Stanford University Ph.D. Oral Defense
Department of Mechanical Engineering
Title: Shear adhesion, friction, and wear at multi-point micro- and nano-scale contacts
Speaker: Wesley Smith
Advisor: Prof. Thomas W. Kenny
Date: Wednesday, June 16th, 2010
Time: 2pm (Refreshments and snacks at 1:45pm)
Location: Allen Building (formerly CIS-X) Auditorium, Room 101
Abstract:
Building an understanding of the fundamental mechanisms that contribute to adhesion, friction, and wear at the micro- and nano-scales is vitally important to develop reliable micro-devices that involve contacting and sliding surfaces. When dimensions are reduced down to the micro- and nano-scale, the surface area-to-volume ratio increases significantly and surface forces begin to play a dominant role in adhesion and friction.
The complicated and often unreliable behavior of contacting and sliding surfaces has limited their adoption in many microelectromechanical systems (MEMS). This study examines the effects of the contact conditions on the friction forces and wear rate to enhance the current understanding of friction at the small scale and lead to the design of reliable sliding surfaces in MEMS devices.
In this presentation, I will discuss the development of a unique experimental setup where friction forces are solely responsible for the measured motion. Friction is measured between an array of single crystal silicon MEMS probe tips and a flat silicon surface. Contact between the surfaces occurs at AFM-like tips that are located at the end of compliant cantilevers. Friction force results from arrays with varying numbers of tips show that the friction forces depend heavily on the true contact area between two sliding surfaces. This work also takes a careful look at the conditions that affect the wear rate of the tips. Methods such as reducing the contact pressure per tip and allowing mechanical compliance of the contacting surface are shown to minimize the detrimental effects of wear.
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