Invariance of the Dissipative Action at Ultrahigh Strain Rates Above the Strong Shock Threshold

We have directly resolved shock structures in pure aluminum in the first few hundred picoseconds subsequent to a dynamic load at peak stresses up to 43 GPa and strain rates in excess of ${10}^{10}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$. For strong shocks we obtain peak stresses, strain rates, and rise times. From these data, we directly validate the invariance of the dissipative action in the strong shock regime, and by comparing with data obtained at much lower strain rates show that this invariance is observed over at least 5 orders of magnitude in the strain rate. Over the same range, we similarly validate the fourth-power scaling of the strain rate with the peak stress (the Swegle-Grady relation).