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RESEARCH PAPERS

Generation of Composite Surfaces With Bimodal Distribution and Contact Analysis for Optimum Tribological Performance

[+] Author and Article Information
Tae Wan Kim

Nanotribology Laboratory for Information Storage and MEMS/NEMS (NLIM), The Ohio State University, 650 Ackerman Road, Suite 255, Columbus, OH 43202-1107

Bharat Bhushan1

Nanotribology Laboratory for Information Storage and MEMS/NEMS (NLIM), The Ohio State University, 650 Ackerman Road, Suite 255, Columbus, OH 43202-1107bhushan.2@osu.edu

1

Corresponding author.

J. Tribol 128(4), 851-864 (Jun 07, 2006) (14 pages) doi:10.1115/1.2345408 History: Received October 27, 2005; Revised June 07, 2006

Most contact analyses assume that the surface height distributions follow a single modal distribution. However, there are many surfaces with multi-modal roughness distributions, e.g., magnetic particulate tape, super alloys with precipitates, and hydrophobic leaves. In this study, an algorithm is developed to generate bimodal surfaces by superimposing particles with radii following a Gaussian distribution on a Gaussian rough surface. Two different cases are presented to produce composite surfaces with particles; the first case is particles sitting on a surface and the other case is particles sitting on the mean plane of a surface. Statistical analysis is carried out for the generated bimodal surfaces to study the effect of the bimodal roughness distributions on the surface’s probability density function shapes. Contact analysis is also conducted to identify optimum bimodal roughness distributions for low friction, stiction, and wear. It is assumed that particles and matrix have uniform elastic properties as it is a reasonable assumption in some applications such as magnetic tapes. Variation of fractional contact area, maximum contact pressure, and relative meniscus force as functions of relative mean radius and relative standard deviation of particles are studied for different values of particle densities. It is found that bimodal surfaces with lower particle density are beneficial to low friction and stiction, whereas those with higher particle density are beneficial to low wear. Relative mean radii of particles of 2–3 in bimodal surfaces with particles sitting on surface and 3–5 in bimodal surfaces with particles sitting on the mean plane of surface are desirable for low friction, stiction, and wear.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Examples of surface with bimodal roughness distribution, (a) magnetic tape, (b) Waspaloy’s bimodal precipitation distribution, (c) hydrophobic leaf (lotus), and (d) contaminants caught into interface

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Figure 2

Three-dimensional surface of computer-generated Gaussian surface with σs=0.08μm, βs*=0.5μm, Sks=0, Ks=3

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Figure 3

Two-dimensional schematic diagram of a composite surface generated by superimposing particles with radii following a Gaussian distribution on a random Gaussian surface with (a) particles sitting on the rough surface and (b) the centers of the particles aligned on the mean plane of the rough surface

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Figure 4

Two-dimensional and three-dimensional diagrams of generated bimodal surface with (a) particles sitting on the surface and (b) particles sitting on the mean plane of the surface (σs=0.08μm, βs*=0.5μm, Sks=0, Ks=3) for two different particle densities

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Figure 6

Roughness distribution parameters σf∕σs and βf* of bimodal surfaces with (a) particles sitting on the surface and (b) particles sitting on the mean plane of the surface

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Figure 7

Three-dimensional diagram of contact pressure for bimodal surfaces with (a) particles sitting on the surface and (b) particles sitting on the mean plane of the surface

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Figure 8

Fractional contact area, maximum pressure, and relative meniscus force as a function of rp¯∕σs and σp∕σs for bimodal surfaces with particles sitting on the surface with (a)σp∕σs=1.0 and (b)rp¯∕σs=3 under Pn=500kPa

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Figure 9

Fractional contact area, maximum pressure, and relative meniscus force as a function of rp¯∕σs and σp∕σs for bimodal surfaces with particles sitting on the mean plane of the surface with (a) σp∕σs=1.0 and (b) rp¯∕σs=3 under Pn=500kPa (scale changed)

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Figure 10

Schematic of the effect of particle distribution on friction and wear

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