Engineering Commons^™

Finite Element Analysis Of Thermal-Mechanical Instabilities In Nonmetallic Friction Composite Material, Joseph-Shaahu Shaahu

Electronic Theses and Dissertations

Thermal-mechanical instability (TMI) has been a research topic of interest as it focuses a lot on transportation systems. Thermal-mechanical instability was first noticed in railway and experimentally studied with a pin-to-pin or pin-to-surface setup of sliding contact. The topic has been extended into brakes and clutches which are two of the most common sliding systems most susceptible to thermal buckling and thermoelastic instability (TEI), where thermal buckling and thermoelastic instability are two sub-categories of thermal-mechanical instability. Thermal-mechanical instability is an ongoing research to better understand the phenomenon and the limits at which such instability occurs. This work delved into the …

Thermo-Mechanical Instabilities In Next-Generation Friction Materials In High-Speed Sliding Systems, Kingsford Koranteng

Electronic Theses and Dissertations

For centuries, the manufacturing industry has incorporated metals like copper into friction materials to enhance thermal properties and minimize thermo-mechanical instabilities (TMI) in high-speed sliding systems. Unfortunately, these metals have adverse environmental effects due to the emission of hazardous particulate matter. As a result, there is a growing movement towards adopting next-generation friction materials as an alternative solution.

The study begins by conducting experimental and numerical investigations to examine the instabilities found in metal-based friction materials. The primary objective is to utilize the insights gained from the investigations to computationally explore effective strategies for mitigating various instabilities that may arise …

Molecular Dynamics Study Of Characterization In Metal-Free Friction Materials, Yizhan Zhang

Electronic Theses and Dissertations

Metallic friction materials currently used in industry may adversely impact the environment. Substitutions for metals in friction materials, on the other hand, can introduce operational safety issues and other unforeseeable issues such as thermal-mechanical instabilities and insufficient strength. In view of it, this dissertation focuses on developing different kinds of materials from simple structure to complex structure and evaluating the material properties with the assistance of molecular dynamics (MD) tools at the nano scale.

First, the concept of the contacted surfaces in friction at the atomic scale was introduced in order to get accurate understanding of the friction process compared …

Fatigue And Fracture Of Electron Beam Melting Ti-6al-4v, William A. Grell

Electronic Theses and Dissertations

For applications in the aerospace field, selection of materials for a given design requires an understanding of critical properties, like fatigue and fracture, in addition to static mechanical and physical properties. With the ongoing advancements in metallic additive manufacturing techniques and the interest in applying the process to aerospace applications, there is a clear need to fully characterize properties. Arguably, the most attractive alloy for applications in aerospace is the Ti-6Al-4V alloy. The current dissertation examines the mechanical properties of the alloy, made by the Electron Beam Melting (EBM) Powder Bed Fusion (PBF) method. As illustrated in this work, the …

The Modernization Of Large Power Transformer Tanks, Babajide O. Williams

Electronic Theses and Dissertations

Due to the current demands placed on the power grid in terms of climate change, increasing urbanization, and terrorist attacks, the U.S. government in response to these demands, mandated that all the grid components be modernized in order to increase their reliability. As a critical component of the grid, Large Power Transformers (LPTs) play a key role in ensuring sustainable power generation and distribution. A literature search performed in this work and the analysis of data retrieved from the search showed that the tanks of these LPTs are critical to their durability, longevity, and reliability. Therefore, the reliability of LPTs …

Monitoring Of State Transitions In Extreme Environment Application Materials Using Fiber Bragg Grating Sensors, Sabuj Khadka

Electronic Theses and Dissertations

By embedding both a single fiber Bragg grating (FBG) sensor and a thermocouple (TC) during the manufacturing for extreme environment applications of certain classes of materials such as metals and polymers, a novel in-situ approach was developed to precisely monitor their entire manufacturing processes. This novel monitoring technique was able to identify many characteristic points during the curing of room and high-temperature epoxies and the solidification processes of metal alloys composed of tin and bismuth which were selected in this research purely for verification purposes. Some of the characteristic points identified for the epoxies were: (i) the gel point, (ii) …

Recycling Of Fiber Polymer Matrix Composites In Cementitious Materials, Edward Patton Clark

Electronic Theses and Dissertations

Recycling options for fiber polymer matrix composite waste materials are limited because they typically cannot be reused, reprocessed for down-cycling, and are generally environmentally unfriendly. The utility industry, specifically electrical distribution, has been increasingly using hybrid carbon, glass fiber, and epoxy resin composite rods for high-voltage (HV) conductor transmission lines. The high-voltage conductor core (HVCC) used in the transmission line can have an optimal in-service-life of roughly several decades, in which the material is then retired to a waste landfill. Currently, there is limited research and recycling methodology for these hybrid composite rods. In this research, powder carbon fiber, glass …

