Date of Award

12-2009

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Mechanical Engineering

Advisor

Fadel, Georges M.

Committee Member

Daqaq , Mohammed

Committee Member

Kennedy , Marian

Committee Member

Rack , Henry

Abstract

Ultrasonic consolidation (UC) is a solid state rapid manufacturing process derived from ultrasonic welding of thin metal foils coupled with contour milling to achieve functional accurate components. The bonding of metal is accomplished by the local application of high frequency vibration energy under pressure producing a metallurgical bond without melting the base material. Its unique nature allows the design and fabrication of structural panels for satellites, production of injection molding tools, functionally graded structures, metal-matrix composites, embedded sensors, armor, and fiber embedded adaptive structures. It is commonly theorized that interfacial motion and friction at the bonding interface play a prominent role in the bonding process by removing surface contaminants, allowing direct metal to metal contact, and producing sufficient stress to induce plastic flow. The substrate's geometry is also crucial in the bonding process. Researchers have experimentally observed that as the height of build specimen approaches its width, the bonding process degrades, and no further foils may be welded. This work explores the process as the dimensions of the build specimen modeled as a standard parallelepiped, approaches the critical geometry through a combination of numerical, analytical and experimental analysis. We examine the resonances of a build feature due to a change in geometry and material properties using a three dimensional Rayleigh-Ritz model. A simple nonlinear dynamic model of the Ultrasonic Consolidation Process examines how the geometry change may influence the overall process dynamics. This simple model is use to provide estimates of how changes is substrate geometry affect the differential motion at the bonding interface and the amount of changing friction force due to build height. The trends of changes in natural frequency, and differential motion, are compared to experimental limits on build height. These analyses lead to several predictions on build height that are verified experimentally. Finally, the work examines the effectiveness of using support material to extend the build height limit of the process. The results show that a proximity to a resonance excitation is clearly responsible for bonding degradation at features built with the nominal tape width of 0.9375 inches. However, for small widths other factors such as surface topography, and contact area may play an important role in bonding degradation.

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