Mechanical Engineering ETDs

Ryan Jamison

Publication Date

6-24-2015

Abstract

Nanoindentation is useful for evaluating the mechanical properties, such as hardness and Youngs modulus, of bulk and thin film materials. Multilayer thin films are an important subset of materials in which alternating layers of two or more materials are deposited on a substrate. Fabrication of multilayer films can result in imperfect layer geometry, particularly the flatness and thickness of each layer. Traditional nanoindentation techniques alone cannot provide insight into the microstructure of each layer. The finite element method is used to investigate the behavior of multilayer aluminum/silicon carbide thin film composites with imperfect internal geometry when subjected to various loadings. Undulating layered geometry is subjected to various loading scenarios, and the response of the structure is measured. The indentation- derived hardness and modulus are shown to be sensitive to the presence of undulating layers and the relative size of the indenter to the undulation. The amount of equivalent plastic strain in the Al layers also increases in the presence of undulating layers. These multilayer films exhibit interesting and complex mechanical behavior under indentation type loading and unloading. The derivation of Young's modulus from nanoindentation testing assumes elastic unloading. It is shown that multilayer thin films may not unload elastically, altering the indentation-derived modulus result. The cyclic behavior of the multilayer thin film is studied in relation to the influence of unloading-induced plasticity. It is found that several cycles are required to minimize unloading-induced plasticity. Lastly, the effect of indentation-induced damage on derived hardness and modulus of multilayer films is investigated.'

Keywords

FEA, Nanoindentation, Thin Films, Delamination

Degree Name

Mechanical Engineering

Level of Degree

Doctoral

Department Name

Mechanical Engineering

First Committee Member (Chair)

Massad, Jordan

Second Committee Member

Tehrani, Mehran

Third Committee Member

Tarefder, Rafiqul

Sponsors

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energys National Nuclear Security Administration under contract DE-AC04-94AL85000.'

Document Type

Dissertation

Language

English

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