Engineering Science and Materials Commons^™

Radiation-Induced Radicals In Polyurea-Crosslinked Silica Aerogel, Benjamin Michael Walters

Masters Theses

Free radicals are atoms or molecules with an odd number of electrons in an outer shell. Since electrons typically occur in pairs, this leaves one electron that is unpaired. In seek of another electron to pair with, free radicals react with and steal electrons from neighboring molecules, which then become free radicals themselves. This can start a chain reaction, cascading into large scale damage.

Ionizing radiation can tear through molecules, just as bullets can tear through things that we see. If free radicals can be detected, and seen to increase in a material upon radiation exposure, this can indicate molecular …

Nanolayer Polymeric Coatings To Enhance The Performance And Service Life Of Inorganic Membranes For High Temperature-High Pressure Biomass Pretreatment And Other Applications, Vincent C. Kandagor

Doctoral Dissertations

Membrane technology has become increasingly attractive in several applications including water filtration, food industry, oil and gas, and biomedical applications. Most recently the quest for renewable, bioenergy has called for use of membranes in biomass pretreatment and other stages of producing biofuel. The success and advancement of the membrane technology for these various applications has, however, been impeded by the fouling of membranes, which causes the pores in the microporous structure to block, resulting in reduced efficiency, and in some cases, total failure of the membranes system. This challenge leads to a tremendous increase in the cost of using membranes …

A Study Of Indentation Cracking In Brittle Materials Using Cohesive Zone Finite Elements, Kurt E. Johanns

Doctoral Dissertations

Cohesive zone finite element simulations of pyramidal indentation cracking in brittle materials have been carried out in order to: (1) critically examine indentation cracking models that relate fracture toughness to indentation data; (2) determine the underlying physical mechanisms of indentation crack growth from a continuum view and their relationship to material properties; (3) explore the influence of indenter geometry on crack extension; and (4) provide a platform from which future simulations can add more complex material behavior as well as guidance for experimental measurements of fracture toughness. Standard fracture toughness geometries in addition to simplified indentation geometries were simulated in …

Structural Analysis Of The Tablerock Thrust Sheet, Grandfather Mountain Window, Northwestern North Carolina: Emplacement Kinematics Of A Large Horse In A Major Thrust System, Ann Elizabeth Walker

Masters Theses

The Tablerock thrust sheet is exposed along the southwestern margin of Grandfather Mountain window in northwestern North Carolina, where it separates basement and cover rocks inside the window from basement thrust sheets of the overriding Blue Ridge-Piedmont megathrust sheet. It is a complex of footwall-derived horses of rifted-margin metasedimentary rocks, including Neoproterozoic to Early Cambrian Chilhowee Group quartzite and phyllite, and Shady Dolomite. Penetrative deformation throughout the Tablerock thrust sheet is defined by an extensively transposed foliation, and strong colinearity between well developed transport lineations and SE/NW-trending tight, isoclinal, and sheath folds. Centimeter- to meter-scale sheath folds are common throughout …

Structure And Energetics Of Nanoparticles And Ionomer Films In Fuel Cell Catalyst Layers, Qianping He

Doctoral Dissertations

Improving the durability and utilization efficiency of the platinum-on-carbon (Pt/C) catalyst is of vital importance to the commercialization of the polymer electrolyte membrane fuel cell (PEMFC). This body of work provides molecular level insights to aid the fulfillment of this goal. Chapter 1 describes the use of molecular dynamics (MD) simulation in an effort to understand the Pt/C degradation issue from the nano-adhesion point of view. The roles of catalyst nanoparticle size, shape, Pt/C surface oxidation and the extent of ionomer film hydration are investigated to study their effects on nano-particle adhesion. It is found that the adhesion force strengthens …

An Automated Finite Element Analysis Framework For The Probabilistic Evaluation Of Composite Lamina Properties, Jonathan Phillips Weigand

Masters Theses

This thesis outlines the development of computational modeling tools used to predict the elastic properties of composite lamina from representative volume elements (RVE) using numerical methods. The homogenization approach involves the use of Gauss’s Theorem to simply the average volumetric strain integral into a surface integral containing which is defined by surface displacements and their direction. Simulations of RVEs under specific loading conditions (longitudinal tension or shear and transverse tension or shear) are then performed in the software package ABAQUS to obtain the surface displacements. It was found that obtaining quality meshes and applying periodic boundary conditions for each RVE …

