Session L6: Equation of State II

Characterization of a Y-TZP Zirconia material for gas gun experiments

A number of shots were carried out on the AWE single stage gas gun with Het-V diagnostics to determine the shock Hugoniot of a commercial Y-TZP Zirconia ceramic material ($\rho $ 6.05 g/cc). Zirconia ceramic has a higher density and acoustic impedance than alumina, this allows for higher shock pressures to be achieved in impact velocity limited scenarios where conductive materials are not suitable. For example, when using electromagnetic particle velocity gauge diagnostics. The grade examined here was highly reflective to 1550 nm wavelengths, which negated the need for window materials when taking free surface velocity measurements. The shock Hugoniot was determined to be linear up to 13.4 GPa with the form U$_{\mathrm{s}}=$ 5.82 $+$ 2.20 U$_{\mathrm{p}}$ and the HEL was in the range of 7-9 GPa. Additionally data from lateral gauge shots examining the failure behavior of the material are reported on. \copyright British Crown Owned Copyright 2017/AWE   

Precise Hugoniot data and EOS properties to 2 Mbars for several high-pressure standards

Pressure calibration in static compression experiments is usually undertaken on the basis of the equation of state (EOS) of materials used as a pressure standard, such as Au, Pt, Ag, Cu, MgO, etc. derived from their Hugoniot-compression curves (Au scale, Pt scale, Ruby scale, etc.). To derive true equations of state (EOS) from these standards, precise Hugoniot data are needed, including material strength in order to drive the isothermal hydrostatic compression curve. To accomplish this objective, we have implemented a high-speed streak camera measurement system consisting of a rotating-mirror type streak camera aBnd a pulsed dye laser combined with a one-stage powder gun and a two-stage light gas gun to obtain Hugoniot curves. We achieved measurement errors for shock and particle velocities of 0.3{\%} and 0.1{\%}--0.2{\%}, respectively, for each shot, which enables us to analyze the influence of shear strength and the Grüneisen parameter. We have obtained highly accurate Hugoniot data for W, Cu, Au, Pt, Ag, MgO up to 2.3 Mbars. We also performed the VISAR experiments to access the strength for several materials. In addition, we initiated a program to measure the Hugoniot data of heated samples to determine the Grüneisen parameter using a high-frequency inductive heating system. Detailed results for W, Cu, Au, etc. will be presented, and the resulting EOS and application as pressure standards will be discussed.   

Sound Velocity and Strength of Beryllium along the Principal Hugoniot using Quartz Windows

The measurement of the interface wave profile is a traditional method to determine the strength of a shocked material. A novel technique was developed to enable wave profile measurements with quartz windows, extending the range of pressures where wave profile measurements are possible beyond lithium fluoride windows. The technique uses the quartz sound velocity to map Lagrangian characteristics from the shock front back to the material interface and determine the particle velocity profile in a sample. This technique was applied to experiments conducted on beryllium at the Sandia Z Accelerator. We present measurements of the longitudinal and bulk sound velocity across the beryllium shock-melt transition and the strength of solid beryllium for pressures from 130 to 200 GPa. Sandia National Laboratories is a multi-mission laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.   

Shock Response of PMMA -- Does Material Pedigree Matter?

We report the results of plate impact experiments on both Spartech Polycast II and Rohm {\&} Haas type II poly methylmethacrylate (PMMA) as part of an effort to determine if material pedigree of PMMA alters shock response, as well as which material properties could be used to differentiate PMMA from different commercial sources. This work is motivated by a desire to obtain accurate models of shock loaded material behavior, which typically assume the shock response of all PMMA is the same as that determined for the no longer available Rohm {\&} Haas PMMA. We describe our approach of measuring the shock response using electromagnetic particle velocity gauges, which were embedded at different depths in the sample. We discuss how the Hugoniot curve, FTIR spectroscopy, and index of refraction data were obtained for Spartech PMMA up to previously unexplored stresses, 10.7 GPa. We report that Spartech PMMA is suitable for use as a shock standard and that there are no significant differences in shock response when compared with data for Rohm {\&} Haas PMMA. Finally, we speculate on whether these findings can be interpreted broadly as an indication that *all* PMMA is equivalent for use in shock studies.   

A Single-Phase Analytic Equation of State for Solid Polyurea and Polyurea Aerogels

Commercially available polymers are commonly used as impactors in high explosive gas-gun experiments. This paper presents a relatively simple, single-phase, analytic equation of state (EoS) for solid polyurea and polyurea aerogels suitable for use in hydrocode simulations. An exponential shock velocity-particle velocity relation is initially fit to available Hugoniot data on the solid material, which has a density of $\sim$1.13 g/cm$^3$. This relation is then converted to a finite strain relation along the principal isentrope, which is used as the reference curve for a Mie-Gruneisen form of EoS with an assumed form for the variation of Gruneisen $\Gamma$ with specific volume. Using the solid EoS in conjunction with the Snowplough model for porosity, experimental data on the shock response of solid polyurea and polyurea aerogels with initial densities of 0.20 and 0.35 g/cm$^3$ can be reproduced to a reasonable degree of accuracy. A companion paper at this conference describes the application of this and other EoS in modelling shock-release-reshock gas-gun experiments on the insensitive high explosive PBX 9502.   

High pressure deep-release impact experiments on high density and ultra-high molecular weight polyethylene

The high pressure dynamic response of polymers is important to a wide variety of applications. The details of compressibility and reactivity can have a large effect on overall behaviors of dynamic systems even when polymers are used in small amounts. Polyethylene is of broad interest for a variety of applications, as an ingredient and as a pure material. It is also of significant interest as a model system to understand the correlating effects of polymer dynamics in a material with a relatively simple chemical composition that can have highly varied properties through the alteration of molecular weight and associated crystallinity of the material. Although a variety of Hugoniot and dynamic information is available for polyethylene, it is a challenge to obtain information on the product equation of state at pressures high enough to achieve decomposition. Following recent successes in producing deep release states in compressed epoxy material, a series of plate impact experiments was performed in the same configuration on high density and ultra high molecular weight polyethylene at high pressures. The experiments and the results, intended to calibrate a product equation of state and compare the behaviors of these two varieties of polyethylene, will be described.