Engineering Commons^™

Thermomechanical Properties Of Novel Lanthanum Zirconate Based Thermal Barrier Coatings - An Integrated Experimental And Modeling Study, Xingye Guo

Open Access Dissertations

Thermal barrier coatings (TBCs) are refractory materials deposited on gas turbine components, which provide thermal protection for metallic components at operating conditions. The current state-of-art TBC material is yttria-stabilized zirconia (YSZ), whose service temperature is limited to 1200 celsius, due to sintering and phase transition at higher temperatures. In comparison, lanthanum zirconate (La2Zr2O7, LZ) has become a promising candidate material for TBCs due to its lower thermal conductivity and higher phase stability compared to YSZ.

The primary objective of this thesis is to design a novel robust LZ-based TBC system suitable for applications beyond 1200 celsius. Due to LZ’s low …

Plasmonic Devices Based On Transparent Conducting Oxides For Near Infrared Applications, Kim Jongbum

Open Access Dissertations

In the past decade, there have been many breakthroughs in the field of plasmonics and nanophotonics that have enabled optical devices with unprecedented functionalities. Even though remarkable demonstration of at photonic devices has been reported, constituent materials are limited to the noble metals such as gold (Au) and silver (Ag) due to their abundance of free electrons which enable the support of plasmon resonances in the visible range. With the strong demand for extension of the optical range of plasmonic applications, it is now a necessity to explore and develop alternative materials which can overcome intrinsic issues of noble metals …

Microstructural Evolution During The Homogenization Heat Treatment Of 6xxx And 7xxx Aluminum Alloys, Pikee Priya

Open Access Dissertations

Homogenization heat treatment of as-cast billets is an important step in the processing of aluminum extrusions. Microstructural evolution during homogenization involves elimination of the eutectic morphology by spheroidisation of the interdendritic phases, minimization of the microsegregation across the grains through diffusion, dissolution of the low-melting phases, which enhances the surface finish of the extrusions, and precipitation of nano-sized dispersoids (for Cr-, Zr-, Mn-, Sc-containing alloys), which inhibit grain boundary motion to prevent recrystallization. Post-homogenization cooling reprecipitates some of the phases, changing the flow stress required for subsequent extrusion. These precipitates, however, are deleterious for the mechanical properties of the alloy …

Energy Localization And Heat Generation In Composite Energetic Systems Under High-Frequency Mechanical Excitation, Jesus O. Mares

Open Access Dissertations

In this work, the ability to use high frequency mechanical excitation to generate significant heating within plastic bonded explosives, as well as single energetic particles embedded within a viscoelastic binder, is studied. In this work, the fundamental mechanisms associated with the conversion of high-frequency mechanical excitation to heat as applied to these composite energetic systems are thoroughly investigated.

High-frequency contact excitation has been used to generate a significant amount of heat within samples of PBX 9501 and representative inert mock materials. Surface temperature rises on the order of 10 °C were observed at certain frequencies over a range from 50 …

Bridge Maintenance To Enhance Corrosion Resistance And Performance Of Steel Girder Bridges, Luis M. Moran Yanez

Open Access Dissertations

The integrity and efficiency of any national highway system relies on the condition of the various components. Bridges are fundamental elements of a highway system, representing an important investment and a strategic link that facilitates the transport of persons and goods. The cost to rehabilitate or replace a highway bridge represents an important expenditure to the owner, who needs to evaluate the correct time to assume that cost. Among the several factors that affect the condition of steel highway bridges, corrosion is identified as the main problem. In the USA corrosion is the primary cause of structurally deficient steel bridges. …

Modeling Fluid Interactions With The Rigid Mush In Alloy Solidification, Alexander J. Plotkowski

Open Access Dissertations

Macrosegregation is a casting defect characterized by long range composition differences on the length scale of the ingot. These variations in local composition can lead to the development of unwanted phases that are detrimental to mechanical properties. Unlike microsegregation, in which compositions vary over the length scale of the dendrite arms, macrosegregation cannot be removed by subsequent heat treatment, and so it is critical to understand its development during solidification processing. Due to the complex nature of the governing physical phenomena, many researchers have turned to numerical simulations for these predictions, but properly modeling alloy solidification presents a variety of …

