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George W. Woodruff School of Mechanical Engineering
George W. Woodruff School of Mechanical Engineering
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ItemHigh Shear Arterial Thrombosis: Microfluidic Diagnostics and Nanotherapeutics(Georgia Institute of Technology, 2019-12-20) Griffin, Michael T.Ischemic cardiovascular events remain the leading causes of death in the world, largely due to ineffective preventative therapies and diagnostic tools. This work investigated the development of a physiologically relevant, low-variability microfluidic thrombosis assay (MTA) capable of screening therapy efficacy. First, an experimental design was implemented to assess the effects of geometry, collagen surface coverage, and anticoagulant selection on MTA occlusion time (OT) variability. It was found that better control of shear rates through novel grayscale lithography techniques decreased OT variability. Fibrillar collagens was also found to have a significant impact. The MTA was then implemented to study the effects of current antiplatelet therapies, aspirin and Plavix, as compared to the endpoints of other platelet function tests (PFTs). It was found that aspirin use significantly increased MTA OT but did not prevent occlusion in the MTA. Results from Plavix use found a stronger response, where 20% of patients had complete OT inhibition. Comparison with other PFTs found that the MTA more closely matched the rates of ischemic events from larger clinical studies. Finally, the MTA was utilized to assess a nanoparticle therapy hypothesized to function through biophysical mechanisms. It was found that negatively charged nanoparticles were more effective than neutral or positively charged nanoparticles. The antithrombotic effect of charged nanoparticles persisted even with different base materials, but the effects of nanoparticle size were not consistent between materials. A mouse bleeding model was also used to show that hemostasis was maintained with the nanoparticle therapy. The implications of all results for clinical diagnostic and future antithrombotic therapy research are discussed.
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ItemFabrication, testing and analysis for non-destructive inspection of bonded composite joints(Georgia Institute of Technology, 2019-12-09) McCracken, Michael ThomasCarbon fiber reinforced polymer (CFRP) has risen in usage among many industries including aerospace, automotive, and wind energy. CFRP is used structurally due to its light weight, corrosion resistance, and mechanical properties. However, there are large differences between CFRP and conventionally used metals. One major issue with using CFRP is creating a reliable bonded joint for joining and repair applications during both manufacturing and services/maintenance. For various reasons, using conventional fasteners is not desirable for creating CFRP joints. Instead, adhesives are widely used to bond CFRP to other materials. Adhesive bonding is not nearly as well understood as conventional fastening. Because adhesives are not well understood, it is difficult to determine how reliable an adhesively bonded joint is. One effective way of assessing the bond reliability is through non-destructive inspection (NDI). There are currently no effective NDI methods available for detecting a “kissing bond,” a bond that has physical contact with the adherend, but very little interfacial strength. Kissing bonds form unexpectedly and can cause a disbond under loads much smaller than expected. In order to study kissing bonds and their detection, these weakened bonds must be reliably fabricated in a controlled environment. In order for NDI detection of kissing bonds to be studied effectively, it must be tested on bonded joints which have been fabricated in a controlled manner. This thesis presents a method of controlled fabrication which can produce reliably strong and weak kissing bonds, specifically for the purpose of NDI research in mind.
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ItemNeutronic, thermal hydraulic, and system design space analysis of a low enriched nuclear thermal propulsion engine(Georgia Institute of Technology, 2019-12-09) Krecicki, Matthew AndrewNuclear thermal propulsion is the high thrust, high specific impulse rocket engine technology of choice for future missions to Mars and beyond. Current designs are focusing on low enriched uranium fuel systems to reduce development costs and regulatory concerns. These designs require careful examination to identify an engine that is able to satisfy NASA’s requirements. Previous work has focused on low enriched, but for limited cases of fuel options and without a fully integrated computational framework and assumed boundary conditions. This thesis relies on and extends previous publicly available NASA studies. Integrated system analyses are developed to account for neutronic, using coupled neutron and gamma transport in Serpent, thermal hydraulic, and system effects on engine performance. The results show that using an integrated system analyses approach yields a systematic assessment and identifies an ideal design space for future higher fidelity analysis to achieve mission needs set by NASA.
