Tribology Letters

, Volume 53, Issue 2, pp 477–486 | Cite as

Friction Reduction in Elastohydrodynamic Contacts by Thin-Layer Thermal Insulation

  • M. BjörlingEmail author
  • W. Habchi
  • S. Bair
  • R. Larsson
  • P. Marklund
Original Paper


Reducing friction is of utmost importance to improve efficiency and lifetime of many products used in our daily lives. Thin hard coatings like diamond-like carbon (DLC) have been shown to reduce friction in full-film-lubricated contacts. In this work, it is shown that contrarily to common belief, the friction reduction stems mainly from a thermal phenomenon and not only a chemical/surface interaction one. It is shown that a few micrometer-thin DLC coating can significantly influence the thermal behavior in a lubricated mechanical system. The presented simulations, validated by experiments, show that applying a thin DLC coating to metal surfaces creates an insulating effect that due to the increased liquid lubricant film temperature at the center of the contact, locally reduces lubricant viscosity and thus friction. The results of the investigation show that the addition of thin insulating layers could lead to substantial performance increases in many applications. On a component level, the contact friction coefficient in some common machine components like gears, rolling element bearings, and cam followers can potentially be reduced by more than 40 %. This will most likely open up the way to new families of coatings with a focus on thermal properties that may be both cheaper and more suitable in certain applications than DLC coatings.


Diamond-like carbon (DLC) EHL Insulation Friction Coating Thermal effects Ball-on-disk 

List of symbols


Temperature coefficient of K 0 (K 1)


Dimensionless heat capacity scaling parameter


Generalized (shear dependent) viscosity (Pa s)


Shear rate (s−1)


Dimensionless conductivity scaling parameter


Limiting stress pressure coefficient


Relaxation time at T R and ambient pressure (s)


Limiting low-shear viscosity (Pa s)


Low shear viscosity at T R and ambient pressure (Pa s)


Viscosity extrapolated to infinite temperature (Pa s)


Lubricants density (kg)


Shear stress (Pa)


Limiting shear stress (Pa)


Dimensionless viscosity scaling parameter


Viscosity scaling parameter for unbounded viscosity


Coefficient in the dimensionless conductivity scaling parameter


Thermal expansivity defined for volume linear with temperature (K−1)


Fragility parameter in the new viscosity equation


Parameter in the heat capacity function (J/m3 K)


Parameter in the conductivity function (W/m K)


Specific heat capacity (J/kg K)


Lubricants volumetric heat capacity


Load (N)


Effective shear modulus (Pa)


Thermodynamic interaction parameter


Thermal conductivity (W/m K)


Pressure rate of change of isothermal bulk modulus at p = 0


K0 at zero absolute temperature (Pa)


Isothermal bulk modulus at p = 0 (Pa)


Contact load (N)


Parameter in the heat capacity function (J/m3 K)


Power law exponent


Pressure (Pa)


Coefficient in the dimensionless conductivity scaling parameter


Ball radius (m)


Exponent in the conductivity scaling model


Slide to roll ratio


Temperature (K)


Reference temperature (K)


Mean entrainment speed (m/s)


Surface velocity (m/s)


Volume (m3)


Volume at p = 0 (m3)


Volume at reference state, T R, p = 0 (m3)



The authors wish to thank Ove Andersson at Umeå University for performing the thermal properties measurements and IonBond AB for providing the DLC coatings used in the tests. The authors from Luleå wish to thank Swedish Foundation for Strategic Research (ProViking) for financial support. Bair was supported by the Center for Compact and Efficient Fluid Power, a National Science Foundation Engineering Research Center funded under cooperative agreement number EEC-0540834.


