Shock Compression Experiments Research Articles

Release dynamics of nanodiamonds created by laser-driven shock-compression of polyethylene terephthalate

Laser-driven dynamic compression experiments of plastic materials have found surprisingly fast formation of nanodiamonds (ND) via X-ray probing. This mechanism is relevant for planetary models, but could also open efficient synthesis routes for tailored NDs. We investigate the release mechanics of compressed NDs by molecular dynamics simulation of the isotropic expansion of finite size diamond from different P-T states. Analysing the structural integrity along different release paths via molecular dynamic simulations, we found substantial disintegration rates upon shock release, increasing with the on-Hugnoiot shock temperature. We also find that recrystallization can occur after the expansion and hence during the release, depending on subsequent cooling mechanisms. Our study suggests higher ND recovery rates from off-Hugoniot states, e.g., via double-shocks, due to faster cooling. Laser-driven shock compression experiments of polyethylene terephthalate (PET) samples with in situ X-ray probing at the simulated conditions found diamond signal that persists up to 11 ns after breakout. In the diffraction pattern, we observed peak shifts, which we attribute to thermal expansion of the NDs and thus a total release of pressure, which indicates the stability of the released NDs.

High-pressure Phase Transition of Olivine-type Mg2GeO4 to a Metastable Forsterite-III type Structure and their Equation of States

Abstract Germanates are often used as structural analogs of planetary silicates. We have explored the high-pressure phase relations in Mg2GeO4 using diamond anvil cell experiments combined with synchrotron X-ray diffraction and computations based on density functional theory. Upon room temperature compression, forsterite-type Mg2GeO4 remains stable up to 30 GPa. At higher pressures, a phase transition to a forsterite-III type (Cmc21) structure was observed, which remained stable to the peak pressure of 105 GPa. Using a 3rd order Birch Murnaghan fit to the experimental data, we obtained V0 = 305.1 (3) Å3, K0 = 124.6 (14) GPa and K0′ = 3.86 (fixed) for forsterite- and V0 = 263.5 (15) Å3, K0 = 175 (7) GPa and K0′ = 4.2 (fixed) for the forsterite-III type phase. The forsterite-III type structure was found to be metastable when compared to the stable assemblage of perovskite/post-perovskite + MgO, as observed during laser-heating experiments. Understanding the phase relations and physical properties of metastable phases is crucial for studying the mineralogy of impact sites, understanding metastable wedges in subducting slabs and interpreting the results of shock compression experiments.

Shock compression experiments using the DiPOLE 100-X laser on the high energy density instrument at the European x-ray free electron laser: Quantitative structural analysis of liquid Sn

X-ray free electron laser (XFEL) sources coupled to high-power laser systems offer an avenue to study the structural dynamics of materials at extreme pressures and temperatures. The recent commissioning of the DiPOLE 100-X laser on the high energy density (HED) instrument at the European XFEL represents the state-of-the-art in combining x-ray diffraction with laser compression, allowing for compressed materials to be probed in unprecedented detail. Here, we report quantitative structural measurements of molten Sn compressed to 85(5) GPa and ∼3500 K. The capabilities of the HED instrument enable liquid density measurements with an uncertainty of ∼1% at conditions which are extremely challenging to reach via static compression methods. We discuss best practices for conducting liquid diffraction dynamic compression experiments and the necessary intensity corrections which allow for accurate quantitative analysis. We also provide a polyimide ablation pressure vs input laser energy for the DiPOLE 100-X drive laser which will serve future users of the HED instrument.

Dynamic response of additively manufactured Ti–5Al–5V–5Mo–3Cr as a function of heat treatment

Both shock and shockless compression experiments were performed on laser powder bed fusion (LPBF) Ti–5Al–5V–5Mo–3Cr (Ti-5553) to peak compressive stresses near 15 GPa. Experiments were performed on the as-built material, containing a purely β (body centered cubic) microstructure, and two differing heat treatments resulting in a dual phase α (hexagonal close packed) and β microstructure. The Hugoniot, Hugoniot elastic limit (HEL), and spallation strength were measured and compared to wrought Ti-6Al-4V (Ti-64). The results indicate the LPBF Ti-5553 Hugoniot response is similar between heat treatments and to Ti-64. The HEL stress observed in the LPBF Ti-5553 was considerably higher than Ti-64, with the as-built, fully β alloy exhibiting the largest values. The spallation strength of the LPBF Ti-5553 was also similar to Ti-64. Clear evidence of initial porosity serving as initiation sites for spallation damage was observed when comparing computed tomography measurements before and after loading. Post-mortem scanning electron microscopy images of the recovered spallation samples showed no evidence of retained phase changes near the spall plane. The spall plane was found to have kinks aligned with the loading direction near areas with large concentrations of twin-like, crystallographic defects in the as-built condition. For the heat-treated samples, the concentrations of twin-like, crystallographic defects were absent, and no preference for failure at the interface between the α and β phases was observed.

