Shock Velocity Research Articles

Amorphization transformation in high-entropy alloy FeNiCrCoCu under shock compression

High-entropy alloys (HEAs) possess immense potential for structural applications due to their excellent mechanical properties. Deeply understanding underlying deformation mechanisms under extreme regimes is crucial but still limited, due to the restrictions of existing experimental techniques. In the present study, dynamic deformation behaviors in equiatomic FeNiCrCoCu HEAs were investigated in terms of various shock velocities through nonequilibrium molecular dynamics simulations. The amorphous atoms by amorphization transformation were corroborated to be conducive to dislocation nucleation and propagation. Also, the dominant plasticity pattern was confirmed to be taken over by amorphization under higher velocities, while dislocation slips merely prevailed for lower shock ones. More importantly, for a shock velocity of 1.4 km/s, multi-level deformation modes appearing in deformation, first amorphization and then a combination of amorphization and dislocation slip, was demonstrated to substantially contribute to the shock wave attenuation. These interesting findings provide important implications for the dynamic deformation behaviors and corresponding mechanisms of the FeNiCrCoCu HEA system.

Spall characteristics of three-dimensional graphene networks with embedded copper: A molecular dynamics study

The phenomenon of shock-induced spallation has garnered significant interest in both scientific and industrial circles. Laminated graphene embedded in graphene-reinforced metal-matrix composites have been shown to improve mechanical properties. This study systematically investigates the dynamic response and spall failure of a three-dimensional graphene network (3DGN) with embedded copper composites (3DGCu) and its dependence on the grain sizes (D). Firstly, increasing the wt% of graphene results in significant increase of shock wave speed due to the intrinsic high modulus of graphene, whilst leading to a reduction in shock pressure. Spallation of 3DGCu at low shock velocity is observed, which is dominated by the bonded interaction at the graphene-metal interface. However, the 3DGCu with higher graphene content (smaller D) exhibits both low density and superior spall resistance. In particular, in the sample with 60 wt% graphene, the complete spallation has never occurred and still maintains a relatively high spall strength within the impact velocity of 3.0 km/s. This is due to the remarkable capacity for 3DGN to absorb the kinetic energy during tension. In addition, during shock loading, the graphene component is responsible to the tension loading, whereas the copper metal matrix undergoes compression, leading to a stable post-shock length. These findings offer a novel approach for tailoring the dynamic properties of advanced graphene-based nano-composites with potential applications in extreme environments.

Effect of non-Planckian spectrum on shock velocities and subsonic to transonic transition in mid-Z witness plate elements

In this work, we obtain the shock velocities in mid-Z elements, namely, Al, Ti, and Cu by performing radiation hydrodynamic simulations using constant radiation drives consisting of equilibrium Planckian distribution along with high-energy Gaussian profiles. The drive temperatures have been varied from 80 to 270 eV, and the fraction of total energy density due to Gaussian distribution (α) changes from 0 to 0.4. Though the shock velocity in all the three elements rise with the strength of the drive temperature, its variation with α is quite complicated. Using simulations, we have shown that rear surface expansion is not responsible for the observed variation in shock velocity with the fraction of hard x rays at various temperatures and explained it in terms of distribution of total extinction coefficient over the spectral form of incident drive source leading to change in albedos. The percentage variations in shock velocities are found to be commensurate with those in albedos as expected for x-ray driven ablation process. Accurate scaling laws relating the drive temperatures with the shock velocities and α have also been obtained. In Al, subsonic to transonic transition temperature is found to increase with α, whereas in Ti it is found to decrease. We have explained the variation in transition temperature in terms of Mach number. As this transition temperature in Cu is anticipated to be high due to its higher atomic number and density, we did not observe any transition up to the temperature (500 eV) considered in this paper.

Shock waves in strongly coupled one-dimensional dusty plasmas under Yukawa interactions

The numerical investigation of shock waves in a chain of dust particles is conducted using the molecular dynamics simulation method. Assuming that the first pulse in the shock front is a solitary wave, we derive an analytical approximate expression to demonstrate how the shock velocity depends on the piston velocity and the system parameters, such as the charge of the dust particles, the initial lattice constant, and the screening parameter. It is found that the shock wave velocity increases as the piston velocity and coupling parameter increase, while it decreases as the screening parameter increases. The analytical results are in good agreement with the molecular dynamics simulation results.