Structure And Morphology Of Sulfonated Polysulfone And Perfluorosulfonic Acid Ionomers, Chen Wang

Doctoral Dissertations

The limitations of conventional perfluorosulfonic acid (PFSA) based membrane materials have provoked the search for alternative materials which can function as the electrolyte in PEM fuel cells operated at higher temperatures (> 100 °C) and without humidification. A novel class of sulfonated poly(phenylene) sulfone (sPSO2) ionomers have shown much higher proton conductivity than typical PFSA membranes at elevated temperatures. In this dissertation, both computational and experimental methods were used to investigate proton transfer, morphological and structural properties of sPSO2 and PFSA ionomers. We have undertaken ab initio electronic structure calculations to understand the primary hydration and the transfer of protons …

Dynamic Mutual Capacitive Sensor For Human Interactions., Jonathan William Huber

Doctoral Dissertations

This dissertation introduces the novel concept of removing the ground conductive plate by utilizing body capacitance as the ground in the capacitive sensor, whereby circuit pressure sensing can occur with only one plate and one dielectric. Additionally, body capacitance sensing was limited to a binary touch-no-touch output, whereas the method presented here can sense various applied pressures. The resulting circuit acts as an antenna that receives local capacitance signals from a human interaction.

The advantage of this design is that it allows for both proximity sensing and pressure sensing (once the body part is touching the dielectric material). This setup …

Validation Of Weak Form Thermal Analysis Algorithms Supporting Thermal Signature Generation, Elton Lewis Freeman

Masters Theses

Extremization of a weak form for the continuum energy conservation principle differential equation naturally implements fluid convection and radiation as flux Robin boundary conditions associated with unsteady heat transfer. Combining a spatial semi-discretization via finite element trial space basis functions with time-accurate integration generates a totally node-based algebraic statement for computing. Closure for gray body radiation is a newly derived node-based radiosity formulation generating piecewise discontinuous solutions, while that for natural-forced-mixed convection heat transfer is extracted from the literature. Algorithm performance, mathematically predicted by asymptotic convergence theory, is subsequently validated with data obtained in 24 hour diurnal field experiments for …

Measurement Of Power-Law Creep Parameters By Instrumented Indentation Methods, Caijun Su

Doctoral Dissertations

New experimental methods have been developed to measure the uniaxial power-law creep parameters α [alpha] and n in the relation έ[epsilon dot]=α[alpha]σⁿ[sigma] (έ [epsilon dot] is the creep strain rate and σ [sigma] is the creep stress) from the load, time, displacement and stiffness data recorded during an instrumented indentation experiment performed with a conical or pyramidal indenter. The methods are based on an analysis of Bower et al., which relates the indentation creep rate to the uniaxial creep parameters based on simple assumptions about the constitutive behavior (Bower et al., 1993 …

A Gps-Based Mobility Power Model For Military Vehicle Applications, George William Bozdech

Masters Theses

In recent years, military vehicles have been equipped with hybrid, diesel-electric drives to improve fuel efficiency and stealth capabilities. These vehicles require an accurate estimate of the power duty cycles during distinct operating conditions. To meet this demand, a GPS-based mobility power and duty cycle analysis is one approach to predict the power requirements of on-road and off-road vehicles. The dynamic vehicle parameters needed to estimate the forces developed during locomotion are determined from the GPS tracking data, and these forces include the following: the motion resistance, gravitational, linear inertia, rotational inertia, and aerodynamic drag. The motion resistance force generated …

Modeling And Development Of A Mems Device For Pyroelectric Energy Scavenging, Salwa Mostafa

Doctoral Dissertations

As the world faces an energy crisis with depleting fossil fuel reserves, alternate energy sources are being researched ever more seriously. In addition to renewable energy sources, energy recycling and energy scavenging technologies are also gaining importance. Technologies are being developed to scavenge energy from ambient sources such as vibration, radio frequency and low grade waste heat, etc. Waste heat is the most common form of wasted energy and is the greatest potential source of energy scavenging.

