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Research Papers: Contact Mechanics

A Model for Contact and Static Friction of Nominally Flat Rough Surfaces Under Full Stick Contact Condition

[+] Author and Article Information
D. Cohen, Y. Kligerman, I. Etsion

Mechanical Engineering Department, Technion, Haifa 32000, Israel

J. Tribol 130(3), 031401 (Jun 20, 2008) (9 pages) doi:10.1115/1.2908925 History: Received November 01, 2007; Revised February 14, 2008; Published June 20, 2008

A model for elastic-plastic nominally flat contacting rough surfaces under combined normal and tangential loading with full stick contact condition is presented. The model incorporates an accurate finite element analysis for contact and sliding inception of a single elastic-plastic asperity in a statistical representation of surface roughness. It includes the effect of junction growth and treats the sliding inception as a failure mechanism, which is characterized by loss of tangential stiffness. A comparison between the present model and a previously published friction model shows that the latter severely underestimates the maximum friction force by up to three orders of magnitude. Strong effects of the normal load, nominal contact area, mechanical properties, and surface roughness on the static friction coefficient are found, in breach of the classical laws of friction. Empirical equations for the maximum friction force, static friction coefficient, real contact area due to the normal load alone and at sliding inception as functions of the normal load, material properties, and surface roughness are presented and compared with some limited available experimental results.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Contact model of nominally flat rough surfaces

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Figure 2

The dimensionless separation, h*, versus the dimensionless normal load, P∕AnY0, for different values of plasticity index, ψ

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Figure 3

The dimensionless contact area, A0∕An, versus the dimensionless normal load, P∕AnY0, for different plasticity indices, ψ

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Figure 4

The parameters in Eq. 26 versus the plasticity index, ψ

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Figure 5

The maximum dimensionless tangential load, Qmax∕AnY0, versus the dimensionless normal load, P∕AnY0, for different plasticity indices, ψ

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Figure 6

The parameters in Eq. 27 versus the plasticity index, ψ

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Figure 7

A comparison between the maximum dimensionless tangential load (friction force at sliding inception), Qmax∕AnY0, of the present model and the KE friction model (24)

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Figure 8

The static friction coefficient, μ, versus the dimensionless normal load, P∕AnY0, for different plasticity indices, ψ

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Figure 9

The dimensionless contact area due to the normal load alone, A0∕An, and at sliding inception, As∕An, versus the dimensionless normal load, P∕AnY0, for different plasticity indices, ψ

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Figure 10

The dimensionless real mean contact pressure P*∕A0* due to the normal load alone, and P*∕As* at sliding inception versus the dimensionless normal load, P∕AnY0, for different plasticity indices, ψ

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Figure 11

The dimensionless tangential load, Qmax∕AnY0, versus the dimensionless contact area at sliding inception, As∕An, for different plasticity indices, ψ

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Figure 12

The dimensionless real contact area at sliding inception, As∕An, versus the dimensionless contact area due to the normal load alone, A0∕An, for different plasticity indices, ψ

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Figure 13

The relative increase in contact area, As∕A0, versus the plasticity index, ψ

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