You limited your search to:

 Department: Department of Materials Science and Engineering
 Degree Level: Master's
 Collection: UNT Theses and Dissertations
Compostable Soy-Based Polyurethane Foam with Kenaf Core Modifiers

Compostable Soy-Based Polyurethane Foam with Kenaf Core Modifiers

Access: Use of this item is restricted to the UNT Community.
Date: August 2016
Creator: Hoyt, Zachary
Description: Building waste and disposable packaging are a major component in today's landfills. Most of these are structural or thermally insulative polymer foams that do not degrade over a long period of time. Currently, there is a push to replace these foams with thermoplastic or biodegradable foams that can either be recycled or composted. We propose the use of compostable soy-based polyurethane foams (PU) with kenaf core modifiers that will offer the desired properties with the ability to choose responsible end-of-life decisions. The effect of fillers is a critical parameter in investigating the thermal and mechanical properties along with its effect on biodegradability. In this work, foams with 5%, 10%, and 15% kenaf core content were created. Two manufacturing approaches were used: the free foaming used by spray techniques and the constrained expansion complementary to a mold cavity. Structure-property relations were examined using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), thermal conductivity, compression values, scanning electron microscopy (SEM), x-ray micro-computed tomography (micro-CT), and automated multiunit composting system (AMCS). The results show that mechanical properties are reduced with the introduction of kenaf core reinforcement while thermal conductivity and biodegradability display a noticeable improvement. This shows that in application properties can be ...
Contributing Partner: UNT Libraries
Microstructural Phase Evolution In Laser Deposited Compositionally Graded Titanium-Chromium Alloys

Microstructural Phase Evolution In Laser Deposited Compositionally Graded Titanium-Chromium Alloys

Access: Use of this item is restricted to the UNT Community.
Date: May 2016
Creator: Thomas, Jonova
Description: A compositionally graded Ti-xCr (10≤x≤30 wt%) alloy has been fabricated using Laser Engineered Net Shaping (LENSTM) to study the microstructural phase evolution along a compositional gradient in both as-deposited and heat treated conditions (1000°C followed by furnace cooling or air cooling). The alloys were characterized by SEM BSE imaging, XRD, EBSD, TEM and micro-hardness measurements to determine processing-structure-property relations. For the as-deposited alloy, α-Ti, β-Ti, and TiCr2 (C15 Laves) phases exist in varying phase fractions, which were influential in determining hardness values. With the furnace cooled alloy, there was more homogeneous nucleation of α phase throughout the sample with a larger phase fraction of TiCr2 resulting in increased hardness values. When compared to the air cooled alloy, there was absence of wide scale nucleation of α phase and formation of ω phase within the β phase due to the quicker cooling from elevated temperature. At lower concentrations of Cr, the kinetics resulted in a diffusionless phase transformation of ω phase with increased hardness and a lower phase fraction of TiCr2. In contrast at higher Cr concentrations, α phase separation reaction occurs where the β phase is spinodally decomposed to Cr solute-lean β1 and solute-rich β2 resulting in reduced hardness.
Contributing Partner: UNT Libraries
Characterization of Ti-6al-4v Produced Via Electron Beam Additive Manufacturing

Characterization of Ti-6al-4v Produced Via Electron Beam Additive Manufacturing

Date: December 2015
Creator: Hayes, Brian J.
Description: In recent years, additive manufacturing (AM) has become an increasingly promising method used for the production of structural metallic components. There are a number of reasons why AM methods are attractive, including the ability to produce complex geometries into a near-net shape and the rapid transition from design to production. Ti-6Al-4V is a titanium alloy frequently used in the aerospace industry which is receiving considerable attention as a good candidate for processing via electron beam additive manufacturing (EBAM). The Sciaky EBAM method combines a high-powered electron beam, weld-wire feedstock, and a large build chamber, enabling the production of large structural components. In order to gain wide acceptance of EBAM of Ti-6Al-4V as a viable manufacturing method, it is important to understand broadly the microstructural features that are present in large-scale depositions, including specifically: the morphology, distribution and texture of the phases present. To achieve such an understanding, stereological methods were used to populate a database quantifying key microstructural features in Ti-6Al-4V including volume fraction of phases, a lath width, colony scale factor, and volume fraction of basket weave type microstructure. Microstructural features unique to AM, such as elongated grains and banded structures, were also characterized. Hardness and tensile testing were ...
Contributing Partner: UNT Libraries
Determining the Emissivity of Roofing Samples: Asphalt, Ceramic and Coated Cedar