Observation Of New Particle Formation In The Northern Hemisphere At Altitude From 4 To 20 Km, Mohamed Saad

Electronic Theses and Dissertations

New particle formation (NPF) is investigated using measurements of aerosol size distributions and meteorological variables made in two continents, including USA and Europe. Despite the considerably different aerosol particle abundances among the sites, a common relationship was found between the characteristics of NPF events and the air mass convective and/or advective transport. CO and O3 act as tracers of tropospheric and stratospheric air, respectively, their statistical relationship can be used to quantify air mass characteristics and origins. The mixing ratio values of CO increased within the upper troposphere layer before/during NPF events, which may serve as an indicator of occurring …

Monitoring Of Overhead Polymer Core Composite Conductors Under Excessive Mechanical Loads Using Fiber Bragg Grating Sensors, Daniel H. Waters

Electronic Theses and Dissertations

This combined experimental and numerical study addresses mechanical effects associated with static and dynamic loading of novel High Temperature Low Sag (HTLS) transmission line polymer core composite conductors. The developed methodology was successfully applied to ACCC® to explain the complex failure mechanisms associated with combined bending and tension loading. Furthermore, the use of Fiber Bragg Grating (FBG) sensors was investigated for the first time to monitor the ACCC® design during installation and in-service.

Transverse low-velocity impacts to the ACCC® conductor having either free or constrained end conditions and large axial tensile loads were performed. It was identified that the most …

Thermally Driven Spin Transport In Ferromagnetic Metals, Wafa Saud Aljuaid

Electronic Theses and Dissertations

Since the discovery in 2008, the spin Seebeck effect has become one of the most active topics in the spin caloritronics research field. It opened a new way to create spin current by a combination of magnetic fields and heat. A temperature gradient in ferromagnetic (FM) metals generates a ow of spin current due to split of spin chemical potential between spin up and spin down electrons. This thermal spin current has been detected using an attached nonmagnetic heavy metal with large spin Hall angle via the inverse spin hall effect (ISHE). A voltage signal is generated since the nonmagnetic …

Graphene/Oxide Interactions With Polymer Networks Modeled Using Molecular Dynamics, Matthew Alan Reil

Electronic Theses and Dissertations

Due to its unique physical properties, graphene has shown great promise as an additive to Polymer Matrix Composites (PMCs) for material property enhancement. Achieving homogeneous dispersion of the graphene platelets within a polymeric network is critical to realizing these enhancements. Research has shown that achieving homogeneous dispersion of graphene platelets within PMCs is challenging as graphene is immiscible with most polymeric networks. This work used Molecular Dynamics (MD) simulations to demonstrate dispersion of graphene platelets within PMCs is inhibited by molecular surface charge potentials. Further simulations were conducted to demonstrate functionalized forms of graphene, specifically graphene oxide, have altered surface …

Ultrasonic-Based Condition Assessment Of Wooden Utility Poles, Yishi Lee

Electronic Theses and Dissertations

More than 300 million utility poles shoulder the utility grid in the United States. However, the ineffectiveness of the current inspection process causes roughly a third of utility poles removed from the service deemed suitable for reuse. Due to the utterly essential role of the power infrastructure, budget shrinkage, and the structural degradation of the modern distribution grid, this Ph.D. dissertation addresses the challenges by proposing a physics-based signal analysis method with a jointly developed ultrasonic UB1000 system c to enhance the objectivity in ultrasonic-based nondestructive evaluation (NDE). The proposed methodology has been deployed commercially in the field and featured …

Synergistic Environmental Aging Of Glass Reinforced Polymer Composites, Tianyi Lu

Electronic Theses and Dissertations

Synergistic effects involved in the environmental degradation of Glass Reinforced Polymer (GRP) composites were examined and a novel synergistic aging model was proposed in this study. Six GRPs based on glass fibers with four different polymer resins and six pure polymer thermoplastic resins were exposed either individually or in combination to ultraviolet (UV) radiation, water condensation and elevated temperature for approximately 1000 h. The composites and polymers were monitored for weight changes as a function of time and their surfaces were examined after the tests using optical and scanning electron microscopes (SEM). Photodegradation of the polymer matrices was analyzed by …

Nanoengineering Of Next Generation Silicone Rubber Materials For Extreme Applications, Monika Bleszynski

