Shock Mitigation Studies of Solid Foams for Z-Pinch Chamber Protection

Solid open-cell Al foams are subjected to dynamic compression testing in a vertical shock tube to model the metallic foam being considered for use in an inertial fusion energy reactor. High porosity (0.89) foam samples (stack of two, 25.4 cm square, 10.2 cm high) of three different cell sizes (10, 20, and 40 pores per inch) are compressed with a strong shock (M=6) in a 25 kPa atmosphere of air and SF₆. The post-shock samples are highly compressed (strains up to 0.8 for the smallest cell size) and have a wavy upper surface indicating structural anisotropy. Energy absorption is found to vary with cell-size (smaller cells, more absorption) while the impulse of the shock wave is independent of cell size. Pressure data indicate the incident shock wave becomes a compression wave with a non-discontinuous gradient inside of the foam. Using an array of pressure transducers with a vertical spacing of 2.54 cm, the wave speed in the foam sample is reduced to 25% of its value without the presence of the foam