Shock waves in pressed aluminum nanopowder

Abstract

The dynamic behavior of the pressed aluminum nanopowder of 29 % porosity is studied in plate impact experiments at shock pressures and strain rates up to ∼2 GPa and 10⁷ s^-1, respectively. The purpose of this work is to explore the effect of the extremely small size of powder grains (100-150 nm on average) on the shock response of this nanomaterial. The two-step structure of propagating shock compaction waves is captured using a laser velocimetry technique. The parameters characterizing the structure of the main compaction wave, maximum strain rate and rise time, are affected by the ultrafine porous structure. The power law relationship between the maximum strain rate within the main wave and the pressure jump within it $\dot{\epsilon }\sim p_s^{3.8}$ describes the collected experimental data. The obtained exponent for the tested nanoporous material is close to four which characterizes the shock structure in dense metals, while the exponent values are much smaller for microporous media. This result agrees well with existing model predictions for aluminum with ultrasmall pores shocked to relatively low pressures. A comparative analysis outlined how the properties of the porous structure of aluminum materials influence the longitudinal sound velocity and the parameters of the precursor wave propagating ahead of the main compaction wave.