Shock Compression Response Research Articles

Shock-induced melting of [100] lithium fluoride: Sound speed and Hugoniot measurements to 230 GPa

Although [100] lithium flouride (LiF) is the most widely used optical window material in dynamic compression experiments, its high stress ($>100\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$) shock compression response, including melting, is not well understood. To address this need, we measured wave profiles in plate impact experiments to determine the Hugoniot states and longitudinal sound speeds in [100] LiF crystals shock compressed to 231 GPa. The measured peak states are fitted well by a linear shock velocity--particle velocity relation, providing an accurate determination of the LiF Hugoniot curve to significantly higher stresses than previous experiments. The longitudinal sound speeds show a near linear increase with density compression to 182 GPa. Between 182 GPa and 195 GPa, the sound speed and the longitudinal modulus decrease abruptly, due to shock-induced melting. The increasing sound speeds and moduli at higher stresses suggest that shock compressed LiF is fully liquid at 195 GPa and above, allowing determination of the Gr\"uneisen parameter for liquid LiF. The melt stress determined here differs from that predicted by current multiphase equations of state for LiF. Our results provide important insight into the high stress solid and liquid states of shock compressed LiF and point to the need for an improved multiphase equation of state at high pressures and high temperatures.

Role of lattice resistance in the shock dynamics of fcc-structured high entropy alloy

The shock response of high entropy alloys (HEAs) would be important for their performance under extreme conditions. However, it is still difficult to obtain the shock response data at the atomic scale over the wide range of loading conditions. Here, the shock compression response of fcc-structured modeled HEAs and pure metals with different degrees of lattice resistance and stacking fault energy has been studied using the molecular dynamics simulations in the terms of the Hugoniot stress, atomic structure, and dislocation density. The results show that the HEA with low lattice resistance exhibits a significantly low shock compression strength in comparison with pure metal. In contrast to pure metal, Shockley partial dislocations and stacking faults with high density were found in HEA with low lattice resistance. Interestingly, during the shock wave propagation in HEA with high lattice resistance to dislocation glide, the crystalline to amorphous phase transformation has been observed to occur behind the shock front. The high lattice resistance slows down the movement of dislocations in HEA, and then promotes the amorphization process. This trend gives an effective toughening mechanism in shock loading of HEAs. In addition, the microstructure-based physical model suggests the obvious effect of lattice resistance on the working hardening of the HEAs after shock compression. It indicates that the lattice resistance of intrinsic chemically disordered structures dominates the rate of dislocation generation and the shock compression strength. The current study provides an important atomic insight for understanding the dynamic mechanical behaviors of HEAs. • Shock compression response of HEAs and pure metals was studied. • HEA with low lattice resistance exhibit low strength in comparison to pure metals. • Amorphization occurred behind the shock front of HEA with high lattice resistance.

Shock-induced chemical decomposition and overdriven detonation in hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) single crystals

Understanding the differences in the shock compression and detonation response of insensitive high explosives (IHEs) and conventional HEs (CHEs) is a long-standing need in HE science and technology. Having previously examined 1,1-diamino-2,2-dinitroethene (FOX-7) IHE single crystals [Winey et al., J. Appl. Phys. 130, 015902 (2021)], the shock and detonation response of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX)—a widely used CHE—was determined using wave profile measurements in ∼250 μm thick single crystals shock compressed to 63 GPa. In marked contrast to FOX-7, RDX single crystals shocked along the [100] and [111] orientations showed wave profile features consistent with chemical decomposition onset at 15 GPa. These features were more pronounced for [100] RDX, suggesting a higher decomposition rate compared to [111] RDX. At 51 GPa and above, flat-topped single waves were observed for both orientations, showing the classic Chapman–Jouget (C–J) detonation response in which the decomposition is completed within the detonation front. The Hugoniot states and sound speeds determined for the detonation products were similar for both [100] and [111] orientations, showing that the overdriven detonation response for RDX does not depend on crystal orientation. The C–J pressure for RDX single crystals (35 GPa)—determined experimentally—is comparable to that of FOX-7. However, compared to FOX-7, chemical decomposition onset for RDX occurs at much lower pressures and the overdriven C–J detonation response occurs at higher pressures. The present findings constitute the first experimental comparison of the shock and detonation response of conventional and insensitive HE single crystals over a broad pressure range below and above the C–J pressure.

