Materials Science and Engineering Commons^™

Characterization Of Hydrogen Embrittlement Sensitivity In High Hardness Steels, David Ahlen Salley

Theses and Dissertations

High hardness steels can be affected by delayed brittle cracking often attributed to hydrogen embrittlement. Improved resistance to hydrogen embrittlement would be beneficial to many industries including military, automotive, and high-rise construction. While other prevention methods include coating, trapping, and barriers, design efforts in this study were focused on improving intrinsic properties to be more resistant to hydrogen embrittlement. Four alloys targeting 477 – 534 HB were designed and produced in-house and compared against a commercial grade 500 HB alloy. Charpy V-notch (CVN) impact toughness and tensile specimens were made according to ASTM E23 and ASTM E8 to characterize mechanical …

Development Of Synergistic Electrochemical Catalysis For Advancing Co2 Utilization, Naohiro Fujinuma

Theses and Dissertations

Electrochemical CO2 utilization is an attractive process for realizing carbon-neutral chemical production due to its electricity-driven ambient conditions, compatibility with renewable energy, and diversified products. This study aims to address unmet challenges hindering the wide adaptation of the process: (I) the absence of a highly selective and scalable catalyst for CO2 reduction reaction (CO2RR), (II) the large number of laborious experiments needed to optimize electrochemical materials/devices, and (III) the lack of an effective scheme for upgrading CO2-derived products. First, a bio-mimicking multi-component catalyst is explored, leading to the discovery of a highly selective Co-pyridine-derived catalyst for CO2RR into CO. The …

Manufacturing Of A Ceramic Turbine Rotor For A Compact Jet Engine, Bryan T. Leicht

Theses and Dissertations

The primary goal of this study was to develop a low-cost, timely, scalable manufacturing method that produced a ceramic turbine that can be tested as a drop-in replacement on a JetCat P400 small scale gas turbine engine. This research compared two processes for manufacturing a ceramic turbine utilizing a pour casting method and 3D printing using stereolithography ceramic manufacturing (SLCM). The pour casting method used Silicon Nitride to create a cast turbine using a sacrificial 3D printed mold. The SLCM method evaluated producing an alumina turbine using an ADMATEC Admaflex 300 SLCM printer to directly print a ceramic turbine. This …

Potential Solution To Meet Growing Demands Of Refractory Metal: Selective Laser Melting Of Molybdenum-Tungsten Alloy, Jae Yu

Theses and Dissertations

Selective laser melting (SLM) of refractory metals has been of high interest in research due to the metals’ potential desirable characteristics in aeronautical and space applications. In particular, molybdenum and tungsten have been the focus of several studies in the search for high temperature and high strength purposes in applications like supersonic aircraft, re-entry vehicles, nuclear fission, power generation, and other space systems. However, there is still a significant knowledge gap to process defect-free alloys and making use of them in practical engineering functions. The aim of this study is to characterize the relationship between the microstructure and mechanical properties …

Thermal Considerations For Film Cooling Materials With Anisotropic Thermal Conductivity, Carol E. Bryant

Theses and Dissertations

Higher performance requirements and reduced core sizes are driving increases in turbine inlet temperature in gas turbine engines, surpassing the melting point of advanced materials. Newer materials, such as composites, are being introduced into the hot sections of gas turbine engines. Components in the hot section use film cooling to prevent melting. One unique aspect of some high-temperature composites is they have a bulk anisotropic thermal conductivity, therefore heat flow differs relative to traditional metallic components. Film cooling designs can be revolutionized by leveraging anisotropy in high-temperature materials. The purpose of this research is to examine thermal considerations for using …

Formulation And Characterization Of Fast-Curing Plastic Scintillators With High-Z Loading, Theodore W. Stephens

Theses and Dissertations

Development of novel fast-curing plastic scintillators is highly advantageous due to their potential to be manufactured via 3D printing. Several formulations were developed that exhibit enhanced photon sensitivity, producing modest but discernible photopeaks at an incident gamma energy of 122 keV. The photon sensitivity is achieved via bismuth high-Z loading; however, this practice typically results in diminished light yields. Subsequent formulations, which varied the photoinitiator concentration and curing time, demonstrated successful curing with sufficient plastic hardness, reduced purple discoloration, reduced heat buildup during curing, and resulted in less cracking during the curing process, all of which were correlated with lower …

Analysis Of Microscopic Carbon Fiber Fragments, Zachary R. Scott

Theses and Dissertations

Carbon Fiber (CF) has different tensile strengths and transverse moduli depending on how they are fabricated. Some CF is export controlled as it can be used for weapons, spacecraft, or gas centrifuges for enriching nuclear fuel. This research project explored a new way to prepare micron sized single CF threads to measure their transverse modulus and compare the moduli of non-export controlled CF to that of an export controlled CF. Five total polyacrylonitrile (PAN) fibers were used in this project, one of which was an export controlled fiber.

