Download - Experimental and Analytical Investigation of Transient Friction

November 14, 2013Mechanical Engineering Tribology Laboratory (METL)

Experimental and Analytical Investigation of Transient

Friction

Abdullah AlazemiPh.D. Research Assistant

2


Outline

• Personal Background• Motivation• Numerical Work• Experimental Work• Summary and Future Work

3


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

4


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.

5


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

6


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]

7


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

8


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

9


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.

10


Friction Test Rig

Z-stage

Ball

Load cell

Load cell

Loading mechanism Actuator

Sapphire window

Sapphire window

11


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

12


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.