Conditions of structural transition for collisionless electrostatic shock.

Collisionless shock acceleration, which transfers localized particle energies to nonthermal energetic particles via electromagnetic potential, is ubiquitous in space plasma. We investigate dynamics of collisionless electrostatic shocks that appear at the interface of two plasma slabs with different pressures using one-dimensional particle-in-cell (PIC) simulations and find that the shock structure transforms to a double-layer structure at the high density gradient. The threshold condition of the structure transformation is identified as density ratio of the two plasma slabs Γ∼40 regardless of the temperature ratio between them. We then update the collisionless shock model that takes into account density expansion effects caused by a rarefaction wave to improve the prediction of the critical Mach numbers. These critical Mach numbers are benchmarked by PIC simulations for a wide range of Γ. Furthermore, we introduce a semianalytical approach to forecast the shock velocity just from the initial conditions based on a concept of the accelerated fraction α.

In situ time-resolved Raman spectroscopy of nitromethane under static and dynamic compression

Energetic materials are extensively used as propellants in rockets demanding the understanding of their chemical and thermal stability for safe storage and transportation as well as ease of decomposition. Nitromethane (NM) is one such material with significant performance advantage over other mono propellants. In this manuscript, we report the detailed molecular-level behavior of NM under static and dynamic compression. Dynamic compression experiments were performed up to ∼6.4 GPa using a 2 J/8 ns Nd: YAG laser coupled with time-resolved Raman spectroscopy (TRRS) setup. Static compression experiments were performed up to ∼20 GPa using a diamond anvil cell. During laser-driven shock compression, NM undergoes three phase transitions at 1.1, 2.5, and 3.4 GPa. However, in the case of static compression, the corresponding phase transitions were observed at 0.3, 1.3–1.8, and 2.5 GPa. TRRS was also performed at 300 mJ (1.47 GW/cm2), 500 mJ (2.45 GW/cm2), and 800 mJ (3.9 GW/cm2) and intensity ratios of shocked and un-shocked Raman peaks were utilized to experimentally calculate the shock velocities, which were determined to be 2.66 ± 0.09, 3.58 ± 0.40, and 3.83 ± 0.60 km/s, respectively. These experimental results were corroborated with the one-dimensional (1D) radiation hydrodynamics simulations, performed to obtain shock pressure. The shock velocities at these laser intensities were calculated to be 2.98, 3.69, and 3.92 km/s, respectively, which are in reasonably close agreement with our observed results.

Shock Wave–Induced Dynamic Mechanical Behavior of Calcium Silicate Aluminate Hydrate at the Molecular Scale

Calcium silicate aluminate hydrate (C-A-S-H) is the main hydration product of cement mixed with industrial wastes. The purpose of this study is to understand the dynamic mechanical behavior and structural transformations of molecular-scale C-A-S-H induced by shock waves. Three C-A-S-H models with Al/Si ratios of 0.0, 0.1, and 0.2 are constructed and reactive molecular dynamics simulations are used to perform shock compressions with different shock velocities from 0.1 km/s to 3.6 km/s. The distributions of particle velocity, pressure, and density along the shock direction are calculated using the binning analysis method, allowing Hugoniot pressure-specific volume curves to be derived. The results reveal that shock waves may induce elastic, elastic-plastic, or shock Hugoniot responses in molecular-scale C-A-S-H, depending on the Al/Si ratio and the shock velocity. Below the Hugoniot elastic limit (HEL), higher Al/Si ratios cause the elastic wave to propagate farther due to the cross-linking effect of aluminate units. Above the HEL, higher Al/Si ratios give rise to a distinct two-wave structure characteristic comprising a plastic front and an elastic precursor. This characteristic becomes less pronounced as the shock velocity increases. Analysis of the molecular structural transformations of C-A-S-H revealed that the main atomic deformation behavior below the HEL involves a reduction of interatomic distances; above the HEL the main response is a densification of water molecules followed by a general collapse of the layered structure as the shock velocity increases.