Shock compression response of additively manufactured AlSi10Mg

We measured the Hugoniot, Hugoniot elastic limit (HEL), and spallation strength of laser powder bed fusion (LPBF) AlSi10Mg via uniaxial plate-impact experiments to stresses greater than 13 GPa. Despite its complex anisotropic microstructure, the LPBF AlSi10Mg did not exhibit significant orientation dependence or sample-to-sample variability in these measured quantities. We found that the Hugoniot response of the LPBF AlSi10Mg is similar to that of other Al-based alloys and is well approximated by a linear relationship: us=5.49+1.39up. Additionally, the measured HELs ranged from 0.25 to 0.30 GPa and spallation strengths ranged from 1.16 to 1.45 GPa, consistent with values reported in other studies of LPBF AlSi10Mg and Al-based alloys. Strain-rate and stress dependence of the spallation strength were also observed.

Bioinspired diamond composites and their dynamic shock performance

The design of high-strength and high-toughness materials that can sustain high shock-wave loadings is crucial for both armor and civil applications. We propose a bioinspired diamond composite that mimics the brick-and-mortar arrangement of nacre from mollusk shells and evaluate its performance for different diamond brick contents using lattice-spring model. In this work, we present a systematic investigation elucidating the effects of volume fraction of diamond brick, on the shock compression response of bioinspired diamond composites. By comparing the nacre-like diamond composite with traditional diamond composite, it was found that the nacre-like diamond composite can reduce damage degree in diamond composite, and improve dynamic strength of diamond composite. More importantly, the damage evolution analysis of the impacted nacre-like diamond composite indicated that there is large-scale crack deflection, which is only cause slight damage to the diamond brick. The obtained numerical results may provide valuable insights into the preparation of superhard composites for numerous engineering applications.

Shock compression of diamonds in silicon carbide matrix up to 110 GPa

We have synthesized the well-performance bulk diamond–SiC composite by the high-temperature and high-pressure method and employed the light gas gun launched flyer plates to investigate shock compression response of the diamond–SiC composite. The plots of shock velocity vs particle velocity demonstrate the presence of double elastic waves in the diamond–SiC composite under shock compression. The first elastic wave travels at 13.1∼13.6km/s and leads to yielding at ∼12.75GPa. The second elastic wave propagates at 12.8∼13.0km/s and does not display the yielding up to ∼110GPa. Such a Hugoniot elastic limit is apparently higher than that of the single crystal diamond. The strengthening mechanism underlying the diamond–SiC composite has been discussed. By simulations of the lattice-spring model, the results revealed that under shock compression, the silicon carbide matrix yields first in the composite, resulting in damage to the substructure surrounding the diamond particles. This damage releases the intense shear stress and protects the diamond from severe crushing. Due to diamonds being hydrostatically confined by the silicon carbide matrix, both dislocation migration and slip band sliding are suppressed significantly, which enhances the strength of diamonds.

High-speed x-ray phase contrast imaging and digital image correlation analysis of microscale shock response of an additively manufactured energetic material simulant

The performance of energetic materials subjected to dynamic loading significantly depends on their micro- and meso-scale structural morphology. The geometric versatility offered by additive manufacturing opens new pathways to tailor the performance of these materials. Additively manufactured energetic materials (AMEMs) have a wide range of structural characteristics with a hierarchy of length scales and process-inherent heterogeneities, which are hitherto difficult to precisely control. It is important to understand how these features affect AMEMs’ response under dynamic/shock loading. Therefore, temporally and spatially resolved measurements of both macroscopic behavior and micro- and meso-level processes influencing macroscopic behavior are required. In this paper, we analyze the shock compression response of an AMEM simulant loaded under several impact conditions and orientations. X-ray phase contrast imaging (PCI) is used to track features across the observed shock front and determine the linear shock velocity vs particle velocity equation of state, as well as to quantify the interior deformation fields via digital image correlation (DIC) analyses. Photon Doppler velocimetry is simultaneously used to measure the particle velocities of the specimens, which are consistent with those obtained from x-ray PCI. The DIC analyses provide an assessment of the average strain fields inside the material, showing that the average axial strain depends on the loading intensity and reaches as high as 0.23 for impact velocities up to 1.5 km/s. The overall results demonstrate the utility of x-ray PCI for probing “in-material” equation of state and interior strains associated with dynamic shock compression behavior of the AMEM simulant.

