Crystal Structure and Melting of Fe Shock Compressed to 273 GPa: In Situ X-Ray Diffraction
Abstract not provided
Turneaure, Stefan J.↗
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Molecular dynamics study of shock compression in porous silica glass.
Abstract not provided.
Jones, Keith↗
Structural transformations including melting and recrystallization during shock compression and release of germanium up to 45 GPa
Abstract not provided
Renganathan, P.↗
Inherent issues regarding the use of in situ x-ray diffraction measurements to determine temperature in shock-compressed metals
Temperature determination in shock compressed solids constitutes an important and long-standing scientific need. Since the reduction of Bragg diffracted peaks due to temperature increase, using the Debye-Waller factor, is well established, we examined the use of this approach to determine temperatures in shock compressed gold and platinum by representing the shocked state as a superposition of density and temperature changes. Comparison of the calculated and measured diffraction peaks did not show good agreement, because x-ray diffraction (XRD) profiles in the shock compressed state are not governed solely by density and temperature changes. XRD results are also influenced measurably by shock wave induced microstructural changes. Our results demonstrate that contributions from microstructural changes need to be incorporated and modeled in the theoretical analysis to use XRD measurements for reliable temperature determination in shock compressed solids.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Optical Radiation from Shock-Compressed Materials
Recent observations of shock-induced radiation from oxides, silicates, and metals of geophysical interest constrain the shock-compressed temperature of these materials. The relationships between the temperature inferred from the observed radiation and the temperature of the shock-compressed film or foil and/or window were investigated. Changes of the temperature field in each target component away from that of their respective shock-compressed states occur because of: shock-impedance mismatch between target components; thermal mismatch between target components; surface roughness at target interfaces; and conduction within and between target components. In particular, conduction may affect the temperature of the film/foil window interface on the time scale of the experiments, and so control the intensity and history of the dominant thermal radiation sources in the target. This type of model was used to interpret the radiation emitted by a variety of shock-compressed materials and interfaces.
Svendsen, Robert F., Jr.↗
Three-dimensional full-field velocity measurements in shock compression experiments using stereo digital image correlation
Shock compression plate impact experiments conventionally rely on point-wise velocimetry measurements based on laser-based interferometric techniques. This study presents an experimental methodology to measure the free surface full-field particle velocity in shock compression experiments using high-speed imaging and three-dimensional (3D) digital image correlation (DIC). The experimental setup has a temporal resolution of 100 ns with a spatial resolution varying from 90 to 200 μm/pixel. Experiments were conducted under three different plate impact configurations to measure spatially resolved free surface velocity and validate the experimental technique. First, a normal impact experiment was conducted on polycarbonate to measure the macroscopic full-field normal free surface velocity. Second, an isentropic compression experiment on Y-cut quartz–tungsten carbide assembly is performed to measure the particle velocity for experiments involving ramp compression waves. To explore the capability of the technique in multiaxial loading conditions, a pressure shear plate impact experiment was conducted to measure both the normal and transverse free surface velocities under combined normal and shear loading. The velocities measured in the experiments using digital image correlation are validated against previous data obtained from laser interferometry. Numerical simulations were also performed using established material models to compare and validate the experimental velocity profiles for these different impact configurations. The novel ability of the employed experimental setup to measure full-field free surface velocities with high spatial resolutions in shock compression experiments is demonstrated for the first time in this work.