Pyroelectricity is the property of some materials to change the surface charge distribution with the change in temperature. These materials produce current as …

Development And Analysis Of Onboard Translunar Injection Targeting Algorithms, Phillippe Lyles Winters Reed

Masters Theses

Several targeting algorithms are developed and analyzed for possible future use onboard a spacecraft. Each targeter is designed to determine the appropriate propulsive burn for translunar injection to obtain desired orbital parameters upon arrival at the moon. Primary design objectives are to minimize the computational requirements for each algorithm but also to ensure reasonable accuracy, so that the algorithm’s errors do not force the craft to conduct large mid-course corrections. Several levels of accuracy for dynamical models are explored, the convergence range and speed of each algorithm are compared, and the possible benefits of the Broyden and trust-region targeters are …

Radiation-Curable Adhesives For Wood Composites, Timothy H. Starr

Masters Theses

Wood composites are widely used in construction applications because of their superior dimensional and structural attributes over raw wood products. However, current wood composite manufacturing practices, which rely on thermal-curing of adhesives, are expensive, energy intensive, time consuming and are prone to manufacturing defects. Use of radiation curable adhesives (RCAs) could potentially answer all of these issues. Specifically, use of electron-beam (e-beam) radiation has been increasing in areas of research and industry where rapid, low-temperature polymerization is required and low energy consumption is desired. For e-beams to be used in wood composites, however, it must be determined whether or not …

Effect Of Moisture Absorption On The Sinter Quality Of Central Solenoid (Cs) Coil Pack, Zeshaan Sher Mohammed

Masters Theses

Fusion energy has been said to be the solution to all the world’s energy problems. The International Thermonuclear Experimental Reactor (ITER) is the flagship project to demonstrate the feasibility of fusion energy. The Central Solenoid (CS), an important component of the reactor, is needed to induce plasma current, initiate, ramp-up, ramp-down, and sustain plasma in a very controlled manner. In order to achieve this, the CS coil packs must be manufactured under controlled conditions. The CS conductor is an advanced cable-in-conduit Nb3Sn superconductor. The CS cable will be made in long continuous sections but with thousands of meter of cable …

Methods For Characterizing Mechanical Properties Of Wood Cell Walls Via Nanoindentation, Yujie Meng

Masters Theses

Nanoindentation is a method of contacting a material whose mechanical properties are unknown with another material whose properties are known. Nanoindentation has the advantage of being able to probe a material’s microstructure while being sensitive enough to detect variations in mechanical properties. However, nanoindentation has some limitations as a testing technique due to the specific formation and structure of some biomaterials. The main objective of this research is to identify any factors that influence the nanoindentation measurement of wood cell walls (a typical biomaterial).

The function of the embedding media in describing the properties of wood cells is poorly understood. …

Nonlinear Acoustics Of Piston-Driven Gas-Column Oscillations, Andrew William Wilson

Masters Theses

The piston-driven oscillator is traditionally modeled by directly applying boundary conditions to the acoustic wave equations; with better models re-deriving the wave equations but retaining nonlinear and viscous effects. These better models are required as the acoustic solution exhibits singularity near the natural frequencies of the cavity, with an unbounded (and therefore unphysical) solution. Recently, a technique has been developed to model general pressure oscillations in propulsion systems and combustion devices. Here, it is shown that this technique applies equally well to the piston-driven gas-column oscillator; and that the piston experiment provides strong evidence for the validity of the general …

Naturally Occurring Nanoparticles From English Ivy: An Alternative To Metal-Based Nanoparticles For Uv Protection, Lijin Xia, Scott C. Lenaghan, Mingjun Zhang, Zhili Zhang, Quanshui Li

Faculty Publications and Other Works -- Mechanical & Aerospace Engineering/Engineering Science (MAES) (UTSI)

Background

Over the last decade safety concerns have arisen about the use of metal-based nanoparticles in the cosmetics field. Metal-based nanoparticles have been linked to both environmental and animal toxicity in a variety of studies. Perhaps the greatest concern involves the large amounts of TiO₂ nanoparticles that are used in commercial sunscreens. As an alternative to using these potentially hazardous metal-based nanoparticles, we have isolated organic nanoparticles from English ivy (Hedera helix). In this study, ivy nanoparticles were evaluated for their potential use in sunscreens based on four criteria: 1) ability to absorb and scatter ultraviolet light, …

