Dynamic response of partially compacted porous aluminum during unloading

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Abstract
Compressed gas gun impact experiments were designed to measure relief wave velocities in 2.16-g/cm3 porous 2024 aluminum compacted to near solid density. The experimental measurements showed that as the porosity decreased to zero, the velocity of the first part of the unloading wave approached the dilatational wave velocity of solid aluminum. Similar results were also obtained from ultrasonic velocity measurements on samples under various degrees of static prestress. These statically loaded samples were laterally confined to simulate the dynamic condition of uniaxial strain. The experimentally measured relief wave and sonic velocities are compared with predictions obtained from the theoretical elastic moduli relations derived by Budiansky, and by Hashin and Shtrikman. Deviations from theoretical predictions were observed for compacted densities less than 90% of solid density; the deviations are attributed to the initial nonspherical void shapes.