Mixture of hydrogen and methane under planetary interior conditions.

We employ first-principles molecular dynamics simulations to provide equation-of-state data, pair distribution functions (PDFs), diffusion coefficients, and band gaps of a mixture of hydrogen and methane under planetary interior conditions as relevant for Uranus, Neptune, and similar icy exoplanets. We test the linear mixing approximation, which is fulfilled within a few percent for the chosen P-T conditions. Evaluation of the PDFs reveals that methane molecules dissociate into carbon clusters and free hydrogen atoms at temperatures greater than 3000 K. At high temperatures, the clusters are found to be short-lived. Furthermore, we calculate the electrical conductivity from which we derive the non-metal-to-metal transition region of the mixture. We also calculate the electrical conductivity along the P-T profile of Uranus [N. Nettelmann et al., Planet. Space Sci., 2013, 77, 143-151] and observe the transition of the mixture from a molecular to an atomic fluid as a function of the radius of the planet. The density and temperature ranges chosen in our study can be achieved using dynamic shock compression experiments and seek to aid such future experiments. Our work also provides a relevant data set for a better understanding of the interior, evolution, luminosity, and magnetic field of the ice giants in our solar system and beyond.

Fluid-phase helium: Shock-compression experiments, quantum molecular dynamics simulations, and development of an equation of state

Fluid-phase helium: Shock-compression experiments, quantum molecular dynamics simulations, and development of an equation of state

Double-Shock Compression Pathways from Diamond to BC8 Carbon.

Carbon is one of the most important elements for both industrial applications and fundamental research, including life, physics, chemistry, materials, and even planetary science. Although theoretical predictions on the transition from diamond to the BC8 (Ia3[over ¯]) carbon were made more than thirty years ago, after tremendous experimental efforts, direct evidence for the existence of BC8 carbon is still lacking. In this study, a machine learning potential was developed for high-pressure carbon fitted from first-principles calculations, which exhibited great capabilities in modeling the melting and Hugoniot line. Using the molecular dynamics based on this machine learning potential, we designed a thermodynamic pathway that is achievable for the double shock compression experiment to obtain the elusive BC8 carbon. Diamond was compressed up to 584GPa after the first shock at 20.5 km/s. Subsequently, in the second shock compression at 24.8 or 25.0 km/s, diamond was compressed to a supercooled liquid and then solidified to BC8 in around 1ns. Furthermore, the critical nucleus size and nucleation rate of BC8 were calculated, which are crucial for nano-second x-ray diffraction measurements to observe BC8 carbon during shock compressions. The key to obtaining BC8 carbon lies in the formation of liquid at a sufficient supercooling. Our work provides a feasible pathway by which the long-sought BC8 phase of carbon can be reached in experiments.

Shock-compression microstructure transformation of the additive manufactured FeCoNiAlTi high-entropy alloy

Investigation into the microstructural deformation mechanisms of a high-entropy alloy (Fe28.0Co29.5Ni27.5Al8.5Ti6.5 (at%)) prepared by laser additive manufacturing and aging treatment, with a three-phase nanocomposite structure, is carried out via shock compression experiments using plate impact. Microstructural characteristics and compositions are inspected using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The microstructure of the high-entropy alloy is comprised of high-density dislocation structures, high-volume-fraction L12 nano-precipitates, a small amount of L21 nano-precipitates, and face-centered cubic (FCC) matrix phases. The lattice arrangement of the FCC matrix phase is disordered, with strong segregation of Fe and Co atoms, while Ni, Al, and Ti atoms are predominantly present in the ordered L12 and L21 nano-precipitates. The FCC matrix or the FCC matrix with high-density stacking faults are bounded by a 9R-phase between two phase boundaries. The mechanisms of microstructural transformation of the high-entropy alloy are discussed in detail.

High precision control of laser energy for laser-matter interaction studies.

