Materials Science and Engineering Commons^™

Crystalline Phase Change In Steel Alloys Due To High Speed Impact, Muna Slewa

UNLV Theses, Dissertations, Professional Papers, and Capstones

The effect of hypervelocity projectile impact on the crystalline grain structure near the target impact location of A36 steel has been studied. A36 steel is a mostly single phase body centered cubic material (BCC). Impact velocities ranged from 3.54 to 6.70 km/sec. Target materials were studied before and after impact to determine if these impact conditions result in a phase change of the A36. Scanning electron microscopy, electron back-scatter diffraction, and x-ray diffraction methods were used to investigate deformation, lattice defects, twinning, and phase transformation. A limited number of impacted targets made from 304L and HY100 steels were also examined. …

Microstructure Alone Induced Wetting Transition From Hydrophilic To Hydrophobic On Silicon And Graphene, Henry L. Ems

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

In the present work, transition from hydrophilic to hydrophobic wetting states for an intrinsically hydrophilic surface (contact angle less than 45 degrees) using only surface microstructuring is presented. The surface microstructures are re-entrant microcavities (inverted trapezoidal microstructures) which promote air entrapment below the water droplet causing a Cassie wetting state as opposed to a Wenzel state where the surface is completely wetted. The microstructures were fabricated on a Silicon-On-Insulator (SOI) wafer through steps of deposition, photolithography, etching, and bonding. Contact angle measurements demonstrated the ability of the microfabricated surfaces to sustain large contact angles above 100°, in comparison to a …

The Influence Of Iron On Arctic Thule Migration Patterns, Alina T. Aquino

UNLV Theses, Dissertations, Professional Papers, and Capstones

Arctic scholars have yet to fully understand the reasons behind the migration of Thule culture from the western to the eastern Arctic. This rapid movement across such a vast area into environmentally diverse regions marks a critical period of cultural change that is usually summarized by two theoretical positions. Ecological theories postulated environmental changes placed selective pressures on traditional food sources that required Thule hunters to follow migrating prey. Theories that focused on material acquisition alternately proposed the Thule followed the trail of meteoric iron eastward into northwestern Greenland.

This research sought to examine the eastward Thule migration from another …

Spare Parts On Demand Using Additive Manufacturing : A Simulation Model For Cost Evaluation., Stefan Jedeck

Electronic Theses and Dissertations

Little is known about the impact of additive manufacturing in the spare part supply chain. A few studies are available, but they focus on specific parts and their applications only. A general model, which can be adapted to different applications, is nonexistent. This dissertation proposes a decision making framework that enables an interested practitioner/manager to decide whether using additive manufacturing to make spare parts on demand is economical when compared to conventional warehousing strategy. The framework consists of two major components: a general discrete event simulation model and a process of designing a wide range of simulation scenarios. The goal …

Comparative Estimates Of Anthropogenic Heat Emission In Relation To Surface Energy Balance Of A Subtropical Urban Neighborhood, Changhyoun Park, Gunnar W. Schade, Nicholas D. Werner, David J. Sailor, Cheolhee Kim

Mechanical and Materials Engineering Faculty Publications and Presentations

Long-term eddy covariance measurements have been conducted in a subtropical urban area, an older neighborhood north of downtown Houston. The measured net radiation (Q*), sensible heat flux (H) and latent heat flux (LE) showed typical seasonal diurnal variations in urban areas: highest in summer; lowest in winter. From an analysis of a subset of the first two years of measurements, we find that approximately 42% of Q* is converted into H, and 22% into LE during daytime. The local anthropogenic heat emissions were estimated conventionally using the long-term residual method and the heat emission inventory approach. We also …

Chemical And Electronic Structure Of Surfaces And Interfaces In Cadmium Telluride Based Photovoltaic Devices, Douglas Arthur Duncan

UNLV Theses, Dissertations, Professional Papers, and Capstones

The surface and interface properties are of the upmost importance in the understanding, optimization, and application for photovoltaic devices. Often the chemical, electronic, and morphological properties of the films are empirically optimized, however when progress slows, a fundamental understanding of these properties can lead to breakthroughs. In this work, surfaces and interfaces of solar cell-relevant films are probed with a repertoire of X-ray analytical and microanalysis techniques including X-ray photoelectron (XPS), X-ray excited Auger electron (XAES), X-ray emission (XES) spectroscopies, and atomic force (AFM) and scanning electron (SEM) microscopies.