Wetting Behavior Of Polymer Melts With Refractory Coatings At High Temperature, Robin Woracek

Masters Theses

Within the scope of this thesis, an experimental system has been designed, developed and manufactured for the determination of the wetting behavior of liquids and polymer melts with solid surfaces (coated and uncoated) at high temperatures (> 200 ºC). The measurement system incorporates a modified Wilhelmy plate technique, using a precision weighing module, a vertical linear stage, custom developed application software using LabView with suitable hardware and a high temperature furnace with thermocouple feedback control. Experiments have been performed and are reported to evaluate the performance of the testing system, using liquids of known wetting properties. A suitable testing procedure …

Flame Retardant Mattress Pads, Manjeshwar Ganeshaq Kamath

Doctoral Dissertations

Focus of this research is on developing cotton-based nonwoven mattress pads with flame retardant (FR) properties by blending cotton with other commercially available fibers, binders, and followed by chemical treatments; offering a cost-effective recipe to meet the upcoming flammability standards. Furthermore this research explores the opportunities taking advantage of possible synergistic effects to achieve maximum performance.

Recent changes in the flammability regulations require improvements in the flame resistance of cotton-containing consumer goods such as upholstered furniture, mattresses, and pillows. Cotton, synthetic fibers, fabrics, and foam are the basic constituents of these goods that are often the first to be engulfed …

High Resolution X-Ray Tomography Of Fiber Reinforced Polymeric Composites, Stephen Andrew Young

Masters Theses

A high resolution x-ray tomography system was used to study chopped fiber polymeric composites made of polypropylene resin, nickel coated carbon fiber and Eglass fiber. Procedures are developed to obtain micro-structured features of importance. In-situ tensile testing system was developed and integrated into the existing hardware for tomography equipment to study the evolution of damage and micro-structural features as a function of mechanical stress. High resolution x-ray tomographic images of glass fiber were collected and viewed on a micron scale. The radiographs were reconstructed to visualize the fiber content of the samples in three dimensional volume. In addition, glass fiber …

A Study Of Irrigation, Fertigation And Plasticulture In Burley Tobacco, With A Focus On Yield, Quality And Tsna Reduction, Eric F. Caldwell

Masters Theses

Nitrogen fertilization is important in attaining high yielding, quality tobacco. However, practices that use excessive N can be uneconomical, threaten the environment and produce leaves that are high in nitrates. Leaves high in nitrates have been positively correlated with leaves that are high in tobacco specific nitrosamines (TSNA), which are considered potent carcinogens. Competition from cheaper, foreign leaf, increasing costs of fertilizers and new market structures which show purchasers seeking low TSNA leaf demand that producers become more efficient in their N use. The objective of this study is an examination of burley (TN 90) and dark (KY 171) tobacco …

A Study Of Indentation Creep Using The Finite Element Method, Sangjoon Sohn

Doctoral Dissertations

Indentation is a useful technique for studying the mechanical properties of a material. Measurable mechanical properties from indentation include time-dependent as well as time independent properties. Among these mechanical properties, time-dependent permanent deformation (creep) is of interest in this study. The purpose of this study is to explore the behavior of creep deformation of a solid under indentation. The main scientific research tool will be the finite element method.

Existing works by others provide limited solutions that allow us to correlate uniaxial creep to indentation creep. In this study, the task is taken a step further to enhance and modify …

Vascular Hemodynamics Cfd Modeling, Shashank Kiran Karra

Masters Theses

Three dimensional pulsatile blood flow CFD simulations in geometrically genuine normal and non-normal (aneurysm) human neck-head vascular systems nominally spanning the aortic arch to the circle of Willis has been performed and studied. CT scans of the human aortic arch and the carotid arteries were interpreted to obtain geometric data defining the boundary for a vascular CFD simulation. This was accomplished by reconstructing the surface from the anatomical slices and by imposing pertinent boundary conditions at the various artery termini. Following automated formation of a non-conformal CFD mesh, steady and unsteady laminar and low turbulent simulations were performed both for …