Determining the Emissivity of Roofing Samples: Asphalt, Ceramic and Coated Cedar

Date: December 2015
Creator: Adesanya, Oludamilola
Description: The goal is to perform heat measurements examine of selected roofing material samples. Those roofing materials are asphalt shingles, ceramics, and cedar. It’s important to understand the concept of heat transfer, which consists of conduction, convection, and radiation. Research work was reviewed on different infrared devices to see which one would be suitable for conducting my experiment. In this experiment, the main focus was on a specific property of radiation. That property is the emissivity, which is the amount of heat a material is able to radiate compared to a blackbody. An infrared measuring device, such as the infrared camera was used to determine the emissivity of each sample by using a measurement formula consisting of certain equations. These equations account for the emissivity, transmittance of heat through the atmosphere and temperatures of the samples, atmosphere and background. The experiment verifies how reasonable the data is compared to values in the emissivity table. A blackbody method such as electrical black tape was applied to help generate the correct data. With this data obtained, the emissivity was examined to understand what factors and parameters affect this property of the materials. This experiment was conducted using a suitable heat source to heat ...
Contributing Partner: UNT Libraries
Effect of Alloy Composition, Free Volume and Glass Formability on the Corrosion Behavior of Bulk Metallic Glasses

Effect of Alloy Composition, Free Volume and Glass Formability on the Corrosion Behavior of Bulk Metallic Glasses

Date: December 2015
Creator: Ayyagari, Venkata Aditya
Description: Bulk metallic glasses (BMGs) have received significant research interest due to their completely amorphous structure which results in unique structural and functional properties. Absence of grain boundaries and secondary phases in BMGs results in high corrosion resistance in many different environments. Understanding and tailoring the corrosion behavior can be significant for various structural applications in bulk form as well as coatings. In this study, the corrosion behavior of several Zr-based and Fe-Co based BMGs was evaluated to understand the effect of chemistry as well as quenched in free volume on corrosion behavior and mechanisms. Presence of Nb in Zr-based alloys was found to significantly improve corrosion resistance due to the formation of a stable passive oxide. Relaxed glasses showed lower rates compared to the as-cast alloys. This was attributed to lowering of chemical potential from the reduced fraction of free volume. Potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) techniques helped in quantifying the corrosion rate and polarization resistance. The effect of alloy composition was quantified by extensive surface analysis using Raman spectroscopy, energy dispersive x-ray spectroscopy and auger spectroscopy. Pitting intensity was higher in the as-cast glasses than the relaxed glasses. The electrochemical behavior of a Zr-Ti-Cu-Ni-Be bulk metallic glass ...
Contributing Partner: UNT Libraries
Synchrotron Radiation X-Ray Diffraction of Nickel-Titanium Shape Memory Alloy Wires during Mechanical Deformation

Synchrotron Radiation X-Ray Diffraction of Nickel-Titanium Shape Memory Alloy Wires during Mechanical Deformation

Access: Use of this item is restricted to the UNT Community.
Date: December 2015
Creator: Zhang, Baozhuo
Description: Shape memory alloys (SMAs) are a new generation material which exhibits unique nonlinear deformations due to a phase transformation which allows it to return to its original shape after removal of stress or a change in temperature. It shows a shape memory effect (martensitic condition) and pseudoelasticity (austenitic condition) properties depends on various heat treatment conditions. The reason for these properties depends on phase transformation through temperature changes or applied stress. Many technological applications of austenite SMAs involve cyclical mechanical loading and unloading in order to take advantage of pseudoelasticity, but are limited due to poor fatigue life. In this thesis, I investigated two important mechanical feature to fatigue behavior in pseudoelastic NiTi SMA wires using high energy synchrotron radiation X-ray diffraction (SR-XRD). The first of these involved simple bending and the second of these involved relaxation during compression loading. Differential scanning calorimetry (DSC) was performed to identify the phase transformation temperatures. Scanning electron microscopy (SEM) images were collected for the initial condition of the NiTi SMA wires and during simple bending, SEM revealed that micro-cracks in compression regions of the wire propagate with increasing bend angle, while tensile regions tend to not exhibit crack propagation. SR-XRD patterns were analyzed ...
Contributing Partner: UNT Libraries
An Assessment of Uncommon Titanium Binary Systems: Ti-Zn, Ti-Cu, and  Ti-Sb

