This thesis describes the development and application of models to predict the equation of mechanical state of materials from first principles, concentrating on the regime of strong shock waves. Most effort was devoted to crystalline solids, though extensions to the fluid phase and higher temperatures are proposed. Equations of state and phase diagrams were predicted for aluminium, silicon and beryllium. The method used is based on quantum mechanical treatments of the electrons in the solid and of the phonon modes. The importance of anharmonic effects (phonon-phonon interactions) was investigated, but was not included rigorously because it did not appear to contribute significantly. With fully <i>ab initio</i> methods, the equation of state and phase diagram could be predicted to a few percent in mass density, the discrepancy being caused mainly by the use of the local density approximation in predicting electron states. The accuracy of the equation of state could be improved considerably by adjusting the internal energy to reproduce the observed mass density at STP. The resulting <i>ab fere initio</i> equation of state could essentially reproduce the observed states on the shock Hugoniot to within the scatter in the experimental data. Because these equations of state are built on firm quantum mechanical and thermodynamic principles, they should predict accurate properties away from the principal Hugoniot, unlike traditional empirical equations of state. Accurate temperatures are important in the development of models of material strength (elasticity and plasticity) based on microstructural phenomena. As an illustration of the versatility of the equations of state, hydrocode simulations were made of the splitting of a shock wave in silicon, caused by the phase change. The splitting appears to be in reasonable agreement with laser-driven shock experiments.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:662664 |
| Date | January 2000 |
| Creators | Swift, D. C. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11446 |
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