47 OTHER INSTRUMENTATION↗
A Tutorial on Bayesian analysis of linear shock compression data
Gas gun and other shock compression experiments often produce shock wave velocity measurements that are linearly associated with particle velocity. Traditionally, this empirical relationship is quantified with a single Hugoniot curve that is estimated using least squares regression. However, for downstream modeling and simulation tasks, it is often more useful to have multiple Hugoniot curves in the pressure–volume plane that are consistent with the data. We employ Bayesian uncertainty quantification methods as a framework for propagating measurement uncertainty through to model parameters and predictions. Specifically, this Tutorial shows how to sample multiple Hugoniot curves in the pressure–volume plane that are consistent with the shock wave-particle velocity measurements in a two-step Bayesian approach. First, we obtain an analytical expression for the posterior distribution of the linear model parameters using Bayesian linear regression. Second, we propagate samples from the posterior distribution through the Rankine–Hugoniot equations to yield Hugoniot curves in the pressure–volume plane. The procedure is demonstrated with publicly available data on argon, copper, and nickel, and compared against bootstrapping and linear regression. The Bayesian procedure is shown to be interpretable, computationally inexpensive, and less sensitive than an alternative bootstrapping approach to the removal of the point in the copper dataset that has the largest particle velocity. As a Tutorial on Bayesian methodology for the shock compression community, we provide several derivations and explanations that make this paper self-contained, and make all code and data available at github.com/llnl/BALSCD.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Sound speed determination in copper shock compressed to 190 GPa
Sound speed measurements in shock compressed solids have long been valuable for the development of equations of state at extreme conditions, shock-induced phase transformations, and a comprehensive characterization of the thermophysical response of high-pressure standards. We present results from plate impact experiments to 190 GPa to determine the longitudinal sound speed in copper—an important high-pressure standard. Surprisingly, the sound speeds determined using the two most common experimental techniques—the front surface impact (FSI) approach and the release wave overtake (RWO) approach—diverge significantly for stresses greater than ~100 GPa. Further analyses, including numerical simulations, show that the FSI experiments provide the correct sound speeds and that fundamental assumptions underlying the RWO method are likely violated due to the complex release response of shock compressed copper. The sound speeds determined using the FSI approach provide for a more accurate high-pressure description of copper in dynamic compression experiments. The present findings are in contrast to the results for shock compressed silver [Wallace et al., Phys. Rev. B 104, 214106 (2021)], where both methods provided consistent sound speed results. Thus, the findings presented here demonstrate the need to experimentally verify the validity of the RWO method on a case-by-case basis. Finally, we note that even at the high stresses in the present work, the copper unloading response shows a time-dependent, quasielastic response often observed in metals at lower stresses.
36 MATERIALS SCIENCE↗
Laser-excited optical emission response of CdTe quantum dot/polymer nanocomposite under shock compression
Laser-driven shock compression experiments and corresponding finite element method simulations are carried out to investigate the blueshift in the optical emission spectra under continuous laser excitation of a dilute composite consisting of 0.15% CdTe quantum dots by weight embedded in polyvinyl alcohol polymer. This material is a potential candidate for use as internal stress sensors. The analyses focus on the time histories of the wavelength blue-shift for shock loading with pressures up to 7.3 GPa. The combined measurements and calculations allow a relation between the wavelength blueshift and pressure for the loading conditions to be extracted. It is found that the blueshift first increases with pressure to a maximum and subsequently decreases with pressure. This trend is different from the monotonic increase of blueshift with pressure observed under conditions of quasistatic hydrostatic compression. Additionally, the blueshift in the shock experiments is much smaller than that in hydrostatic experiments at the same pressure levels. The differences in responses are attributed to the different stress states achieved in the shock and hydrostatic experiments and the time dependence of the mechanical response of the polymer in the composite. The findings offer a potential guide for the design and development of materials for internal stress sensors for shock conditions.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Insight into the chemistry of TNT during shock compression through ultrafast absorption spectroscopies