  1. 1.
    Bair, S.: Reference liquids for quantitative elastohydrodynamics. Tribol. Lett. 22(2), 197–206 (2006). doi: 10.1007/s11249-006-9083-y CrossRefGoogle Scholar
  2. 2.
    Bair, S., McCabe, C., Cummings, P.T.: Calculation of viscous EHL traction for squalane using molecular simulation and rheometry. Tribol. Lett. 13(4), 251–254 (2002). doi: 10.1023/A:1021011225316 CrossRefGoogle Scholar
  3. 3.
    Bair, S., McCabe, C., Cummings, P.T.: Comparison of nonequilibrium molecular dynamics with experimental measurements in the nonlinear shear-thinning regime. Phys. Rev. Lett. 5(4), 583021–583024 (2002). doi: 10.1103/PhysRevLett.88.058302 Google Scholar
  4. 4.
    Balandin, A., Shamsa, M., Liu, W., Casiraghi, C., Ferrari, A.C.: Thermal conductivity of ultrathin tetrahedral amorphous carbon films. Appl. Phys. Lett. 93(4), 043115 (2008). doi: 10.1063/1.2957041 CrossRefGoogle Scholar
  5. 5.
    Björling, M., Habchi, W., Bair, S., Larsson, R., Marklund, P.: Towards the true prediction of ehl friction. Tribol. Int. 66, 19–26 (2013). doi: 10.1016/j.triboint.2013.04.008 CrossRefGoogle Scholar
  6. 6.
    Björling, M., Isaksson, P., Marklund, P., Larsson, R.: The influence of DLC coating on EHL friction coefficient. Tribol. Lett. 47(2), 285–294 (2012). doi: 10.1007/s11249-012-9987-7 CrossRefGoogle Scholar
  7. 7.
    Björling, M., Larsson, R., Marklund, P., Kassfeldt, E.: Elastohydrodynamic lubrication friction mapping: the influence of lubricant, roughness, speed, and slide-to-roll ratio. Proc. Inst. Mech. Eng. J J. Eng. Tribol. 225(7), 671–681 (2011). doi: 10.1177/1350650111403363 CrossRefGoogle Scholar
  8. 8.
    Choo, J.H., Glovnea, R.P., Forrest, A.K., Spikes, H.A.: A low friction bearing based on liquid slip at the wall. J. Tribol. 129(3), 611–620 (2007). doi: 10.1115/1.2736704 CrossRefGoogle Scholar
  9. 9.
    Elsharkawy, A.A., Holmes, M.J.A., Evans, H.P., Snidle, R.W.: Micro-elastohydrodynamic lubrication of coated cylinders using coupled differential deflection method. Proc. Inst. Mech. Eng. J J. Eng. Tribol. 220(1), 29–41 (2006). doi: 10.1243/13506501J10005 CrossRefGoogle Scholar
  10. 10.
    Evans, R.D., Cogdell, J.D., Richter, G.A.: Traction of lubricated rolling contacts between thin-film coatings and steel. Tribol. Trans. 52(1), 106–113 (2009). doi: 10.1080/10402000802180144 CrossRefGoogle Scholar
  11. 11.
    Habchi, W., Bair, S., Vergne, P.: On friction regimes in quantitative elastohydrodynamics. Tribology I 58, 107–117 (2013). doi: 10.1016/j.triboint.2012.10.005 Google Scholar
  12. 12.
    Habchi, W., Eyheramendy, D., Bair, S., Vergne, P., Morales-Espejel, G.: Thermal elastohydrodynamic lubrication of point contacts using a newtonian/generalized newtonian lubricant. Tribol. Lett. 30(1), 41–52 (2008). doi: 10.1007/s11249-008-9310-9 CrossRefGoogle Scholar
  13. 13.
    Habchi, W., Eyheramendy, D., Vergne, P., Morales-Espejel, G.: A full-system approach of the elastohydrodynamic line/point contact problem. ASME J. Tribol. 130,021501, 1–10 (2008). doi: 10.1115/1.2842246 Google Scholar
  14. 14.
    Habchi, W., Eyheramendy, D., Vergne, P., Morales-Espejel, G.: Stabilized fully-coupled finite elements for elastohydrodynamic lubrication problems. Adv. Eng. Softw. 46(1), 4–18 (2012). doi: 10.1016/j.advengsoft.2010.09.010 CrossRefGoogle Scholar
  15. 15.
    Habchi, W., Vergne, P., Bair, S., Andersson, O., Eyheramendy, D., Morales-Espejel, G.E.: Influence of pressure and temperature dependence of thermal properties of a lubricant on the behaviour of circular tehd contacts. Tribol. Int. 43(10), 1842–1850 (2010). doi: 10.1016/j.triboint.2009.10.002 CrossRefGoogle Scholar
  16. 16.
    Höglund, E.: Influence of lubricant properties on elastohydrodynamic lubrication. Wear 232(2), 176–184 (1999). doi: 10.1016/S0043-1648(99)00143-X CrossRefGoogle Scholar
  17. 17.
    Jahanmir, S., Hunsberger, A., Heshmat, H.: Load capacity and durability of h-dlc coated hydrodynamic thrust bearings. J. Tribol. 133(3), 031,301 (2011). doi: 10.1115/1.4003997 CrossRefGoogle Scholar
  18. 18.
    Kalin, M., Polajnar, M.: The correlation between the surface energy, the contact angle and the spreading parameter, and their relevance for the wetting behaviour of dlc with lubricating oils. Tribol. Int. 66, 225–233 (2013). doi: 10.1016/j.triboint.2013.05.007 CrossRefGoogle Scholar
