Analysis of shockless dynamic compression data on solids to multi-megabar pressures: Application to tantalum

Abstract

Magnetically-driven, planar shockless-compression experiments to multi-megabar pressures were performed on tantalum samples using a stripline target geometry. Free-surface velocity waveforms were measured in 15 cases; nine of these in a dual-sample configuration with two samples of different thicknesses on opposing electrodes, and six in a single-sample configuration with a bare electrode opposite the sample. Details are given on the application of inverse Lagrangian analysis (ILA) to these data, including potential sources of error. The most significant source of systematic error, particularly for single-sample experiments, was found to arise from the pulse-shape dependent free-surface reflected wave interactions with the deviatoric-stress response of tantalum. This could cause local, possibly temporary, unloading of material from a ramp compressed state, and thus multi-value response in wave speed that invalidates the free-surface to in-material velocity mapping step of ILA. By averaging all 15 data sets, a final result for the principal quasi-isentrope of tantalum in stress-strain was obtained to a peak longitudinal stress of 330 GPa with conservative uncertainty bounds of ±4.5% in stress. The result agrees well with a tabular equation of state developed at Los Alamos National Laboratory.

Estimating Material Properties Under Extreme Conditions by Using Bayesian Model Calibration with Functional Outputs

“…Second, we compare with a state of the art theoretical calculation given by Greeff et al . (), which has been used to simulate these types of Ta experiments accurately in previous studies (Brown et al ., ; Davis et al ., ). The posterior mean lies just above the theoretical calculation with the lower credible interval coincidentally overlapping it.…”

“…We note that ρ 0 and the physical parameters B 0 and B 0 are constant between experiments since all samples were cut from the same Ta plate (Buchheit et al, 2014), whereas the rest of the parameters in γ vary between experiments. We further note that previous analytic analyses incorporated uncertainties only in x Al , x Ta and Δt (Davis et al, 2014).…”

Results from new multi-megabar shockless compression experiments at the Z machine

“…At lower stress, averaging all 15 Ta experiments, each exhibiting particular systematic deviations depending on pulse shape, resulted in good agreement with a reference model. 2 Alleviating this issue could allow accurate data to be obtained to higher stress from fewer experiments.…”

“…Details of the stripline load configuration as well as the inverse (or iterative) Lagrangian analysis (ILA) method of extracting quasi-isentropic mechanical response, and its limitations, have been published elsewhere. 2 After briefly reviewing this earlier work, this paper will describe recent improvements to the experimental method, focusing primarily on the use of lithium fluoride (LiF) windows at high pressures, and present preliminary results from improved experiments on copper, gold, and platinum to 350-500 GPa peak stress. These materials are all relevant as pressure calibrants for high-pressure static work in diamond-anvil cells (DAC).…”

Pulsed power accelerator for material physics experiments

“…Currently the refurbished Z accelerator (also referred to as ZR) produces tailored current pulses to drive samples quasi-isentropically to pressures as high as 500 GPa over timescales as long as 1 μs [3,4].…”