Determination Of Nonlinear Optical Properties For Gallium Arsenide Phosphide Ternary Compounds And For Tin Thiohypodiphosphate, Peter F. Norris

Theses and Dissertations

The Department of Defense and the commercial sector rely on coherent light sources to emit light that transmits through the atmosphere. Nonlinear optical effects in crystalline materials can be used to generate the laser waves, but certain nonlinear effects negatively impact the performance of laser generating materials. This thesis focuses on characterizing nonlinear optical properties for gallium arsenide phosphide ternary compounds and for tin thiohypodiphosphate. The Maker Fringe experiment is used to determine the d-coefficients of the materials, which describe the magnitude of the nonlinear response of the material. The Z-Scan experiment is used to calculate the nonlinear refractive …

Towards The Integration Of Ferroelectric Negative Capacitance With Gallium Oxide Semiconductors For High Power Applications, Guillermo A. Salcedo

Theses and Dissertations

Gallium oxide is a relatively new semiconductor material with characteristics auspicious for high frequency and high-voltage applications. Although several research groups have already demonstrated radio-frequency (RF) devices on Ga₂O₃ with remarkable features, there is still room for improvement. For instance, the operating frequency of RF field-effect transistors (FET) decreases with the parasitic capacitance, which can be counteracted by higher gate capacitance. Implementing ferroelectric dielectrics with suitable parameters in Ga₂O₃ FET promises to enhance the gate capacitance and therefore increase operating frequency. This work investigated the effect of various factors (film composition, film thickness, TiN …

Design And Fabrication Of Nanostructured Electrodes For Complementary Electrochemical And Photoelectrochemical Water Splitting, Kholoud El Sayed Abousalem

Theses and Dissertations

Designing highly active, durable, and nonprecious electrodes for overall water splitting is of urgent scientific importance to realize sustainable hydrogen production. Accordingly, the need to search efficient energy production systems is of crucial necessity. In this thesis, two various systems for sustainable hydrogen production have been reported using electrochemical and photoelectrochemical pathways. In the first part of the thesis, electrochemical water splitting involving both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been established. To this end, an innovative approach is demonstrated to synthesize flower-like 3D homogenous trimetallic Mn, Ni, Co phosphide catalysts directly on nickel foam via …

Centrifugal Assembly Of Bijel Ropes Via Helical Microfluidics, Shankar P. Kharal

Theses and Dissertations

Bicontinuous interfacially jammed emulsion gels (bijels) are soft materials that retain a liquid bicontinuous network stabilized by an interfacially jammed layer of nanoparticles. In this thesis, we investigated a microfluidic twisting method to fabricate micro-ropes of nano-structured bijel fibers. This method shows how weak microfibers with tensile strengths of a few kPa can be reinforced by 4 orders of magnitude by means of microfluidic twisting. Microfluidic twisting allows to produce continuous bijel fiber ropes of controllable architecture. Modelling the fluid flow field reveals the rope geometry dependence on a subtle force balance composed of rotational and translational shear stresses. However, …

Molten Salt Technologies For Advanced Nuclear Fuel Cycles And Molten Salt Reactors, Dimitris Killinger

Theses and Dissertations

This dissertation provides five topics—an assessment of different monitoring and analytical techniques often cited in the literature for molten salt systems and designs for nuclear engineering applications. First, we explored commonly used materials for quasi-reference electrodes in molten chloride salts. Second, the limitations of the electrochemical analysis known as cyclic voltammetry due to the concentration of uranium(III) present were being investigated. Third, we provided an experimental assessment on the development of a spectroelectrochemical cell for interrogating various spectroelectrochemical techniques, namely chronoabsorptometry and chronofluorometry, and their limitations due to the presence of uranium(III) ions. Fourth, a study on the corrosion resistance …

Effects Of Additive Manufacturing Techniques On The Magnetocaloric Properties And Chemical Stability Of Lafexcoysi13-X-Y Alloys, Binyam Wodajo

