Materials Science and Engineering Commons^™

The Significance Of Equi-Biaxial Bubble Inflation In Determining Elastomeric Fatigue Properties, Stephen Jerrams, Niall Murphy, John Hanley

Books/Book Chapters

It is well documented that for the effective modelling of the static and dynamic behaviour of elastomeric components using the finite element (FE) method it is essential to obtain material parameters that are derived from a range of physical tests. For a conventional linear solid, uniaxial testing suffices to fully characterise the material, but for rubber it is necessary to test in at least two deformation modes. Also, the determination of fatigue lives of rubber components is still in its infancy and a reliable, repeatable fatigue test for rubber will have important consequences for component design, functionality, maintenance and cost. …

Effect Of Impurities On The Superheating Field Of Type-Ii Superconductors, F. Pei-Jen Lin, A. Gurevich

Physics Faculty Publications

We consider the effect of nonmagnetic and magnetic impurities on the superheating field H_s in a type-II superconductor. We solved the Eilenberger equations, which take into account the nonlinear pairbreaking of Meissner screening currents, and calculated H_s(T) for arbitrary temperatures and impurity concentrations in a single-band s-wave superconductor with a large Ginzburg-Landau parameter. At low temperatures, nonmagnetic impurities suppress a weak maximum in H_s(T), which has been predicted for the clean limit, resulting, instead, in a maximum of H_s as a function of impurity concentration in a moderately clean limit. It is shown that …

Encapsulation Of High Temperature Phase Change Materials For Thermal Energy Storage, Rupa Nath

USF Tampa Graduate Theses and Dissertations

Thermal energy storage is a major contributor to bridge the gap between energy demand (consumption) and energy production (supply) by concentrating solar power. The utilization of high latent heat storage capability of phase change materials is one of the keys to an efficient way to store thermal energy. However, some of the limitations of the existing technology are the high volumetric expansion and low thermal conductivity of phase change materials (PCMs), low energy density, low operation temperatures and high cost. The present work deals with encapsulated PCM system, which operates at temperatures above 500°C and takes advantage of the heat …

Effective Dielectric Constant Of Two Phase Systems, Vladimir Petrovsky, Piotr Z. Jasinski, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Theoretical approaches to electrical characterization of two phase systems are mostly limited to the systems where the individual components exhibit the same type of conductivity (pure dielectric or pure conductive systems). In this article, the brick wall geometry is extended to the mixed conductive systems with percolation. Impedance spectroscopy techniques were used for experimental investigation of slurries. Various metal oxide powders and host liquids were analyzed using a wide range of solids loadings. Comparison of experimental results with theoretical predictions shows good fitting of the experimental data. Parameters (the values of permittivity for both phases and percolation threshold) calculated from …

Deposition Of Cerium-Based Conversion Coatings On Aluminum Alloy 380, Ci Lin, Surender Maddela, William Fahrenholtz, Matthew O'Keefe

Materials Science and Engineering Faculty Research & Creative Works

Cerium-based conversion coatings were deposited on as-cast aluminum alloy 380 substrates by a spontaneous immersion process. In this study, the effects of rinsing temperature prior to immersion in the coating deposition solution were studied with respect to the surface morphology, electrochemical response, and corrosion resistance of the coatings. Panels rinsed at 25 degrees celsius prior to coating had large cracks and holes in the coating. In contrast, panels rinsed at 100 degrees celsius prior to coating had a uniform coating morphology with fewer, smaller cracks. Electrochemical testing revealed that coatings deposited on substrates rinsed at 100 degrees celsius had higher …

Directional Anisotropy In The Mechanical Behavior Of Friction Stir Processed And Aged Az91 Alloy, Vipin Jain, Wei Yuan, R. S. Mishra, Gouthama, Anil K. Gupta

Materials Science and Engineering Faculty Research & Creative Works

Friction stir processing (FSP) is an emerging grain refinement technique for magnesium alloys. in this study, a cast AZ91 alloy was processed by a single-pass FSP to achieve an average grain size of ∼6 μm in the nugget zone. the FSP is found to introduce texture in the alloy due to preferred alignment of basal poles in the processing direction. the mechanical behavior is significantly influenced by texture. after FSP, the alloy was aged at different temperatures and times for continuous and discontinuous precipitation of β-Mg17Al12. a high anisotropy in yield stress is observed in the processing and transverse direction …

