November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Experimental and Analytical Investigation of Transient Friction Abdullah Alazemi Ph.D. Research Assistant
Feb 23, 2016
November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Experimental and Analytical Investigation of Transient
Friction
Abdullah AlazemiPh.D. Research Assistant
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Outline
• Personal Background• Motivation• Numerical Work• Experimental Work• Summary and Future Work
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Motivation• Lack of clearly and completely understanding of the friction nature and behavior• Dry friction of a particular surface is caused by normal force, adhesion force, and
interlocking between asperities .• Bowden and Tabor model: Ff = τ∙A
• Joined METL – Jan, 2013.• M.S. in Mechanical Engineering, Kuwait University (June, 2009)- GPa 4.0• B.S. in Mechanical Engineering, Kuwait University (June, 2006)- GPa 3.85
Personal Background
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Numerical Work
• MD simulation represents friction on a single asperity.
• Finite element modeling can be used to study friction on a larger scale where each asperity force interaction is taken from MD simulation.
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Molecular Dynamic (MD) simulation
• Nano-indentation of a single asperity• Measuring adhesion forces during approaching and separating• Approaching and separating speed: 1 m/s
1
2-10 -5 0 5 10 15 20
-200
-150
-100
-50
0
50
100
150
Displacement (Angstrom)
Con
tact
For
ce (n
N)
LoadingUnloading
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Molecular Dynamic (MD) simulation
• Sliding friction • Material: Pt-Au,• Sliding velocity: 1 m/s,• Load: 8 nN
Load
Sliding direction
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1-20
-15
-10
-5
0
5
10
15
20
Displacement (nm)
Fric
tion
Forc
e (n
N)
ForwardBackward
Si3N4 tip on HOPG[Y. Hoshi et al., 2000]
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Atomic Force Microscope (AFM)
• Experimentally study single asperity friction• Tip diameter: 5 µm - 10 nm• A laser beam that is reflected off the
cantilever into a photodiode monitors the bending and twisting of the cantilever.
Source: www.appnano.com
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Atomic Force Microscope (AFM)
• Scanning using Si tip on SiO2 steps on Si wafer,
• Scanning size = 5000 nm,• Scanning speed = 10 µm/s
Surface topography0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
-100
-50
0
50
100
Distance in X direction (m)
Late
ral F
orce
Sig
nal (
mV)
ForwardBackward
BackwardForward
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Friction Test Rig
1. Study friction on the micro-scale,
2. Small ball diameter (about 5-1 mm),
3. Small normal load (about 1 N),
4. Using actuator with small linear displacement increment (about 100 nm),
5. Perform the experiment in vacuum conditions.
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Friction Test Rig
Z-stage
Ball
Load cell
Load cell
Loading mechanism Actuator
Sapphire window
Sapphire window
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Measurements of the Real Contact Area (RCA)
1. Optical observation technique [A. Ovcharenko et al., 2006]
2. Using Optical Profiling System
Before applying load After applying load
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November 14, 2013Mechanical Engineering Tribology Laboratory (METL)
Summary and Future Work
• Transient friction experimental investigations can be done on the Nano-scale using AFM and on the Micro-scale using Friction test rig.
• Transient friction analytical investigations can be done on the Nano-scale using MD simulation and then connected to FE modeling to investigate Micro-scale friction.
• Future AFM experiments are friction on smooth substrate and substrate with low roughness.
• Future MD simulations are sliding friction of different surface geometries, normal loads, and speeds.