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Non-steady wave profiles and the fourth-power law
The strain rate in steady shock waves is proportional to the fourth power of shock amplitude for a wide variety of materials over a broad range of strain rates. A model based on this observation gives good agreement not only with steady-wave profiles but also with data on non-steady waves in aluminum. In apparent contrast, data on vanadium and uranium at low strain rates indicates a departure from the fourth power law if the wave profiles are assumed to be steady. However, when predicted profiles are produced by allowing the waves to propagate and evolve over the actual experimental sample thickness, the fourth power model gives excellent agreement with the wave profile data even though the wave profiles in the calculations have not yet reached steady state. The implication is that the experimental data do not represent steady waves, and the model is predicting the correct evolution of non-steady waves in vanadium and uranium. 7 refs., 2 figs.