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Research Papers: Friction & Wear

A Computational Study of Dry Static Friction Between Elastoplastic Surfaces Using a Statistically Homogenized Microasperity Model

[+] Author and Article Information
Bhargava Sista

Department of Mechanical and
Materials Engineering,
University of Cincinnati,
Cincinnati, OH 45221
e-mail: sistasa@mail.uc.edu

Kumar Vemaganti

Associate Professor of Mechanical Engineering
Department of Mechanical and
Materials Engineering,
University of Cincinnati,
Cincinnati, OH 45221
e-mail: Kumar.Vemaganti@uc.edu

1Corresponding author.

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received June 5, 2014; final manuscript received October 23, 2014; published online December 12, 2014. Assoc. Editor: James R. Barber.

J. Tribol 137(2), 021601 (Apr 01, 2015) (11 pages) Paper No: TRIB-14-1126; doi: 10.1115/1.4028998 History: Received June 05, 2014; Revised October 23, 2014; Online December 12, 2014

Friction is a complex phenomenon that arises from the interaction of deforming surface microasperities and adhesive forces at very small length scales. In this work, we use a computational model to understand the effects of various physical parameters on the friction response between two similar linearly elastic-perfectly plastic surfaces. The main ingredients of the computational model are a statistical model of the surface based on a Gaussian autocorrelation function (ACF), a parametric representation of the normal and shear responses of a single microasperity, and a statistical homogenization procedure to compute the overall friction response. The surfaces are assumed to be isotropic in nature. We employ this computational model to develop constitutive relationships for the friction force and coefficient of friction for Aluminum 6061 and stainless steel surfaces. We study the effects of various quantities such as surface roughness, material properties, normal load, and adhesive forces on the overall friction response. Our results show that the model is able to capture a wide variety of friction responses. Our results also suggest that the root mean squared (RMS) roughness of the surface alone is insufficient to describe the friction characteristics of a surface, and that an additional parameter is needed. We propose one such parameter, the aspect ratio, which is the ratio of the RMS roughness to the correlation length.

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Figures

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Fig. 1

Sum surface of two interacting rough surfaces

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Fig. 2

Schematic of contact between the sum surface and a rigid flat plane under the action of both normal and shear forces

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Fig. 3

The von Mises stress contours in a linearly elastic-perfectly plastic asperity at three stages of its deformation: (a) no yielding, (b) subsurface yielding, and (c) surface yielding. In the areas corresponding to the lightest shade of gray, the von Mises stress has reached the yield strength of the material.

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Fig. 4

The variation of the expected macroscopic (a) shear stress and (b) coefficient of friction with increasing normal load between the Al 6061 surfaces

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Fig. 5

Surface profiles of Al 6061 surfaces generated with different RMS roughness and aspect ratios

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Fig. 6

The variation of expected coefficient of friction with increasing normal load between Al 6061 the surfaces with three different RMS roughness values for σ/λ ratio = (a) 0.005 and (b) 0.01. Note that the three responses overlap.

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Fig. 7

Total number of asperities and fractions of asperities undergoing different types of deformations changing with normalized separation between the Al 6061 surfaces, at different aspect ratios and RMS roughness

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Fig. 8

The variation of coefficient of friction with increasing normal stress for a stainless steel surface at three different RMS roughness values. The aspect ratio σ/λ is 0.005.

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Fig. 9

The variation of (a) normal and (b) shear stresses with separation between Al 6061 surfaces with three different surface energies at σ = 2.5 μm and σ/λ = 0.01

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Fig. 10

The variation of coefficient of friction with normal stress between Al 6061 surfaces with three different surface energies at σ = 2.5 μm and σ/λ = 0.01

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