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%.

No abstract

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.