Electronic Theses and Dissertations

Silicone rubber materials are frequently used in extreme environments, including aviation, space, high voltage and other applications. In service, however, complex and difficult to predict damage mechanisms in the rubbers can occur which can lead to severe failures of essential infrastructural components. For example, Non-Ceramic Insulators (NCIs), which support some of the most critical high voltage lines in the world, regularly exhibit severe polymer aging due to environmental pollution, ultra-violet (UV) radiation, and dry band and corona arcing. Designing silicone rubbers to resist aging in these demanding environments is difficult and requires an interdisciplinary approach, including correctly assessing the actual …

Computational Prediction Of Conductivities Of Disk-Shaped Particulate Composites, Jian Qiu

Electronic Theses and Dissertations

The effective conductivities are determined for randomly oriented disk-shaped particles using an efficient computational algorithm based on the finite element method. The pairwise intersection criteria of disks are developed using a set of vector operations. An element partition scheme has been implemented to connect the elements on different disks across the lines of intersection. The computed conductivity is expressed as a function of the density and the size of the circular disks or elliptical plates. It is further expressed in a power-law form with the key parameters determined from curve fittings. The particle number and the trial number of simulations …

Variable Oxidation & Defects In Ti-6al-4v Material In Electron Beam Melting Additive Manufacturing, Edward Patton Clark

Electronic Theses and Dissertations

Powder-based metal in additive manufacturing (AM) is advantageous for rapid prototyping of parts and components, with the benefit of reusing powder to reduce production costs. A common driver in the aerospace industry is free-form complex geometries which can be created using CAD software to optimize specifications with strength-to-weight ratios in components. Weight optimization of aircraft components using additive manufacturing reduces material, which significantly reduces production cost in comparison to cast and wrought metallic products. Large biomedical and aerospace industries heavily invest in feedstock metal powders that have low density under structural stresses and high temperatures, resulting in superior resistance to …

Computational Modeling Of Percolation Conduction And Diffusion Of Heterogeneous Materials, Jian Qiu

Electronic Theses and Dissertations

Heterogeneous materials provide a unique combination of desirable mechanical, thermal or electrical properties. This dissertation presents several micro-structure modeling approaches to predict the effective properties of heterogeneous materials and demonstrates its certain application toward two highly heterogeneous, unconventional structural composite materials (carbon fiber reinforced composite materials and graphene nanoplatelets composite). By using the efficient computational algorithm based on the FEA, a randomly oriented disk-shaped particles system are generated. A new element partition scheme based on the vector operations and geometry of inclusion has been implemented to mesh the intersected disks. The computed equivalent conductivity is expressed as a power-law function …

Aging Assessment Of High Voltage Single Component Room Temperature Vulcanized Silicone Rubber (Rtv-1) Subjected To Aqueous Salt, Monika Bleszynski

Electronic Theses and Dissertations

Single component room temperature vulcanized (RTV-1) silicone based caulk used in high voltage insulators and other applications is frequently subjected to environmental pollutants. Aging of RTV-1 silicone rubber is the result of various stressors, including environmental aging conditions such as UV, acid, and salt exposure from ocean mist. Loss of hydrophobicity due to damage of the hydrophobic methyl groups, as well as loss of mechanical strength due to depolymerization via hydrolysis as a result of aqueous salt exposure were the two main factors of material aging assessed in this work. Multiple RTV-1 formulations were initially assessed for resistance to aging …

Synthesis And Characterization Of Kesterite Cu2znsns4 (Czts) Thin Films For Solar Cell Application, Mohamed M.A. Abusnina

Electronic Theses and Dissertations

The quaternary compound Cu₂ZnSnS₄ (CZTS) gained considerable attention in the last decade due to its potential as an active-layer semiconductor for low-cost thin-film solar cells. The material is composed of nontoxic and Earth-abundant constituents, has optical properties suitable for photovoltaic application, and can be synthesized using a wide variety of methods.

Polycrystalline CZTS was grown in this work using vacuum-based deposition to first deposit metal films (precursors) of Cu, Zn, and Sn. In a subsequent step, the precursors underwent an annealing treatment in sulfur vapor environment (sulfurization) to form CZTS. Using sputtering, a physical vapor deposition (PVD) …

On Thermal Aging Prevention In Polymer Core Composite Conductor Rods, Joe D. Hoffman

Electronic Theses and Dissertations

Increased energy usage in the United States and worldwide is driving the demand for new technologies to transmit electrical power in greater quantities and with reliable, safe, and more efficient methods. One recent innovation is to replace the standard Aluminum Conductor Steel Reinforced electrical transmission conductor with a new conductor design that utilizes a fiber reinforced polymer core rod to support a fully annealed aluminum conductor. This new technology that includes a hybrid carbon fiber/epoxy and glass fiber/epoxy support core allows for better efficiency and for greater current to be transmitted in the same size and weight line. These new …

Thermal And Structural Modeling Of Electrochromics On Glass, Mahesh B. Manandhar

Electronic Theses and Dissertations

Advanced glazing is a type of window glazing that interacts with the surrounding environment to change its thermal and optical properties to create a more comfortable and energy efficient indoor environment. Electrochromics are one type of such advanced glazing materials that change their properties in response to an externally applied voltage controllable by the user or by automation.

