Effect of the slide-to-roll ratio and the contact kinematics on the elastohydrodynamic friction in diamond-like-carbon contacts with different wetting behavioursPolajnar, Marko (Avtor) Kalin, Mitjan (Avtor) EHD lubricationDLCsurface energywettingslide-to-roll ratioIn 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 surprising new finding from this investigation is that the friction in DLC contacts is significantly reduced for high SRRs, i.e. a difference of up to 27 % was measured in the DLC/DLC contacts when the SRR increased from 0.5 (rolling prevails) to 1.8 (sliding prevails). However, even more surprising is the effect of the SRR on the friction in mixed steel/DLC contacts, which is related to the contact design and its kinematics. We found that if the DLC is coated on the slower surface, a high SRR will not reduce the friction to any significant extent, typically about 5 %, and at most 13 %, compared to steel/steel contacts. However, a significant friction reduction is observed when applying a low-surface-energy DLC coating to the faster surface-on average about 20 % and as high as 33 %. In this case (a high SRR and DLC on the faster surface), mixed steel/DLC surfaces can experience a very similar friction as that seen for DLC/DLC contacts. Qualitatively, the same behaviour was found for both positive and negative SRR values.20152019-03-14 13:39:52Članek v reviji106740UDK: 539.92(045)ISSN pri članku: 1023-8883DOI: 10.1007/s11249-015-0593-3COBISS_ID: 14197019OceCobissID: 2806555sl