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Research Papers: Contact Mechanics

Experimental Study of a Creeping Polymer Sphere in Contact With a Rigid Flat

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

Department of Mechanical Engineering, Technion, Haifa 32000, Israel

I Etsion1

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

1

Corresponding author.

J. Tribol 131(1), 011404 (Dec 04, 2008) (7 pages) doi:10.1115/1.3002330 History: Received May 29, 2008; Revised September 21, 2008; Published December 04, 2008

The creep of a polymer sphere contacting a rigid flat under a constant normal load is investigated experimentally. An optical technique is used to observe in situ the evolution of the contact area while the increase of contact interference is measured simultaneously. The experimental results obtained with polytetrafluoroethylene (PTFE) spheres of different diameters pressed against a sapphire flat under different normal loads are presented, and the effect of sphere diameter and normal load on the creep of the contact parameters is discussed. The present experimental study validates recently published theoretical results of a contact model for a creeping sphere and a rigid flat showing that a universal similarity solution exists for the dimensionless creep interference and dimensionless creep contact area as functions of the dimensionless time.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic description of a deformable sphere and a rigid flat (the original undeformed sphere is presented by the dashed line)

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Figure 2

Schematic representation of the experimental setup: parallelogram frame (1), proximity probe (2), rigid lever (3), normal loading module (4), and optical module (5)

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Figure 3

PTFE rods with spherical tip specimens

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Figure 4

3D surface images of : (a) the sapphire flat (scan of 180×240 μm, ×25 magnification) and (b) a 10 mm diameter spherical specimen (scan of 90×120 μm, ×50 magnification)

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Figure 5

Typical contact area images of a 5 mm diameter PTFE sphere: (a) at the end of the normal loading process (P=5 N) and (b) after 195 s under a load of 5 N

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Figure 6

Typical test results of interference, contact area, and normal load of a 5 mm PTFE sphere as a function of global time (P=2.3 N)

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Figure 7

Creep interference for 3 mm, 5 mm, and 10 mm diameter PTFE spheres under different normal loads as a function of time

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Figure 8

Creep contact area for 3 mm, 5 mm, and 10 mm diameter PTFE spheres under different normal loads as a function of time

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Figure 9

Dimensionless creep interference as a function of dimensionless time for the entire population of sphere diameters and normal loads (tr=20 s)

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Figure 10

Dimensionless creep contact area as a function of dimensionless time for the entire population of sphere diameters and normal loads (tr=20 s)

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Figure 11

The ratio of the creep contact area, Acr, over πRωcr as a function of dimensionless time for the entire population of sphere diameters and normal loads

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