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Research Papers: Contact Mechanics

Multiscale Analysis on Two Dimensional Nanoscale Sliding Contacts of Textured Surfaces

[+] Author and Article Information
Ruiting Tong1

School of Mechanical Engineering,  Northwestern Polytechnical University, Xi’an 710072, P. R. C.tongruiting@nwpu.edu.cnMechanics of Materials Research Group, Department of Engineering,  University of Leicester, University Road, Leicester LE1 7RH, UKtongruiting@nwpu.edu.cn

Geng Liu, Tianxiang Liu

School of Mechanical Engineering,  Northwestern Polytechnical University, Xi’an 710072, P. R. C.Mechanics of Materials Research Group, Department of Engineering,  University of Leicester, University Road, Leicester LE1 7RH, UK

1

Corresponding author.

J. Tribol 133(4), 041401 (Oct 06, 2011) (13 pages) doi:10.1115/1.4004759 History: Received July 19, 2010; Revised June 25, 2011; Published October 06, 2011; Online October 06, 2011

Nanoscale sliding contacts are the major factors that influence the friction and result in wear in micro/nanoelectromechanical systems. Many experimental studies indicated that some surface textures could help improve the contact characteristics and reduce friction forces. However, the experimental results may be biased, due to the contamination of the sample surface or substantial defects in the materials. Numerical methods, such as continuum mechanics, meet great challenges when they are applied at length of nanoscale, and the time cost of molecular dynamics (MD) simulation can be extremely high. Therefore, multiscale method, which can capture atomistic behaviors in the region underlying micro/nano physical processes by MD simulations and models other regions by continuum mechanics, offers a great promise. Coupling MD simulation and finite element method, the multiscale method is used to investigate two dimensional nanoscale sliding contacts between a rigid cylindrical tip and an elastic substrate with textured surface, in which adhesive effects are considered. Two series of nanoscale surface textures with different asperity shapes, different asperity heights, and different spacings between asperities are designed. For different heights of asperities or different spacings between asperities, average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces are compared to observe how these parameters influence friction characteristics; then, the optimal asperity height or spacing is discovered. Through the average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces comparisons between smooth surface and textured surfaces, a better shape is advised to indicate that asperity shape plays an important role in friction force reduction. The influences of the indentation depth and radius of the rigid cylindrical tip are analyzed to find out the sensitivity of surface textures to these two parameters. Effects of sliding speed on the characteristics of nanoscale sliding contacts are also discussed. The results show that, with proper asperity height and proper spacing between asperities, surface textures can reduce friction forces effectively. Coefficients of friction (COFs) of all the cases are calculated and compared. Some negative COFs caused by significant adhesive effects are discovered, which are different from traditional macroscopic phenomena.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Two dimensional nanoscale sliding contact between a rigid cylindrical tip and an elastic substrate

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Figure 2

Overlap region and the idea of multiscale method

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Figure 3

Flow chart for multiscale contact analysis

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Figure 4

Topographies of textured surfaces

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Figure 5

Depth profile of the textured surface

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Figure 6

von Mises stresses along the centerline of the model

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Figure 7

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different asperity heights (surface I, 9 asperities)

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Figure 8

Atoms distributions during the sliding process (surface I, 9 asperities, 2 layers)

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Figure 9

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different asperity heights (surface II, 9 asperities)

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Figure 10

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different asperity spacings (surface I, 4 layers)

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Figure 11

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different asperity spacings (surface II, 4 layers)

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Figure 12

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different texture shapes (7 asperities, 4 layers)

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Figure 13

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different texture shapes (9 asperities, 4 layers)

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Figure 14

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different indentation depths (surface I, 7 asperities, 4 layers)

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Figure 15

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different indentation depths (surface II, 7 asperities, 4 layers)

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Figure 16

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different radii (surface I, 9 asperities, 4 layers)

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Figure 17

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different radii (surface II, 9 asperities, 4 layers)

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Figure 18

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different sliding speeds (surface I, 9 asperities, 4 layers)

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Figure 19

Comparisons of average potential energy, normal forces, mean normal forces, friction forces, and mean friction forces with different sliding speeds (surface II, 9 asperities, 4 layers)

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