A Type II Radio Burst Driven by a Blowout Jet on the Sun

Type II radio bursts are often associated with coronal shocks that are typically driven by coronal mass ejections (CMEs) from the Sun. Here we conduct a case study of a type II radio burst that is associated with a C4.5-class flare and a blowout jet, but without the presence of a CME. The blowout jet is observed near the solar disk center in the extreme-ultraviolet (EUV) passbands with different characteristic temperatures. Its evolution involves an initial phase and an ejection phase with a velocity of 560 ± 87 km s−1. Ahead of the jet front, an EUV wave propagates at a projected velocity of ∼403 ± 84 km s−1 in the initial stage. The velocity of the type II radio burst is estimated to be ∼641 km s−1, which corresponds to the shock velocity against the coronal density gradient. The EUV wave and the type II radio burst are closely related to the ejection of the blowout jet, suggesting that both are likely the manifestation of a coronal shock driven by the ejection of the blowout jet. The type II radio burst likely starts lower than those associated with CMEs. The combination of the velocities of the radio burst and the EUV wave yields a modified shock velocity at ∼757 km s−1. The Alfvén Mach number is in the range of 1.09–1.18, implying that the shock velocity is 10%–20% larger than the local Alfvén velocity.

Effect of shock tunnel geometry on shockwave and vortex ring formation, propagation, and head on collision

Vortex ring research primarily focuses on the formation from circular openings. Consequently, the role of tunnel geometry is less understood, despite there being numerous research studies using noncircular shock tunnels. This experimental study investigated shockwaves and vortex rings from different geometry shock tunnels from formation at the tunnel opening to head on collision with another similarly formed vortex ring using schlieren imaging and statistical analysis. The velocity of the incident shockwave was found to be consistent across all four shock tunnel geometries, which include circle, hexagon, square, and triangle of the same cross-sectional area. The velocity was 1.2 ± 0.007 Mach and was independent of the tunnel geometry. However, the velocities of the resulting vortex rings differed between the shapes, with statistical analysis indicating significant differences between the triangle and hexagon vortex velocities compared to the circle. Vortex rings from the square and circle shock tunnels were found to have statistically similar velocities. All vortex rings slowed as they traveled due to corner inversion and air drag. All shock tunnels with corners produce a wobble in the vortex rings. Vortex rings interact with opposing incident shockwaves prior to colliding with each other. Vortex velocity before and after shock–vortex interaction was measured and evaluated, showing statistically similar results. Shock–vortex interaction slows the shockwave upon interaction, while the shock–shock interaction resulted in no change in shock velocity. Although the vortex rings travel at different velocities, all head-on vortex ring collisions produce a perpendicular shockwave that travels at 1.04 ± 0.005 Mach.

Graphene enables equiatomic FeNiCrCoCu high-entropy alloy with improved TWIP and TRIP effects under shock compression

Graphene (Gr) reinforced high-entropy alloy (HEA) matrix composites are expected as potential candidates for next-generation structural applications in light of outstanding mechanical properties. A deep comprehension of the underlying deformation mechanisms under extreme shock loading is of paramount importance, however, remains lacking due to experimentally technical limitations in existence. In the present study, by means of nonequilibrium molecular dynamics simulations, dynamic deformation behaviors and corresponding mechanisms in equiatomic FeNiCrCoCu HEA/Gr composite systems were investigated in terms of various shock velocities. The resistance to dislocation propagation imparted by Gr was corroborated to encourage the elevated local stress level by increasing the likelihood of dislocation interplays, which facilitated the onset of twins and hexagonal close-packed (HCP) martensite laths. Meanwhile, the advent of Gr was demonstrated to endow the HEA with an additional twinning pathway that induced a structural conversion from HCP to parent face-centered cubic (FCC) inside HCP martensite laths, different from the classical one that necessitated undergoing the intermediate procedure of extrinsic stacking fault (ESF) evolution. More than that, by virtue of an increase in flow stress, the transformation-induced plasticity (TRIP) effect was validated to be additionally evoked as the predominant strain accommodation mechanism at higher strains on the one hand, but which only assisted plasticity in pure systems, and on the other hand, can also act as an auxiliary regulation mode together with the twinning-induced plasticity (TWIP) effect under intermediate strains, but with enhanced contributions relative to pure systems. One may expect that TRIP and TWIP effects promoted by introducing Gr would considerably inspire a synergistic effect between strength and ductility, contributing to the exceptional shock-resistant performance of FeNiCrCoCu HEAs under extreme regimes.

