Single-crystal and polycrystalline specimens (including powder compacts of various densities) of titanium dioxide have been subjected to shock-wave pressures in the 150–1000–kbar range. Hugoniot measurements have disclosed a phase transition commencing below 200 kbar, and x-ray diffraction studies of specimens recovered after shocking to various pressures above 150 kbar have shown the presence of an orthorhombic phase with the α-PbO2 structure. Calculated lattice parameters are a = 4.55 Å, b = 5.46 Å, and c = 4.92 Å, which correspond to a crystal density of 4.34 g/cm3. The orthorhombic phase appears to result on release of pressure from a considerably denser phase of TiO2 (postulated to have approximately 8:4 oxygen-titanium coordination) that dynamic measurements indicate is formed under shock. Yields of the α-PbO2 phase as high as about 90% have been obtained from [001]- and [111]-oriented rutile crystals shocked to 450 kbar. At atmospheric pressure this phase can be retained indefinitely at temperatures below 340°C, but reverts to rutile rapidly at 550°C. An activation energy of 66 ± 5 kcal/g-mole has been computed for reversion of specimens containing predominantly the orthorhombic phase but also containing some nuclei of rutile. The average crystallite size of shocked material is typically as small as 100–200 Å, and crystallites obtained from initially single-crystal rutile exhibit preferred orientation. Shocked specimens of rutile and of the orthorhombic phase have ESR spectra that exhibit surface-sensitive behavior, but which do not appear to be dependent upon the relative amounts of rutile and orthorhombic phase present. Petrographic and electron microscopy observations of shocked material are also reported.

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For guidance in constructing a mathematical model for porous materials, impact tests were conducted with a light-gas gun on samples of porous copper, iron, tungsten, and polyurethane foam using manganin and quartz transducer techniques. Both Hugoniot (thick flyer) and attenuation (thin flyer) experiments were conducted on the porous metal specimens, which were initially at 70% of solid density. The Hugoniot elastic limits were 1, 2.5, and 10 kbar and maximum stresses attained were 60, 50, and 140 kbar in copper, iron, and tungsten, respectively. In impacts above 20 kbar, porous iron and copper compacted to solid but tungsten was not consolidated at 140 kbar. The mathematical model was incorporated into a one-dimensional wave propagation computer program, and stress histories were computed to compare with the transducer records. Computed peak stresses and arrival times agreed with the recorded values within 20%.

Shock propagation and attenuation have been studied in porous graphite and aluminum foams (40% to 80% of crystal density). The effects of such material parameters as particle (or pore) shape, size, and size distribution on response of the materials to shock loading were investigated, and Hugoniot measurements below 25 kbar were made. It was found that in the pressure and porosity range studied, the ``compacted'' volumes for pressures above a few kilobars are essentially those of the solid materials at the same pressure. The densities of specimens of aluminum foam recovered after shocking to about 10 kbar correspond approximately to that of solid aluminum, while the densities of recovered specimens of ATJ graphite are very close to their initial densities, even after shocking to 50 kbar. An artificial viscosity computer code has been successfully adapted to calculation of shock attenuation in porous solids. Within the idealizations of the models employed, calculated transit times and shock profiles are in reasonably good agreement with the experimentally measured quantities.