Fabrication And Characterization Of Cellulose Nanocrystal Enhanced Sustainable Polymer Nanocomposites Through Surface Chemistry And Processing, Shane X. Peng

Open Access Dissertations

Cellulose nanocrystals (CNCs) belong to a class of cellulose based nanomaterials that are extracted from renewable and sustainable sources and have excellent mechanical and thermal properties. While applications for CNCs have been expanding, one of the challenges of utilizing CNCs is to overcome their low dispersibility in hydrophobic polymers. In the present work, several approaches are utilized to improve the interfacial compatibility and overall performance of CNC/epoxy and CNC/polyamide nanocomposite.

For a two-part epoxy system, a novel approach was taken to disperse CNC in epoxy matrix by pre-formulating CNC into the hardeners. Three types of hardeners were evaluated for their …

Nanoparticle-Based Electrochemical Sensors For The Detection Of Lactate And Hydrogen Peroxide, Aytekin Uzunoglu

Open Access Dissertations

In the present study, electrochemical sensors for the detection of lactate and hydrogen peroxide were constructed by exploiting the physicochemical properties of metal ad metal oxide nanoparticles. This study can be divided into two main sections. While chapter 2, 3, and 4 report on the construction of electrochemical lactate biosensors using CeO2 and CeO2-based mixed metal oxide nanoparticles, chapter 5 and 6 show the development of electrochemical hydrogen peroxide sensors by the decoration of the electrode surface with palladium-based nanoparticles. First generation oxidase enzyme-based sensors suffer from oxygen dependency which results in errors in the response current of the sensors …

Modeling Transport Phenomena And Uncertainty Quantification In Solidification Processes, Kyle S. Fezi

Open Access Dissertations

Direct chill (DC) casting is the primary processing route for wrought aluminum alloys. This semicontinuous process consists of primary cooling as the metal is pulled through a water cooled mold followed by secondary cooling with a water jet spray and free falling water. To gain insight into this complex solidification process, a fully transient model of DC casting was developed to predict the transport phenomena of aluminum alloys for various conditions. This model is capable of solving mixture mass, momentum, energy, and species conservation equations during multicomponent solidification. Various DC casting process parameters were examined for their effect on transport …

Modeling Picking On Pharmaceutical Tablets, Shrikant Swaminathan

Open Access Dissertations

Tablets are the most popular solid dosage form in the pharmaceutical industry because they are cheap to manufacture, chemically and mechanically stable and easy to transport and fairly easy to control dosage. Pharmaceutical tableting operations have been around for decades however the process is still not well understood. One of the common problems faced during the production of pharmaceutical tablets by powder compaction is sticking of powder to the punch face, This is known as 'sticking'. A more specialized case of sticking is picking when the powder is pulled away form the compact in the vicinity of debossed features. In …

Analytical And Experimental Investigation Of Microstructural Alterations In Bearing Steel In Rolling Contact Fatigue, Sina Mobasher Moghaddam

Open Access Dissertations

Rolling Contact Fatigue (RCF) is one the most common failure modes in bearings. RCF is usually associated with particular microstructural alterations. Such alterations (i.e. white etching cracks, butterflies, etc.) which lead to RCF failure are known to be among the most concerning matters to bearing industry.

In the current work, an analytical as well as experimental approaches are used to investigate “butterfly wing” formation, crack initiation and propagation from inclusions. A new damage evolution equation coupled with a FE model is employed to account for the effect of mean stresses and alternating stresses simultaneously to investigate butterfly formation. The proposed …

Atomic Level Study Of Water-Gas Shift Catalysts Via Transmission Electron Microscopy And X-Ray Spectroscopy, Mehmed Cem Akatay

Open Access Dissertations

Water-gas shift (WGS), CO + H₂ O [Special characters omitted.] CO₂ + H₂ (ΔH° = -41 kJ mol ^-1 ), is an industrially important reaction for the production of high purity hydrogen. Commercial Cu/ZnO/Al₂ O₃ catalystsare employed to accelerate this reaction, yet these catalysts suffer from certain drawbacks, including costly regeneration processes and sulfur poisoning. Extensive research is focused on developing new catalysts to replace the current technology. Supported noble metals stand out as promising candidates, yet comprise intricate nanostructures complicating the understanding of their working mechanism.

