Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2009. / Thesis Advisor(s): McNelley, Terry R. ; Su, Jianqing. "June 2009." Description based on title screen as viewed on July 10, 2009. Author(s) subject terms: Friction Stir Processing, Superplasticity, Elevated Temperature, Aluminum, Grain Refinement, Strain Rate. Includes bibliographical references (p.49-50). Also available in print.

A study of slip continuity across grain boundaries in high-purity aluminum has been carried out, both on bicrystals and on polycrystal strip. Metaliographic methods have been used to show that slip continuity is not confined to the surface, but is a true continuity present within the metal. Orientations favouring continuity have been determined, which indicate that screw dislocations can pass through grain boundaries more easily than edge or mixed dislocations. / Applied Science, Faculty of / Mining Engineering, Keevil Institute of / Graduate

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published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

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The sonic testing method employed in this thesis provides data for the calculation of several of the mechanical properties or aluminum and for a qualitative analysis of the visco-elastic behavior of this material. Young's modulus of elasticity is determined for aluminum bars with various lengths and cross sections using the resonant frequency (in flexure) of each bar. This property varies linearly with the length to depth ratio of the test specimens, decreasing as the L/D ratio decreases. Certain nonlinear relationships exist between the length to depth ratios, resonant frequencies and Young's modulus, and are depicted in figures 8 and 9. In addition, the logarithmic decrement, a measure or the internal damping of the material, is computed from the nondimensional amplitude-frequency response curves and is observed to increase as the test specimens become shorter. This is an indication that the internal damping increases as the lengths of the test specimens become shorter. Due to the visco-elastic nature or aluminum, the manner in which this damping varies is unknown. An attempt to qualitatively analyze this phenomena is made by analyzing a one-dimensional mechanical model incorporating both a nonlinear restoring force and nonlinear viscous damping in its system. Observations of the test results show that the restoring force is best described by a linear spring, but that the damping can indeed be described, at least qualitatively, by a nonlinear dashpot. This qualitative analysis of aluminum can at best provide only a concept of the physical characteristics of this material in the light of experimental results. / Master of Science

Aluminum single crystals were cyclically deformed in single-slip at small strain amplitudes at 77 K to presaturation. The observed mechanical behavior is consistent with other recent work. The dislocation substructure was analyzed in detail. The structure can be described as consisting of dense bundles or veins of dislocation dipoles, separated by lower dislocation density regions where debris is evident. This debris was determined to be principally relatively short dipole segments. Screw dislocations with the same Burgers vector span the channels. Dislocations were essentially all of the same Burgers vector. In-situ cyclic deformation experiments were successfully performed by the X-Y technique where thin foils are stressed in alternating perpendicular directions. Screw dislocations span the channel and easily move and reverse direction with shear reversal. Our experiments indicate that loops frequently expand from the dipole bundles into the channels and the edge component is absorbed by nearby bundles leaving screw segments behind. Dipole "flipping" was not observed and these edges are relatively difficult to mobilize. There is no obvious evidence for internal backstresses that assist plastic deformation on reversal of the applied shear. / Graduation date: 1996

Submitted towards the Degree of Master of Technology in Mechanical Engineering at the Cape Peninsula University of Technology / A Small Punch Test is a non-destructive technique for evaluating mechanical behaviour. The main advantage of this testing technique is the fact that material can be extraxted from a component in service due to the small dimensions of the speciments.Typical test specimens cut from components are similar in size to a normal human fingernail.

The atomization of a liquid by an air stream has been an item of much concern in the past, and there have been numerous experimental studies of the process made in an effort to correlate liquid and air- stream physical properties into a general model which will predict the degree of and the time required for atomization for a given physical situation. The breakup of liquid drops, a major portion of the atomization process, finds application in the field of meteorology, where the formation, breakup, and shape of raindrops is an item of much concern; in the field of internal combustion engines, where the carburization of a fuel is of major importance; in the industrial field, where the atomization of paint and plant insecticides and spray drying processes are oft-mentioned objects of concern; in the chemical industries, where the emulsification of liquid- liquid systems, the formation of froths, the production of aerosols, and dispersion processes in general are most important considerations; and in the science of rheology, wherein the motion and dispersion of liquids, gases, and solids must take into consideration various breakup mechanisms. Despite the oft-mentioned importance of such liquid atomization processes, there has been little theoretical work done in .an effort to mathematically correlate the important variables and parameters common to all breakup and dispersion processes in general.