Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item EVALUATION OF IMPACT OF NOVEL BARRIER COATINGS ON FLAMMABILITY OF A STRUCTURAL AEROSPACE COMPOSITE THROUGH EXPERIMENTS AND MODELING(2021) Crofton, Lucas; Stoliarov, Stanislav; Fire Protection Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Composites have become a integral part of the structure of airplanes, and their use within aircraft continues to grow as composites continue to improve. While polymer composites are an improvement in many facets to traditional airspace materials, their flammability is something called into question. The work performed for this study was to create a pyrolysis model for a particular aerospace composite, IM7 graphite fiber with Cytec 5250-4 Bismaleimide matrix (BMI), and three innovative composite barrier coatings that could be applied to the BMI to potentially improve its performance in fire scenarios. The composites were all tested individually, in a series of milligram-scale tests, and the test results were inversely analyzed to determine stoichiometry, chemical kinetics, and thermodynamics of their thermal decomposition and combustion. Gram-scale experiments using the Controlled Atmosphere Pyrolysis Apparatus II (CAPA II) were performed on the BMI by itself and then again with one of each of the composite barrier coatings applied in a defined thickness. This data were inversely analyzed to define the thermal conductivity of the sample and resolve it’s emissivity. It was found after fully defining a pyrolysis model for each composite material that the composite barrier coatings did not provide any benefit to the base composite BMI, and only added more fuel load which in turn contributed to a increase in heat release rate when computational simulations were run to mimic a airplane fuel fire.Item Characterization of Exfoliated Graphite and Latex Composite as Temperature Sensors to Produce Thermal Images(2014) Sauerbrunn, Elizabeth; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Temperature sensing is crucial in spacecraft to ensure all systems remain within operating temperatures. Sensing over an area would allow thermal management systems to effectively see the temperature profile in real time, which is not being done with thermocouple and RTD systems used today. The resistance response as a function of temperature for exfoliated graphite and latex composite sensors was investigated. The effect of the substrate CTE and the EG loading level were observed and 30 wt% EG sensors were calibrated on a carbon fiber substrate. Above room temperature, the percent resistance change and temperature relationship is linear, while below room temperature the relationship is exponential. The resistance response from twelve sensor grids was converted into a temperature field to produce thermal images over a surface. These temperature profiles were compared to thermal simulation data, proving that the sensor grids successfully mapped the proper temperature patterns.Item Determination of Mixed Mode Energy Release Rates in Laminated Carbon Fiber Composite Structures Using Digital Image Correlation(2012) Puishys, Joseph Francis; Bruck, Hugh A; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Carbon fiber composites have recently seen a large scale application in industry due to its high strength and low weight. Despite numerous beneficial attributes of composite materials, they are subject to several unique challenges; the most prevalent and troubling is delamination fracture. This research program is focused on developing an appropriate damage model capable of analyzing microscopic stress strain growth at the crack tip of laminated composites. This thesis focuses on capturing and identifying the varying stress and strain fields, as well as other microstructural details and phenomena unique to crack tip propagation in carbon fiber panels using a novel mechanical characterization technique known as Digital Image Correlation (DIC).Item Fracture of Brittle Layers Joined with High Elastic Modulus Composite(2007-04-25) Lee, James Jin-Wu; Lloyd, Isabel K; Lawn, Brian R; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ceramic properties such as biocompatibility and inertness have secured their use in biomedical prosthetics. The brittle nature of ceramics governs their application in any design and fabrication technique. Current all-ceramic dental crowns have a reported failure rate of approximately 3% a year. An investigation into a possible improved design over current all-ceramic dental crowns is performed. Current methods of fabricating all-ceramic dental crowns involve laborious and time consuming application of porcelain veneer layers onto a core material. The proposed design is to join independently fabricated veneer and core layers together using a high elastic modulus composite. Fracture behavior of brittle layers joined by a high elastic modulus composite is studied in this dissertation. There are two dominant fracture mechanisms of concern for dental crowns when joining brittle layers with a more compliant interlayer; the formation of radial cracks in the veneer or core and the propagation of cracks between brittle layers. The occlusal loading on dental crowns can be simulated with the use of Hertzian contact testing on flat brittle laminates, which allow for the study of radial cracks in the veneer. It is shown for the first time that bottom-surface radial cracks in the veneer due to flexure can be suppressed using a high elastic modulus joining interlayer. The relationship between the critical loads for radial crack formation, Pcr and the interlayer modulus and thickness is elucidated. Furthermore, using the high modulus composite as an interlayer increases the long term cyclic loading lifetime over joins with similar moduli to currently available dental adhesives. The propagation of cracks between adjacent brittle layers is shown to be controlled by a reinitiation mechanism and not penetration through the adhesive. Cracks that traverse the layer of origin arrest at the join interface in brittle laminates. Reinitiation loads are dictated by strength of the adjacent brittle layer and modulus of adhesive. This study shows that it is possible to use a high modulus composite as a joining material in the fabrication of dental crowns, while suppressing the formation of radial cracks in the veneer and limiting the propagation of cracks between adjacent brittle layers.Item Composite Construction of an Unmanned Aerial Vehicle(2006-08-15) Valente, Evandro Gurgel do Amaral; Wereley, Norman; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The purpose of this thesis is to develop an understanding of composite construction while building a systematic manufacturing and assembly process for the construction of an all-composite Unmanned Aerial Vehicle. This thesis in intended for both beginners and advanced composite builders and documents the entire construction of a molded composite aircraft from CAD to Runway. Several processes are discussed including CNC Plug Milling and Foam Cutting, Wet Lay-up, Tooling Manufacturing and Vacuum Assisted Resin Transfer Molding (VARTM - Infusion). Materials extensively used such as polyester resin/MEKP, gel coat, random directional matting, and carbon reinforcement are presented in an illustrated "how-to" approach to building.