Stereodeposition is a freeform fabrication technique which accomplishes the computer-controlled, layerwise buildup of an object through direct placement of a fluid which rapidly solidifies. Current materials compatible with stereodeposition include functional ceramics and metals, engineering polymers, and composites. The key to this flexibility is stereodeposition's ability to operate under a wide range of liquid-to-solid transformation rates. Understanding and controlling the material parameters involved in the liquid-to-solid transition is critical, as solidification ultimately impacts the precision and quality of the final object. A model of the liquid-to-solid transition has been developed in which a bead spreading on a curved surface is followed as a series of state "snapshots", whereby an applied force produces an incremental bead motion in an increment of time. This approach differs from most liquid spreading models, but allows flexibility in the time and geometry dependence of forces associated with a solidifying stereodeposition liquid. The model predicts bead contact angle as a function of time based on initial liquid properties (surface tension, viscosity, yield strength) and the solidification strategy employed, namely rheology control, mass transfer, or thermal transfer. Three parameter groupings are identified: alpha, which controls final contact angle, beta, which controls spreading rate, and delta, which controls amount of liquid transformation occurring during spreading. To validate the model, dynamic measurements are performed on the spreading of slurries of silica particles in various liquids. The model is found to predict the early stage of spreading (5 s) under one of the two proposed boundary conditions, and is shown to be equivalent in the limit to the more traditional dynamic wetting models employing an energy rate balance. An explanation is presented for the failure of the model to accurately predict the final contact angle for highly shear-thinning slurries.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/288900 |
| Date | January 1997 |
| Creators | Crockett, Robert Sinclair, 1966- |
| Contributors | Calvert, Paul |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Dissertation-Reproduction (electronic) |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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