Effect of porosity on rapid dynamic compaction of nickel nanopowder

The shock-loading behavior of nanomaterials requires careful investigation because these complex systems are widely used in environments subjected to impulsive loads. Planar plate impact experiments are conducted to study shock compaction waves in 94% porous nickel powder containing spherical ∼55 nm particles in the pressure and strain rate ranges of 0.1-0.4 GPa and 10⁶-10⁷ s^-1, respectively. The distinct two-step structure of these waves is captured by a laser velocimetry technique with high time resolution. This structure is caused by the formation of faster precursor waves traveling ahead of main compaction waves. The complexity of the shock Hugoniot curve of the tested nanomaterial is described using the obtained two-wave data and earlier results for higher pressures. The effect of initial porosity on the fronts of both waves and compressed states behind them is demonstrated using the current data and those that were collected previously for 50% porous samples of similar nanopowder.