Thin films of trinitrotoluene (TNT) were shock compressed using the ultrafast laser shock apparatus at Los Alamos National Laboratory. Visible (VIS) and mid-infrared (MIR) transient absorption spectroscopies were simultaneously performed to probe for electronic and vibrational changes during shock compression of TNT. Additionally, three shock pressures (16 GPa, 33 GPa, and 45 GPa) were selected to observe no reaction, incipient reaction, and strongly developed reactions for TNT within the experimental time scale of <250 ps. Negligible absorption changes in MIR or VIS absorptions were observed at 16 GPa. At 33 GPa, MIR absorptions in the 3000 cm -1 –4000 cm -1 range were observed to increase during the shock and continue to increase during the rarefaction, in contrast to the VIS absorption measurements, which increased during the shock and almost fully recovered during rarefaction. At 45 GPa, both VIS and MIR absorptions were strong and irreversible. The intense and spectrally broad MIR absorptions were attributed to short lived intermediates with strong, spectrally broad absorptions that dominate the spectral response. The MIR and VIS absorption changes observed at 33 GPa and 45 GPa were credited to shock induced chemistry, most likely including the formation of a very broad hydrogenic stretch feature. The results from these experiments are consistent with the chemical mechanisms that include O–H or N–H formation such as CH 3 oxidation or C–N homolysis.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Amorphization and nanocrystallization of silcon under shock compression
High-power, short-duration, laser-driven, shock compression and recovery experiments on [001] silicon unveiled remarkable structural changes above a pressure threshold. Two distinct amorphous regions were identified: (a) a bulk amorphous layer close to the surface and (b) amorphous bands initially aligned with {111} slip planes. Further increase of the laser energy leads to the re-crystallization of amorphous silicon into nanocrystals with high concentration of nano-twins. This amorphization is produced by the combined effect of high magnitude hydrostatic and shear stresses under dynamic shock compression. Shock-induced defects play a very important role in the onset of amorphization. Calculations of the free energy changes with pressure and shear, using the Patel-Cohen methodology, are in agreement with the experimental results. Molecular dynamics simulation corroborates the amorphization, showing that it is initiated by the nucleation and propagation of partial dislocations. As a result, the nucleation of amorphization is analyzed qualitatively by classical nucleation theory.
36 MATERIALS SCIENCE↗
Inelastic deformation of diamond single crystals shock compressed to multimegabar stresses: Wave profile calculations
As the archetypal strong solid, the response of diamond shock compressed to multimegabar stresses is important for fundamental science and for numerical simulations of wave profiles for applications in high energy density physics experiments. Previous experiments and analysis have shown that the commonly used hydrodynamic assumption is invalid for diamond shock compressed to stresses below melt and an elastic–inelastic description is needed. Here, we present a phenomenological material model for calculating wave profiles in shock compressed diamond single crystals that incorporates this description. Also, to support the modeling effort, we carried out wave profile measurements on shock compressed diamond single crystals at the Sandia Z facility to augment previous measurements. Wave profiles for [100] and [111] diamond calculated using the material model provide a good match to the elastic–inelastic response (observed two-wave structure) measured at ∼325 and ∼360 GPa. Furthermore, the calculated peak stresses for single (overdriven) waves provide a good match to the measured Hugoniot states for stresses reaching ∼700 GPa, which is near melting conditions. The present results show that the diamond single crystal response at multimegabar shock stresses is characteristic of a brittle solid—pressure-dependent strength and strength loss due to inelastic deformation.
Deformation↗
Absolute Hugoniot measurements in low-density plastic foams on the NIKE shock compression platform
The propagation of Mbar-range shock waves in low-density foam materials is of interest to target design in all approaches to inertial confinement fusion, high energy density physics, and laboratory astrophysics. We report absolute Hugoniot measurements for CH 1.72 N 0.086 O 0.37 plastic foams with 73 and 94 mg/cm 3 densities in the 32–107 km/s shock velocity range. The experiments were performed on the shock compression platform developed on the NIKE KrF laser facility at the U.S. Naval Research Laboratory. NIKE's 4 or 8-ns long flat-top laser pulses drive steady shock waves into foam targets at the ablative pressures of 1–7 Mbar. The propagation of the ablation and shock fronts is tracked continuously in time using streaked side-on monochromatic x-ray imaging radiography. The straight x−t trajectories of the shock and ablation fronts in the recorded streak images confirmed their steadiness. The SESAME tabulated equation of state predictions generally agrees with our Hugoniot data within a 95% confidence band. The experimental uncertainty of the evaluated shock density compression ratios remains large, indicating the need for more experiments and improved theoretical understanding of the strong shock propagation mechanisms in dry foams.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Using simultaneous x-ray diffraction and velocity interferometry to determine material strength in shock-compressed diamond
We determine the strength of laser shock-compressed polycrystalline diamond at stresses above the Hugoniot elastic limit using a technique combining x-ray diffraction from the Linac Coherent Light Source with velocity interferometry. X-ray diffraction is used to measure lattice strains, and velocity interferometry is used to infer shock and particle velocities. These measurements, combined with density-dependent elastic constants calculated using density functional theory, enable determination of material strength above the Hugoniot elastic limit. Furthermore, our results indicate that diamond retains approximately 20 GPa of strength at longitudinal stresses of 150–300 GPa under shock compression.
