Mechanical Engineering ETDs

Publication Date

7-1-2016

Abstract

Polymeric materials exhibit a viscoelastic (time-dependent) behavior, which is characterized using creep, stress-relaxation, and dynamic mechanical analysis (DMA) tests at different temperatures. Nanoindentation techniques are non-destructive and only require a small sample to perform experiments. While instrumented indentation has enabled high-throughput measurement of many mechanical properties for bulk and thin-film polymer samples such as elastic modulus, hardness, and creep compliance, there is no available technique to accurately extract the temperature-dependent viscoelastic properties using nanoindentation. On the macro-scale, DMA can measure damping factor (tanδ) for viscoelastic solids and glass transition temperature (Tg) can be readily determined from temperature-dependent tanδ ï€ measurements. This thesis attempts to find correlations between nanoindentation creep and impact tests to the macroscale viscoelastic properties measured via DMA. For this purpose, epoxy nanocomposites with different types and loadings of multiwalled carbon nanotubes (MWCNTs) were fabricated and characterized. Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Raman spectroscopy were used to assess carbon nanotube quality, dispersion state, and epoxy curing. Modulus, hardness, and strain rate sensitivity were measured at elevated temperatures using nanoindentation and compared to DMA results.

Keywords

Carbon Nanotubes, CNT, epoxy, nanocomposites, DMA, nanoindentation, nanocreep, glass transition temperature, storage modulus

Degree Name

Mechanical Engineering

Level of Degree

Masters

Department Name

Mechanical Engineering

First Committee Member (Chair)

Shen, Yu-Lin

Second Committee Member

Taha, Mahmoud Reda

Third Committee Member

None

Document Type

Thesis

Language

English

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