Date of Award

8-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Materials Science and Engineering

Major Professor

George M. Pharr

Committee Members

Warren C. Oliver, Dayakar Penumadu, Easo P. George

Abstract

The purpose of this work is to further develop experimental methodologies using flat punch nanoindentation to measure the constitutive behavior of viscoelastic solids in the frequency and time domain. The reference material used in this investigation is highly plasticized polyvinylchloride (PVC) with a glass transition temperature of -17 degrees Celsius. The nanoindentation experiments were conducted using 103 and 983 micron diameter flat punches. For comparative purposes, the storage and loss modulus obtained by dynamic mechanical analysis are also presented. Over the frequency range of 0.01 to 50 Hz, the storage and loss modulus measured using nanoindentation and uniaxial compression are shown to be in excellent agreement. The creep compliance function predicted from nanoindentation data acquired in the frequency domain is also found to be in excellent agreement over two decades in time with the creep compliance function measured using a constant stress test performed in uniaxial compression. A constraint factor of 1.55 is found to overlay the creep compliance function measured by nanoindentation in the time domain with the creep function measured in uniaxial compression.

A new method is proposed to determine the elastic modulus and residual stress of free-standing thin films based on nanoindentation techniques. The experimentally measured stiffness-displacement response is applied to a simple membrane model that assumes the film deformation is dominated by stretching as opposed to bending. Experimental verification of the method is demonstrated for Al/0.5 weight percent Cu films nominally 22 microns wide, 0.55 microns thick, and 150, 300, and 500 microns long. The estimated modulus for the four freestanding films matches the value measured by electrostatic techniques within 2 percent, and the residual stress within 19.1percent. The difference in residual stress can be completely accounted for by thermal expansion and a modest change in temperature of 3 degrees Celsius.

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