Hugoniot states and optical response of soda lime glass shock compressed to 120 GPa

In contrast to relatively pure silica glass (fused silica—FS), commercial silica-rich glasses contain significant fractions of additional oxide components. In particular, soda-lime glass (SLG) consists of approximately 71% SiO2 by weight, which raises the question: what is the effect of additional cations on the shock compression response of silica-rich glasses? To address this question, plate impact experiments were conducted to determine the high-pressure Hugoniot states for shocked SLG (37 to 120 GPa) and compared with recently reported results on FS. Using laser interferometry, particle velocity profiles were measured at the impact surface and at the SLG/LiF window interface. In all experiments, the transmitted profiles show a single shock wave, with no features indicative of a phase transformation. The Hugoniot states determined from the wave profiles are described well using a linear shock velocity–particle velocity relation. Interferometry measurements (using 1550-nm wavelength laser) at the impact surface show that SLG is transparent when shocked to 55 GPa, transparent for tens of nanoseconds after impact between 55 and 81 GPa, and opaque beyond 81 GPa. From impact surface measurements, a linear relationship between the apparent and true particle velocity was observed, resulting in a linear relationship between the refractive index (at 1550 nm) and density. At 120 GPa, the SLG density is nearly twice its ambient value, indicating that SLG can achieve highly dense amorphous states. When compared to FS, shocked SLG is much less compressible and likely does not transform to a crystalline phase. A plausible explanation for this difference is suggested.

Shock compression response of diamond single crystals at multimegabar stresses

Shock compressed diamond response at multimegabar stresses---of fundamental interest to high pressure science and relevant for high energy density experiments related to inertial confinement fusion---is often assumed to be hydrodynamic. To examine this assumption, plate impact experiments were conducted to measure wave profiles in diamond single crystals shocked to $\ensuremath{\sim}900\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ elastic impact stress (EIS). For the [110] and [111] orientations, two-wave structures (elastic-inelastic response) were observed to \ensuremath{\sim}900 GPa EIS; in contrast, single (overdriven) waves were observed at 480 GPa EIS and above for the [100] orientation. The elastic wave velocities for the [110] and [111] orientations were significantly larger than those for the [100] orientation. Strong orientation dependence was also observed for the elastic wave amplitudes; for [110] and [111] diamond, the amplitudes increased significantly with increasing elastic impact stress. The observed two-wave structures and the strong orientation dependence (elastic wave speeds and amplitudes) demonstrate unequivocally that the shock response of diamond single crystals is not hydrodynamic at stresses below the melt transition. As such, appropriate elastic-inelastic material descriptions are needed to accurately model the high stress response of diamond and other strong solids.

Shock compression response of an insensitive high explosive single crystal: 1,1-diamino-2,2-dinitroethene (FOX-7)

Insensitive high explosives (IHEs)—which do not compromise performance—are of considerable interest as a safer alternative to conventional high explosives, such as pentaerythritol tetranitrate and cyclotrimethylenetrinitramine. Despite the strong interest in using IHEs, shock compression experiments on IHE single crystals have not been reported. To address this need, plate impact experiments were conducted to measure wave profiles in 1,1-diamino-2,2-dinitroethene (FOX-7) single crystals—a representative IHE crystal—shocked to 21 GPa longitudinal stress. Particle velocity histories, measured using laser interferometry, show a clear two-wave structure (elastic–inelastic response) at modest stresses (<3.8 GPa). Wave profiles at higher stresses show a single (overdriven) wave. Measured shock velocities and wave profiles provide accurate Hugoniot data to 21 GPa. The measured wave profiles to 21 GPa show no sign of energy release due to chemical decomposition and constitute the first demonstration of an IHE single crystal insensitivity under plane shock compression. Numerical simulations using a phenomenological material model developed for FOX-7 showed good agreement with the measured wave profiles. The experimental findings and continuum simulations presented here constitute a significant first step in gaining an insight into the shock compression response of IHE single crystals.

Structure of shock waves in particulate composites

The shock compression response of particulate heterogeneous solids was investigated using normal plate impact experiments and numerical simulations. A model composite system of silica glass spheres embedded in a matrix of thermoplastic polymer, polymethyl methacrylate, was developed to mimic the impedance mismatch of structural and energetic heterogeneous materials. Shock wave profiles were measured at multiple points on the rear surface of the composite specimens to characterize shock dispersion and spatial heterogeneity in material response due to the random distribution of particles. Composites with single mode as well as bimodal bead diameter distributions were subjected to plate impact loading at ∼1000 m/s resulting in an average shock stress of ∼4 GPa. Shock rise times were measured for composites of 30% and 40% glass by volume, with spherical particles of diameters in the range of 100–1000 μm. In the case of single mode composites, the shock wave rise times were observed to scale linearly with particle diameter divided by the bulk shock wave speed. The addition of a second bead size to a base size in a 30% glass by volume composite mix resulted in significant increases in shock rise time. Numerical simulations were used to develop insights into scattering and the development of shock structure in particulate composites. Shock disruption mechanisms due to particles and matrix/interface damage effects are discussed.