The effectiveness of electrochromics depends upon how well it can keep off extreme temperature conditions from outdoors all year round as well as how structurally stable it can remain at such conditions. This research investigates the use of COMSOL, a finite element …

Stress Corrosion Cracking In Polymer Matrix Glass Fiber Composites, Jonathan Kosak

Electronic Theses and Dissertations

With the use of Polymer Matrix Glass Fiber Composites ever expanding, understanding conditions that lead to failure before expected service life is of increasing importance. Stress Corrosion Cracking (SCC) has proven to be one such example of conditions found in use in high voltage transmission line applications that leads to brittle fracture of polymer matrix composites.

SCC has been proven to be the result of acid buildup on the lines due to corona discharges and water buildup. This acid leaches minerals from the fibers, leading to fracture at low loads and service life. In order to combat this problem, efforts …

Degradation Of High Voltage Glass Fiber-Reinforced Polymer Matrix Composites By Aggressive Environmental Conditions, Tianyi Lu

Electronic Theses and Dissertations

Polymer matrix composites reinforced with either E glass or ECR glass fibers-reinforced are used in a variety of high voltage electrical applications because of their advantages like lower weight and cost. However, they can be damaged by aggressive in-service conditions such as high temperature, ultraviolet radiation, moisture, ozone and corrosive environments. Different degradation mechanisms can develop in high voltage PMCs under those extreme environments, which, in turn, can affect the long term structural durability of the composites. A set of PMCs reinforced with ECR-glass and E-glass fibers embedded in four different resins has been investigated in this study. In addition, …

Aging Of A Polymer Core Composite Conductor Under Combined Ozone And Temperature Conditions, James M. Middleton

Electronic Theses and Dissertations

The next generation High Temperature Low Sag Polymer Core Composite Conductors (HTLS PCCC) can experience harsh in-service environments including high temperature and highly concentrated ozone. In some extreme cases, it is possible that the conductors will experience temperatures of up to 180°C and ozone concentrations as high as 1% (10,000 ppm). Therefore, the primary goal of this research was to determine the most damaging aging conditions which could negatively affect the in-service life of the conductors. This included characterizing the aging in ozone and at high temperature of the HTLS PCCC hybrid composite rods and neat resin. It was found …

Dynamic Materials And Devices For Controlling Solar Heat Gain In Buildings, David Alie

Electronic Theses and Dissertations

Modern technology and materials science, coupled with an understanding of our energy consumption patterns, allows for the opportunity to realize large-scale energy savings through the implementation of more efficient, adaptive technologies. More efficient heating and cooling of both commercial and residential buildings is a strong candidate for such advancements. Indeed, a significant portion of the annual US energy budget is devoted to the heating, ventilation, and air conditioning (HVAC) of commercial and residential buildings in order to maintain safe, comfortable internal environments.

Dynamic tint windows, both traditional electrochromic devices and reflective devices, are promising candidates to help in the effort …

New Open Source Software For Building Molecular Dynamics Systems, Bruce Michael Allen

Electronic Theses and Dissertations

The context of this work is the development of open source software to support researchers to quickly build systems of molecules for molecular dynamics (MD) simulations. The goal is achieved through the integration of three open source programs by judicious modifications and creation of new source code, which allows the creation of molecular models, MD cells and the LAMMPS geometry input files. The software changes work together supporting an easy and intuitive process for simulation system creation. Creation of multiple MD cells for research simulations becomes quicker and provides needed standardization to the simulation process. The researcher can select from …

High Frequency Thermally Actuated Single Crystalline Silicon Micromechanical Resonators With Piezoresistive Readout, Amir Rahafrooz

Electronic Theses and Dissertations

Over the past decades there has been a great deal of research on developing high frequency micromechanical resonators. As the two most common and conventional MEMS resonators, piezoelectric and electrostatic resonators have been at the center of attention despite having some drawbacks. Piezoelectric resonators provide low impedances that make them compatible with other low impedance electronic components, however they have low quality factors and complicated fabrication processes. In case of electrostatic resonators, they have higher quality factors but the need for smaller transductions gaps complicates their fabrication process and causes squeezed film damping in Air. In addition, the operation of …