Numerical Simulation Of Natural Convection In Rectangular Enclosures Of Varying Aspect Ratios And Its Feasibility In Environmental Impact Management Studies, Charles R. Walker

College of Graduate Studies: Theses & Dissertations

Author's abstract: Numerical simulation was used to investigate natural convection in horizontal and vertical enclosures with and without an internal heat source. Natural convection in rectangular enclosures is found in many real-world applications. Included in these applications are the energy efficient design of buildings, operation and safety of nuclear reactors, solar collector design, passive energy storage, heat transfer across multi-pane windows, thermo-electric refrigeration and heating devices, and the design-for-mitigation of optical distortion in large-scale laser systems. Considering all these applications, especially controlling heat transfer in nuclear power plants, knowledge and research results of natural convection in enclosure play a vital …

Development And Validation Of Probabilistic Fatigue Models Containing Out-Life Suspensions, Noel S. Murray

College of Graduate Studies: Theses & Dissertations

Author's abstract: In the area of reliability engineering it is necessary to be confident that a component or system of components will not fail under use for safety and cost reasons. One major mechanism of failure to a mechanical component is fatigue. This is the repetitious motion of loading and unloading of the material, typically below the ultimate tensile strength of the material, which ultimately leads to a catastrophic failure. To ensure this does not happen, engineers design components based on tests to determine the life of these components. These tests are typically conducted on a bench type tester in …

Growth Analysis Of (Ag,Cu)Inse2 Thin Films Via Real Time Spectroscopic Ellipsometry, S. A. Little, V. Ranjan, R. W. Collins, S. Marsillac

Electrical & Computer Engineering Faculty Publications

In situ and ex situ characterization methods have been applied to investigate the properties of (Ag,Cu)InSe₂ (ACIS) thin films. Data acquired from real time spectroscopic ellipsometry (RTSE) experiments were analyzed to extract the evolution of the nucleating, bulk, and surface roughness layer thicknesses. The evolution of these layer thicknesses suggests a transition from Volmer-Weber to Stranski-Krastanov type behavior when Cu is replaced by Ag. The complex dielectric functions of ACIS at both deposition and room temperature as a function of film composition were also extracted from the RTSE data, enabling parameterization of the alloy optical properties.

Ferroelectric Control Of Magnetocrystalline Anisotropy At Cobalt/Poly(Vinylidene Fluoride) Interfaces, Pavel Lukashev, Tula R. Paudel, Juan M. López-Encarnación, Shireen Adenwalla, Evgeny Y. Tsymbal, Julian P. Velev

Shireen Adenwalla Papers

Electric field control of magnetization is one of the promising avenues for achieving high-density energy-efficient magnetic data storage. Ferroelectric materials can be especially useful for that purpose as a source of very large switchable electric fields when interfaced with a ferromagnet. Organic ferroelectrics, such as poly(vinylidene fluoride) (PVDF), have an additional advantage of being weakly bonded to the ferromagnet, thus minimizing undesirable effects such as interface chemical modification and/or strain coupling. In this work we use first-principles density functional calculations of Co/PVDF heterostructures to demonstrate the effect of ferroelectric polarization of PVDF on the interface magnetocrystalline anisotropy that controls the …

Role Of Alloy Additions On Strengthening In 17-4 Ph Stainless Steel, Arpana S. Murthy

Doctoral Dissertations

"Alloy modifications by addition of niobium (Nb ), vanadium (V), nitrogen (N) and cobalt (Co) to cast 17-4 PH steel were investigated to determine the effect on mechanical properties. Additions of Nb, V, and N increased the yield strength from 1120 MPa to 1310 MPa while decreased the room temperature charpy V notch (CVN) toughness from 20 J to four Joules. The addition of Co to cast 17-4 PH steel enhanced the yield strength and CVN toughness from 1140 MPa to 1290 MPa and from 3.7 J to 5.5 J, respectively. In the base 17-4 PH steel, an increase in …

Plastic Strain Accommodation And Acoustic Emission During Melting Of Embedded Indium Particles In Aluminum, Michael M. Kuba

Masters Theses

"Melting of micron-sized (0.2 to 3 µm diameter) indium particles embedded in an aluminum matrix was discovered to produce acoustic emission. Melting of embedded immiscible particles produces a pure dilation during the phase transformation and has no long-range diffusion field to control the speed of transformation. It was found that acoustic emission can no longer be considered as a criterion of displacive transformations and that melting of micron-sized embedded particles is strain energy controlled. Acoustic emission was confirmed to result from the rapid relaxation of aluminum around indium particles embedded on grain boundaries. Prismatic punching of dislocation loops is proposed …

