Abstract
Magnetic loading was used to shocklessly compress four different metals to extreme pressures. Velocimetry monitored the behavior of the material as it was loaded to a desired peak state and then decompressed back down to lower pressures. Two distinct analysis methods, including a wave profile analysis and a novel Bayesian calibration approach, were employed to estimate quantitative strength metrics associated with the loading reversal. Specifically, we report for the first time on strength estimates for tantalum, gold, platinum, and iridium under shockless compression at strain rates of sim 5 times 10^5/s in the pressure range of sim 100–400 GPa. The magnitude of the shear stresses supported by the different metals under these extreme conditions are surprisingly similar, representing a dramatic departure from ambient conditions.
Highlights
The development of shockless compression experimental capabilities marked a key departure from more traditional shock loading platforms
One of the electrodes is arranged in the so-called drive configuration, in which a single-crystal lithium fluoride (LiF) window is glued to the electrode, and the VISAR [11] diagnostic is used to measure the velocity of this interface
A summary of the measured velocities is shown in Fig. 2 where the profiles are arbitrarily shifted in time for clarity
Summary
The development of shockless compression experimental capabilities marked a key departure from more traditional shock loading platforms. In shock compression the entropy generated by the shock results in significant heating, and in the case of most metals impact stresses on the order of several hundred GPa are sufficient to cause melting. Shockless (or ramp) compression, on the other hand, utilizes finite loading rates to continuously drive the material to a peak state orders of magnitude more slowly than the near-instantaneous rise of a shock. Ramp compression results in a low-temperature thermodynamic trajectory that enables loading to extreme pressures without melting. An understanding of how metals compress to high energy density (HED) conditions, typically defined as pressures > 100 GPa, is required for modeling a range of applications from descriptions of stellar and planetary interiors to planetary formation dynamics to inertial confinement fusion implosions [1]. High precision ramp compression data can be used in the development of standards. With the development of two-stage DACs, researchers are reaching pressures of over 600 GPa [3, 4], and the quality of the pressure standard is paramount to the interpretation of these experiments
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