Computational Studies of Energetic Property Peculiarities in Trinitrophenyl-Substituted Nitramines

This research was performed using Becke’s three-parameter hybrid functional approach with non-local correlation provided by Lee, Yang, and Parr and the cc-pVTZ basis set. The geometry, total energy, and heat of formation of the most stable conformers of the nitramines under study were obtained to obtain the density, resistance to shock stimuli, detonation pressure, and velocity of the materials under study. The results obtained allow us to predict new multipurpose energetic materials with a good balance between energy and stability. Our findings show that N-(2-nitroethyl)-N-(2,4,6-trinitrophenyl)nitramine, N-(2,4,6-trinitrophenyl)-N-[(3,4,5-trinitro-1H-pyrazol-1-yl)methyl]nitramine, N-(2,2-dinitroethyl)-N-(2,4,6-trinitrophenyl)nitramine, N-(2,2,2-trinitroethyl)-N-(2,4,6-trinitrophenyl)nitramine, and N-(trinitromethyl)-N-(2,4,6-trinitrophenyl)nitramine possess better explosive properties and a greater stability compared to tetryl, although they remain sensitive to shock stimuli. Referring to the results obtained, we recommend new tetryl analogs containing dinitroethyl, trinitroethyl, and trinitromethyl substituents for practical usage.

On kinematics of one‐dimensional radially symmetric shocks in non‐ideal reacting gases

In this manuscript, the advancement of one‐dimensional shock waves propagating through a non‐ideal reacting gas is examined. Considering the shock wave as a propagating discontinuity surface, a pair of evolution equations describing the strength of the shock and the first‐order discontinuity for variable initial data are obtained. The truncation approximations are used to obtain the exponent of shock velocity for the case of strong shock with constant initial data and compared with those exponents obtained from Guderley's scheme and Chisnell–Chester–Whitham (CCW) rule. The effects of non‐ideal and reaction parameters on the shock evolution in the case of arbitrary shock strength are examined and compared with those obtained from the CCW rule. Furthermore, the global behaviors of shock strength and induced discontinuity for different values of non‐ideal and reaction parameters are analyzed.

Shock excitation of H2 in the James Webb Space Telescope era

Context. Molecular hydrogen, H2, is the most abundant molecule in the Universe. Thanks to its widely spaced energy levels, it predominantly lights up in warm gas, T ≳ 102 K, such as shocked regions externally irradiated or not by interstellar UV photons, and it is one of the prime targets of James Webb Space Telescope (JWST) observations. These may include shocks from protostellar outflows, supernova remnants impinging on molecular clouds, all the way up to starburst galaxies and active galactic nuclei. Aims. Sophisticated shock models are able to simulate H2 emission from such shocked regions. We aim to explore H2 excitation using shock models, and to test over which parameter space distinct signatures are produced in H2 emission. Methods. We here present simulated H2 emission using the Paris-Durham shock code over an extensive grid of ~14 000 plane-parallel stationary shock models, a large subset of which are exposed to a semi-isotropic external UV radiation field. The grid samples six input parameters: the preshock density, shock velocity, transverse magnetic field strength, UV radiation field strength, the cosmic-ray-ionization rate, and the abundance of polycyclic aromatic hydrocarbons, PAHs. Physical quantities resulting from our self-consistent calculations, such as temperature, density, and width, have been extracted along with H2 integrated line intensities. These simulations and results are publicly available on the Interstellar Medium Services platform. Results. The strength of the transverse magnetic field, as quantified by the magnetic scaling factor, b, plays a key role in the excitation of H2. At low values of b (≲0.3, J-type shocks), H2 excitation is dominated by vibrationally excited lines; whereas, at higher values (b ≳ 1, C-type shocks), rotational lines dominate the spectrum for shocks with an external radiation field comparable to (or lower than) the solar neighborhood. Shocks with b ≥ 1 can potentially be spatially resolved with JWST for nearby objects. H2 is typically the dominant coolant at lower densities (≲104 cm−3); at higher densities, other molecules such as CO, OH, and H2O take over at velocities ≲20 km s−1 and atoms, for example, H, O, and S, dominate at higher velocities. Together, the velocity and density set the input kinetic energy flux. When this increases, the excitation and integrated intensity of H2 increases similarly. An external UV field mainly serves to increase the excitation, particularly for shocks where the input radiation energy is comparable to the input kinetic energy flux. These results provide an overview of the energetic reprocessing of input kinetic energy flux and the resulting H2 line emission.

