Low-Stress Shock and Release Wave Behavior of Porous Carbon

Abstract

Shock‐reverberation techniques and transmitted‐wave experiments were used to determine multiple shock states and release adiabats from shock‐induced states for a 0.68‐g/cm³ graphite foam and a 1.37 g/cm³ carbon felt. These experiments indicated that the samples were not compacted to solid density in the 1–3 μsec duration of the stress pulse, even though the peak pressures were well in excess of the quasistatic yield strength of the materials. For the very low‐density graphite foam, release adiabats centered at initial shock states between 0.7 and 3.2 kbar were found to be indistinguishable from the principal Hugoniot; whereas for the more dense material, release adiabats centered between 0 and 25 kbar were substantially different from the principal Hugoniot. This seemingly anomalous behavior of the graphite foam is likely due to a separation of the solid portions of the sample from the gauge. A prediction of the distance at which a short stress pulse is overtaken by trailing relief waves is given for the carbon felt.