Research Papers: Contact Mechanics

Motion Analysis of Micropart in Dry Friction Environment Due to Surface Excitation Considering Microscale Forces

[+] Author and Article Information
M. Rizwan

Mechanical and Aerospace Engineering Department,  The University of Texas at Arlington, Arlington, Texas 76019mohsin.rizwan@mavs.uta.edu

P. S. Shiakolas

Mechanical and Aerospace Engineering Department,  The University of Texas at Arlington, Arlington, Texas 76019shiakolas@uta.edu

J. Tribol 133(4), 041405 (Oct 17, 2011) (12 pages) doi:10.1115/1.4004455 History: Received October 18, 2010; Accepted June 06, 2011; Published October 17, 2011; Online October 17, 2011

This manuscript investigates the motion of a micropart on a dry nonlubricated controlled deformable surface considering the dynamically changing microforces while in contact with the surface. The motion analysis of a micropart on a flexible surface under controlled deformation is the first step to initiate feasibility of a micromanipulation device. At the micro/nanoscale, the surface force of attraction becomes more significant than the inertia force; thus motion analysis requires estimating and accommodating these forces in a dynamic model. The model considers microscale forces and surface roughness conditions (asperity deformation), while dynamically evaluating the friction coefficient and attraction force due to the dynamic asperity deformation as the micropart moves on a controlled deformation active surface. The parameters considered in the model include the micropart mass and size, the relative roughness between the micropart and surface, the surface and micropart material, and input actuator frequency, stroke, and deformation profile. The simulation results indicate that predictable micropart motion could be achieved but only within a certain range of input actuator frequencies. At lower frequencies no motion is possible while at higher frequencies the micropart detaches from the surface. The understanding of the effects of the microforces on the dynamic model and micropart motion would pave the way towards controlled micropart translocation and manipulation employing a flexible surface for microassembly or for processes requiring controlled micropart handling for heterogeneous microdevice mass production.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Schematic of the deformation of a surface and the resultant micropart motion

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Figure 2

Acceleration (ytt ) and velocity (yt ) of the micropart while on the flexible surface; subscripts α and β represent the corresponding components along and perpendicular to the surface respectively. (a) Acceleration and resultant force on the micropart. (b) Velocity decomposed along and perpendicular to the surface.

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Figure 3

Rough surface in contact with flat surface. Dotted line shows the original asperity profile where the solid line shows the profile after compression. The compressed asperity has profile Z = f(r).

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Figure 4

Forces acting on micropart and surface

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Figure 5

Friction logic flow chart

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Figure 6

Estimated applied load as function of separation distance and curve fit corresponding to steel surfaces with σ = 20 nm and ψ = 2.5

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Figure 7

Separation distance versus forces acting on the micropart. σ = 20 nm, Δγ = 1 J/m2 , H = 1 GPa, ɛ = 0.4, An  = 10− 8 m2 . (a) Separation distance as function of contact and attraction force, the graphs intersect at 73 nm. (b) Separation distance versus applied load, minimum point marked on the applied force graph represents the maximum pull off force required to separate two surfaces.

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Figure 8

Flow chart of simulation logic flow for assessing micropart motion on a deformable surface

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Figure 9

Global and local coordinate systems. (a) Original surface with micropart resting on it. (b) Tilting surface. (c) Surface under controlled deformation.

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Figure 10

Schematic of micropart on flat surface with acceleration input along the surface

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Figure 11

(a) Separation distance versus applied load. (b) Friction force versus separation distance. (c) Coefficient of friction (COF) versus separation distance.

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Figure 12

(a) Friction force during actuator movement. (b) Micropart velocity during complete stroke.

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Figure 13

Distance traveled by micropart as function of actuator input frequency

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Figure 14

Distance traveled by micropart as function of actuator input frequency (actuator stroke 250 μ m and surface energy 1 J/m2 remain constant)




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