An Assessment of Uncommon Titanium Binary Systems: Ti-Zn, Ti-Cu, and Ti-Sb

Date: May 2015
Creator: Brice, David
Description: The current study focuses on phase stability and evolution in the titanium-zinc titanium-copper and titanium-antimony systems. The study utilized the Laser Engineering Net Shaping (LENS™) processing technique to deposit compositionally graded samples of three binary system in order to allow the assessment of phase stability and evolution as a function of composition and temperature the material is subjected to. Through LENS™ processing it was possible to create graded samples from Ti-xSb (up to 13wt%) and Ti-xCu (up to 16wt%). The LENS™ deposited gradient were solutionized, and step quenched to specific aging temperature, and the resulting microstructures and phase were characterized utilizing XRD, EDS, SEM, FIB and TEM. The Ti-Zn system proved incapable of being LENS™ deposited due to the low vaporization temperature of Zn; however, a novel processing approach was developed to drip liquid Zn onto Ti powder at temperatures above β transus temperature of Ti (882 ◦C) and below the vaporization temperature of Zn (907 ◦C). The product of this processing technique was characterized in a similar way as the graded LENS™ depositions. From measurements performed on Ti-Sb it seems that Sb could be a potential α stabilizer in Ti due to the presence of a mostly homogeneous α ...
Contributing Partner: UNT Libraries
Nanohybrids Based on Solid and Foam Polyurethanes

Nanohybrids Based on Solid and Foam Polyurethanes

Date: May 2015
Creator: Bo, Chong
Description: Polymer nanocomposites are a going part of Materials Science and Engineering. These new composite materials exhibit dimensional and thermal stability of inorganic materials and toughness and dielectric properties of polymers. Development of nanocomposites become an important approach to create high-performance composite materials. In this study silica, fly ash, silica nanotubes and carbon black particles have been added to modify polyurethane foam and thermoplastic polyurethanes. It has been found that the addition of silica can diminish the size of foam bubbles, resulting in an increased stiffness of the material, increase of the compressive strength, and greater resistance to deformation. However, the uniformity of bubbles is reduced, resulting in increased friction of the material. Fly ash added to the foam can make bubbles smaller and improve uniformity of cells. Therefore, the material stiffness and compressive strength, resistance to deformation, and has little impact on the dynamic friction of the material. Adding nanotubes make bubble size unequal, and the arrangement of the bubble uneven, resulting in decreased strength of the material, while the friction increases. After the addition of carbon black to the polyurethane foam, due to the special surface structure of the carbon black, the foam generates more bubbles during the foaming ...
Contributing Partner: UNT Libraries
Processing and Characterization of Polycarbonate Foams with Supercritical Co2 and 5-Phenyl-1h-Tetrazole

Processing and Characterization of Polycarbonate Foams with Supercritical Co2 and 5-Phenyl-1h-Tetrazole

