Research Papers: Contact Mechanics

Experimental Study of Adhesive Static Friction in a Spherical Elastic-Plastic Contact

[+] Author and Article Information
A. Ovcharenko, G. Halperin

Mechanical Engineering Department, Technion, Haifa 32000, Israel

I. Etsion1

Mechanical Engineering Department, Technion, Haifa 32000, Israeletsion@technion.ac.il


Corresponding author.

J. Tribol 130(2), 021401 (Mar 03, 2008) (6 pages) doi:10.1115/1.2842247 History: Received August 09, 2007; Revised December 10, 2007; Published March 03, 2008

The elastic-plastic contact between a deformable sphere and a rigid flat during presliding is studied experimentally. Measurements of friction force and contact area are done in real time along with an accurate identification of the instant of sliding inception. The static friction force and relative tangential displacement are investigated over a wide range of normal preloads for several sphere materials and diameters. Different behavior of the static friction is observed in the elastic and in the elastic-plastic regimes of sphere deformation. It is found that at low normal loads, the static friction coefficient depends on the normal load in breach of the classical laws of friction. The presliding displacement is found to be less than 5% of the contact diameter, and the interface mean shear stress at sliding inception is found to be slightly below the shear strength of the sphere material. Good correlation is found between the present experimental results and a recent theoretical model in the elastic-plastic regime of deformation.

Copyright © 2008 by American Society of Mechanical Engineers
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Figure 5

The static friction coefficient of various diameters of copper and steel spheres versus the dimensionless normal preload P* in the elastic-plastic regime of deformations

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Figure 6

The dimensionless maximum friction force Q*max versus the dimensionless contact area As∕Ac at sliding inception for the entire population of sphere diameters and materials.

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Figure 1

Schematic representation of the experimental setup with four modules: (I) actuation module consisting of parallelogram frame (1), mechanical lever (2), piezoelectric actuator (3), and proximity probe (4); (II) friction force measurement module (5); (III) normal force module (6); and (IV) optical module (7)

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Figure 2

Static friction coefficient of a 15mm steel sphere at P*=0.98 as a function of the number of test repetitions

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Figure 3

The dimensionless friction force Q∕P versus the dimensionless relative displacement ux∕ω0 during presliding

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Figure 4

The static friction coefficient of 10mm and 15mm diameter steel and copper spheres versus the dimensionless normal preload P* in the elastic regime of deformations



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