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Research Papers: Micro-Nano Tribology

Study on Contact Characteristic of Nanoscale Asperities by Using Molecular Dynamics Simulations

[+] Author and Article Information
Tianxiang Liu

School of Mechatronic Engineering, Northwestern Polytechnical University, 710072 Xi’an, China; Institute of Mechanics and Computational Mechanics, Leibniz University of Hannover, 30167 Hannover, Germany

Geng Liu1

School of Mechatronic Engineering, Northwestern Polytechnical University, 710072 Xi’an, Chinanpuliug@nwpu.edu.cn

Peter Wriggers

Institute of Mechanics and Computational Mechanics, Leibniz University of Hannover, 30167 Hannover, Germany

Shijun Zhu

School of Mechatronic Engineering, Northwestern Polytechnical University, 710072 Xi’an, China

1

Corresponding author.

J. Tribol 131(2), 022001 (Mar 03, 2009) (10 pages) doi:10.1115/1.3063812 History: Received January 18, 2008; Revised October 14, 2008; Published March 03, 2009

The nanoscale contacts, which play a key role in nanotechnology and micro-/nanoelectromechanical systems, are fundamentally important for a wide range of problems including adhesion, contact formation, friction and wear, etc. Because continuum contact mechanics has limitations when it is applied at length of nanoscale, molecular dynamics (MD) simulations, which can investigate internal physical mechanisms of nanostructures by atomic motions in detail, become one of the most promising approaches for investigating mechanical behaviors of contacts in nanoscale. First, contacts between rigid cylindrical probes with different radii and an elastic half-space substrate are studied by using MD simulations with the assistance of the classical Lennard-Jones potential. For contacts without adhesion, the relationship between the applied force and the contact half-width is analyzed. The von Mises stress distributions are then discussed. For contacts with adhesion, the phenomena of the jump-to-contact, the break-off contact, and the hysteresis are observed. The pressure distributions and the von Mises stress contours in the contact region agree with the existing solutions. Second, the effects of the surface topography on adhesive contacts are studied by using MD simulations with the embedded atom method potential. The adhesive contact mechanical characteristic of a series of asperities with different shapes, different sizes, and different numbers on contacting surfaces are discovered and compared. The results show that the surface topography is one of the major factors, which may influence the contact behaviors between the interfaces of nanoscale components.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic illustration of initial atomic configuration of contact system between the rigid cylindrical probe and the elastic substrate (the initial minimum gap is 3.0r0 and atom A is considered as the apex of the probe)

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Figure 2

External force-contact half-width relationship for the contacts without adhesion

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Figure 3

Contact regions without adhesion when the probe displacement is 3.030r0(R=10r0): (a) atomic configurations and (b) von Mises stress contours (in the units of ε⋅r0−3)

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Figure 4

Contacts with adhesion when the probes approach to and withdraw from the substrate (R=10r0): (a) relationship between the contact force and the probe displacement and (b) relationship between the mean square displacement and the probe displacement

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Figure 5

Atomic configurations of the contacts with adhesion (R=10r0): (a) jump-to-contact and (b) break-off contact

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Figure 6

Pressure distributions at the moments of jump-to-contact and break-off contact (R=10r0)

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Figure 7

Pressure distributions of the contacts with adhesion when the contact force is zero

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Figure 8

von Mises stress contours (in the units of ε⋅r0−3) of the contacts with adhesion (Case 1: jump-to-contact; Case 2: contact state under the zero force; Case 3: contact state when the probe displacement is 3.360r0; Case 4: break-off contact): (a) R=10r0, (b) R=20r0, and (c) R=30r0

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Figure 9

Maximum von Mises stresses in the substrate of the adhesive contacts when the probe is approaching to the substrate

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Figure 10

von Mises stress distributions along the depth of the centerline of the probe when the probe displacement is 3.360r0: (a) contacts without adhesion and (b) contacts with adhesion

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Figure 11

Different contacting states of the adhesive contacts with different shapes of asperities: (a) surface I, (b) surface II, and (c) surface III

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Figure 12

Displacement-load relationship of the adhesive contacts with different shapes of asperities: (a) surface I, (b) surface II, and (c) surface III

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Figure 13

Different contacting states of the adhesive contacts with different sizes and numbers of asperities: (a) surface I and (b) surface II

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Figure 14

Displacement-load relationship of the adhesive contacts with different sizes and numbers of asperities: (a) surface I and (b) surface II

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