36 MATERIALS SCIENCE↗
Shock compression response of highly reactive Ni + Al multilayered thin foils
The shock-compression response of Ni + Al multilayered thin foils is investigated using laser-accelerated thin-foil plate-impact experiments over the pressure range of 2 to 11 GPa. The foils contain alternating Ni and Al layers (parallel but not flat) of nominally 50 nm bilayer spacing. The goal is to determine the equation of state and shock-induced reactivity of these highly reactive fully dense thin-foil materials. The laser-accelerated thin-foil impact set-up involved combined use of photon-doppler-velocimetry to monitor the acceleration and impact velocity of an aluminum flyer, and VISAR interferometry was used to monitor the back free-surface velocity of the impacted Ni + Al multilayered target. The shock-compression response of the Ni + Al target foils was determined using experimentally measured parameters and impedance matching approach, with error bars identified considering systematic and experimental errors. Meso-scale CTH shock simulations were performed using real imported microstructures of the cross-sections of the multilayered Ni + Al foils to compute the Hugoniot response (assuming no reaction) for correlation with their experimentally determined equation of state. It was observed that at particle velocities below ∼150 m/s, the experimentally determined equation of state trend matches the CTH-predicted inert response and is consistent with the observed unreacted state of the recovered Ni + Al target foils from this velocity regime. At higher particle velocities, the experimentally determined equation of state deviates from the CTH-predicted inert response. A complete and self-sustained reaction is also seen in targets recovered from experiments performed at these higher particle velocities. The deviation in the measured equation of state, to higher shock speeds and expanded volumes, combined with the observation of complete reaction in the recovered multilayered foils, confirmed via microstructure characterization, is indicative of the occurrence of shock-induced chemical reaction occurring in the time-scale of the high-pressure state. TEM characterization of recovered shock-compressed (unreacted) Ni + Al multilayered foils exhibits distinct features of constituent mixing revealing jetted layers and inter-mixed regions. These features were primarily observed in the proximity of the undulations present in the alternating layers of the Ni + Al starting foils, suggesting the important role of such instabilities in promoting shock-induced intermetallic-forming reactions in the fully dense highly exothermic multilayered thin foils.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Compression Shocks of Detached Flow
It is known that compression shocks which lead from supersonic to subsonic velocity cause the flow to separate on impact on a rigid wall. Such shocks appear at bodies with circular symmetry or wing profiles on locally exceeding sonic velocity, and in Laval nozzles with too high a back pressure. The form of the compression shocks observed therein is investigated.
Eggink↗
Behavior of soda-lime silicate glass under laser-driven shock compression up to 315 GPa
Shock experiments give a unique insight into the behavior of matter subjected to extremely high pressures and temperatures. Understanding the behavior of materials under such extreme conditions is key to modeling material failure and deformation dynamics under impact. While studies on pure silica are extensive, the shock behavior of other commercial silicates that contain additional oxides has not been systematically investigated. To better understand the role of composition in the dynamic behavior of silicates, we performed laser-driven dynamic compression experiments on soda-lime glass (SLG) up to 315 GPa. Using the accurate pulse shaping offered by the long pulse laser system at the Matter in Extreme Conditions end-station at the Linac Coherent Light Source, SLG was shock compressed along the Hugoniot to multiple pressure-temperature points. Velocity Interferometer System for Any Reflector was used to measure the velocity and determine the pressure inside the SLG. The U s –u p relationship obtained agrees well with the previous parallel plate impact studies. Within the error bars, no transformation to the crystalline phase was observed up to 70 GPa, which is in contrast to the behavior of pure silica under shock compression. Our studies show that the glass composition strongly influences the shock compression behavior of the silicate glasses.
36 MATERIALS SCIENCE↗