  19. 19.
    Kalin, M., Velkavrh, I., Viintin, J.: The stribeck curve and lubrication design for non-fully wetted surfaces. Wear 267(5–8), 1232–1240 (2009). doi: 10.1016/j.wear.2008.12.072 CrossRefGoogle Scholar
  20. 20.
    Kim, J.W., Yang, H.S., Jun, Y.H., Kim, K.C.: Interfacial effect on thermal conductivity of diamond-like carbon films. J. Mech. Sci. Technol. 24(7), 1511–1514 (2010). doi: 10.1007/s12206-010-0416-2 CrossRefGoogle Scholar
  21. 21.
    Liu, Y., Chen, W.W., Zhu, D., Liu, S., Wang, Q.J.: An elastohydrodynamic lubrication model for coated surfaces in point contacts. J. Tribol. 129(3), 509–516 (2007). doi: 10.1115/1.2736433 CrossRefGoogle Scholar
  22. 22.
    Liu, Y., Wang, Q.J., Zhu, D.: Effect of stiff coatings on EHL film thickness in point contacts. J. Tribol. 130(3), 031501 (2008). doi: 10.1115/1.2908908 CrossRefGoogle Scholar
  23. 23.
    Pit, R., Hervet, H., Lger, L.: Friction and slip of a simple liquid at a solid surface. Tribol. Lett. 7(2-3), 147–152 (1999). doi: 10.1023/A:1019161101812 CrossRefGoogle Scholar
  24. 24.
    Pit, R., Hervet, H., Lger, L.: Direct experimental evidence of slip in hexadecane: solid interfaces. Phys. Rev. Lett. 85(5), 980–983 (2000). doi: 10.1103/PhysRevLett.85.980 CrossRefGoogle Scholar
  25. 25.
    Reynolds, O.: On the theory of lubrication and its application to mr beuchamp tower’s experiments, including an experimental determination of the viscosity of olive oil. Philos. Trans. R Soc. 177, 157–234 (1886)CrossRefGoogle Scholar
  26. 26.
    Shamsa, M., Liu, W., Balandin, A., Casiraghi, C., Milne, W., Ferrari, A.: Thermal conductivity of diamond-like carbon films. Appl. Phys. Lett. 89(16), 161921 (2006). doi: 10.1063/1.2362601 CrossRefGoogle Scholar
  27. 27.
    Spikes, H.A.: The half-wetted bearing. Part 1: Extended reynolds equation. Proc. Inst. Mech. Eng. J J. Eng. Tribol. 217(1), 1–14 (2003). doi: 10.1243/135065003321164758 CrossRefGoogle Scholar
  28. 28.
    Spikes, H.A.: The half-wetted bearing. part 2: Potential application in low load contacts. Proc. Inst. Mech. Eng. J J. Eng. Tribol. 217(1), 1–14 (2003). doi: 10.1243/135065003321164776 CrossRefGoogle Scholar
  29. 29.
    Thompson, P., Troian, S.: A general boundary condition for liquid flow at solid surfaces. Nature 389(6649), 360–362 (1997). doi: 10.1038/38686 CrossRefGoogle Scholar
  30. 30.
    Tower, B.: Second report on friction experiments (experiments on the oil pressure in a bearing). Proc. Inst. Mech. Eng. pp. 58–70 (1885)Google Scholar
  31. 31.
    Wong, P., Li, X., Guo, F.: Evidence of lubricant slip on steel surface in ehl contact. Tribol. Int. 61, 116–119 (2013). doi: 10.1016/j.triboint.2012.12.009 CrossRefGoogle Scholar
  32. 32.
    Xu H. (2005) Development of a generalized mechanical efficiency prediction methodology for gear pairs. Ph.D. thesis, Graduate School of The Ohio State UniversityGoogle Scholar
  33. 33.
    Yang, P., Wen, S.: A generalized reynolds equation for non-newtonian thermal elastohydrodynamic lubrication. J. Tribol. 112(4), 631–636 (1990)CrossRefGoogle Scholar
  34. 34.
    Zhu, Y., Granick, S.: Rate-dependent slip of newtonian liquid at smooth surfaces. Phys. Rev. Lett. 87(9), 961051–961054 (2001). doi: 10.1103/PhysRevLett.87.096105 Google Scholar
  35. 35.
    Zhu, Y., Granick, S.: Limits of hydrodynamic no-slip boundary condition. Phys. Rev. Lett. 88(10), 1061021–1061024 (2002). doi: 10.1103/PhysRevLett.88.106102 Google Scholar

Copyright information

© Springer Science+Business Media New York 2013

Authors and Affiliations

  • M. Björling
    • 1
    Email author
  • W. Habchi
    • 2
  • S. Bair
    • 3
  • R. Larsson
    • 1
  • P. Marklund
    • 1
  1. 1.Division of Machine Elements, Department of Engineering Science and MathematicsLuleå University of TechnologyLuleåSweden
  2. 2.Department of Industrial and Mechanical EngineeringLebanese American UniversityByblosLebanon
  3. 3.Georgia Institute of Technology, Centre for High Pressure RheologyG.W. Woodruff School of Mechanical EngineeringAtlantaUSA

Personalised recommendations