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ItemMechanical and high-frequency electrical study of printed, flexible antenna under deformation(Georgia Institute of Technology, 2019-12-05) Zhou, YiFlexible hybrid electronics (FHE) has wide range of applications including medical devices, wearable devices, communication devices, automotive and aerospace sensors, and various consumer Internet of Things (IoT). This thesis has a focus on inkjet-printed antenna, and inkjet printing is a maskless, material-saving and fully additive technique which allows a variety conductive inks to be deposited on a wide range of flexible substrates. During usage, the FHE components are often stretched, bent, folded, and/or twisted to conform to underlying structure. Therefore, the electrical and mechanical characteristics of flexible printed electronic components should be studied under such deformation during operation. In this work, tests have been developed for characterizing the mechanical and high-frequency electrical behavior of inkjet-printed patch antennas under uniaxial and biaxial bending. The antenna samples have been fabricated by inkjet printing silver nanoparticle ink on flexible polyethylene terephthalate (PET) substrates. Polycarbonate cylindrical mandrels of different diameters have been used as test fixtures for the uniaxial bending test. Special sculptured surfaces have been 3D printed in polylactic acid (PLA) to perform the biaxial bending test. During bending tests, the S11 (return loss) response has been measured by a vector network analyzer (VNA) in both bent and flat configurations. Mechanical simulations have been performed to study the strain distribution in the printed elements which will lead to changes in electrical behavior. High-frequency electrical simulations have also been performed to correlate with the bending experimental data. It is seen that, the conductivity of the printed structure changes differently in different zones, due to the various values of strain they undergo. Although the cracks are observed in the printed structures, the maximum shift in the measured resonant frequency is less than 80 MHz in both tests.
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ItemAn analysis of the MSRE U-233 initial criticality for benchmark problem development(Georgia Institute of Technology, 2019-12-04) Burke, Paul E.The Molten Salt Reactor Experiment (MSRE) was a demonstration molten salt reactor operated at Oak Ridge National Laboratory in the 1960's. The reactor was operated in two phases: one with 235U-based fuel salt, and one with 233U-based fuel salt. This work assesses the feasibility of using experimental data from the 233U zero-power initial critical experiment for the development of a criticality benchmark problem. This includes a reconstruction of best-estimate values for several key model inputs (including reactor geometry elements, experimental conditions, and material composition), as well as an initial uncertainty analysis to quantify the standard uncertainty that could be expected for an associated benchmark description.
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ItemUltra-small modular reactor: Economic and design analysis(Georgia Institute of Technology, 2019-12-03) Kaffezakis, Naiki A.This thesis presents the pre-conceptual computational and economic analysis of a high-temperature (>1300 K), ultra-small (<10 MWe) modular reactor with a coupled high-efficiency (>50%) thermophotovoltaic (TPV) power block. Inspired by decreasing costs in TPV manufacturing, the integration of the TPV power block would allow for improved electrification efficiency over the heat cycles of traditional nuclear power plants. Further, by not requiring a pressure vessel and coolant loops, a USMR powered plant could feature significantly lower capital costs and be would be impervious to many of the major accident scenarios of typical plants. However, allowing for heat removal solely through radiative and passive convective cooling puts steep limitations on the USMR operational power densities and the selection of materials. This thesis reports on three phases of the USMR study: an initial sampling of the design space, a comprehensive economic analysis, and a focused study on improving fuel utilization. The preliminary sampling of the design space was performed using coupled thermal and neutronic analysis on a simplified model and resulted in the decision to focus on uranium carbide and uranium nitride fuels as the most promising fuel candidates. A top-down differential economic analysis, utilizing the Gen IV International Forum cost estimation guidelines and the Energy Economic Database, showed that USMR could potentially outperform larger plants in levelized cost of electricity, an extraordinary feat for a microreactor. An examination of power scaling factors and learning curves was also undertaken and suggests that there is a route for multi-unit siting to overcome loss of economies of scale for the USMR. The economic analysis highlighted fuel utilization as a major factor in USMR cost which led to a more focused exploration of the USMR design space, examining the tradeoff between maximum power density and fuel utilization while varying the moderation ratio of the core. This led to a converged design that could potentially produce electricity with a levelized cost as low as $39 per MWhr, as compared to the $93 per MWhr cost of the typical generation III+ nuclear plant.
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ItemTHERMAL MODELING OF AIR COOLED OUTDOOR DIGITAL DISPLAYS(Georgia Institute of Technology, 2019-12-03) Kim, JehoThe thermal design process for many electronic products often minimizes the use of computational fluid dynamics and heat transfer (CFD/HT) software in favor of quick prototyping and testing to determine the thermal characteristics of the product. For large-scale products with many thermal challenges, such a strategy may be impractical. In such cases, thoroughly developed simulation models are very valuable in driving the product design. Based on this idea, a methodology in designing a reliable CFD/HT model for outdoor digital displays is described in this study. Both the surrounding ambient temperature and solar irradiance are the major contributors to a temperature rise in such displays, but most CFD/HT software packages are limited in simulating solar irradiance through semi-transparent materials and multiple surfaces. Therefore, the contribution from solar irradiance must be treated with care when creating CFD/HT models especially when an optimum number of mesh elements is used to minimize the necessary processing power and solution computation time. To best accommodate the effect of solar irradiance, in lieu of defining the solar irradiance as a heat flux, a methodology to determine the power that should be imposed on the sun-exposed vandal glasses is described. Simulation results are obtained in the range of environmental temperature/irradiance values that can be experimentally tested. The study examines variation in simulation results between mesh element sizes, meshing techniques and heat loads assigned on the vandal glass assembly. In addition, this study explores the effect of adjusting the gap distance between the vandal glass and the liquid crystal display (LCD) to see how the maximum LCD temperature and fan performance are influenced.