In this study, the structure of the supported …

Response Of Plasma Facing Components In Tokamaks Due To Intense Energy Deposition Using Particle-In-Cell(Pic) Methods, Filippo Genco

Open Access Dissertations

Damage to plasma-facing components (PFC) due to various plasma instabilities is still a major concern for the successful development of fusion energy and represents a significant research obstacle in the community. It is of great importance to fully understand the behavior and lifetime expectancy of PFC under both low energy cycles during normal events and highly energetic events as disruptions, Edge-Localized Modes (ELM), Vertical Displacement Events (VDE), and Run-away electron (RE). The consequences of these high energetic dumps with energy fluxes ranging from 10 MJ/m2 up to 200 MJ/m2 applied in very short periods (0.1 to 5 ms) can be …

Mechanisms Of Microstructure Formation Under The Influence Of Ultrasonic Vibrations, Milan Rakita

Open Access Dissertations

Positive effects of ultrasound on crystallization have been known for almost 90 years. Application of ultrasound has been very successful in many industries, most notably in chemistry, creating a new branch of science - sonochemistry. However, ultrasonication has not found wide commercial application in the solidification processing. The reason for that is the complexity of underlying phenomena and the lack of predicting models which correlate processing parameters with the properties of a product. The purpose of this study is to give some contribution toward better understanding of mechanisms that lead to changes in the solidifying microstructure. It has been found …

Dynamic Behavior Of Sandwich Beams With Internal Resonators, Bhisham Nar Narain Sharma

Open Access Dissertations

Dynamic behavior of sandwich beams with internal resonators was investigated. The effect of inserting spring-mass resonators into the sandwich core was theoretically analyzed and it was shown that a wave attenuation bandgap exists due to local resonance. Steady state experiments were used to demonstrate such an attenuation bandgap. Frequency response functions were obtained for a beam with resonators and without resonators. It was shown that insertion of resonators into the core causes a wave attenuation bandgap to open up. The experimental results were verified using finite element simulations. Further experiments were carried out by tuning the resonators at 12 Hz …

The Comparison Of Composite Aircraft Field Repair Method (Cafrm) With Traditional Aircraft Repair Technologies, Peng Hao Wang

Open Access Dissertations

In the aviation industry, manufacturers made the transition from aluminum to composite materials for the majority of their primary structures over the last few decades. While the design and manufacturing techniques have consistently evolved, field repair methods were consistently overlooked. In this study, specimens fabricated using some of the common repair methods such as the autoclave repair method, and Double Vacuum Debulk (DVD) repair method were tested against the Composite Aircraft Field Repair Method (CAFRM) proposed by the researcher. Specimens were tested with microscopy, acid digestion, short beam shear, and mode I fracture tests. The researcher was able to determine …

Utilizing Electron Microscopy And Spectroscopy Methods To Understand Water Structure And Water Doping, Lior Miller

Open Access Dissertations

Water is the second most common element in the universe and the most studied material on earth. Most of the studies concerning water are from the fields of chemistry and biology. Hence, the structure of water molecules and short range order and interactions are well characterized and understood. However, the collective arrangement of water molecules and the long range order are still missing. Understanding of this long range order in water is needed, as it is the key to many water activities.

To fill this gap, this study utilizes a new direct method for characterization of water in the vapor …

Applicability Of Continuum Fracture Mechanics In Atomistic Systems, Shao-Huan Cheng

Open Access Dissertations

By quantitating the amplitude of the unbounded stress, the continuum fracture mechanics defines the stress intensity factor K to characterize the stress and displacement fields in the vicinity of the crack tip, thereby developing the relation between the stress singularity and surface energy (energy release rate G). This G-K relation, assigning physical meaning to the stress intensity factor, makes these two fracture parameters widely used in predicting the onset of crack propagation. However, due to the discrete nature of the atomistic structures without stress singularity, there might be discrepancy between the failure prediction and the reality of nanostructured materials. Defining …