Date: May 2015
Creator: Cloarec, Thomas
Description: Since their discovery in the 1930s, polymeric foams have been widely used in the industry for a variety of applications such as acoustical and thermal insulation, filters, absorbents etc. The reason for this ascending trend can be attributed to factors such as cost, ease of processing and a high strength to weight ratio compared to non-foamed polymers. The purpose of this project was to develop an “indestructible” material made of polycarbonate (PC) for industrial applications. Due to the high price of polycarbonate, two foaming methods were investigated to reduce the amount of material used. Samples were foamed physically in supercritical CO2 or chemically with 5-phenyl-1H-tetrazole. After thermal characterization of the foams in differential scanning calorimetry (DSC), we saw that none of the foaming methods had an influence on the glass transition of polycarbonate. Micrographs taken in scanning electron microscopy (SEM) showed that foams obtained in physical and chemical foaming had different structures. Indeed, samples foamed in supercritical CO2 exhibited a microcellular opened-cell structure with a high cell density and a homogeneous cell distribution. On the other hand, samples foamed with 5-phenyl-1H-tetrazole had a macrocellular closed-cell structure with a much smaller cell density and a random cell distribution. Compression testing showed ...
Contributing Partner: UNT Libraries
Surface Topography and Aesthetics of Recycled Cross-Linked Polyethylene Wire and Cable Coatings

Surface Topography and Aesthetics of Recycled Cross-Linked Polyethylene Wire and Cable Coatings

Access: Use of this item is restricted to the UNT Community.
Date: December 2014
Creator: Xie, Wa
Description: Our research focuses on re-using a waste a material, cross-linked polyethylene abbreviated XLPE, which is a widely used coating for wires. XLPE is strong and has excellent thermal properties due to its chemical structure - what leads to the significance of recycling this valuable polymer. Properties of XLPE include good resistance to heat, resistance to chemical corrosion, and high impact strength. A wire is usually composed of a metal core conductor and polymeric coating layers. One creates a new coating, including little pieces of recycled XLPE in the lower layer adjacent to the wire, and virgin XLPE only in the upper layer. Industries are often wasting materials which might be useful. Mostly, some returned or excess products could be recycled to create a new type of product or enable the original use. This method helps cleaning the waste, lowers the costs, and enhances the income of the manufacturing company. With the changing of the thickness of the outer layer, the roughness changes significantly. Moreover, different processing methods result in surfaces that look differently.
Contributing Partner: UNT Libraries
Atomistic Computer Simulations of Diffusion Mechanisms in Lithium Lanthanum Titanate Solid State Electrolytes for Lithium Ion Batteries

Atomistic Computer Simulations of Diffusion Mechanisms in Lithium Lanthanum Titanate Solid State Electrolytes for Lithium Ion Batteries

Date: August 2014
Creator: Chen, Chao-Hsu
Description: Solid state lithium ion electrolytes are important to the development of next generation safer and high power density lithium ion batteries. Perovskite-structured LLT is a promising solid electrolyte with high lithium ion conductivity. LLT also serves as a good model system to understand lithium ion diffusion behaviors in solids. In this thesis, molecular dynamics and related atomistic computer simulations were used to study the diffusion behavior and diffusion mechanism in bulk crystal and grain boundary in lithium lanthanum titanate (LLT) solid state electrolytes. The effects of defect concentration on the structure and lithium ion diffusion behaviors in LLT were systematically studied and the lithium ion self-diffusion and diffusion energy barrier were investigated by both dynamic simulations and static calculations using the nudged elastic band (NEB) method. The simulation results show that there exist an optimal vacancy concentration at around x=0.067 at which lithium ions have the highest diffusion coefficient and the lowest diffusion energy barrier. The lowest energy barrier from dynamics simulations was found to be around 0.22 eV, which compared favorably with 0.19 eV from static NEB calculations. It was also found that lithium ions diffuse through bottleneck structures made of oxygen ions, which expand in dimension by 8-10% ...
Contributing Partner: UNT Libraries
Thermoplastic and Thermoset Natural Fiber Composite and Sandwich Performance