The Effect Of Sulfur On Structure And Conversion Of Bioactive Borate Glasses, Ali Mohammadkhah

Masters Theses

"The effect of sulfur on glass structure and the conversion process of bioactive CaO-LI₂O-B₂O₃ glasses were studied. One glass without and two glasses with different amounts of sulfur were made using conventional melting and dry quenching techniques. These glasses reacted with a phosphate solution and converted to hydroxyapatite. Particles (150-355µm) were reacted in 0.25 and 0.5 molar K₂HPO₄ solutions at 37⁰C for 2 to 96 hours. The weight loss of the particles and the final pH of the solution were measured. The weight loss measurements indicated that the reaction rate increases with …

Development Of Third Generation Advanced High Strength Steels, Meghan C. Mcgrath

Doctoral Dissertations

"Lightweight duplex steels with combinations of either bainite, acicular ferrite, and austenite or martensite and austenite were investigated as third generation advanced high strength steels targeted for automotive applications. Large additions of manganese (>13 wt%) and carbon (

Duplex steels with different volume fractions of primary δ -ferrite were used to study the crystallography of austenite formed during the peritectic reaction. Solute profiles across the peritectic interface showed aluminum segregated near the interface which promoted bainitic ferrite formation. Thermal treatments were used to manipulate the concentration and type of oxides and the ferrite plate density was found to correlate …

Influence Of Temperature And Microstructural Modification On Formability Of Magnesium Alloys, Arun Mohan

Doctoral Dissertations

"The ß-precipitate free AZ31, ß-precipitate rich AZ91 and a few Mg-Y-Zn alloys were studied to understand the dependence of Mg formability on microstructural condition and temperature. Friction stir processing (FSP) was used to refine the grain size and to obtain desirable distribution of precipitates in the matrix. Since Mg alloys exhibit challenges in achieving room temperature formability, superplastic deformation was utilized. This work focused on high strain rate superplasticity (HSRS, ≥10⁻² s⁻¹) which is more attractive for industrial applications as compared to the slower rates of conventional superplasticity.

Thermally stable fine grains and pinning particles at HSRS temperatures were essential …

Stress Corrosion Cracking Behavior Of Friction Stir Processed Ultrafine Grained Light Metal Alloys, Gaurav Ramchandra Argade

Doctoral Dissertations

"The influence of friction stir processing (FSP), a microstructural modification tool, on the corrosion behavior of Al-Mg, Al-Mg-Sc, Mg-Al-Zn and Mg-Y-RE alloys has been studied. An attempt has been made to establish correlation between processing parameters and the subsequent microstructural evolution especially matrix grain size on the corrosion and stress corrosion properties of the alloys. A relationship between grain size and corrosion rate for Mg-Y-RE alloys was envisaged and power law type behavior was proposed. Ultrafine fine grained (UFG) microstructure showed one order magnitude lower corrosion rate.

Grain refinement achieved through different FSP parameters showed lower corrosion currents for Al-Mg …

Densification And Thermal Properties Of Zirconium Diboride Based Ceramics, Matthew Joseph Thompson

Doctoral Dissertations

"The research presented in this dissertation focuses on the processing and thermomechanical properties of ZrB₂ based ceramics. The overall goal was to improve the understanding of thermal and mechanical properties based on processing conditions and additives to ZrB₂. To achieve this, the relationships between the thermal and mechanical properties were analyzed for ZrB₂ ceramics that were densified by different methods, varying amounts of carbon, B₄C, or TiB₂ additions. Four main areas were investigated in this dissertation. The first showed that decreased processing times, regardless of densification method, improved mechanical strength to >500 MPa. This study also revealed that lower oxygen …

Thermal Properties Of Spinel Based Solid Solutions, Kelley R. Wilkerson

Doctoral Dissertations

"Solid solution formation in spinel based systems proved to be a viable approach to decreasing thermal conductivity. Samples with systematically varied additions of MgGa₂O₄ to MgAl₂O₄ were prepared and thermal diffusivity was measured using the laser ash technique. Additionally, heat capacity was measured using differential scanning calorimetry and modeled for the MgAl₂O₄-MgGa₂O₄ system. At 200⁰C thermal conductivity decreased 24% with a 5 mol% addition of MgGa₂O₄ to the system. The solid solution continued to decrease the thermal conductivity by 13% up to 1000⁰C with 5 mol% addition. The decrease in thermal conductivity ultimately resulted in a decrease in heat flux …