A Study Of Material Properties And Relevant Microstructure Parameters That May Influence The V50 Ballistic Limit Velocity Of Composite Ceramics, Adolphus Mcdonald

Masters Theses

The purpose of this research is to evaluate, compare, and correlate the microstructure and mechanical properties of a selected group of ceramic armor samples to the V₅₀ ballistic limit velocity. This study is to identify any relation between the desired material properties and the relevant microstructure parameters that significantly influence the ballistic limit velocity. The ceramic materials, silicon carbide and boron carbide, were produced and provided by five foreign companies. These companies were under contract by the United States Army, Research, Development, and Engineering Command to provide ceramic armor for comparative testing and material evaluation.

Ballistic testing was carried …

Comparative Properties Of Polymers Guiding The Development Of An Abdominal Aorta Model, Benjamin Michael Lamie

Masters Theses

Hemodynamics, the study of the forces involved in the circulation of blood, is an area that researchers have approached in various manners for many years. The study of how blood flows through arteries and veins as well as the effect of the composition of the blood has been defined and thoroughly characterized in past studies. Although in-depth studies have been performed on the flow characteristics of blood, most often the observations are made as the fluid flows through tubes composed of some rigid material. It is well known that the arteries and veins have a layered histology that show varying …

A Computational Model To Predict In Vivo Kinetics In Implanted And Non-Implanted Shoulders, Matthew Brennon-Kyle Kubo

Masters Theses

The purpose of this study was to develop and implement a computational model designed to input in vivo kinematic and predict in vivo forces and torques for the shoulder, elbow, and wrist in normal, rotator cuff-deficient (RCD), reverse shoulder arthroplasty (RSA) and total shoulder arthroplasty (TSA) shoulder subjects. Twenty subjects, divided evenly amongst the four shoulder types, performed a box-lift activity while under fluoroscopic surveillance. Three dimensional (3D) in vivo kinematics was determined for the subjects using implant models and bone models created from CT (computed tomography) scans in a 2D-to-3D registration process. The kinematics were used as input for …

Correlation Of Wear And Mechanics For Subjects Having A Metal-On-Polyethylene Total Hip Arthroplasty Measured In Vivo, Katherine Suzanne Alford

Masters Theses

Femoral head separation from the acetabular shell has been recorded, but clinical significance of this phenomenon has not yet been established. The objective of the study was to determine if there is a correlation between femoral head separation (sliding of the femoral head away from the acetabular cup), hip joint forces, and acetabular liner wear. Twenty subjects were strategically selected to participate in this study. All subjects were asked to perform gait on a treadmill while under fluoroscopic surveillance. The number of incidences involving femoral head separation was tallied and acetabular bearing surface forces were determined for each subject. A …

Real-Time Monitoring And Quantification Of Drug Induced Changes In Endothelial Cytoskeleton Filaments Using A Cellular Impedance Biosensor, Vijay Nandakumar

Masters Theses

The analysis of electrical signals originating from biological cells and tissues have yielded a large amount of useful information over the past years. Technologies have been developed, wherein we can monitor the health of the biological material of interest using these electrical signals. Instruments for the study of living cells have historically been of significant importance for such things as basic neuroscience, cell biology, pharmaceutical screening, environmental monitoring, and toxin detection. One of the practical realizations of these methods was successfully implemented by Giaver and Keese with their Electric Cell-Substrate Impedance Sensing (ECIS) system. The purpose of this Masters Thesis …

Determination And Comparison Of In Vivo Forces And Torques In Normal And Degenerative Lumbar Spines, Shaun Kevin Stinton

Masters Theses

In vivo motions of normal and degenerative lumbar spine patients performing extension/flexion were obtained using video fluoroscopy. 3-D models of each patient’s vertebrae were registered to the 2-D fluoroscopy images using a process developed at Rocky Mountain Musculoskeletal Research Laboratory. Temporal equations representing the motions were input into a math model and the forces at the contact point between vertebral levels and the body torques between the vertebrae were the output. The vertical forces in the normal and degenerative patients were similar and ranged from 0.35-0.42 times the body weight of the patient. The maximum torques were higher in the …