No description available.

No description available.

A model was devised and used as the basis of a computer simulation to predict the shape of and physical phenomena in the keyhole during deep penetration laser welding. The shape of the weld cavity was determined as a part of the solution, and a convection-dominated vaporization model was utilized. Deep penetration welding is characterized by the formation of the keyhole. Beyond a certain threshold laser power, the laser beam rapidly evaporates material creating a strong back pressure, which pushes the molten material sideways forming a cavity. Hence, the laser power is effectively transferred to the bottom of the cavity and penetrates into the material until an energy balance is achieved around the keyhole. Around the keyhole three different regions (solid, liquid, and vapor) are analyzed, each region with its most suitable method. The heat transfer within the solid region is solved by Boundary Element Method. A thin layer approximation is made to simplify the analysis in the liquid region. A scaling analysis shows that fluid dynamics in the liquid region does not contribute significantly to the heat transfer in the liquid region. In the vapor region, a one-dimensional gas dynamic model is adopted from the literature. The solutions in the three regions are matched to satisfy conservation of mass at the liquid-vapor interface and of energy at the solid-liquid interface. Specifically, the matching technique of energy at the solid-liquid interface is called the matching scheme, and with it the shape of the solid-liquid interface is calculated. Then the shape of the liquid-vapor interface can readily be obtained from the shape of the solid-liquid interface and the thin liquid layer approximation. The matching scheme and the use of modules combine to make a model which is capable of predicting the shape of the solid-liquid interface; depth of penetration; surface temperature of the keyhole; pressure acting on the keyhole; energy distribution, such as the energy of vaporization, fusion, and conduction; and the thickness of the liquid layer. As a model material, pure iron was analyzed in this study. The calculated penetration depths are compared to empirical data, in order to verify the current study, and good agreement was observed.

Thesis (Ph. D.)--Oregon Graduate Center, 1981.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xix, 253 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Karl Graff, Dept. of Industrial, Welding and Systems Engineering. Includes bibliographical references (p. 223-230).

No description available.

Thermite reactions were well studied in the past few decades; however, implementation of these reactions with nanoscale components is a new interest for today’s researchers both for military and civil industries. Nanothermites are mixtures of a metal fuel and a metal oxide, undergoing a redox reaction while heated, and generating a large amount of energy (heat/thrust) which can reach combustion temperatures above 3000K. Aluminum is commonly used as the fuel because of its abundance, easy handling, high reactivity and benign products. By using nano-sized components, the surface energy, contact area, and mixing homogeneity increase. These properties result in greatly improved reactivity and propagation rate as well as easier ignition compared to traditional thermites, which make them attractive as advanced propellants, pyrotechnics, and heat and thrust generators. They also find civil applications such as joining. Here, the application of nanothermites for joining metal to ceramic/glass is investigated. To approach this goal, composites of nanothermite modified by Copper powder were developed for the first time and their related properties were studied to find the best composition for joining. These energetic composites can be applied where a localized heat source is required. The advantage of using nanothermite for joining is its fast reaction, high energy density and liquid products that can wet surfaces. In this research, the reaction products were studied by X-Ray Diffraction spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-ray spectroscopy. The overall thermite reaction corresponding to the Al-NiO nanothermite was found producing the AlNi phase in a fuel-rich mixture. The microstructures of these reaction products showed the formation of a composite made from copper, AlNi and AlNi/Al2O3 spheres in an Al2O3 matrix. On the other hand, the influences of the fuel (Al) to oxidizer (NiO or CuO) mass ratio and the amount of Cu additive, on the ignition temperature and energy release were characterized using Differential Scanning Calorimetry. It was found that both parameters do not affect the ignition temperature significantly but change the energy release dramatically. Furthermore, according to these results, (Al-33%NiO)-50%Cu was selected and applied to join dissimilar materials such as copper, alumina-silica and glass. As a proof of concept, joint cross-sections were studied by SEM-EDAX revealing that the alumina phase produced by this reaction was joined to the glass/ceramic, while the metal phase wetted the metallic surfaces. Therefore, this composite was introduced as a good interlayer for dissimilar metal/ceramic surfaces.

Thesis (Ph.D.)--Tennessee Technological University, 2007. / Bibliography: leaves 71-75.

Thesis (Ph.D.)--Tufts University, 2002. / Submitted to the Dept. of Mechanical Engineering. Includes bibliographical references (leaves 225-230). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph. D.)--University of Adelaide, Dept. of Mechanical Engineering, 1996? / Includes bibliographical references (leaves 260-302).