Correlations between dislocation density evolution and spall strengths of Cu/Ta multilayered systems at the atomic scales: The role of spacing of KS interfaces

The deformation and failure (spallation) behavior of Cu/Ta multilayered systems with Kurdjumov–Sachs (KS) orientation relationship is investigated at the atomic scales under shock loading conditions. Molecular dynamics (MD) simulations investigate the role of spacing between KS interfaces on the nucleation, evolution and interaction of defect structures (dislocations) in the Cu/Ta multilayered microstructures with layer thicknesses ranging from 3 nm to 47 nm. The shock compression response and failure response is investigated using the computed values of the Hugoniot elastic limit (HEL) and the spall strengths, respectively. KS interfaces serve as strong barriers to dislocation propagation and transmission across the interface and the spacing of the interfaces is observed to influence the spall behavior. The variation of the spall strength values suggests a critical interface spacing of 6 nm, below which the spall strength of the multilayered microstructure is observed to be lower than that for single-crystal Cu for the same loading conditions. The correlations between the temporal evolution of densities of various types of dislocation at the spall planes for the various microstructures and the resulting values of the spall strengths provide a clear rationale for why a microstructure results in increased/decreased spall strength values for the multiphase system.

Deformation and spallation of shock-loaded graphene: Effects of orientation and grain boundary

We perform molecular dynamic simulations to investigate the effects of orientation and grain boundary (GB) on shock response of graphene, including shock-induced slip and spall. For compression under different loading orientations, the critical resolved shear stress for slip is constant along a given growth direction (armchair or zigzag) in single-crystal graphene, and spall initiates in elastically deformed graphene via tension-induced debonding. For bicrystal graphene, the locations of compression-induced slip and initial spall are influenced by preexisting stress field at GB and the interactions between GB and shock waves, respectively. Both of these two factors are related to GB structure, including the density of pentagon-heptagon pairs at GB. However, bicrystals show negligible anisotropy in shock-compression response. For polycrystalline graphene at high shock strength, slips initiate at GBs and triple junctions under shock compression, develop along GBs or toward grain interior, and serve as nucleation sites for spall damage.

Enhanced shock performance by disperse porous structure:A case study in PZT95/5 ferroelectric ceramics

AbstractThe porosity and corresponding microstructural features ultimately determine the properties of the macroporous materials. In this work, porous PZT95/5 ferroelectric ceramics having a common bulk density but with disperse and agglomerated pore distribution were prepared to study their influence on the physical properties. It is experimentally demonstrated that pore distribution exhibits significant influence on the shock compression response behaviors. Porous PZT95/5 ferroelectric ceramics with disperse pores exhibit enhanced shock resistance and thus higher breakdown strengths than its counterparts with agglomerated voids. To explain the underlying physical mechanism, a lattice‐spring model was employed to simulate both macroscopic shock response and mesoscopic evolution of the microstructures under shock compression. Our simulation results are concordant with our experimental observations. The enhanced shock resistance and larger shock plasticity of porous PZT95/5 ferroelectric ceramics with disperse pores under shock compression was found to be responsible for the superior performance.

Shock compression response of cold-rolled Ni/Al multilayer composites

Uniaxial strain, plate-on-plate impact experiments were performed on cold-rolled Ni/Al multilayer composites and the resulting Hugoniot was determined through time-resolved measurements combined with impedance matching. The experimental Hugoniot agreed with that previously predicted by two dimensional (2D) meso-scale calculations [Specht et al., J. Appl. Phys. 111, 073527 (2012)]. Additional 2D meso-scale simulations were performed using the same computational method as the prior study to reproduce the experimentally measured free surface velocities and stress profiles. These simulations accurately replicated the experimental profiles, providing additional validation for the previous computational work.

Investigation of the shock-induced chemical reaction (SICR) in Ni + Al nanoparticle mixtures

Molecular dynamics (MD) simulations are used to investigate the shock-compression response of Ni + Al spherical nanoparticles arranged in a NaCl-like structure. The deformation and reaction characteristics are studied from the particle level to the atomic scale at various piston velocities. Shock-induced chemical reactions (SICRs) occur during non-equilibrium processes, accompanied by a sharp rise in temperature and rapid mixing of atoms. The preferentially deformed Al particles form a high-speed mass flow relative to the Ni at the shock front, which impinges on the Ni particles, and mixing of Ni and Al atoms occurs immediately at the interface. The particle velocity dispersion (PVD) that appears at the shock front has important implications for the initiation of shock-induced chemical reactions. We show that dislocations are mainly generated at the beginning of particle deformation or at the shock front, and do not directly affect the occurrence of SICRs. The intimate contact of the molten Al and the amorphous Ni is found to be critical to the subsequent reactions for the extensive mixing of Ni and Al. We conclude that the mechanisms of SICRs involve mechanochemical processes near the shock front and subsequent interdiffusion processes.

