Thermal and mechanical phenomena in nanoscale constrained domains

Guo, Liying
Major Professor
Xinwei Wang
Committee Member
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Mechanical Engineering
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Mechanical Engineering

In the manufacturing area, the laser has attracted increasing attention in recent year as an important tool in the practice of micro/nano scale manufacturing, such as surface microfabrication and processing, pulsed laser deposition of films and coatings, laser machining of metals and non-metallic materials, and laser surface cleaning. During the laser assisted nanostructuring process, intensive heating will cause the material to experience fast phase change that the non-equilibrium state will lead to shock wave near the heating spot. In nanostructures, thermal movements of molecules/atoms show strong statistical variations in space since the equilibrium state cannot be established. Molecular dynamics (MD) simulation, which directly tracks the movements of molecules/atoms, is capable of exploring physical phenomena down to molecular/atomic levels and predicting processes under different conditions. The previous work done in our group have investigated the evolution of density, temperature, pressure, and shock wave front Mach number. Chapter 2 is an introduction to the basics of MD simulation. In chapter 3, the evolution of the interaction zone and energy exchange between the plume and the ambient gas are studied with respect to different gas/solid molecular mass ratios and different ambient gas densities. The evolutions of shock wave front position as well as velocity and Mach number in different ambient gases are also studied.

Lasers also have wide spread popularity in characterization physical properties of materials. When illuminating the surface of materials, the laser light can be absorbed by the material and cause the temperature and thermal radiation variation at the surface. These phenomena have been intensively studied in the past. A photothermal (PT) technique has been developed in our group for characterizing thermal physical properties of different materials. For the thermal properties characterization of amorphous titanium dioxide (TiO2) nanotube arrays, this technique provides the experimental data of the as-prepared sample density and the thermal conductivity along the tube length direction. The thermal conductivity in the cross-tube direction is measured by the transient electrothermal (TET) technique. Combining the two techniques, the contact resistance between the TiO2 nanotubes is also investigated. Chapter 4 is for the experimental setup for the studying of nanoscale thermal transport. Chapter 5 analyzes the experimental data in detail and compares with work done by other researchers.

The emphasis of future work is outlined and described in Chapter 6.