Theses and Dissertations

Additive manufacturing (AM) is an emerging process to fabricate net shape, intricate, engineering components with minimal material waste; however, traditionally it has been largely applied to structural materials. AM of functional materials, such as magnetic materials, has received much less attention and the field is still in its infancy. To date, AM of magnetocaloric regenerators for magnetic refrigeration (an energy-efficient alternative to the conventional vapor-compression cooling technology), remains a challenge. There are several magnetic refrigerator device designs in existence today that are predicted to be highly energy-efficient, on condition that suitable working materials can be developed. This challenge in manufacturing …

Rational Design Of Flexible And Stretchable Electronics Based On 3d Printing, Yuanhang Yang

Theses and Dissertations

Flexible and stretchable electronics have been considered as the key component for the next generation of flexible devices. There are many approaches to prepare the devices, such as dip coating, spin coating, Mayer bar coating, filtration and transfer, and printing, etc. The effectiveness of these methods has been proven, but some drawbacks cannot be ignored, such as lacking pattern control, labor consuming, requiring complex pretreatment, wasting conductive materials, etc.

In this investigation, we propose to adopt 3D printing technology to design flexible and stretchable electronics. The objective is to rationally design flexible and stretchable sensors, simplify the preparation process, form …

Rational Design Of Metal-Organic Frameworks (Mofs)-Based Functional Materials Towards Better Air Quality, Zan Zhu

Theses and Dissertations

Air pollution is a major threat to environmental safety and public health. Volatile organic compounds (VOCs), particulate matter (PM), and airborne microorganisms are three typical air pollutants. Conventional strategies to prevent and mitigate air pollution have been employed, which, however, are generally passive. For instance, VOC sensing through solid-state devices is a conventional approach, which, however, is not capable of capturing and removing VOCs. On the other hand, air filters and face masks are useful equipment to protect people from inhaling PM and airborne microorganisms. But most commercial filters can only capture them on the surfaces, which may cause secondary …

Understanding Structure/Process-Property Relationships To Optimize Development Lifecycle In Yttria-Stabilized Zirconia Aerogels For Thermal Management, Rebecca C. Walker

Theses and Dissertations

Aerogels are mesoporous materials with unique properties, including high specific surface area, high porosity, low thermal conductivity, and low density, increasing these materials’ effectiveness in applications such as catalyst supports, sorption media, and electrodes in solid oxide fuel cells. Zirconia (ZrO₂) aerogels have special interest for high-temperature applications due to the high melting point of ZrO₂ (2715°C) and stability between 600°C and 1000°C, where other aerogel systems often begin to sinter and densify. These properties and unique pore structure make zirconia aerogels advantageous as thermal management systems, especially in aeronautics and aerospace applications. However, to be effective …

Branched Chain Amino Acid Strain State Monitoring With Raman Spectroscopy And Plasmonic Bowtie Nanoantenna Devices For Early Disease Detection, Caroline A. Campbell

Theses and Dissertations

This work centers on the development and the down-selection of nano-manufactured devices to be used in conjunction with Raman spectroscopy for probing a branched chain amino acid. The nano-manufactured devices integrate plasmonic nanoantennas for the purpose of amplifying molecular fingerprints, which are otherwise difficult to detect, through Surface Enhanced Raman Spectroscopy (SERS). Plasmonic nanostructures can be utilized for a variety of biomedical and biochemical applications to detect the characteristic fingerprint provided by Raman Spectroscopy. The nano-manufactured devices create an electric field that amplifies minute perturbations and raises the signal above background noise. This may provide a deeper understanding of signal …

Study Of Alloy And Process Modifications To Design Hydrogen Resilient High Hardness Steels, William R. Williams

Theses and Dissertations

High hardness steels (HHS) are vulnerable to hydrogen embrittlement, which can lead to rapid degradation of mechanical properties. Improved resistance to hydrogen embrittlement would be beneficial to many industries including construction, automotive, and military. A comparison study was performed to assess the hydrogen susceptibility of select commercially available and in-house designed HHS alloys. Slow strain rate tensile tests, performed with specimens charged with various levels of hydrogen, provided a macroscopic view of the onset of hydrogen embrittlement. Hydrogen permeation and thermal desorption spectroscopy tests determined the uptake and diffusivity of hydrogen through the material. The evaluation of hydrogen susceptibility for …

Predictive Computational Materials Modeling With Machine Learning: Creating The Next Generation Of Atomistic Potential Using Neural Networks, Mashroor Shafat Nitol