Precise, highly reproducible control of the laser energy is required for high confidence laser-matter interaction research such as in dynamic compression science and high energy density physics. The energy must be adjustable without affecting the pulse shape (time varying intensity) or beam smoothness. We have developed a convenient two-stage energy tuning method for a nominal 100J, 351nm (UV) laser. The energy is adjusted in 10J (10%) increments by operating the laser at full energy and inserting a beam splitter in the laser output. As the splitter is located after the final frequency tripling optics, the UV pulse shape is unchanged. The energy is varied by substituting a splitter of different reflectivity. For finer 3J (3%) increments, the infrared pulse is attenuated inside the laser before the final amplifier. This requires modest tuning to preserve the pulse shape. The demonstrated variation in shot-to-shot reproducibility is less than +/-2.5J (5% of the full energy), irrespective of the laser output energy. These approaches can be adapted to most ∼100J class lasers. We describe these techniques and show two examples where they have elucidated the underlying physics in laser shock compression experiments. One used only the beam splitters to establish the pressure for melting in iron. The other combined both techniques to finely increment the peak stress (∼2GPa steps) in germanium to precisely determine the onset and completion of melting-including the melting kinetics. These unambiguous results would not be possible without the developments described here.

High-pressure shock compression of olivine: Dynamic pulverization and frictional melting

In order to study seismo-mechanochemical processes, two kinds of shock compression experiments – the recovery and the in-situ VISAR (velocity interferometer system for any reflector) experiments – were performed, using a single crystal of forsteritic olivine and a single-stage powder propellant gun. The generated peak shock pressures were 31.1 GPa for both the recovery and the VISAR experiments. Many shear planes were generated in the olivine crystal. The VISAR experiment revealed detailed time profiles for the particle and shock wave velocities during the compression and yielded the Hugoniot elastic limit (HEL) of the olivine to be 7.44 GPa. We observed, in one recovered sample, a clear local melting occurring along a shear plane. The microstructural observations of the shear plane and its walls using a field-emission scanning electron microscopy (SEM) and an analytical transmission electron microscopy (ATEM) revealed that plastically-deformed olivine was pulverized into a few hundred-nanometer size particle assemblages within a few-micrometers narrow zone along the shear plane and, locally have partially melted. Moreover, injection veins filled with olivine melt were found in the wall of the same shear plane. It was shown from the estimate of the critical resolved shear stress (CRSS) along the shear planes and the inferred slip velocity using the Hugoniot elastic limit (HEL) data that the power generated by the friction was large enough for melting to occur in the olivine. The whole process occurred in a time scale <0.6 microsecond. Pulverization (comminution) before melting is considered to be a common phenomenon in the formation of pseudotachylytes and in dynamically expanding seismic faults upon earthquakes.

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 100ns with a spatial resolution varying from 90 to 200μm/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.

High pressure phase transition and strength estimate in polycrystalline alumina during laser-driven shock compression

Alumina (Al2O3) is an important ceramic material notable for its compressive strength and hardness. It represents one of the major oxide components of the Earth’s mantle. Static compression experiments have reported evidence for phase transformations from the trigonal α-corundum phase to the orthorhombic Rh2O3(II)-type structure at ∼90 GPa, and then to the post-perovskite structure at ∼130 GPa, but these phases have yet to be directly observed under shock compression. In this work, we describe laser-driven shock compression experiments on polycrystalline alumina conducted at the Matter in Extreme Conditions endstation of the Linac Coherent Light Source. Ultrafast x-ray pulses (50 fs, 1012 photons/pulse) were used to probe the atomic-level response at different times during shock propagation and subsequent pressure release. At 107 ± 8 GPa on the Hugoniot, we observe diffraction peaks that match the orthorhombic Rh2O3(II) phase with a density of 5.16 ± 0.03 g cm−3. Upon unloading, the material transforms back to the α-corundum structure. Upon release to ambient pressure, densities are lower than predicted assuming isentropic release, indicating additional lattice expansion due to plastic work heating. Using temperature values calculated from density measurements, we provide an estimate of alumina’s strength on release from shock compression.

Argon equation of state data to 1 TPa: Shock compression experiments and simulations

Cryogenic liquid noble gases, because of their noble nature and monatomic fluid behavior, are ideal for comparing experiments and theory at high pressures and temperatures. Using both magnetically accelerated flyer plates and laser-driven decaying shocks, the authors obtain here high-precision measurements on shock-compressed liquid argon to 1 TPa. The data are used to calibrate two different EOS models. The results show that even if two models are calibrated to the same data set, they can exhibit different responses at extreme conditions.

