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The Z accelerator at Sandia National Laboratories was used to measure the compression isentrope of 6061-T6 aluminum to 185GPa. The isentropic compression experimental technique uses a rapidly increasing, planar magnetic field to simultaneously subject multiple planar aluminum samples of different thicknesses to a ramped magnetic stress load. This magnetic stress load causes a ramped compression wave to propagate in the aluminum. Motion histories at the rear surface of each aluminum sample are measured through a LiF window using laser velocity interferometry. Backward and forward integration of the one-dimensional equations of motion are used to analyze the data. Imposing the requirement that each motion history comes from the same magnetic stress load is sufficient to determine both the stress load and the stress-strain behavior of the aluminum. Because of shocks that grow in the LiF, the usual VISAR interferometer analysis was modified. The measured compression curve obtained on different aluminum samples for volumetric strains to 46% agrees to within about 2% of peak stress with an isentrope obtained from the often-used Mie-Gruneisen equation of state that was derived from previous Hugoniot data.

Hugoniot measurements were performed on aluminum (6061-T6) in the stress range of 100–500 GPa (1–5 Mbar) using a magnetically accelerated flyer plate technique. This method of flyer plate launch utilizes the high currents, and resulting magnetic fields produced at the Sandia Z Accelerator to accelerate macroscopic aluminum flyer plates (approximately 12×25 mm in lateral dimension and ∼300 μm in thickness) to velocities in excess of 20 km/s. This technique was used to perform plate-impact shock-wave experiments on aluminum to determine the high-stress equation of state (EOS). Using a near-symmetric impact method, Hugoniot measurements were obtained in the stress range of 100–500 GPa. The results of these experiments are in excellent agreement with previously reported Hugoniot measurements of aluminum in this stress range. The agreement at lower stress, where highly accurate gas gun data exist, establishes the magnetically accelerated flyer plate technique as a suitable method for generating EOS data. Furthermore, the present results exhibit increased accuracy over the previous techniques used to obtain data in the higher-stress range. This improved accuracy enhances our understanding of the response of aluminum to 500 GPa, and lends increased confidence to the use of aluminum as a standard material in future impedance matching experiments.

Isentropic compression experiments (ICE) on Sandia National Laboratories’ Z Accelerator are used to make continuous measurements of the index of refraction in single crystal Z-cut sapphire as the longitudinal stress is gradually increased to 20 GPa (uniaxial strain of about ∼3.9%). A planar, ramp compression wave, generated by a large magnetic field, propagates through a planar copper base plate. Part of the rear surface of the base plate is a free surface and part is covered with a sapphire window. Comparisons are made of velocity histories measured simultaneously at the free surface and at the copper/sapphire interface using a velocity interferometer system for any reflector (VISAR). This is sufficient to determine the index of refraction of the sapphire continuously as a function of density. Perturbations to the compression waves caused by interactions with the free surface and with the sapphire are accounted for by backward or forward solutions to the equations of motion. The effect of the unsteady na...

A magnetic loading technique was used to ramp load pure aluminum and 6061 aluminum alloy to peak stresses of approximately 29GPa. The peak loading rate was approximately 106∕s, followed by unloading from peak stress at a rate of about 105∕s. The pure aluminum samples had impurity levels ranging from about 10ppmto0.5wt% and average grain sizes in the range of 144–454μm. The 6061 alloy was prepared in either the T6 condition with grain sizes of 5–50μm, or in the T0 or T6 heat treatment condition with a grain size of about 40μm. A wave profile technique was used to estimate the compressive strength during unloading. It was found that the compressive strength estimated during unloading increased with peak stress for all materials and that the change in strength was insensitive to initial material properties. This observation is in agreement with previous results obtained from shock loading of the same materials [H. Huang and J. R. Asay, J. Appl. Phys. 98, 033524 (2005)] and suggests that the deformation mecha...

Isentropic compression experiments (ICE) have been performed on the Z accelerator facility at Sandia National Laboratory. We describe the experimental design that used large magnetic fields to slowly compress samples to pressures in excess of 400 kbar. Velocity wave profile measurements were analyzed to yield isentropic compression equations of state (EOS). The method can also yield material strength properties. We describe magnetohydronamic simulations and results of experiments that used the “square short” configuration to compress copper and discuss ICE EOS experiments that have been performed with this method on tantalum, molybdenum, and beryllium.