Silicon-based devices currently dominate the solar market, which is rather inflexible …

Effect Of Nano-Oxide Particle Size On Radiation Resistance Of Ironechromium Alloys, Weizong Xu, Lulu Li, James A. Valdez, Mostafa Saber, Yuntian Zhu, Carl C. Koch, Ronald O. Scattergood

Mechanical and Materials Engineering Faculty Publications and Presentations

Radiation resistance of Fe-14Cr alloys under 200 keV He irradiation at 500 ­*C was systematically investigated with varying sizes of nano oxide Zr, Hf and Cr particles. It is found that these nano oxide particles acted as effective sites for He bubble formation. By statistically analyzing 700-1500 He bubbles at the depth of about 150-700 nm from a series of HRTEM images for each sample, we established the variation of average He bubble size, He bubble density, and swelling percentage along the depth, and found them to be consistent with the He concentration profile calculated from the SIRM program. Oxide …

Imaging Thermal Conductivity With Nanoscale Resolution Using A Scanning Spin Probe, Abdelghani Laraoui, Halley Aycock-Rizzo, Yang Gao, Xi Lu, Elisa Riedo, Carlos A. Meriles

Advanced Science Research Center

The ability to probe nanoscale heat flow in a material is often limited by lack of spatial resolution. Here, we use a diamond-nanocrystal-hosted nitrogen-vacancy centre attached to the apex of a silicon thermal tip as a local temperature sensor. We apply an electrical current to heat up the tip and rely on the nitrogen vacancy to monitor the thermal changes the tip experiences as it is brought into contact with surfaces of varying thermal conductivity. By combining atomic force and confocal microscopy, we image phantom microstructures with nanoscale resolution, and attain excellent agreement between the thermal conductivity and topographic maps. …

Volatile Condensible Material Deposition In Leo Simulated Environment, Jinya Pu

Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research

Room Temperature Vulcanized (RTV) silicone and compounds are widely used in outer-space for bonding or potting spacecraft components. In geosynchronous equatorial orbit (GEO), the silicone may outgas species which can condense on optically sensitive surfaces and degrade their performance, therefore shortening the lifetime of spacecraft. In low-earth-orbit (LEO), the silicone rubber is subject to an energetic and corrosive environment. Atomic oxygen (AO) and ultraviolet radiation can cause abrasion and degradation of the silicone rubber, cause changes in existing condensed VCM films and affect the properties of VCM films condensing in this atmosphere. Experiments were performed to simulate GEO conditions. In …

In Vacuo Fabrication And Electronic Structure Characterization Of Atomic Layer Deposition Thin Films, Michael Schaefer

USF Tampa Graduate Theses and Dissertations

Improvement of novel electronic devices is possible by tailor-designing the electronic structure at device interfaces. Common problems observed at interfaces are related to unwanted band alignment caused by the chemical diversity of interface partners, influencing device performance negatively. One way to address this problem is by introducing ultra-thin interfacial dipole layers, steering the band alignment in a desired direction. The requirements are strict in terms of thickness, conformity and low density of defects, making sophisticated deposition techniques necessary. Atomic layer deposition (ALD) with its Ångstrom-precise thickness control can fulfill those requirements.

The work presented here encompasses the implementation of an …

Investigation Of Low Thermal Conductivity Materials With Potential For Thermoelectric Applications, Kaya Wei

USF Tampa Graduate Theses and Dissertations

Thermoelectric devices make it possible for direct energy conversion between heat and electricity. In order to achieve a high energy conversion efficiency, materials with a high thermoelectric figure of merit (ZT = S²σT/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature, and κ is the thermal conductivity) are in great demand. The standard approach is to optimize charge carrier transport while at the same time scatter the heat transport, a task that is easier said than done. Improving the electrical properties in order to increase ZT is limited since electrons …

Near-Field Microwave Microscopy For Surface And Subsurface Characterization Of Materials, Maria Fernanda Cordoba Erazo

USF Tampa Graduate Theses and Dissertations

This dissertation presents an investigation on the capabilities of Near-Field Microwave Microscopy (NFMM) for the characterization of surface and subsurface materials. Subsurface characterization refers to the detection, differentiation and imaging of dielectric, and metallic features that are coated with an insulating layer. The design, simulation and modeling, and testing of a dielectric resonator (DR)-based NFMM and a coaxial transmission line resonator-based NFMM are discussed in detail in this work. Additionally, materials differentiation and imaging capabilities of each microscope are examined using several bulk samples, liquids, GaAs MMIC circuits, and gold/glass testing patterns.

The 5.7 GHz DR-based NFMM uses a microwave …

Structure And Corrosion Behavior Of Sputter Deposited Cerium Oxide Based Coatings With Various Thickness On Al 2024-T3 Alloy Substrates, Yuanyuan Liu, Jiamu Huang, James B. Claypool, Carlos E. Castano, Matthew J. O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

Cerium oxide-based coatings from ∼100 to ∼1400 nm in thickness were deposited onto Al 2024-T3 alloy substrates by magnetron sputtering of a 99.99% pure CeO₂ target. The crystallite size of CeO₂ coatings increased from 15 nm to 46 nm as the coating thickness increased from ∼100 nm to ∼1400 nm. The inhomogeneous lattice strain increased from 0.36% to 0.91% for the ∼100 nm to ∼900 nm thick coatings and slightly decreased to 0.89% for the ∼1400 nm thick coating. The highest adhesion strength to Al alloy substrates was for the ∼210 nm thick coating, due to a continuous …

Augmented Finite Element Method For Virtual Testing Of High Temperature Cmcs, Qingda Yang, Jaedal Jung, Bao-Chan Do

Composites at Lake Louise (CALL 2015)

