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Characterization Of Residual Stress And Precipitate Evolution In Aluminum 2xxx Self-Reacting Friction Stir Welds, Benjamin Joe Wing

Doctoral Dissertations

2xxx series aluminum alloys possess attractive properties for structural aerospace applications including high strength to weight ratio, corrosion resistance, and stable cryogenic performance. Solid state joining processes are often employed to reduce weld defects and improve weld performance/consistency as many alloys of this range have poor weldability for traditional fusion based joining techniques. One such process, self-reacting friction stir welding (SRFSW) allows for consistent high-quality, welding of large and curved articles is often used in the construction of large structures such as launch vehicle liquid propellant tanks.

Despite the merits of this process, joint softening (a decrease in mechanical properties …

Development Of A Novel Casting Alloy Composed Of Aluminum And Cerium With Other Minor Additions, Zachary Cole Sims

Doctoral Dissertations

Eutectic casting alloys of aluminum and cerium are a recent discovery and early research describes an alloy with great potential to meet the growing demand for a lightweight, economical, high specific strength material for use in high-temperature or extremely corrosive environments. The broad application of aluminum alloys across industry sectors is driven by their collection of balanced properties including economical cost, high specific strength, and flexibility of their production pathways. Additionally, their high corrosion resistance makes them a good choice for structural materials. Despite this, the push to use aluminum alloys in ever more extreme environments with higher temperatures, stresses, …

On The Thermal Stability Of Theta Prime Precipitates In Al-Cu-Mn-Zr Alloys, Patrick Shower

Doctoral Dissertations

Al-Cu-Mn-Zr (ACMZ) alloys demonstrate vastly improved mechanical properties at temperatures between 250 C and 350 C compared to conventional theta’-strengthened Al alloys. The improved high temperature mechanical properties of Al-Cu-Mn-Zr are due to the thermal stability of strengthening theta’ precipitates against transformation to the detrimental theta-phase. This is illustrated by a study of the high-temperature compression response of an Al-Cu-Mn-Zr alloy that retains theta’ precipitates at elevated temperatures and a conventional alloy that does not. It is shown that the divergence in microstructure leads to a divergence in deformation mechanisms.The thermal stability of strengthening theta’ particles is due to their …

Damage Analysis Of Aluminum Structure Repaired With A Composite Patch, Bozhi Heng

Doctoral Dissertations

The interest in the application of high strength aluminum alloy in marine structures has been increasing in recent years due to its high strength-weight ratio and excellent corrosion resistance. However, those marine grade aluminum alloy unavoidably experience fatigue and stress corrosion cracking during their service life. Developing a reliable repair method is essential to address the damage problems. The composite patch has been demonstrated as a promising method to repair the damaged or reinforce the under-designed aluminum structures. This research focuses on creating a comprehensive understanding of damage mechanisms involved in the composite patch repaired structures. The compact tension testing …

Spectroscopic Imaging Of Aluminum Containing Plasma, David Michael Surmick

Doctoral Dissertations

This dissertation aims to characterize laser-induced plasma from a physics point of view as warm, dense matter. Use of nominal nanosecond pulsed laser radiation initiates a plasma with electron temperatures of the order of 10 electron volts and electron densities of the order of air species densities at standard ambient temperature and pressure. For laser ablation and/or optical breakdown at or near a solid surface, the electron density can amount to be 1000 times greater. Spectroscopic investigations of the plasma emissions provide a method by which the electron density, temperature, and shockwave expansion may be determined. Of particular interest are …

Development And Demonstration Of Critical Components Of Aluminum Based Energy Storage Devices Using The Chloroaluminate Ionic Liquids, Mengqi Zhang

Doctoral Dissertations

This dissertation considers the development of porous carbon materials as the substrates for Al deposition/dissolution in an Al based ionic liquid flow battery (ILFB) and demonstration of an Al based hybrid supercapacitor. The Aluminum chloride/ 1-ethyl-3-methylimidazolium chloride chloroaluminate ionic liquid is utilized as the electrolyte for these Al based energy storage devices. The ILFB has less capital cost than the all-vanadium redox flow battery because of the inexpensive AlCl₃. The feasibility to equip a tank of solid aluminum chloride in an ILFB system aiming to improve energy density is investigated. A critical range of temperature data (50-130 celsius …

The Synthesis And Characterization Of Novel Group 13 Nanostructured Building Block Heterogeneous Silicate Catalysts, Joshua G. Abbott

Doctoral Dissertations

A building block approach and sequential addition methodology were utilized to prepare heterogeneous silicate catalysts containing atomically dispersed group 13 metal (B, Al, Ga) centers. The octa(trimethyltin) silsequioxane, Si8[sub]O12[sub](OSnMe3[sub])8[sub], was used as the building block for the synthesis of these materials. Reaction of the building block with a variety of group 13 metal chlorides led to the formation of cross-linked matrices. All prepared materials were characterized by gravimetric analysis, gas absorption, IR, and NMR. In addition, aluminum and boron samples where characterized by 27[sup]Al and 11[sup]B solid state NMR, and gallium samples were studied using x-ray absorption techniques.

Studies found …

Cracking In Cycloaliphatic Epoxy/Aluminum Composite Electrical Bushings, Keith Alan Parker

Doctoral Dissertations

The problem of cracking in electrical apparatus bushings as a result of thermal stresses was investigated. The bushings were composed of cycloaliphatic epoxy insulators with embedded aluminum conductors. The problem is due to the difference in coefficients of thermal expansion of the two materials. A solution to the problem had been to coat the conductors before they were formed together with the epoxy insulators. The coating was assumed to prevent cracking by allowing movement between the two materials as their dimensions changed during thermal expansion and contraction. The contribution of the coating was to be established.

The hypothesis was that …