana)H-Index: 5
#2Mitjan Kalin (University of Ljubljana)H-Index: 38
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 ...
9 CitationsSource
#1Mitjan Kalin (University of Ljubljana)H-Index: 38
#2M. Polajnar (University of Ljubljana)H-Index: 5
Abstract The importance of wetting is becoming increasingly obvious and its control is inevitable in many engineering applications, including tribology and interface nanotechnology. However, the relations between the key parameters affecting surface–liquid wetting behaviour under realistic conditions are not very well understood, especially for typical engineering materials and lubricants (oils), often leading to exceptions and contradictions, which impede their use in engineering models and the...
128 CitationsSource
#1Mitjan Kalin (University of Ljubljana)H-Index: 38
#2M. Polajnar (University of Ljubljana)H-Index: 5
Abstract In this study we investigate the correlation between the wetting, the contact angle, the spreading, the surface energy and the surface tension for five types of DLC coatings (doped, non-doped, hydrogenated and non-hydrogenated) and steel, wetted with synthetic, non-polar, polyalphaolefin (PAO) oils with two distinctly different viscosities. We show how these parameters correlate with each other and how and why they change when different DLC or steel surfaces come into contact with the o...
96 CitationsSource
#1Mitjan Kalin (University of Ljubljana)H-Index: 38
#2M. Polajnar (University of Ljubljana)H-Index: 5
This work shows the influence of solid–liquid interactions between engineering surfaces (steel and several types of DLC coatings) and lubricating oil (polyalphaolefin, PAO) on the coefficient of friction in the elastohydrodynamic lubrication (EHL) regime. Specifically, it confirms that the spreading parameter, rather than the contact angle, is the relevant parameter to evaluate the wetting behaviour of these surfaces with oils. Both the spreading parameter and the surface energy correlate very w...
67 CitationsSource