Hollow Hydroxyapatite Microspheres As Devices For Controlled Delivery Of Proteins And As Scaffolds For Tissue Engineering, Hailuo Fu

Doctoral Dissertations

"Hollow HA microspheres were prepared by converting Li₂O-CaO-B₂O₃ glass microspheres in a K₂HPO₄ solution. Process parameters, such as reaction temperature (25°C-60°C) and concentration of the phosphate solution (0.02-0.25 M) significantly influenced the microstructure of the hollow HA microspheres. Microspheres with the largest hollow core size were obtained at lower temperature or with low K₂HPO₄ concentration. In comparison, microspheres with high surface area (~140 m²/g) were obtained at higher K₂HPO₄ concentration (0.25 M). Upon heat treatment (up to 900°C), the surface area of the hollow HA microspheres decreased (from ~100 m²/g to ~2 m²/g), and the rupture strength increased (from ~11 …

Modeling And Synthesis Of Pvdf-Based Dielectrics For Energy Storage Applications, Xuhui Lu

Doctoral Dissertations

"The purpose of this research was to develop dielectric films for high energy density capacitor applications. Also desired was to develop a deeper understanding of dielectric breakdown and electric energy storage related phenomena through simulation, theoretical analysis, and experimental investigation.

An analytical model incorporating Weibull dielectric strength statistics was developed to establish quantitative relationships between material properties and device performance of self-healing capacitors. The model is useful for designing high voltage capacitors and developing dielectric materials where the effects of electric field-dependent permittivity need to be considered.

In the experimental work, solution-cast poly(vinylidene difluoride) (PVDF) homopolymer PVDF films with high …

Sputter Deposition Of Thin-Film Capacitors Onto Low Temperature Co-Fired Ceramic Substrates, Jack Murray

Masters Theses

"Single layer thin film capacitor structures were fabricated on the surface of low temperature co-fired ceramic (LTCC) substrates using sputter deposition. The capacitor structures had areas between ~10⁴ µm² to ~10⁶ µm² and featured ~200 nm Al or Pt electrodes with 150-1500 nm Al₂O₃ dielectric layers. Impedance analysis and current-voltage testing were carried out to determine the effect of electrode material and dielectric thickness upon capacitor performance. Capacitance values for devices with Al electrodes ranged from ~10 to ~700 pF, depending on capacitor area and dielectric thickness, and the fit to expected values was better than devices with Pt or …

Ultrasonic Wave Propagation Assessment Of Native Cartilage Explants And Hydrogel Scaffolds For Tissue Engineering, Sean S. Kohles, Shelley S. Mason, Anya P. Adams, Robert J. Berg, Jessica Blank, Fay Gibson, Johnathan Righetti, Lesha S. Washington, Asit K. Saha

Mechanical and Materials Engineering Faculty Publications and Presentations

Non-destructive techniques characterising the mechanical properties of cells, tissues, and biomaterials provide baseline metrics for tissue engineering design. Ultrasonic wave propagation and attenuation has previously demonstrated the dynamics of extracellular matrix synthesis in chondrocyte-seeded hydrogel constructs. In this paper, we describe an ultrasonic method to analyse two of the construct elements used to engineer articular cartilage in real-time, native cartilage explants and an agarose biomaterial. Results indicated a similarity in wave propagation velocity ranges for both longitudinal (1500-1745 m/s) and transverse (350-950 m/s) waveforms. Future work will apply an acoustoelastic analysis to distinguish between the fluid and solid properties including …

Plasma Levels Of Polychlorinated Biphenyls, Non-Hodgkin Lymphoma, And Causation, Michael D. Freeman, Sean S. Kohles

Mechanical and Materials Engineering Faculty Publications and Presentations

Polychlorinated biphenyls (PCBs) are synthetic chlorinated hydrocarbons that have extensively polluted the environment and bioaccumulated in the food chain. PCBs have been deemed to be probable carcinogens by the Environmental Protection Agency, and exposure to high levels of PCBs has been consistently linked to increased risk of non-Hodgkin lymphoma (NHL). In the present article we present a forensic epidemiologic evaluation of the causal relationship between NHL and elevated PCB levels via application of the Bradford-Hill criteria. Included in the evaluation is a meta-analysis of the results of previously published case-control studies in order to assess the strength of association between …