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George W. Woodruff School of Mechanical Engineering
George W. Woodruff School of Mechanical Engineering
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ItemProcess Modeling and In-Situ Monitoring of Photopolymerization for Exposure Controlled Projection Lithography(Georgia Institute of Technology, 2020-05) Wang, JennyOne of the main challenges in additive manufacturing is to ensure the consistent production of accurate and precise parts. Investigation of real-time monitoring and closed-loop feedback control for these processes is an area with great potential for discovery and innovation. These capabilities can vastly improve the quality and efficiency of production, and make additive manufacturing a lucrative option in a wide range of applications. Among the burgeoning field of additive manufacturing, stereolithography has proven to be an effective process to create a variety of products. However, the process lacks the resolution to manufacture small parts with a high degree of accuracy and precision. In order to meet the demand of modern technology, in which the use of micro-and nano-scale products is becoming more and more ubiquitous, a method of in-situ measurement and control for micro-stereolithography is being developed. Exposure controlled projection lithography (ECPL) is a micro-stereolithography process in which UV light is projected by a dynamic mask through a transparent substrate onto photopolymer resin to grow features from the substrate surface. The interferometric curing monitoring (ICM) system monitors the ECPL fabrication in real time, using the principles of interference optics to measure small changes in the dimensions of the cured part. Additionally, ECPL has been simulated using COMSOL software to characterize the reaction kinetics. The work presented in this thesis models the curing process based the simulation and based on information from the ICM system, and compares these results to develop a more complete understanding of the optical properties of ECPL. This could be used to establish a more accurate model to estimate the dimensions of the cured part in real time, which could then be used in a feedback-controlled system to fabricate more accurate and precise parts using ECPL.
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ItemSynthesis and Characterization of Macromolecules for Intra-Articular Retention and Clearance(Georgia Institute of Technology, 2020-05) Shaver, JosephBased on the studies conducted, 40 kDa PEG NIR, 50 kDa HA-NIR and Albumin NIR can be successfully synthesized and purified and are therefore suitable for injection for in vivo imaging. In addition to the synthesis and purification of the tracers, various considerations were discovered during the synthesis of tracers containing sulfhydryl functional groups, such as the formation of disulfide bridges. Therefore, we determined that the optimal reactive group is primary amines, and have elected to use them going forward. In this thesis, we also explored the ability to modify the zeta potential of polymers using methyl-PEG NHS Ester. We found that if the charge is the result of primary amines, the charge can be significantly reduced after being reacted with methyl-PEG NHS Ester. Methyl PEGylation would enable the effect of a molecule’s charge on its clearance rate to be studied in vivo and should be studied with more negatively charged molecules like HA. Lastly, we also showed that amine functionalized HA can be characterized and conjugated to NIR dye. However, further work is needed to purify this bioconjugate. Also, in order to mimic naturally occurring HA in the knee space, HA-NIR must be able to be enzymatically degraded, which has not yet been demonstrated. Despite this, 1.5 and 2.5 MDa HA-NIR can still be used in vivo to investigate how HA is cleared from the knee space when it cannot be degraded by HYAL and to explore other mechanisms by which it can be degraded and transported in the joint.
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ItemControlling Interfacial Properties of Solid-State Lithium Batteries Using Atomic Layer Deposition(Georgia Institute of Technology, 2018-12) Joshi, KiritSolid-state lithium batteries (SSLiBs) could enable improved safety and higher energy density compared to traditional lithium-ion batteries due to the use of metal anodes without dendrite growth. However, successful implementation of solid electrolytes within batteries is contingent upon controlling the chemical, mechanical, and electronic properties at solid electrolyte/electrode interfaces. SSLiB interfaces can exhibit poor wetting properties, leading to interfacial void spaces and high impedance. Furthermore, many solid electrolytes are chemically unstable in contact with electrodes. This project aims to stabilize traditionally unstable interfaces between lithium metal and ceramic electrolytes through the use of atomic layer deposition (ALD) of thin film oxide protection layers. It is expected that these protection layers will improve wetting properties and prevent or slow detrimental anode-electrolyte interactions. A custom ALD instrument has been designed and constructed for this project. This fully-automated instrument allows for the deposition of ternary oxides with atomic precision. It features pneumatic control of valves, a custom LabVIEW Virtual Instrument interface, and real-time pressure feedback control. This instrument is ideal for coating nanometer-scale films on either bulk solid electrolyte pellets or on powder. The custom reactor is used to coat NASICON-type solid electrolytes, including Li1.4Al0.6Ge1.4(PO4)3 (LAGP), with oxide thin films (Al2O3, ZnO). These NASICON materials are shown to readily react in contact with Li metal. The effect of these ALD protection films on electrochemical behavior and lifetime are compared to that of uncoated materials to determine whether the ALD coating improves battery performance and stability. Ultrathin oxide layers are found to improve the stability of the solid electrolytes in contact with Li during galvanostatic cycling. In particular, the ALD layers are shown to substantially extend the time to failure during cycling and to alter degradation pathways within cells. In conjunction with other students, ex situ and in situ characterization is used to uncover the evolution of these layers during cycling. These results are important for the development of stabilized, high-conductivity solid electrolytes for solid-state batteries.
