experimental and analytical investigation of transient friction
DESCRIPTION
Experimental and Analytical Investigation of Transient Friction . Abdullah Alazemi Ph.D. Research Assistant. Outline. Personal Background Motivation Numerical Work Experimental Work Summary and Future Work. Motivation. Personal Background. Joined METL – Jan, 2013. - PowerPoint PPT PresentationTRANSCRIPT
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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.