Thermoplastic and Thermoset Natural Fiber Composite and Sandwich Performance

Access: Use of this item is restricted to the UNT Community.
Date: May 2014
Creator: Yang, Bing
Description: The objective of this thesis is to investigate the effects of adding natural fiber (kenaf fiber, retted kenaf fiber, and sugarcane fiber) into polymer materials. The effects are obtained by considering three main parts. 1. Performance in thermoplastic composites. The effect of fiber retting on polymer composite crystallization and mechanical performance was investigated. PHBV/PBAT in 80/20 blend ratio was modified using 5% by weight kenaf fiber. Dynamic mechanical analysis of the composites was done to investigate the glass transition and the modulus at sub-ambient and ambient temperatures. ESEM was conducted to analyze fiber topography which revealed smoother surfaces on the pectinase retted fibers. 2. Performance in thermoset composites. The effect of the incorporation of natural fibers of kenaf and of sugarcane combined with the polyester resin matrix is investigated. A comparison of mechanical properties of kenaf polyester composite, sugarcane polyester composite and pure polyester in tensile, bending, dynamic mechanical thermal analysis (DMA) and moisture test on performance is measured.. 3. Performance in sandwich composites. The comparison of the performance characteristics and mechanical properties of natural fiber composites panels with soft and rigid foam cores are evaluated. A thorough test of the mechanical behavior of composites sandwich materials in tensile, bending ...
Contributing Partner: UNT Libraries
Dynamic Precipitation of Second Phase Under Deformed Condition in Mg-nd Based Alloy

Dynamic Precipitation of Second Phase Under Deformed Condition in Mg-nd Based Alloy

Date: December 2013
Creator: Dendge, Nilesh Bajirao
Description: Magnesium alloys are the lightweight structural materials with high strength to weigh ratio that permits their application in fuel economy sensitive automobile industries. Among the several flavors of of Mg-alloys, precipitation hardenable Mg-rare earth (RE) based alloys have shown good potential due to their favorable creep resistance within a wide window of operating temperatures ranging from 150°C to 300°C. A key aspect of Mg-RE alloys is the presence of precipitate phases that leads to strengthening of such alloys. Several notable works, in literature, have been done to examine the formation of such precipitate phases. However, there are very few studies that evaluated the effect stress induced deformation on the precipitation in Mg-RE alloys. Therefore, the objective of this work is to examine influence of deformation on the precipitation of Mg-Nd based alloys. To address this problem, precipitation in two Mg-Nd based alloys, subjected to two different deformation conditions, and was examined via transmission electron microscopy (TEM) and atom probe tomography (APT). In first deformation condition, Md-2.6wt%Nd alloy was subjected to creep deformation (90MPa / 177ºC) to failure. Effect of stress-induced deformation was examined by comparing and contrasting with precipitation in non-creep tested specimens subjected to isothermal annealing (at 177ºC). In ...
Contributing Partner: UNT Libraries
Laser Surface Modification on Az31b Mg Alloy for Bio-wettability

Laser Surface Modification on Az31b Mg Alloy for Bio-wettability

Date: December 2013
Creator: Ho, YeeHsien
Description: Laser surface modification of AZ31B Magnesium alloy changes surface composition and roughness to provide improved surface bio-wettability. Laser processing resulted in phase transformation and grain refinement due to rapid quenching effect. Furthermore, instantaneous heating and vaporization resulted in removal of material, leading the textured surface generation. A study was conducted on a continuum-wave diode-pumped ytterbium laser to create multiple tracks for determining the resulting bio-wettability. Five different laser input powers were processed on Mg alloy, and then examined by XRD, SEM, optical profilometer, and contact angle measurement. A finite element based heat transfer model was developed using COMSOL multi-physics package to predict the temperature evolution during laser processing. The thermal histories predicted by the model are used to evaluate the cooling rates and solidification rate and the associated changes in the microstructure. The surface energy of laser surface modification samples can be calculated by measuring the contact angle with 3 different standard liquid (D.I water, Formamide, and 1-Bromonaphthalen). The bio-wettability of the laser surface modification samples can be conducted by simulated body fluid contact angle measurement. The results of SEM, 3D morphology, XRD, and contact angle measurement show that the grain size and roughness play role for wetting behavior of ...
Contributing Partner: UNT Libraries
Tribological Behavior of Spark Plasma Sintered Tic/graphite/nickel Composites and Cobalt Alloys

Tribological Behavior of Spark Plasma Sintered Tic/graphite/nickel Composites and Cobalt Alloys