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ItemPhysical Removal of Ablated Aluminum with Titanium Scraper(Georgia Institute of Technology, 2018-12) Gyorfi, Tibor JohnA railgun is a high velocity launcher which relies on the Lorenz force to accelerate projectiles commonly made of aluminum. When a railgun is fired, the large current required to accelerate the projectile to high speeds causes a portion of the armature’s contacting surface to ablate onto copper rails with the largest concentration located at the startup region. This ablation impedes the path of fired armatures causing deformation of subsequent armatures. In addition, aluminum buildup can hasten the rate of rail wear by increasing the incidence of voltage spikes due to poor continuity as well as high velocity shearing of the copper substrate. The goal of this project was to design a scraper which could remove the ablated aluminum without damaging the soft copper rail surface and increase the useful life of a set of railgun rails, decreasing the number of costly and time-consuming teardowns. Since previous research did not exist on the topic, numerous materials were investigated for use as a high velocity scraper, however it was found that titanium Ti-6AL-4V had the best combination of conductivity, stiffness, strength, light weight, and fracture toughness to handle the immense forces within the railgun. A plow shaped tip was designed to attach to existing armature types. The combination was then tested on a set of rails with massive aluminum ablation and was shown to be a success after the rail returned to a favorable condition and excessive deposits were removed. After launching approximately 100 standard shots through the test gun, the scraper was fired, and results were observed to be acceptable. Future work will include improvements in armature manufacturability by utilizing selective laser sintering 3d printing technology.
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ItemDevelopment of a Self-Powered Hydraulic Sensing Node(Georgia Institute of Technology, 2018-05) Toothman, MaxwellIn modern industrial settings, a significant amount of energy is wasted in the form of sound, physical vibrations, and pressure variations in gases and liquids. Given the recent advances in low power processing and communication devices, there is now an opportunity to capture this energy and use it to power sensing and communication components. A device that is able to power itself using ambient energy would be an innovative replacement to wired or battery-powered sensors which can be costly and difficult to maintain. Past efforts in this area have been stymied by the low energy densities that are present in ambient sources such as light and vibrations, but pressure fluctuations in hydraulic systems offer a much denser energy source. Previous work developing a piezoelectric energy harvesting device has generated 2.6mW of power from a hydraulic test rig operating at a static pressure of 5.5 MPa with a 9-piston pump operating at 1500 RPM. This Hydraulic Pressure Energy Harvester (HPEH) device has the potential to generate power which could be used for remote sensing and communication purposes in a variety of hydraulic systems. This paper presents an implementation of a HPEH device connected to a communications system that allows it to store energy and communicate sensor readings via Bluetooth Low Energy. The levels of power that are produced by the energy harvester and consumed by the communication components are analyzed, with special attention paid to the power consumption of a connected microcontroller during different operations. Additionally, an evaluation of the wireless data transmission rates that can be supported by the power output of a HPEH device is included.
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ItemPercolation, Electrical Conductivity, and EMI Shield Analysis of CNT Composites(Georgia Institute of Technology, 2016-07-18) Song, Won SupAnalysis of Carbon Nano-Tube (CNT) filled polymer composites is the focus of this work. CNT composites have far-reaching applications ranging from being applied in electronics as conductive polymer thin-films, in light weight aircraft structural components, and in many other engineering disciplines. These nano-composites are challenging to process and scalability and cost-effectiveness in manufacturing are yet to be achieved. Upfront models for electrical characterization of CNT composites are developed and analyzed for quick what-if analysis, and cost-effective solutions in manufacturing for various applications. Representative Volume Element (RVE) models with material homogenization conditions are developed in generating a 3D network of fillers within the RVE, which involve placing fillers that exceed the RVE into their respective position on the opposite face of RVE as if the RVE is part of a larger network of RVEs. The RVE models with 3D network of CNTs within RVE developed are used for percolation, electrical conductivity and Electromagnetic interference (EMI) shield effectiveness (SE) of CNT-based polymer composites.
