Mechanical Engineering ETDs

Publication Date

1-28-2015

Abstract

Different forces scale differently with decreasing length scales. Van der Waals and surface tension are generally ignored at the macro scale, but can become dominant at the micro and nano scales. This fact, combined with the considerable compliance and large surface areas of micro and nano devices, can leads to adhesion in MicroElectroMechanical Systems (MEMS) and NanoElectroMechanical Systems (NEMS) - a.k.a. stiction-failure. The adhesive forces between MEMS devices leading to stiction failure are characterized in this dissertation analytically and experimentally. Specifically, the adhesion energy of poly-Si μcantilevers are determined experimentally through Mode II and mixed Mode I&II crack propagation experiments. Furthermore, the description of a high-frequency Michelson Interferometer is discussed for imaging of crack propagation of the μcantilevers with their substrate at the nano-scale and harmonic imaging of MEMS/NEMS. Van der Waals forces are also responsible for the adhesion in nonwoven carbon nanofiber networks. Experimental and modeling results are presented for the mechanical and electrical properties of nonwoven (random entanglements) of carbon nanofibers under relatively low and high-loads, both in tensions and compression. It was also observed that the structural integrity of these networks is controlled by mechanical entanglement and flexural rigidity of individual fibers as well as Hertzian forces at the fiber/fiber interface.

Keywords

Stiction Failure, Adhesion Energy, Critical Strain Energy Release Rate, MEMS, Interferometry, carbon nano foams

Degree Name

Mechanical Engineering

Level of Degree

Doctoral

Department Name

Mechanical Engineering

First Advisor

Leseman, Zayd

First Committee Member (Chair)

Shen, Yu-Lin

Second Committee Member

Sorrentino, Francesco

Third Committee Member

Hossein-Zadeh, Mani

Sponsors

NSF

Document Type

Dissertation

Language

English

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