Search

Using temporal pulse shaping, laser ablation can generate shocks or ramp loading in samples. Shock data can often be analyzed using analytic calculations, but integrated calculations are required in the case of ramps. When phase transitions occur, surface velocity histories may become much more complicated, requiring accurate hydrocode simulations for interpretation. The shock may be split by phase transitions and the slope of the ramp interacts with phase transition kinetics. The analysis of these experiments requires a good knowledge of phase transition thermodynamics i.e. an accurate multiphase equation of state (EOS). Recently, laser experiments have been performed on samples exhibiting phase transitions, complemented by a general model of multiphase EOS developed at CEA. The aim of the present study was to compare equilibrium multiphase EOS with qualitative and quantitative features of the experimental data. Multiphase EOS were constructed for Ti and Zr using static data. Good agreement was found between most experiments and calculations, demonstrating the accuracy of the multiphase EOS. In some cases, the experimental data show obvious kinetic effects. [ABSTRACT FROM AUTHOR]

In the XIXth century, Riemann gave the equations system and the exact solution for the isentropic flows in the case of the ideal gas. But to our knowledge, nothing has been done to apply it to condensed media. Many materials of practical interest, for instance metals, obey to the linear law D = c+s u, where D is the shock velocity, u the particle velocity, and c and s properties of the material. We notice that s is strongly linked to the fundamental derivative. This means that the assumption of constant fundamental derivative is useful in this case, as it was with the isentropic gamma in the Riemann solution. Then we can apply the exact Riemann solution for these materials. Although the use of the hypergeometric function is complicated in this case, we obtain a very good approximation with the development in power series. [ABSTRACT FROM AUTHOR]

For several decades, experiments have shown the behavior under shock of materials featuring phase transitions. They exhibit shock splitting and rarefaction shocks. If the main phenomena are now understood, most studies are limited to the qualitative behavior, and a quantitative analysis of experimental results remains to be done in most cases involving complex materials, waves or geometries. In the present study, we have undertaken calculations on ice to reproduce quantitatively an impact experiment on ice with double phase transition. We have built a six phases equation of state (EOS) for ice which reproduces experimental equilibrium phase diagram and Hugoniot curves. Our first hydro calculations provide the pressure levels, but exhibit an elastic precursor and kinetics of phase transition effects. [ABSTRACT FROM AUTHOR]

Our purpose is to provide the explanation of the successive waves which can occur in the general case when a wave propagates through a material with a non-convex equation of state. We show that decrease of the sound speed introduces isentropic compression waves (ICW) inside shock waves (SW) and rarefaction shocks (RS) inside isentropic release (IR) fans. After basic phenomena explanations, we illustrate them on the example of a virtual material which gathers all these cases. Hydrocode calculations based on this material show the difficulties of high-order numerical schemes to reproduce the physical features. [ABSTRACT FROM AUTHOR]

When a shock wave crosses a solid material and subjects it to solid-solid or solid-liquid phase transition, related phenomena occur: shock splitting, and the corresponding released shock wave after reflection. Modelling of these phenomena raises physical and numerical issues. After shock loading, such materials can reach different kinds of states: single-phase states, binary-phase states, and triple points. The thermodynamic path can be studied and easily understood in the (V,E) or (V,S) planes. In the case of 3 phase tin (β,γ, and liquid) submitted to shock waves, seven states can occur: β,γ, liquid, β-γ, β-liquid, γ-liquid, and β-γ-liquid. After studying the thermodynamic properties with a complete 3-phase Equation of State, we show the existence of these seven states with a hydrodynamic simulation. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The use of the up-to-date theoretical and semi-empirical equations of state (EOS) in modern thermochemical codes allows one to accurately predict the thermodynamic properties of the detonation products of high explosives (HE). However, in most cases, the direct incorporation of such EOS into hydrocodes results in too high computer time expenses. Here we demonstrate two simpler approaches to hydrodynamic simulations that combine high predictive ability of modern thermochemical codes and low expenses of computer time. The first approach employs a pre-calculated EOS in a tabular form produced by the TDS thermochemical code. The second approach uses the CW2 EOS in a compact analytical form. Both approaches are compared to each other using the EFAE hydrocode. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]