Access: Use of this item is restricted to the UNT Community.
Date: December 2013
Creator: Kinkenon, Douglas
Description: Monolithic composites are needed that combine low friction and wear, high mechanical hardness, and high fracture toughness. Thin films and coatings are often unable to meet this engineering challenge as they can delaminate and fracture during operation ceasing to provide beneficial properties during service life. Two material systems were synthesized by spark plasma sintering (SPS) and were studied for their ability to meet these criteria. A dual hybrid composite was fabricated and consisted of a nickel matrix for fracture toughness, TiC for hardness and graphite for solid/self‐lubrication. An in‐situ reaction during processing resulted in the formation of TiC from elemental Ti and C powders. The composition was varied to determine its effects on tribological behavior. Stellite 21, a cobalt‐chrome‐molybdenum alloy, was also produced by SPS. Stellite 21 has low stacking fault energy and a hexagonal phase which forms during sliding that both contribute to low interfacial shear and friction. Samples were investigated by x‐ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x‐ray spectroscopy (EDS), and electron back‐scattered diffraction (EBSD). Tribological properties were characterized by pin on disc tribometry and wear rates were determined by profilometry and abrasion testing. Solid/self‐lubrication in the TiC/C/Ni system was investigated by Raman and Auger ...
Contributing Partner: UNT Libraries
Corrosion Protection of Aerospace Grade Magnesium Alloy Elektron 43™ for Use in Aircraft Cabin Interiors

Corrosion Protection of Aerospace Grade Magnesium Alloy Elektron 43™ for Use in Aircraft Cabin Interiors

Date: August 2013
Creator: Baillio, Sarah S.
Description: Magnesium alloys exhibit desirable properties for use in transportation technology. In particular, the low density and high specific strength of these alloys is of interest to the aerospace community. However, the concerns of flammability and susceptibility to corrosion have limited the use of magnesium alloys within the aircraft cabin. This work studies a magnesium alloy containing rare earth elements designed to increase resistance to ignition while lowering rate of corrosion. The microstructure of the alloy was documented using scanning electron microscopy. Specimens underwent salt spray testing and the corrosion products were examined using energy dispersive spectroscopy.
Contributing Partner: UNT Libraries
Dislocation Dynamics Simulations of Plasticity in Cu Thin Films

Dislocation Dynamics Simulations of Plasticity in Cu Thin Films

Date: August 2013
Creator: Wu, Han
Description: Strong size effects in plastic deformation of thin films have been experimentally observed, indicating non-traditional deformation mechanisms. These observations require improved understanding of the behavior of dislocation in small size materials, as they are the primary plastic deformation carrier. Dislocation dynamics (DD) is a computational method that is capable of directly simulating the motion and interaction of dislocations in crystalline materials. This provides a convenient approach to study micro plasticity in thin films. While two-dimensional dislocation dynamics simulation in thin film proved that the size effect fits Hall-Petch equation very well, there are issues related to three-dimensional size effects. In this work, three-dimensional dislocation dynamics simulations are used to study model cooper thin film deformation. Grain boundary is modeled as impenetrable obstacle to dislocation motion in this work. Both tension and cyclic loadings are applied and a wide range of size and geometry of thin films are studied. The results not only compare well with experimentally observed size effects on thin film strength, but also provide many details on dislocation processes in thin films, which could greatly help formulate new mechanisms of dislocation-based plasticity.
Contributing Partner: UNT Libraries
Laser Deposition, Heat-treatment, and Characterization of the Binary Ti-xmn System

Laser Deposition, Heat-treatment, and Characterization of the Binary Ti-xmn System

Date: August 2013
Creator: Avasarala, Chandana
Description: The present research seeks to characterization of an additively manufactured and heat-treated Ti-xMn gradient alloy, a binary system that has largely been unexplored. In order to rapidly assess this binary system, compositionally graded Ti-xMn (0<x<15 wt%) specimens were fabricated using the LENS (Laser Engineered Net Shaping) and were subsequently heat-treated and characterized using a wide range of techniques. Microstructural changes with respect to the change in thermal treatments, hardness and chemical composition were observed and will be presented. These include assessments of both continuous cooling, leading to observations of both equilibrium and metastable phases, including the titanium martensites, and to direct aging studies looking for composition regimes that produce highly refined alpha precipitates – a subject of great interest given recent understandings of non-classical nucleation and growth mechanisms. The samples were characterized using SEM, EDS, TEM, and XRD and the properties probed using a Vickers Microhardness tester.
Contributing Partner: UNT Libraries
A Study of Mechanisms to Engineer Fine Scale Alpha Phase Precipitation in Beta Titanium Alloy, Beta 21S

