Research ArticleSURFACE SCIENCE

Boundary lubrication of heterogeneous surfaces and the onset of cavitation in frictional contacts

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Science Advances  25 Mar 2016:
Vol. 2, no. 3, e1501585
DOI: 10.1126/sciadv.1501585
  • Fig. 1 MD simulation setup.

    The fluid is confined between two surfaces. There is no slip on the top surface and the bottom surface is patterned into slipping and sticking domains.

  • Fig. 2 Profiles of dimensionless velocity Embedded Image across the normalized film thickness Embedded Image for the heterogeneous system.

    (A to C) Sticking domain (A), slipping domain (B), and corresponding normalized slip length Embedded Image (C) along the shearing direction Embedded Image .

  • Fig. 3 Dimensionless pressure distribution along the shearing direction.

    Points indicate MD results; the line is the result from the hydrodynamic model. Reference conditions are u2 = 30 m/s , h = 5 nm , L = 95.91 nm , and pentane viscosity η = 0.50 mPa•s at an external applied pressure Pext = 250 MPa . The legend indicates variations of these values. (Inset) Probability distribution of the dimensionless pressure in the presence of N randomly distributed slipping and sticking domains along the shearing direction. Points are obtained from MD simulations with L = 191.8 nm and for six realizations each of N = 24 (λ = 8 nm), N = 48 (λ = 4 nm) , and N = 192 (λ = 1 nm) . Scaling with Embedded Image collapses MD data to a single Gaussian distribution with standard deviation Embedded Image.

  • Fig. 4 Snapshot of a cavitation bubble under shearing and corresponding dimensionless pressure distribution along the shearing direction.

    The hydrodynamic model is applied to the noncavitated domains λ1 and λ2, whose extents are obtained from MD results with the condition P > 0. System parameters are u2 = 10 m/s, h = 5.5 nm, L = 143.9 nm , and Pext = 1 MPa. At this pressure, the fluid (n-decane) has viscosity η = 0.30 mPa•s .

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/3/e1501585/DC1

    Discussion S1. Analytical solution of the Reynolds equation with slip and a cavitated zone.

    Discussion S2. Pressure excursion for random alternations of slip.

    Fig. S1. Pressure excursion for two-dimensional slip patterns.

    Movie S1. Formation of a cavitation bubble under shearing.

    Reference (34)

  • Supplementary Materials

    This PDF file includes:

    • Discussion S1. Analytical solution of the Reynolds equation with slip and a cavitated zone.
    • Discussion S2. Pressure excursion for random alternations of slip.
    • Fig. S1. Pressure excursion for two-dimensional slip patterns.
    • Legend for movie S1.
    • Reference (34)

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    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.avi format). Formation of a cavitation bubble under shearing

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