Study on The Method for Predicting The Explosion Source Point Based on The Characteristics of Shock Wave

To improve the accuracy in predicting the blast initiation position in tests from the measured data, a method of computing the blast source coordinates based on the average velocity of the blast shock and the corresponding correction and iteration methodology is proposed, and the accuracy of the method is verified and validated by comparing with the available data. The results show that: the accuracy of the method is good and its reliability is also high, and a spherical charge data correction method is proposed based on the characteristics of the shock wave, which can effectively improve the prediction accuracy. Using it, the coordinate error of the explosion source point is reduced from 0.656m to 0.084m, and the maximum relative error is reduced from 4.95% to 0.31%. The coordinate error of the dynamic explosion example is 1.68m, and the maximum relative error is 16.1%. The study found that the error of the original data has a great influence on prediction accuracy, and to ensure the high accuracy of the prediction results, the data with excessive errors should be excluded.

Numerical simulations of polarisation in gamma-ray burst afterglows

Abstract We compute the linear polarisation during the afterglow phase of gamma-ray bursts, for both on-axis and off-axis observers. We use numerical simulations of the deceleration of a relativistic jet, and compute the polarisation by post-processing the results of the numerical simulations. In our simulations, we consider a magnetic field that is chaotic in the plane of the shock, in addition to a magnetic field component that is parallel to the shock velocity. While the linear polarisation computed for on-axis observers is consistent with previous analytical estimates, we found that lateral expansion, which is accurately handled in our simulations, plays a crucial role in determining the linear polarisation for off-axis observers. Our results show that the off-axis linear polarisation, as seen by off-axis observers, exhibits a single peak, in contrast to the two peaks inferred by previous analytical studies. The maximum polarisation degree is 40 per cent at an observing angle θobs = 0.4 rad, and it decreases as the observing angle increases, which is opposite to what predicted by analytical models, where polarisation increases with larger observing angles. From the upper limit of 12 per cent in the linear polarisation obtained at 244 days for the GRB 170817A, we also infer an anisotropy factor of B∥/B⊥ = 0.5 − 0.9, consistent with the post-shock magnetic field being amplified by turbulence.

Impact of dissipation ratio on vanishing viscosity solutions of the Riemann problem for chemical flooding model

The solutions for a Riemann problem arising in chemical flooding models are studied using vanishing viscosity as an admissibility criterion. We show that when the flow function depends non-monotonically on the concentration of chemicals, non-classical undercompressive shocks appear. The monotonic dependence of the shock velocity on the ratio of dissipative coefficients is proven. For that purpose we provide the classification of the nullcline configurations for the traveling wave dynamical systems and analyze the saddle–saddle connections.

Anisotropic orientation dependent shock wave responses of monocrystalline molybdenum

Molybdenum (Mo) demonstrates excellent industrial application potentials in micro-nano devices, which are inevitably subjected to shock loads during their application under harsh service environments. This study employs molecular dynamics (MD) simulations to investigate the shock responses of Mo under high-strain loading conditions with respect to the effects of crystal orientations. The findings reveal that monocrystalline Mo, along the shock direction of [111], exhibits inhomogeneous microstructure features characterized by significantly high-density and high-temperature localized regions. Once the rarefaction wave is produced, the physical parameters, including density and lateral pressure, will gradually decrease while normal pressure retains a residual value. The us-up, Pzz-up, and Pzz-V/V0 relations along the shock loading direction of [111] show deviations from those of [001] and [110] directions, with this difference being more pronounced for Pzz-V/V0. The formation of dislocations and the magnitude of shear stress experienced within the post-shock region are strongly dependent on crystal orientations. Specifically, an elevated probability of dislocation formation was observed along the [110] direction. Moreover, the magnitude of shear stress induced by shock loading along the [001] and [110] directions can exceed that of the [111] direction when the shock velocity is 1.5 km/s. The MD simulation results can serve as a valuable supplement to the investigations of mechanical properties pertaining to Mo.