Interfacial Effects on the Dispersion and Dissipation of Shock Waves in Ni/Al Multilayer Composites

The influence of interfacial density, structure, and strength in addition to material strengths on the dispersion and dissipation of a shock wave traveling parallel to the layers in a laminar, multilayer composite was investigated using two-dimensional, meso-scale simulations incorporating a real, heterogeneous microstructure. Optimum interfacial densities for maximizing wave dispersion and dissipation were identified. Interfacial structure strongly influenced the dispersion by altering the wave interactions internal to the composite. Interfacial strength effected both the dispersion and dissipation through drastic changes to the interfacial strain generated. Lastly, material strength influenced only the dissipation of the shock wave by altering the compressibility of the constituents. The combined results identified interfacial strain as the driving mechanism influencing the shock compression response of the Ni/Al multilayered composites.

Decaying shock studies of phase transitions in MgO‐SiO2 systems: Implications for the super‐Earths' interiors

AbstractWe report an experimental study of the phase diagrams of MgO, MgSiO3, and Mg2SiO4 at high pressures. We measured the shock compression response, including pressure‐temperature Hugoniot curves of MgO, MgSiO3, and Mg2SiO4 between 0.2–1.2 TPa, 0.12–0.5 TPa, and 0.2–0.85 TPa, respectively, using laser‐driven decaying shocks. A melting signature has been observed in MgO at 0.47 ± 0.04 TPa and 9860 ± 810 K, while no such phase changes were observed either in MgSiO3 or in Mg2SiO4. Increases of reflectivity of MgO, MgSiO3, and Mg2SiO4 liquids have been detected above 0.55 TPa (12760 K), 0.15 TPa (7540 K), 0.2 TPa (5800 K), respectively. In contrast to SiO2, melting and metallization of these compounds do not coincide, implying the presence of poorly electrically conducting liquids close to the melting lines. This has important implications for the generation of dynamos in super‐Earth's mantles.

Complete equation of state for shocked liquid nitrogen: Analytical developments.

The thermodynamic response of liquid nitrogen has been studied extensively, in part, due to the long-standing interest in the high pressure and high temperature dissociation of shocked molecular nitrogen. Previous equation of state (EOS) developments regarding shocked liquid nitrogen have focused mainly on the use of intermolecular pair potentials in atomistic calculations. Here, we present EOS developments for liquid nitrogen, incorporating analytical models, for use in continuum calculations of the shock compression response. The analytical models, together with available Hugoniot data, were used to extrapolate a low pressure reference EOS for molecular nitrogen [R. Span et al., J. Phys. Chem. Ref. Data 29, 1361 (2000)] to high pressures and high temperatures. Using the EOS presented here, the calculated pressures and temperatures for single shock, double shock, and multiple shock compression of liquid nitrogen provide a good match to the measured results over a broad range of P-T space. These calculations provide the first comparison of EOS developments with recently measured P-T states under multiple shock compression. The present EOS developments are general and are expected to be useful for other liquids that have low pressure reference EOS information available.

Exploration of CdTe quantum dots as mesoscale pressure sensors via time-resolved shock-compression photoluminescent emission spectroscopy

The nanometer size of CdTe quantum dots (QDs) and their unique optical properties, including size-tunable narrow photoluminescent emission, broad absorption, fast photoluminescence decay, and negligible light scattering, are ideal features for spectrally tagging the shock response of localized regions in highly heterogeneous materials such as particulate media. In this work, the time-resolved laser-excited photoluminescence response of QDs to shock-compression was investigated to explore their utilization as mesoscale sensors for pressure measurements and in situ diagnostics during shock loading experiments. Laser-driven shock-compression experiments with steady-state shock pressures ranging from 2.0 to 13 GPa were performed on nanocomposite films of CdTe QDs dispersed in a soft polyvinyl alcohol polymer matrix and in a hard inorganic sodium silicate glass matrix. Time-resolved photoluminescent emission spectroscopy was used to correlate photoluminescence changes with the history of shock pressure and the dynamics of the matrix material surrounding the QDs. The results revealed pressure-induced blueshifts in emitted wavelength, decreases in photoluminescent emission intensity, reductions in peak width, and matrix-dependent response times. Data obtained for these QD response characteristics serve as indicators for their use as possible time-resolved diagnostics of the dynamic shock-compression response of matrix materials in which such QDs are embedded as in situ sensors.