Engineering Commons^™

Mechanics Of The Solid-State Bonding Under Severe Thermomechanical Processes, Xue Wang

Doctoral Dissertations

Friction stir welding (FSW) has found increased applications in automotive and aerospace industries due to its advantages of solid-state bonding, no fusion and melting, and versatility in various working conditions and material combinations. The extent and quality of the solid-state bonding between workpieces in FSW is the ultimate outcome of their industrial applications. However, the relationship among processing parameters, material properties, and bonding extent and fidelity remains largely empirical, primarily because of the lack of the mechanistic understanding of (1) tool-workpiece frictional behavior, and (2) bonding formation and evolution.

In this dissertation, to study the underlying mechanism of tool-workpiece frictional …

Enhanced Kinetics And Modeling Of Pan-Based Carbon Felt Anodes In Vanadium Redox Flow Batteries, Michael Cyrus Daugherty

Doctoral Dissertations

All-vanadium redox flow batteries (VRFBs) are a promising technology for grid-level energy storage, however, there are still several limitations in the forms of durability, efficiency, and overall costs, which are barriers to its commercial viability. With both bulk electrolyte flowing through its porous matrix and species flux at the solid-electrolyte interface, electrodes are the component of VRFB systems which host electrochemical reactions and facilitate contact between the liquid phase electrolyte and the electronically conductive solid phase. While the more limiting electrode in VRFB systems is dependent on the material, for polyacrylonitrile (PAN)-based carbon felts, the anode constitutes a larger portion …

Processing-Structure-Performance Relationships In Fused Filament Fabricated Fiber Reinforced Abs For Material Qualification, William Howard Ferrell

Doctoral Dissertations

This dissertation uses the processing-structure-performance relationships to elucidate future needs in qualification of materials manufactured by fused filament fabrication and also introduces a previously unused testing method for the determination of fracture toughness in these materials. Fused filament fabrication (FFF) is an additive manufacturing technique that utilizes the layering of deposited molten plastic in two dimensional shapes to create three dimensional objects. This technique has gained traction over the past two decades as a disruptive manufacturing technology that promises many benefits. In order for FFF to truly be a staple in manufacturing spaces across the world for the production of …

A Method For Developing And Testing Nuclear Reactor Systems With Space Applications And Improving Performance Of Heat Pipe Reactor Systems, David Duff Dixon

Doctoral Dissertations

The concept of using nuclear reactor technology in propulsion systems is nearly as old as nuclear reactors themselves. Numerous publications, many at very primitive conceptual levels, suggested nuclear propulsion in the 1940s. Since then, numerous attempts have been made to build and fly a nuclear rocket, yet there have been no such systems advanced to the point of a system test in more than half a century.

This dissertation presents an approach to reactor system development, a testing approach developed by the author that resulted in the operation of the world’s first heat pipe reactor system, and the world’s first …

Vibration Behavior In Modulated Tool Path (Mtp) Turning, Ryan William Copenhaver

Doctoral Dissertations

This project studies the process dynamics and surface finish effects of modulated tool path (MTP) turning. In MTP turning, a small amplitude (typically less than 0.5 mm), low frequency oscillation (typically less than 10 Hz) is superimposed on the feed motion by the machine controller to intentionally segment the traditionally long, continuous chips. The basic science to be examined is the vibration behavior of this special case of interrupted cutting, which is not turning because the chip formation is intentionally discontinuous and is not milling because the time-dependent chip geometry is defined by the oscillatory feed motion, not the trochoidal …

Dynamic Neuromechanical Sets For Locomotion, Aravind Sundararajan

Doctoral Dissertations

Most biological systems employ multiple redundant actuators, which is a complicated problem of controls and analysis. Unless assumptions about how the brain and body work together, and assumptions about how the body prioritizes tasks are applied, it is not possible to find the actuator controls. The purpose of this research is to develop computational tools for the analysis of arbitrary musculoskeletal models that employ redundant actuators. Instead of relying primarily on optimization frameworks and numerical methods or task prioritization schemes used typically in biomechanics to find a singular solution for actuator controls, tools for feasible sets analysis are instead developed …

Characterization Of A Digital Holography Diagnostic For In Situ Erosion Measurement Of Plasma-Facing Components In Fusion Devices, Cary Dean Smith

Doctoral Dissertations

Fusion energy devices, particularly tokamaks, face the challenge of interior surface damage occurring over time from the heat flux of the high-energy plasma they generate. The ability to monitor the rate of surface modification is therefore imperative, but to date no proven technique exists for real-time erosion measurement of planar regions of interest on plasma-facing components in fusion devices. In order to fill this diagnostic gap, a digital holography system has been established at ORNL [Oak Ridge National Laboratory] for the purpose of measuring the erosion effects of plasma-material interaction in situ.

The diagnostic has been designed with the …

Cracking And Earing Phenomenon In Deep-Drawn Stainless Steel Alloys: Role Of Transformation Kinetics, Microstructure, And Texture, Peijun Hou

Doctoral Dissertations

The enhancement of formability of advanced high-strength TRIP-assisted steel alloys is a challenging assignment for industrial application due to the cracking phenomenon. The critical factor governing the cracking behavior is residual-stress concentration resulting from the inhomogeneous plastic deformation and microstructural evolution during the forming processes. Martensitic phase transformation kinetics, constituent phases, and crystallographic texture in TRIP-assisted steel alloys are correlated to the microstructure evolution, resulting in phase-specific stress concentration. In the current study, we are aiming at understanding the fundamental mechanisms responsible for the cracking phenomenon and thus improving the formability of TRIP-assisted steel alloys. Four stainless steel (SS) alloys …