Investigation of shock transmission and amplification/mitigation in aluminium foams

The present work investigates factors which control the stress generated at the back face of end wall-mounted shock-loaded aluminum foam. When the applied shock pressure is higher than the plastic strength of the foam, the foam deforms plastically generating a compaction wave traveling below shock velocity. Wave reflection and momentum transfer at the end wall result in shock amplification. With increasing foam length, the stress at the end wall decreases, finally leading to shock mitigation. A relation between compaction wave characteristics, foam densification, and stress generated at the end wall is established.

Ultrasonic-assisted removal of cationic and anionic dyes residues from wastewater using functionalized triptycene-based polymers of intrinsic microporosity (PIMs)

In this work, a series of hypercrosslinked polymers of intrinsic microporosity (HCP-PIMs), namely nitro-triptycene (TRIP-NO2), amino-triptycene (TRIP-NH2), sulfonated-triptycene (TRIP-SO3H) and hydrocarbon-triptycene (TRIP-HC), are employed for the adsorption of organic dyes from wastewater. The materials show the efficient removal of cationic (malachite green, MG) and anionic (methyl orange, MO) dyes. The adsorption parameters herein investigated include the initial pH, the adsorbate concentration and the contact time, with the aim to elucidate their effect on the adsorption process. Furthermore, the adsorption kinetic and isotherms are studied, and the findings suggest the results fit well with pseudo-second-order kinetics and Langmuir model. The reported maximum adsorption capacity is competitive for all the tested polymers. More specifically, TRIP-SO3H and TRIP-HC exhibit adsorptions of ~ 303 and ~ 270 mg g−1 for MG and MO, respectively. The selectivity toward cationic and anionic dyes is assessed by mixing the two dyes, and showing that TRIP-HC completely removes both species, whereas TRIP-NO2, TRIP-NH2 and TRIP-SO3H show an enhanced selectivity toward the cationic MG, compared to the anionic MO. The effect of the type of water is assessed by performing ultrasonic-assisted adsorption experiments, using TRIP-SO3H and TRIP-HC in the presence of either tap or seawater. The presence of competing ions and their concentrations is evaluated by ICP-MS. Our study shows that tap water does not have a detrimental effect on the adsorption of both polymers, whereas, in the presence of seawater, the performance of TRIP-HC toward MO proved to be more stable than MG with TRIP-SO3H, which is probably due to a larger concentration of competing ions. Comparison between ultrasonic-assisted and magnetic stirring adsorption demonstrates that the former exhibits a greater efficiency. This seems due to a more rapid mass transfer, driven by the formation of high velocity micro-jets, acoustic microstreaming and shock waves, at the polymer surface. Reusability studies show a good stability up to five adsorption–desorption cycles.

Molecular dynamics simulation of mechanical response of Cu50Zr50 metallic glass under double shock loading

In real applications, materials are often subjected to multiple shock loadings, under which the mechanical response is rather complicated and needs in-depth studies. In this paper, molecular dynamics simulations of Cu50Zr50 metallic glass (MG) that has broad application prospects in various fields under double-shock loading have been carried out in order to uncover the deformation mechanism of MG in the dynamic process. By varying the velocity and the time interval from the first shock, we found that the double shock can lead to different phenomena such as recompaction, second spallation, uncompaction, or non-spallation. We further investigated the characteristics of these different phenomena through analyzing the damage area, stress distribution, density, and temperature in the shock processes. It was found that the void collapse caused high local stress and high temperature. We also found that the shear deformation resistance of the recompaction region cannot be recovered after recompaction through the quantitative statistics of the icosahedral clusters. Moreover, the material softening caused by high temperature in the recompaction region was the main reason for second spallation. In addition, a small second shock velocity could not induce the recompaction and a small interval time between two shocks inhibited the occurrence of the first spallation. The insights gained in this study contribute to a better understanding of the dynamic response of MGs under double-shock loadings.