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ItemOpen source CNC control with CAM and digital twin integration(Georgia Institute of Technology, 2019-12-02) Williams, KyleHigh bandwidth internet connectivity and ubiquitous computation are poised to enable automated quality assurance, high efficiency predictive maintenance and an integrated logistic support infrastructure for modern manufacturing. Information technology is in the process of revolutionizing production, as it has revolutionized so many other industries. However, old and new CNC systems alike are unable to fully claim this advantage. Milling machines are a significant capital investment; it is impractical to regularly replace them; aging systems continue to see use, but are increasingly unable to meet modern demands. These demands include tighter machining tolerances, three and five axis automation, and internet connectivity. On the other hand, modern machines evolved in a niche market with a high price for entry; these systems meet performance demands, but employ obfuscated, proprietary hardware/software systems that stifle free market innovation and offer limited bandwidth communication interfaces. They are often prohibitively expensive as well. In this body of work, an aging CNC mill is upgraded with a modern electrical power system and an open source firmware/software architecture for control and communication. A digital twin of the machine tool is developed directly in the CAM environment, where toolpaths are generated. Leveraging this open platform, the CAM software is connected directly to the machine tool over the internet, enabling remote monitoring and control. This report presents the engineering behind the system, in the broader context of the need for open source control and the demands on modern machine tools. The system is vetted out on a 1986 Mori Seiki vertical milling station and experimentally verified.
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ItemProcessing of post-industrial unidirectional prepreg tapes using SMC equipment(Georgia Institute of Technology, 2019-12-02) Chadwick, ConnerThe aerospace industry has an issue of what to do with waste, unused carbon fiber unidirectional prepreg tapes. One idea is to repurpose unused prepreg tapes for the manufacture of sheet-molding compound (SMC). The resulting material, per Sultana [1], should be stronger due to their carbon fiber and high strength epoxy resin, as compared to traditional SMC, which has lower strength glass fibers and epoxy resin. The cure state of the epoxy resin in the prepreg tapes, which is affected by the amount of time the material has spent at elevated temperatures or room temperature, significantly changes the ability of the material to be chopped into short fiber SMC. In addition, several equipment-related factors impact the material’s ability to be chopped into SMC. This thesis characterized each of the factors impacting the process and used statistical methods to design experiments to investigate the impact each of these material-related and equipment-related factors on the success of the cutting portion of the process. The cure state, as measured by endothermic peak, glass-transition temperature (Tg), or heat of reaction/degree of cure, has the greatest impact on the cutting process. For material with a moderate level of cure, the sharpness of the blades in the cutting roller also has a major impact on the success of the process. The cutting pressure, roller speed, and tape tension also have an impact on the success of the process, but impact of these factors lessens for feedstock prepreg with a sufficient high level of cure. An optimal setup was determined, and general rules of thumb for selecting material and equipment settings were established.
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ItemADHESION EVALUATION AND ASSEMBLY PROCESS DEVELOPMENT FOR PRINTED SILVER INK ON FLEXIBLE SUBSTRATES(Georgia Institute of Technology, 2019-11-20) Taylor, Christine L.Flexible substrates with printed electronics are being increasingly sought for the widespread and cost-effective use of flexible electronics. With printed ink on flexible substrates, several items need to be examined: synthesis of ink, deposition of ink, curing of ink, line and spacing of ink, adhesion of ink, fracture strength of ink, electrical characteristics of ink, etc. Among these items, adhesion of ink to the substrate plays an important role in the overall reliability of printed ink on flexible substrate. In this work, the adhesion and interfacial characteristics of printed conductors were determined though modified shear and peel experimental techniques. Modification to the tests were needed for handling the ink-jet printed films due to manufacturing considerations. (1) These films often are designed to be porous so that the films are more flexible by lower the stiffness. (2) Ink-jetting films often are composed of thin layers that are stacked-up to reach the desired thickness. (3) Depending on the tool and the file conversion to bitmap (or designated file extension) for the printer, the film may show indication of the path taken by the tool head with slight spaces between passes. A numerical model based on sequential crack growth was developed to examine how much the plastic deformation accounts for the experimentally measured peel energy. Lastly, a fully-additive printing process was demonstrated with resistors which resulted in around 6.5 MPa shear strength. For the assemblies, the joint strength of the ink for the joint to traces was stronger than the adhesion strength of the ink to flexible substrate.