A Study of Mechanisms to Engineer Fine Scale Alpha Phase Precipitation in Beta Titanium Alloy, Beta 21S

Date: August 2013
Creator: Behera, Amit Kishan
Description: Metastable b-Ti alloys are titanium alloys with sufficient b stabilizer alloying additions such that it's possible to retain single b phase at room temperature. These alloys are of great advantage compared to a/b alloys since they are easily cold rolled, strip produced and can attain excellent mechanical properties upon age hardening. Beta 21S, a relatively new b titanium alloy in addition to these general advantages is known to possess excellent oxidation and corrosion resistance at elevated temperatures. A homogeneous distribution of fine sized a precipitates in the parent b matrix is known to provide good combination of strength, ductility and fracture toughness. The current work focuses on a study of different mechanisms to engineer homogeneously distributed fine sized a precipitates in the b matrix. The precipitation of metastable phases upon low temperature aging and their influence on a precipitation is studied in detail. The precipitation sequence on direct aging above the w solvus temperature is also assessed. The structural and compositional evolution of precipitate phase is determined using multiple characterization tools. The possibility of occurrence of other non-classical precipitation mechanisms that do not require heterogeneous nucleation sites are also analyzed. Lastly, the influence of interstitial element, oxygen on a precipitation ...
Contributing Partner: UNT Libraries
A Study of Power Generation From a Low-cost Hydrokinetic Energy System

A Study of Power Generation From a Low-cost Hydrokinetic Energy System

Date: August 2013
Creator: Davila Vilchis, Juana Mariel
Description: The kinetic energy in river streams, tidal currents, or other artificial water channels has been used as a feasible source of renewable power through different conversion systems. Thus, hydrokinetic energy conversion systems are attracting worldwide interest as another form of distributed alternative energy. Because these systems are still in early stages of development, the basic approaches need significant research. The main challenges are not only to have efficient systems, but also to convert energy more economically so that the cost-benefit analysis drives the growth of this alternative energy form. One way to view this analysis is in terms of the energy conversion efficiency per unit cost. This study presents a detailed assessment of a prototype hydrokinetic energy system along with power output costs. This experimental study was performed using commercial low-cost blades of 20 in diameter inside a tank with water flow speed up to 1.3 m/s. The work was divided into two stages: (a) a fixed-pitch blade configuration, using a radial permanent magnet generator (PMG), and (b) the same hydrokinetic turbine, with a variable-pitch blade and an axial-flux PMG. The results indicate that even though the efficiency of a simple blade configuration is not high, the power coefficient is ...
Contributing Partner: UNT Libraries
Surface Modifications to Enhance the Wear Resistance and the Osseo-integration Properties of Biomedical Ti-alloy

Surface Modifications to Enhance the Wear Resistance and the Osseo-integration Properties of Biomedical Ti-alloy

Date: August 2013
Creator: Kami, Pavani
Description: The current study focuses on improving the wear resistance of femoral head component and enhancing the osseo-integration properties of femoral stem component of a hip implant made of a new generation low modulus alloy, Ti-35Nb-7Zr-5Ta or TNZT. Different techniques that were adopted to improve the wear resistance of low-modulus TNZT alloy included; (a) fabrication of graded TNZT-xB (x= 0, 1, 2 wt%) samples using LENS, (b) oxidation, and (c) LASER nitriding of TNZT. TNZT-1B and TNZT-O samples have shown improved wear resistance when tested against UHMWPE ball in SBF medium. A new class of bio-ceramic coatings based on calcium phosphate (CaP), was applied on the TNZT sample surface and was further laser processed with the objective of enhancing their osseo-integration properties. With optimized LASER parameters, TNZT-CaP samples have shown improved corrosion resistance, surface wettability and cellular response when compared to the base TNZT sample.
Contributing Partner: UNT Libraries
Effect of Retting on Surface Chemistry and Mechanical Performance Interactions in Natural Fibers for High Performance Polymer Composites

