Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
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.
Browse
3 results
Search Results
Item Arcing Failure of ROHS Compliant Electromagnetic Relays(2012) Boettcher, Robert Donald; McCluskey, F. Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Electronic relay contacts have traditionally been made of materials, primarily Ag/CdO, which are resistant to welding under short, high power pulses. However, since 2006, RoHS prohibits the use of cadmium in electronics, driving the elimination of Ag/CdO and its replacement with Ag/SnO2. The reliability of relays made with Ag/SnO2 contacts has been shown to be vendor specific. This thesis focuses on developing an understanding of the metallurgical and design factors that vary by manufacturer and their effect on welding susceptibility of Ag/SnO2 electromagnetic relay contacts and other related relay failure mechanisms. In addition, it aims to predict a safe operating area of power and energy over which specific relay contacts will not weld under high power DC conditions. Relays from various manufacturers were subjected to capacitor discharge pulses of 250 V at 10-80 uF to characterize relay reliability. Failure analysis was then conducted on the welded contacts using scanning electron microscopy (SEM) and wavelength-dispersive spectroscopy (WDS) in order to address material properties and design variations that affect the welding susceptibility of relays. The incidence and extent of degradation is correlated to material characteristics including contact composition, oxide content, hardness, contact geometry, and surface roughness using a physics of failure approach. The relays with a higher percent content of indium oxide exhibited a greater reliability than those without. Both power and energy were then varied to further investigate the one cycle to failure boundary region and a failure map is presented.Item Methods of Making(2007-05-15) Lock, Benjamin Christopher; Ruppert, John; Art; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)I am drawn to tools, their applications, and the way things work. The action and process of manipulating and transforming material to create formal visual statements is vital to my sculpture. I utilize and respond to material and process, allowing for the work to develop through its creation. Relationships of form and space interest me. Not only do I find beauty in material, it also exists in the tension and the power of a space within or between forms. These interactions in my work help formulate the visual language through which the metaphor is present. I hope to capture and express a sensibility to which one can relate. This thesis will further discuss the manner in which I make sculpture. It will be a compliment to the artwork and an attempt to put to words the conceptual basis for the forms I create and the spaces they compose.Item Dynamics of Near-Alpha Titanium Welding(2004-10-12) Neuberger, Brett William; Ankem, Sreeramamurthy; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Typically, when gas tungsten arc welding (GTAW) is employed to join near-alpha titanium alloys, the resulting weld fusion zone (FZ) is much harder than that of the base metal (BM), thereby leading to lost ductility. The aim of this investigation was to improve FZ ductility of Ti-5Al-1Sn-1V-1Zr-0.8Mo by modifying filler metal chemistry. In this regard, metallic yttrium was added to the filler metal and aluminum concentration reduced. It was believed that additions of yttrium would lead to formation of yttria in the weld melt, thereby promoting heterogeneous nucleation. Since oxygen and aluminum both act as alpha-stabilizers, expected pickup of oxygen during the welding process will be offset by the aluminum reduction. Tensile testing indicated that modified filler metal welds showed a dramatic increase in ductility of the FZ. Fracture toughness testing showed that while JIC values decreased in all welds, the tearing modulus, T, in modified filler metal welds was significantly higher than that of matching filler metal welds. Microhardness mapping of the weld zones illustrated that modified filler metal welds were significantly softer than matching filler metal welds. Microstructural examinations were completed through the use of optical, SEM and TEM studies, indicating that there was a presence of nano-particles in the weld FZ. XPS analysis identified these particles as yttrium oxysulfate. WDS analysis across the welds' heat affected zones demonstrated that there is an internal diffusion of oxygen from the BM into the FZ. Research results indicate yttrium oxysulfide particles form in the weld pool, act as a drag force on the solidification front and limit growth of prior-beta grain boundaries. The reduced prior-beta grain size and removal of interstitial oxygen from the matrix in modified filler metal welds, further enhanced by oxidation of yttrium oxysulfide to yttrium oxysulfate, leads to increased ductility in the weld's FZ. Addition of yttrium to the weld also acts to modify the surface tension of the melt, leading to an increased weld depth penetration. Results of this work indicate that the goals of this project and a significant advancement in the understanding of yttrium effects on titanium grain refinement have been achieved.