November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Experimental and Analytical Investigation of Transient Friction Abdullah Alazemi Ph.D. Research Assistant

2 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Outline Personal Background Motivation Numerical Work Experimental Work Summary and Future Work

3 November 14, 2013 Mechanical 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: F f = τ∙A Joined METL – Jan, 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 November 14, 2013 Mechanical 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.

5 November 14, 2013 Mechanical 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

6 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Molecular Dynamic (MD) simulation Sliding friction Material: Pt-Au, Sliding velocity: 1 m/s, Load: 8 nN Load Sliding direction Si 3 N 4 tip on HOPG [Y. Hoshi et al., 2000]

7 November 14, 2013 Mechanical 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:

8 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Atomic Force Microscope (AFM) Scanning using Si tip on SiO 2 steps on Si wafer, Scanning size = 5000 nm, Scanning speed = 10 µm/s Surface topography  Backward Forward 

9 November 14, 2013 Mechanical 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.

10 November 14, 2013 Mechanical Engineering Tribology Laboratory (METL) Friction Test Rig Z-stage Ball Load cell Loading mechanism Actuator Sapphire window

11 November 14, 2013 Mechanical 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

12 November 14, 2013 Mechanical 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.