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Research Papers: Friction & Wear

Junction Growth and Energy Dissipation at the Very Early Stage of Elastic-Plastic Spherical Contact Fretting

[+] Author and Article Information
A. Ovcharenko

Department of Mechanical Engineering, Technion, Haifa 32000, Israel

I. Etsion1

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

1

Corresponding author.

J. Tribol 131(3), 031602 (May 26, 2009) (8 pages) doi:10.1115/1.3123345 History: Received December 21, 2008; Revised March 20, 2009; Published May 26, 2009

The contact area, friction force, and relative displacement evolution at the very early stage of fretting are investigated experimentally. Copper and steel spheres of various diameters are loaded against a hard sapphire flat by a range of normal loads deep into the elastic-plastic regime of deformation. A reciprocating tangential loading is then applied with a maximum loading below the static friction to avoid gross slip. Real-time and in situ direct measurements of the contact area, along with accurate measurements of the friction force and relative displacement, reveal substantial junction growth and energy dissipation mainly in the first loading cycle. The so-called “slip amplitude” is found to be attributed to residual tangential plastic deformation rather than to interfacial slip. Elastic shake-down is observed for the 2.5% hardening steel spheres while plastic shake-down is observed in the case of the elastic perfectly-plastic copper spheres.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 2

Schematic presentation 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). (IV) Optical module (7).

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Figure 10

The dimensionless junction growth A/A0 versus the dimensionless normal preload P∗ for the first positive tangential loading in comparison with one and nine tangential loading cycles of different diameters copper spheres.

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Figure 9

The dimensionless junction growth A/A0 versus the number of tangential loading cycles of different diameters copper and steel spheres under various normal loads

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Figure 6

Contact area evolution as a function of the reciprocating friction force for the same four cases presented in Fig. 5

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Figure 5

Friction loops of the first three cycles of reciprocating tangential loading: copper spheres having diameters of (a) 10 mm (P∗=50) and (b) 5 mm (P∗=100); steel spheres with diameters of (c) 5 mm (P∗=50) and (d) 3 mm (P∗=100)

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Figure 4

Time variations of the contact area A, friction force Q, and relative displacement ux during reciprocating tangential loading of a copper sphere with 5 mm diameter under a normal load P=60 N(P∗=150)

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Figure 3

Stress strain diagrams for the (a) copper and (b) steel rods under a standard tensile test

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Figure 1

Characteristic friction loops for different fretting regimes: (a) stick, (b) partial slip, and (c) gross slip corresponding to different slip amplitudes As

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Figure 8

The dimensionless junction growth A/A0 versus the dimensionless normal preload P∗ for the first positive tangential loading of different diameters copper and steel spheres

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Figure 7

Contact area images depicting substantial junction growth and plastic deformation in a 3 mm diameter copper sphere under P∗=273: in situ images (a) after the first positive loading and (b) after nine reciprocating cycles; (c) ex situ image after nine reciprocating cycles

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