Theses and Dissertations

Machine learning techniques using artificial neural networks (ANNs) have proven to be effective tools to rapidly mimic first principles calculations. These tools are capable of sub meV/atom accuracy while operating with linear scaling with respect to the system size. Here novel interatomic potentials are constructed based on the rapid artificial neural network (RANN) formalism. This approach generates precise force fields for various metals that have historically been difficult to describe at the atomic scale. These force fields can be utilized in molecular dynamics simulations to provide new physical insights. The RANN formalism, which is incorporated into a LAMMPS molecular dynamics …

Effects Of Bonding Pressure And Lamina Thickness On Mechanical Properties Of Clt Composed Of Southern Yellow Pine, Cody S. Bates

Theses and Dissertations

This study produced cross-laminated timber panels at a range of four lamina thickness (5/8, 1, 1 1/8, and 1 1/4 inch) and three bonding pressures (50, 125, 200 psi), producing a total of 12 panels for mechanical testing. The goal of this study is to observe how the thickness and pressure trends affect the mechanical properties of CLT. Tests include flatwise bending, flatwise shear, internal-bond, and delamination. Results showed that bending MOE decreases as the panel thickness increases while bonding pressure had no significance. Bending MOR was less significant for the thickness and more significant for pressure compared to the …

Creep Behavior And Deformation Mechanisms Of Spark Plasma Sintered Oxide Ceramics For Aerospace Systems At 1300˚C - 1400˚C, David D. Swanson

Theses and Dissertations

The mechanical behavior of YAG and LuAG was investigated at elevated temperatures. The specific materials investigated in this work include high-purity, polycrystalline YAG, high-purity, polycrystalline LuAG, and two doped variants of YAG: 2at% Yb-doped, polycrystalline YAG and 2at% Er-doped, polycrystalline YAG. Several billets of each material were prepared and processed by means of spark plasma sintering (SPS). Many different sintering parameters were utilized in order to obtain materials with various physical properties and to identify the effects of sintering parameters on the average grain size of the resulting materials. The compressive creep behavior of these materials was investigated at 1300°C …

Fabrication And Comparative Study Of Horizontal And Vertical Electrospun Protein-Polysaccharide Nanofiber Biomaterials, Ashley Rivera-Galleti

Theses and Dissertations

The use of biocompatible and biodegradable composite materials for biomedical applications has attracted the attention of many researchers in the past few years. In this study, we fabricated nanofibers of silk fibroin and cellulose and its derivatives to amalgamate their unique properties into a single material. The production of these nanofibers via electrospinning is of particular interest, and whereas several studies have been done on normal nanofibers, the formation of branched nanofibers is an exciting area not currently explored. Blend solutions are formed by dissolving silk and cellulose/cellulose acetate in formic acid separately and mixing to achieve the desired ratios. …

Improvements To Emissive Plume And Shock Wave Diagnostics And Interpretation During Pulsed Laser Ablation Of Graphite, Timothy I. Calver

Theses and Dissertations

This dissertation covers nanosecond pulsed laser ablation of graphite for 4-5.7 J/cm² fluences with 248 nm and 532 nm lasers in 1-180 Torr helium, argon, nitrogen, air, and mixed gas. Three experiments were performed to improve the interpretation of common diagnostics used to characterize pulsed laser ablation, find simple but universal scaling relationships for comparing dynamics across different materials and ablation conditions, and provide a systematic analysis of graphite emissive plume and shock wave dynamics. A scaling of the Sedov-Taylor energy ratio was developed and validated for a range of studies despite differences in wavelength, pulse duration, fluence, and …

Optimization Of Load-Bearing And Impact Energy Absorption Capacities Of Honeycomb Structures By Density Gradation, Oyindamola Khadijat Rahman

Theses and Dissertations

Density gradation has been analytically and experimentally proven to enhance the load-bearing and energy absorption efficiency of cellular solids. This research focuses on the analytical optimization (by virtual experiments) of polymeric honeycomb structures made from flexible thermoplastics to achieve density-graded structures with desired mechanical properties. The global stress-strain curves of single-density honeycomb structures are used as input to an analytical model that enables the characterization of the constitutive response of density-graded hexagonal honeycombs with discrete and continuous gradations and for various gradients. The stress-strain outputs are used to calculate the specific energy absorption, efficiency, and ideality metrics for all density-graded …

Investigation Of Single, Binary, And Ternary Metal Oxides Of Iridium, Rhodium, And Palladium For Neural Interfacing Applications, Gregory Vincent Taylor

