Compaction dynamics of metallic nano-foams: A molecular dynamics simulation study

SUMMARY This study was driven by the NIF Energy and Scienceprograms. We investigated the generic features of thecompaction dynamics of metallic nano-foams as relatedto current ICF and science interests. A successful atom-istic method was implemented for creating a computernano-foam. The microscopic processes in the compactiondynamics showed that a strong compaction front passingthrough a foam induces acceleration, crushing, ablationand mixing of the foam material within the porous back-ground. Depending on the piston speed, the ejecta couldbe a solid front, a liquid, an imperfect vapor, or a hotgas. The MD simulations agreed with limited experi-mental measurements. As should be expected, the sim-ple snowplow model gavean overallaccurate macroscopicdescription of the dynamics. The EOS of the compactedfoam is a direct consequence of the atomistic simulation,though its accuracy depends of a robust description ofthe atomic behavior over a wide range temperatures andpressures. Our simple interatomic potential did not fulfillthat requirement because of the constrained neutrality ofthe atoms. However, simple model estimates of the ion-ization were made and are believed to be reasonable. Thecrushing of the foam is a highly complex evolving stateas one moves from the front toward the piston.