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ItemEngineering a chondrogenic microenvironment to promote MSC chondrogenesis(Georgia Institute of Technology, 2016-05) Saraogee, ApoorvOsteoarthritis (OA) is characterized by the degradation of articular cartilage and affects 27 million people in the US. Mesenchymal stem cells (MSCs) are a promising cell source for OA therapies because of their immunomodulatory properties and ability to be differentiated along a chondrogenic lineage. Traditional chondrogenic differentiation of MSCs relies on using growth factors such as TGF-βs, but cells rapidly undergo hypertrophy and are not able to withstand the same mechanical load as healthy hyaline cartilage. Decellularized cartilage contains important growth factors and extracellular matrix (ECM) proteins to support chondrogenesis at physiologically relevant concentrations and may be an alternative or additive to improve chondrogenic differentiation. The objective of this study was to investigate whether digested cartilage ECM incorporation into MSC pellets could improve chondrogenic differentiation alone or in combination with exogenous growth factors such as TGF-β1. Porcine articular cartilage was decellularized and then digested in pepsin to form an ECM digest. The ECM digest was incorporated into 250,000 cell pellets at various concentrations to determine an appropriate dose. The ECM digest was then subsequently incorporated into MSCs with and without the addition of TGF-β1. The chondrogenic TGF-β1 treated control with no additional ECM was negative for glycosaminoglycan (GAG) staining after 21 days in culture, so subsequent experiments investigated the role of donor-to-donor variability, passage number, and media composition in affecting MSC chondrogenic differentiation. Chondrogenic differentiation of MSC pellets had better glycosaminoglycan (GAG) content with TGF-β3 induction compared to TGF-β1, but this differentiation was greatly limited in multiple donors with high (>p4) passage number. Future studies will compare ECM addition with chondrogenic induction of MSCs from earlier passages.
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ItemThe Effect of Low Frequency Cycling & Mill Scale on Stress Corrosion Cracking of Pipeline Steel in Simulated Fuel-Grade Ethanol(Georgia Institute of Technology, 2015-01-28) Elsayed, Omar HeshamUsing non-renewable fossil fuel energy resources has become a major concern in modern day society. Major efforts have been made to decrease the effect of such hazardous materials. Ethanol (CH3CH2OH, or EtOH) has been proven to be a promising alternative option to fuel. Approximately 10-15% of the commercial fuel used nowadays is composed of fuel-grade ethanol (FGE). However, field failures due to stress corrosion cracking (SCC) of carbon steel pipelines and storage tanks used in FGE transportation have been reported. Leaks are found at stress concentration points, such as heat affected zones and geometric discontinuities. Prior research on the effect of EtOH chemistry and electrochemical conditions on crack initiation, growth and propagation behavior has shown that contaminants and/or additives are important factors in causing SCC in FGE pipelines. The role of low frequency stress fluctuations on SCC initiation and propagation on the inner surface in FGE pipelines was not understood. The main objective of this research is to evaluate low frequency cyclic effects on SCC behavior under simulated conditions, and thus use the obtained information to optimize productivity and prevent catastrophe. A four-point bend test on a pipeline section immersed in an ethanol solution will be used to simulate the service conditions experienced during operation. It has been conjectured that SCC is not experienced with a static applied load below or above yield stress levels, therefore indicating that dynamic or cycling loading is required for SCC to occur. A smoother surface finish results in significantly less SCC than a rougher surface, emphasizing the importance of surface roughness in SCC behavior. A smaller R-ratio results in lower crack density, nucleation rate and crack velocity than larger R-ratios, hence indicating the importance of fluctuating stresses in SCC behavior. A higher cyclic frequency results in increasing crack density, nucleation rate, velocity and crack length, with a possible threshold leading to crack propagation. Longer test durations resulted in reduced crack velocity, indicating that cracks grow slowly with time due to a number of factors, including crack shielding. Finally, oxygen supply is essential for SCC to occur, which support previously conducted research by X. Lou et. al and Sridhar et. al.