Observations of twinning microstructure in iron ramp-compressed through the α−ε phase transition.

Single crystal iron was ramp-compressed along the [100] axis at 4 GPa/ns through the $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\epsilon}$ phase transformation at 13 GPa. Unlike shock experiments, in these ramp compression experiments the bcc lattice is observed to be nearly isotropically relaxed before the phase transition. There was a mixed $\ensuremath{\alpha}/\ensuremath{\epsilon}$ phase region starting at $\ensuremath{\sim}13$ GPa, which was observed for 0.75 ns until the peak stress of 18 GPa was reached. In situ x-ray diffraction measurements show the formation of new hcp orientations not reported in shock or quasistatic compression experiments. The new hcp orientations appear to be caused by ${10\overline{1}1}\ensuremath{\langle}10\overline{1}\overline{2}\ensuremath{\rangle}\ensuremath{\rightarrow}{\overline{1}011}\ensuremath{\langle}\overline{1}01\overline{2}\ensuremath{\rangle}$ sequential twins that occur during the phase transition. This twinning mechanism relieves the shear strain caused by the bcc-hcp phase transition from the isotropically relaxed bcc phase while subject to uniaxial compression. These results show that in iron the induced microstructure through a phase transition and the phase transition mechanism depend on the loading history.

Research on Seismic Wave Quality Factor of Marble Jointed Rock Mass under SHPB Impact

In order to quantitatively describe the energy dissipation law of jointed rock mass, we obtained the jointed cores in laboratory conditions using marble from the roof and floor of Jinchanghe Lead–zinc mine in Baoshan. The dissipative degree of stress wave in marble jointed rock mass is measured by introducing quality factor Qs parameter. Based on the experimental principle of Split Hopkinson Pressure rod loading device (SHPB), we proposed a three-wave energy method of incident wave, reflected wave and projected wave for calculating jointed rock samples’ quality factor Qs based on stress wave energy. Using the SHPB test system for multiple specimens taken from the same piece of rock mass shock compression experiment, the three groups of specimens under different loading conditions gained incident wave and reflected wave and transmission wave experimental data, using the method of stress wave energy to deal with stress wave data, and calculate the joint sample maximum storage energy, dissipation energy and Qs quality factors. The results show that: ① The non-destructive breaking time–history strain of Dali rock mass under impact load is obtained by SHPB dynamic test system; combined with the deformation energy and dissipation energy calculation principle of quality factor, six groups of Qs experimental values are obtained. Although the Qs experimental values are discrete, the overall deviation is small with an average of 43.07. ② AUTODYN-Code was used to simulate the damage and fracture characteristics of rock mass with different quality factors under explosive dynamic load. The results showed that the radius of rock mass compression shear damage area gradually increased with the increase in porosity, but it was not obvious.

Novel fabrication tools for dynamic compression targets with engineered voids using photolithography methods

Mesoscale imperfections, such as pores and voids, can strongly modify the properties and the mechanical response of materials under extreme conditions. Tracking the material response and microstructure evolution during void collapse is crucial for understanding its performance. In particular, imperfections in the ablator materials, such as voids, can limit the efficiency of the fusion reaction and ultimately hinder ignition. To characterize how voids influence the response of materials during dynamic loading and seed hydrodynamic instabilities, we have developed a tailored fabrication procedure for designer targets with voids at specific locations. Our procedure uses SU-8 as a proxy for the ablator materials and hollow silica microspheres as a proxy for voids and pores. By using photolithography to design the targets' geometry, we demonstrate precise and highly reproducible placement of a single void within the sample, which is key for a detailed understanding of its behavior under shock compression. This fabrication technique will benefit high-repetition rate experiments at x-ray and laser facilities. Insight from shock compression experiments will provide benchmarks for the next generation of microphysics modeling.

