Engineering Commons^™

Processing And Characterization Of High Performance Structural Nanocomposites, Dennis C. Working

Mechanical & Aerospace Engineering Theses & Dissertations

Carbon nanotubes are considered to be a revolutionary material breakthrough due to their unique combination of properties. While many applications for SWCNTs have been projected, realization of these potential uses have been hampered by the high cost of limited supplies of high quality SWCNTs and the difficulty in the development of a suitable processing method that does not damage the filler thus diminishing the desirable properties of this material. In spite of these technical challenges, their potential to enable the fabrication of multifunctional materials is being investigated in earnest. The goal of this thesis is to investigate the feasibility of …

Robust Shape Design Techniques For Steady-State Metal Forming Processes, Jalaja Repalle

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Metal forming is a process that transforms a simple shape of a workpiece into a predetermined complex shape through the application of compressive/tensile forces exerted by dies. In the design of a forming process, the only factors that are known are the final component shape and the material with which it is to be made. Then the engineer has to design a process to make defect-free product, subject to limitations of shape, material properties, cost, time, and other such factors. The design cycle can be enhanced if performance sensitivity information is available that could be used with any commercially available …

Investigation Into The Behavior Of Bolted Joints, Steven M. Page

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Models to capture the physics of jointed structures have been proposed for over 40 years. These models approximate the behavior of the joint under carefully developed operating conditions. When these conditions change, the model has to be changed. Recent developments in numeric codes like finite elements have created interest in incorporating joint models into the design process but joint models need to represent the joined structure over a broader operating range. This work investigates the dynamic response of a structure with a joint. Isolation of a few dominant effects may give way to a model able to capture a broader …

Computational Study Of Ring-Cusp Magnet Configurations That Provide Maximum Electron Confinement, Taiwo A. Ogunjobi

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Enhancing the confinement of primary electrons within the plasma in a discharge chamber of an ion thruster improves plasma ionization and consequently the thruster's performance. This work computationally calculates the location, position, and orientation of the permanent magnets that provide a ring-cusp magnetic field that maximizes electron confinement in an axi-symmetric cylindrical aluminum-wall discharge chamber. Small samarium cobalt magnets are circumferentially arranged in a ring around the front, side, or back wall of the chamber. The generated ring-cusp magnetic field for any specified magnet configuration is calculated using MAXWELL2D, a two dimensional electromagnetic field simulation computer code. For various magnet …

Using In-Situ Error Tracking For Mode Selection In Proper Orthogonal Decomposition Reduced Order Modelling, Michael Richard Maddux

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Proper Orthogonal Decomposition (POD) provides a method of analyzing data and/or creating a Reduced Order Model (ROM). In this thesis, POD is used to create a ROM comprised of basis functions onto which the governing equations of a Computational Fluid Dynamics (CFD) problem are projected via Galerkin's method. The model is of reduced order since the basis functions span a space smaller than the space from which they were created. A full order simulation called the training period is conducted first to obtain data to be used for creating the ROM using POD. The dominant characteristics are extracted from the …

Relationship Between Vertical Shear Rate And Kinetic Energy Dissipation Rate In Stably Stratified Flows, Stephen De Bruyn Kops, D. Hebert

Stephen de Bruyn Kops

High resolution direct numerical simulations of strongly stratified turbulence are analyzed in order to investigate the relationship between vertical shearing of horizontal motions and the dissipation rate of kinetic energy. The relative magnitude of each component of the dissipation rate is examined as a function of the Reynolds number and of the buoyancy Reynolds number. From the simulation results, in conjunction with published laboratory results, it is concluded that (1) the simulation results are consistent with the laboratory data but span a much larger range of buoyancy Reynolds number, (2) the ratio of the square of the vertical shear rate …

Melt Dispersion Mechanism For Fast Reaction Of Nanothermites, Valery I. Levitas, Blaine W. Asay, Steven F. Son, Michelle Pantoya

Steven F. Son

An unexpected mechanism for fast oxidation of Alnanoparticles covered by a thin oxide shell (OS) is proposed. The volume change due to melting of Al induces pressures of 0.1–4GPa and causes spallation of the OS. A subsequent unloading wave creates high tensile pressures resulting in dispersion of liquid Al clusters, oxidation of which is not limited by diffusion (in contrast to traditional mechanisms). Physical parameters controlling this process are determined. Methods to promote this melt dispersion mechanism, and consequently, improve efficiency of energetic nanothermites are discussed.

30 Adet Pantone Rengin Ink Formulation Programi Kullanilarak Hazirlanmasi, Bilge N. Altay, Nazli Burcu Taklak

Bilge Nazli Altay

Modeling Of The Effects Of Athermal Flow Strength And Activation Energy For Dislocation Glide On The Nanoindentation Creep Of Nickel Thin Film At Room Temperature

A.S. Md Abdul Haseeb

Nanoindentation creep behaviour of nickel at room temperature has been modeled based on the obstacle-controlled dislocation glide mechanism. Using the model, the effects of two important materials parameters viz. the activation free energy required by dislocation to overcome an obstacle without any aid from external stress, ΔF and the athermal flow strength, τ0, which is the flow strength of solids at 0 K are systematically studied. It has been found that ΔF plays a dominant role in room temperature creep properties of nickel. The role of ΔF is particularly dominant in determining the time dependent deformation. On the other hand, …