Effect of Retting on Surface Chemistry and Mechanical Performance Interactions in Natural Fibers for High Performance Polymer Composites

Access: Use of this item is restricted to the UNT Community.
Date: May 2013
Creator: Ramesh, Dinesh
Description: Sustainability through replacement of non-renewable fibers with renewable fibers is an ecological need. Impact of transportation costs from South-east Asia on the life cycle analysis of the composite is detrimental. Kenaf is an easily grown crop in America. Farm based processing involves placing the harvested crop in rivers and ponds, where retting of the fibers from the plant (separation into fibers) can take 2 weeks or more. The objective of this thesis is to analyze industrially viable processes for generating fibers and examine their synergistic impact on mechanical performance, surface topography and chemistry for functional composites. Comparison has been made with commercial and conventional retting process, including alkali retting, enzymatic retting, retting in river and pond water (retting occurs by natural microbial population) with controlled microbial retting. The resulting kenaf fibers were characterized by dynamic mechanical analysis (DMA), Raman spectroscopy (FT-Raman), Fourier transform infrared spectroscopy (FT-IR), polarized optical microscopy (POM), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) optical fluorescence microscopy, atomic force microscopy (AFM) and carbohydrate analysis. DMA results showed that pectinase and microbe treated fibers have superior viscoelastic properties compared to alkali retting. XPS, Raman, FT-IR and biochemical analysis indicated that the controlled microbial and pectinase retting was ...
Contributing Partner: UNT Libraries
Interspecimen Study of Bone to Relate Macromechanical, Nanomechanical and Compositional Changes Across the Femoral Cortex of Bone

Interspecimen Study of Bone to Relate Macromechanical, Nanomechanical and Compositional Changes Across the Femoral Cortex of Bone

Access: Use of this item is restricted to the UNT Community.
Date: May 2013
Creator: Nar, Mangesh
Description: Mechanics of bone is widely studied and researched, mainly for the study of fracture. This has been done mostly on a macro scale. In this work hierarchical nature of bone has been explored to investigate bone mechanics in more detail. Flexural test were done to classify the bones according to their strength and deflection. Raman spectroscopy analysis was done to map the mineralization, collagen crosslinking changes across the thickness of the bone. Nanoindentation was done to map indentation hardness and indentation modulus across femoral cortex of the bone. The results indicate that the composition of the bone changes across the thickness of the femoral cortex. The hypothesis is confirmed as increase in mineralization, carbonate to phosphate ratio and collagen crosslinking shows the effect as increased indentation hardness and modulus and decreased deflection.
Contributing Partner: UNT Libraries
An Integrated Approach to Determine Phenomenological Equations in Metallic Systems

An Integrated Approach to Determine Phenomenological Equations in Metallic Systems

Date: December 2012
Creator: Ghamarian, Iman
Description: It is highly desirable to be able to make predictions of properties in metallic materials based upon the composition of the material and the microstructure. Unfortunately, the complexity of real, multi-component, multi-phase engineering alloys makes the provision of constituent-based (i.e., composition or microstructure) phenomenological equations extremely difficult. Due to these difficulties, qualitative predictions are frequently used to study the influence of microstructure or composition on the properties. Neural networks were used as a tool to get a quantitative model from a database. However, the developed model is not a phenomenological model. In this study, a new method based upon the integration of three separate modeling approaches, specifically artificial neural networks, genetic algorithms, and monte carlo was proposed. These three methods, when coupled in the manner described in this study, allows for the extraction of phenomenological equations with a concurrent analysis of uncertainty. This approach has been applied to a multi-component, multi-phase microstructure exhibiting phases with varying spatial and morphological distributions. Specifically, this approach has been applied to derive a phenomenological equation for the prediction of yield strength in a+b processed Ti-6-4. The equation is consistent with not only the current dataset but also, where available, the limited information regarding certain ...
Contributing Partner: UNT Libraries
FIRST PREV 1 2 3 NEXT LAST