Modelling the anomalous shock response of titanium diboride

In planar shock compression experiments, polycrystalline titanium diboride ( TiB 2 ) often exhibits double-yield phenomena, atypical among non-transforming ceramics, in particle velocity histories. A finite-strain phase-field theory, with order parameters accounting for fracture and dilatation, followed by limited plastic slip and compaction, is specialized to study the uniaxial shock response of TiB 2 . The model accurately depicts longitudinal stress up to 120 GPa on the Hugoniot from multiple published sources, as well as shear stress inferred elsewhere from experimental shock data. A novel phase-field analysis enables one-, two- or three-wave structures depending on impact stress. These results are observed in experimental data and have not been successfully captured by prior numerical models. Results support the conjecture that (i) fracture and dilatation, followed by (ii) plastic deformation and compaction, and then (iii) fragmentation to a comminuted, viscous granular medium is a plausible sequence of physical mechanisms as shock stress increases. The first break in the velocity profile always corresponds to micro-cracking in the model, which correlates with the first yield point on the Hugoniot. In the three-wave regime, two plastic waves correlate with two yield points, where the first plastic wave after the precursor is due to fracture and the second dominated by plasticity. When impact is severe enough such that the second plastic wave overtakes the first, a single plastic waveform with multiple kinks emerges in particle velocity histories, consistent with some experimental data. These kinks are well explained by pressure-dependent viscosity in crack kinetics and by small-magnitude plastic deformation, and corresponding stress perturbations need not precisely correspond to particular cusps on the stress–volume Hugoniot.

Design optimization for Richtmyer–Meshkov instability suppression at shock-compressed material interfaces

The Richtmyer–Meshkov instability (RMI) is a phenomenon that occurs at the interface of two substances of different densities due to an impulsive acceleration, such as a shock wave passing through this interface. Under these conditions, the instability can be seen as interface perturbations begin to grow into narrow jets or spikes of one substance that propagate into the other. In some cases, this interface may involve an elastic–plastic material, which can play a significant role in the development and behavior of the RMI. The ability to effectively control RMI jetting and spike growth is one major limiting factor in technological challenges, such as inertial confinement fusion, that involve using high-pressure shock waves to implode a fuel target. The propagation of RMI growth can lead to increased asymmetry in this implosion process and significantly reduce the obtained energy yield. We use hydrodynamics simulations of impactor shock-compression experiments and methods based in design optimization to suppress RMI spike growth by altering the geometry and other properties of a shock-compressed elastic–plastic material target that shares an interface with atmospheric air. These hydrodynamics simulations use an arbitrary Lagrangian–Eulerian method with a high-order finite element approach. Our results demonstrate that RMI suppression can be achieved by intentionally creating a separate upstream interface instability to counteract the growth of long narrow RMI spikes at an interface with initial perturbations.

Accurate equation of state of rhenium as pressure scale up to 130 GPa and 3200 K

The equations of states (EOSs) of inert metals are generally used as pressure scales in a high-pressure experiment. However, the thermodynamic model and the method used to constrain the parameters of the EOSs of these metals may cause pressure deviations of up to 7% at 100 GPa and room temperature, and even higher at higher pressures and higher temperatures. In this study, we provide a new approach for obtaining accurate EOS of inert metals. First, we use a set of thermodynamic models, within the quasi-Debye framework, to describe the thermodynamics. Second, both the volume vs pressure data from the shock compression experiment and the volume vs sound velocity data from the static compression experiment are used to constrain the parameters in the EOS formula. In the fitting process, a weighted least-square method based on the uncertainty of these data is used. The calculated Grüneisen parameter shows a strong dependence not only on volume but also on temperature. The variation of the Grüneisen parameter of Re can increase by up to 7% per 103 K under the same volume, which means the previous temperature-independent approximation of the Grüneisen parameter may cause an underestimate of the pressure at high temperature. The pressure–volume–temperature EOS of Re up to 140 GPa and 3200 K is established, which can be used as a high-pressure and high-temperature pressure gauge in the future.

A sub-nanosecond pyrometer with broadband spectral channels for temperature measurement of dynamic compression experiments

Time-resolved temperature measurement of dynamic-compressed material is critical in the high-pressure research fields. For higher temporal resolution requirement of the dynamic experiments, a broadband optical pyrometer was developed, with a rise time of ∼70 ps and a measurable temperature range of 2500 K to higher than 10000 K. Expanding the detecting bandwidth to 100 nm∼300 nm for each channel, sensitivity of the detection system increases by nearly one order of magnitude compared to the conventional configuration. An improved temperature calibration procedure and data processing method was proposed, and temperature results of the shock compression experiments using a light gas gun were identical to the simultaneous measurements by a narrowband pyrometer. The dynamic radiation from the laser shocked matter also can be perfectly captured by the developed pyrometer, and the temporal profile of temperature agreed well with the shock velocity profile in both the shape and the duration time.