Theses and Dissertations

In this dissertation, thin film single, binary, and ternary metal oxides of iridium (Ir), ruthenium (Ru), rhodium (Rh), and palladium (Pd) were synthesized for use as electrode/microelectrode coatings for neural interfacing applications using DC reactive magnetron sputtering. Synthesis conditions which enhanced the electrochemical properties of films as measured by cyclic voltammetry and electrochemical impedance spectroscopy in a phosphate buffered saline solution of the single metal oxides were identified to be 30 mTorr working pressure, 20% oxygen partial pressure, and cathode power densities ≤ 4.9 W/cm². These parameters were then used to develop the binary and ternary metal oxide …

Assessment Of Carbon Dioxide Emission And Its Impact On High-Rise Mixed-Use Buildings In Egypt, Ahmed Salah Hamza

Theses and Dissertations

With Egypt's vision of 2030 focusing on sustainable development with a true emphasis on Carbon Dioxide (CO₂) emission reduction in the newly built cities and high-rise buildings, efforts are exerted on various levels towards accomplishing the vision’s goals. This is achieved through multiple tools and models associated with aiding the reduction of carbon emissions, yet not a clear one was introduced for the mixed-use buildings in Egypt.

Through this work, a significant gap was identified with respect to high-rise buildings carbon emission assessment in Egypt. This was a main driving force for this work in an attempt to …

Design And Fabrication Of Zinc Oxide Optofluidic Laser Elements, Kyle T. Bodily

Theses and Dissertations

This thesis systematically goes through the derivation, simulation, and experimentation of Zinc Oxide optofluidic micro laser elements. Single and coupled ring resonators were simulated to show single mode transmission as well as enhanced coupling capabilities when surrounded by high refractive index liquid. Devices with diameters ranging from 100-500 µm were successfully fabricated inexpensively through standard cleanroom procedures. The devices were tested using two different pump laser systems. Testing included such factors as high pump intensity, various angles of excitation, and low temperature. In all cases PL emission was observed and recorded.

Static Fatigue Of Hi-Nicalon™ S Ceramic Fiber Tows At 600°C In Air And Silicic Acid-Saturated Steam, Caleigh M. Nelson

Theses and Dissertations

Ceramic matrix composites (CMCs) have the potential to be utilized in applications such as hypersonic vehicles, aircraft leading edges, hot sections of engines, and rocket nozzles. Of particular interest are advanced SiC/SiC composites that can withstand the elevated temperatures and harsh oxidizing environments while maintaining their properties and structural integrity under an applied load. Steam, a major component of combustion environment, is one such aggressive oxidizing environment. As steam passes through the SiC/SiC composite, entering the composite interior through the cracks in the SiC matrix, it becomes saturated with silicic acid, Si(OH)₄. Before incorporating SiC/SiC composites in the …

Static Fatigue Of Hi-Nicalon S Fiber Tows At 500°C In Air And In Silicic Acid-Saturated Steam, Richard J. Reinink

Theses and Dissertations

Recent developments in aerospace propulsion systems, along with emerging interest in hypersonic air vehicles has emphasized the need for materials which can withstand extreme service environments. The leading candidates for the structural components expected to operate in these environments are SiC-based ceramic matrix composites (CMCs). When a CMC component is subjected to thermomechanical loads in an aggressive environment during service, surface cracks form. As steam penetrates cracks in the SiC matrix, it becomes saturated with silicic acid, (SI(OH)₄) and attacks the SiC fibers. The interaction between the Hi-Nicalon™ S SiC fibers and the (SI(OH)₄)-saturated steam is …

Fatigue Of Two Oxide/Oxide Ceramic Matrix Composites At 1200°C In Air And In Steam. Effect Of Diamond Drilled Effusion Holes, Anthony R. Cabri

Theses and Dissertations

The tension-tension fatigue behavior of two oxide-oxide ceramic matrix composites (CMCs) was investigated at 1200°C in laboratory air and steam. Both composites consist of a porous oxide matrix reinforced with laminated, woven mullite/alumina (NextelTM720) fibers. The first composite had an alumina matrix, while the second had an alumina-mullite matrix. First, we assessed the effects of incorporating mullite into the matrix material on fatigue performance by studying the tension-tension fatigue behavior of alumina-mullite matrix CMC. Second, we evaluated the effects of effusion holes on the alumina matrix CMC's fatigue performance. Specimens containing an array of 17 effusion holes of 0.5-mm diameter …