Ceramic matrix composites (CMCs) have been increasingly used in high heat flux applications due to their ultra-high temperature resisting capabilities. However, CMCs are prone to processing-induced or in-serve cracking due to the large thermal stresses. Thermally-induced cracking are dangerous because they provide pathways for further damaging processes such as oxidation and vapor-assisted corrosion, which may lead to catastrophic failure [1]. High-fidelity thermal-mechanical analyses to CMCs with consideration of arbitrary cracking are very challenging because the heterogeneous nature makes it impossible to know the cracking locations a priori. Yet correct and efficient treatment of crack coalescence and bifurcation is critical …

Novel Anti-Decay Self-Setting Paste Of Hydroxyapatite/Collagen Nanocomposite Utilizing Gptms, Masanori Kikuchi, Taira Sato, Mamoru Aizawa, Yuki Shirosaki

Composites at Lake Louise (CALL 2015)

Bone is a typical inorganic/ortganic nanocomposite mainly composed of hydroxyapatite (HAp) nanocrystals and collagen molecules. The composition and nanostructure is closely related to bone’s biomechanical and biochemical properties. One of the most important things for bone is a bone remodeling process that maintains mechanical strength of bone to allow walking and running as well as homeostasis of calcium in our body. In fact, sintered HAp composed of HAp crystals approximately 1 µm in particle size is considered as non-bioresorbable; however HAp nanocrystals easily resorbed by osteoclasts. A hydroxyapatite/collagen bone-like nanocomposite (HAp/Col) was successfully synthesized by the authors via self-organizing process. …

Physical Aging And Glass Transition Of Single Component Nanocomposites, Hilmar Koerner

Composites at Lake Louise (CALL 2015)

Matrix free assemblies of polymer-grafted, “hairy” nanoparticles (HNP) exhibit novel morphology, dielectric and mechanical properties, as well as providing means to overcome dispersion challenges ubiquitous to conventional polymer-inorganic blended nanocomposites. Physical aging of the amorphous polymer glass between the close-packed nanoparticles (NPs) will dominate long-term stability. However, the energetics of cooperative relaxation of tethered chains confined within the interstitial spaces in single component nanocomposites is unknown. Herein, we compare glass transition temperature (Tg) and physical aging behavior of matrix free assemblies of HNPs (aHNPs) to conventional NP-polymer blends, across different nano-silica loadings (0-50 v/v%) and brush architecture of grafted polystyrene …

Printed And Structurally Integrated Electronics For Air Force Applications, Daniel Berrigan, Benjamin Leever, Michael Durstock

Composites at Lake Louise (CALL 2015)

Both printed and flexible electronic systems promise to integrate functional devices into new form factors (e.g., structures or clothing) and environments. Of particular interest are the mechanically harsh environmental conditions to which military systems are sometimes exposed, which can be quite severe (i.e., upward of 100,000 G peak acceleration within 0.1 ms), and commercial off-the-shelf components are not designed to maintain functionality under such rugged conditions. The overarching aim of this project is to leverage the unique ability of additive manufacturing to digitally control materials properties in three dimensions to create multifunctional systems whose structure is ruggedized for mechanically these …

Ice Formation In Iron Containing Hydrogel Films, Hyun-Joong Chung

Composites at Lake Louise (CALL 2015)

The states of water in polymers, including ice formation, is of increasing interest for a broad range of science and engineering, including the application and the longevity of water-bourne polymeric coatings, cryogenic preservation of cells and organs, ice mediated porous structure formation, freeze-drying process in food preservation, low temperature operation of batteries and supercapacitors, and the tailing pond sedimentation in oil sands production. The freezing point of water is heavily influenced by the polymer-water interaction and the concentration of ionic species in the water and in the polymer backbones. Various species of salt ions are abundant in the operating conditions …

Simultaneously Strong And Tough Continuous Nanofibers For Next Generation Structural Supernanocomposites, Yuris Dzenis

Composites at Lake Louise (CALL 2015)

Modern advanced composites and fibers are strong but brittle. Optimization of damage progression in composites has led only to moderate toughening. The advent of novel nanomaterials such as CNT and graphene has raised hopes for the development of strong and tough structural materials. However, problems with dispersion, alignment, achieving high volume fraction of discontinuous nanoreinforcement, and interfacial stress transfer proved to be more difficult than was initially thought. Recently, a different class of nanomaterials, i.e. continuous nanofibers, has been shown to possess unusual mechanical properties. This presentation will review recent breakthroughs on ultra-high-performance continuous nanofibers and their composites. Controlled nanofiber …

Biopolymer Composites From High-Cellulose Pulps And/Or Nanocellulose, Fabiola Vilaseca

Composites at Lake Louise (CALL 2015)

Increasingly our society seeks an economy based on renewable resources (bio-based economy) with the goal of providing materials of high value and from renewable resources. One popular renewable resource is cellulose, or forest products in general. In this study, cellulose derivatives will be combined together with bio-plastics to produce granules of thermoplastic nano-biocomposites by melt processing. The intention is to get bio-based materials with highly advanced properties that can be shaped into complex geometries using widely used industrial melt-processes such as extrusion or injection molding.

The challenges in this study deal with production technologies for the realization of nanocomposites for …