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Research Papers

Rough Surface Normal Nanocontact Stiffness: Experimental Measurements and Rough Surface Contact Model Predictions

[+] Author and Article Information
Jungkyu Lee

Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801;

Ali Beheshti

Department of Mechanical Engineering,
Lamar University,
Beaumont, TX 77710

Andreas A. Polycarpou

Department of Mechanical
Science and Engineering,
University of Illinois at Urbana-Champaign,
Urbana, IL 61801;
Department of Mechanical Engineering,
Texas A&M University,
College Station, TX 77843
e-mail: apolycarpou@tamu.edu

1Present address: Seagate Technology, LLC, Minneapolis, MN 55416.

2Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received November 19, 2016; final manuscript received December 15, 2016; published online January 12, 2017. Editor: Yonggang Huang.

J. Appl. Mech 84(3), 031006 (Jan 12, 2017) (9 pages) Paper No: JAM-16-1568; doi: 10.1115/1.4035524 History: Received November 19, 2016; Revised December 15, 2016

This work presents experimental contact stiffness measurements for various thin films as well as homogenous materials through pressing a flat punch onto a nominally flat rough surface. These materials are typically used in micro/nano technological applications with thickness of the order of few nanometers. The experimental contact stiffness results are compared with predictions by different statistical rough surface contact models to assess their predictive accuracy for thin-film applications and, in addition, to get better insight to the physics of the contact. It is observed that rough surface contact models that account for asperity interaction show good agreement with the experimental results of the thin-layered specimens contact response. This indicates the importance of accounting for asperity interaction in surface roughness contact modeling of relatively smooth thin-film materials. It is verified that interfaces with compliant films on stiff substrates as well as homogeneous materials compare relatively well with statistical models accounting for asperity interactions.

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References

Figures

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Fig. 1

(a) SEM image of flattened diamond indenter tip (punch) fabricated with focused ion beam (flat area is 21.21 μm2), (b) typical optical microscopic image of samples 1–4 with nominal pedestal area of 88,000 μm2, and (c) optical microscopic image of sample 5 with nominal pedestal area of 40,000 μm2

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Fig. 2

Schematic of cross section of thin-layered films: (a) samples 1 and 2 and (b) sample 5

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Fig. 3

AFM roughness images of the samples measured at 10 μm × 10 μm scan size: (a) smooth DLC on AlTiC, (b) rough DLC on AlTiC, (c) smooth AlTiC, (d) rough AlTiC, and (e) Ti on Au (refer to Table 1)

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Fig. 4

Typical load–displacement curve of flat punch indentation

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Fig. 5

Typical load–displacement curves of flat punch indentation for sample 1 (smooth DLC on AlTiC) obtained at (a) 1 mN, (b) 3 mN, (c) 5 mN, and (d) 7 mN contact forces

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Fig. 6

Measured contact stiffness values versus contact stiffness predictions using various contact models: (a) sample 1—smooth DLC layer on AlTiC stiffer substrate and (b) sample 2—rough DLC layer on AlTiC stiffer substrate. Measured stiffness values are the average of five measurements for each contact force with maximum standard deviation of 0.174 MN/m (a) and 0.153 MN/m (b) at the highest load. Measured dimensionless contact stiffness versus dimensionless contact load compared directly with KE model stiffness [6] for (c) sample 1 and (d) sample 2.

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Fig. 7

Measured contact stiffness values versus contact stiffness predictions using various contact models: (a) sample 3—smooth AlTiC and (b) sample 4—rough AlTiC. Measured stiffness values are the average of five measurements for each contact force with maximum standard deviation of 0.352 MN/m (a) and 0.159 MN/m (b) at the highest load. Measured dimensionless contact stiffness versus dimensionless contact load compared directly with the KE model stiffness results [6] for (c) sample 3 and (d) sample 4.

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Fig. 8

Measured contact stiffness values versus contact force compared with various contact models for sample 5, stiffer layer on softer “substrate” (Ti/Au). Measured stiffness values are the average of five measurements for each contact force with maximum standard deviation of 0.140 MN/m at the highest load.

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