Shock Wave Velocity Research Articles

Dynamic response of a Li2O-Al2O3-SiO2 transparent glass-ceramic under shock compression

Li2O-Al2O3-SiO2 transparent glass-ceramics (LAS-TGCs) are promising candidates for transparent armour materials due to their excellent physical and mechanical capabilities. In this work, the dynamic behaviour of a LAS-TGC were further investigated using the planar impact technique and photon Doppler velocimetry. The shock stress, shock wave velocity, failure wave velocity and spall strength were obtained. In addition, the recompression signal, as a signature of failure waves, was observed to evolve into an oscillation signal as the impact stress decreases, indicating that the failure wave is gradually formed at a threshold. It has been noted that the failure wave velocity decreases with the increase in external loading and then turns upwards. The damage parameter of the LAS-TGC was assessed to be 0.410(5) under a shock stress of ~5.5 GPa, which is smaller than that of K9 glass. It is suggested that the LAS-TGC has better shock resistance than K9 glass.

Improved shock tube method for dynamic calibration of the sensitivity characteristic of piezoresistive pressure sensors

The dynamic calibration of pressure sensors with shock tube system are inevitably affected by the non-ideal shock wave characteristics and complex noise interferences, which limits the achievable accuracy of the dynamic pressure measurements. This paper proposes an improved shock tube (IST) method for identifying the sensitivity characteristic of piezoresistive pressure sensors. The incident shock wave (ISW) velocity attenuation model is first established by a distributed ISW velocity measurement combined with least squares fitting to compensate the shock wave pressure in shock tube. Besides, a signal correction method based on the hybrid adaptive mode decomposition is presented to eliminate the effects of complex noise on the response signals of pressure sensor. An accurate dynamic calibration result of the sensitivity characteristic is finally achieved with the compensated shock wave pressure and corrected response signal. A series of dynamic calibration experiments for a piezoresistive pressure sensor are carried out to verify the performance of the IST method. Results show that the IST method is able to effectively reduce the effects of the non-ideal shock wave and complex noises on the sensitivity calibration results. The mean relative error of sensitivity calibration results with the IST method is only 0.55%, which is about 1/7 times of the results obtained by the usual shock tube method. Furthermore, the sensitivity calibration uncertainty is evaluated and the smaller uncertainty results further verify the superiority of the IST method in high-accuracy dynamic calibration of piezoresistive pressure sensors.

The renormalization method for singular perturbation of solitons

By the renormalization method based on the Taylor expansion (TR method, for simplicity), a new direct scheme to compute the singular perturbation of solitons is proposed. The proposed method can also be applied to perturbation of other solvable nonlinear evolution equations. The biggest advantage of the method is that the secular terms in perturbation series need not to be considered at all in our method. But, in other perturbation methods, the most important task is to eliminate the secular terms. In addition, comparing with the other direct approaches, we need not the multi-scale procedure. As an illustration example, the perturbation of shock wave for the perturbed Burgers equation is solved in detail, and a uniform asymptotical solution is obtained to describe the dynamics of the shock wave under the small perturbation and long time. By taking a concrete perturbation and computing the exact solution, we show that the renormalization solution gives exact correction of velocity of shock wave. In final, we compute the perturbation of the single soliton of the damping KdV equation.

Iron‐Carbon Alloy Under Shock Compression: Implications for the Carbon Concentration in Earth’s Inner Core

AbstractCarbon has been proposed to be a potential light element in the Earth’s solid inner core. However, its presence and concentration in the core remain limited constrained. In this study, we measured the equation of state of an iron‐carbon alloy with ∼1.5 wt.% (∼6.64 at.%) carbon up to ∼185 GPa and ∼3,750 K via shock compression. The Hugoniot equation of state of the Fe‐1.5wt.%C alloy was determined to be Us (km/s) = 3.94 (0.15) + 1.62 (0.08) Up with an initial density of 7.77 (0.03) g/cm3, where Us and Up are the shock wave velocity and particle velocity, respectively. Hugoniot data combined with the Mie‐Grüneisen equation of state allow us to build the thermal equations of state of the Fe‐C alloy at high pressure‐temperature (P‐T) conditions. Investigations on the pressure‐density relation of Fe‐C alloys by the shock experiments and synchrotron X‐ray diffraction measurements by Pamato et al. (2020), https://doi.org/10.1029/2020jb020159 have indicated that carbon should occupy interstitial sites of iron lattice at high P‐T conditions. The thermal equation of state of the Fe‐1.5wt.%C alloy provided here shows that Fe‐1.5wt.%C is ∼1.65% denser than the inner core under conditions relevant to the inner‐core boundary. This study indicates that iron alloyed with an upper bound of ∼2.2 (0.3) wt.% (∼10.7 [1.6] at.%) carbon may match with the Preliminary Reference Earth Model (PREM) in the Earth’s inner core. Thus, interstitial carbon in iron helps to explain the observed density deficit of the inner core, although other light elements are also expected.

Experimental study of effect of equivalence ratio and initial turbulence on the explosion characteristics of LPG/DME clean blended fuel

The effects of initial turbulence and equivalence ratio on the explosion characteristics of LPG/DME clean blended fuel were investigated experimentally. The results showed that as equivalence ratio increase, the explosion overpressure, rate of pressure rise, and propagation velocity of shock wave assume a "three-zone" structure, that is, first acceleration zone, then attenuation zone, finally stabilization zone. With the increase of initial turbulence, the explosion characteristic parameters such as the maximum explosion overpressure, the maximum pressure rise rate, and the maximum shock wave propagation velocity all showed different degrees of increase, and the reasons for these growths are not the same, which leads to the inconsistent levels of growth. However, the chain-based growth rate of these explosion characteristics parameters decreases with the increase of initial turbulence, which meant that the influence of initial turbulence on explosion intensity was weakened gradually. The maximum explosion overpressure and the maximum rate of pressure rise basically conformed to a linear relationship with the initial turbulence. The results of the paper can provide more basic but important information for the practical use of LPG/DME clean blended fuel, especially in safety protection strategies.

Effects of non-collimated radiation during the decay of laser-induced spark

A fast-computing radiative heat transfer on-the-fly interpolation database was developed for high temperature radiative-gas dynamic simulations under local thermodynamic equilibrium (LTE). The absorption coefficient includes Atomic (Bound-Bound, Bound-Free, Free-Free) transitions and Molecular band systems. A 2D finite-volume radiative transfer equation (RTE) solver was developed and coupled with a compressible reacting flow solver to simulate a laser-induced decaying spark (LIDS) in air. Part spectrum correlated k-distribution with Gauss-Chebyshev quadrature and mixing model were applied to reduce the number of RTE runs. Non-collimated radiative heat loss was calculated in LIDS and the effects of radiation loss on the shock wave and kernel cooling were investigated. Total radiation loss was accounted to be approximately 2.3% of the absorbed energy which happens in a micro-second timescale and most of the kernel energy is taken away by the shock wave. Two simulations with and without RTE were compared to analyse the effects of radiative transfer. The radiation loss results in attenuation of shock wave velocity and delaying the emanation of blast wave. The cooling of the plasma kernel is accelerated due to energy loss by radiative transfer. Radiation increases the cooling rates in the primary cooling regime and decreases during the secondary regime due to an energy deficit in the kernel. The transition from primary to the secondary cooling regime is not uniform throughout the kernel.

Origins of plastic shock waves in single-crystal Cu

We investigate shock wave propagation in single-crystal Cu with large-scale molecular dynamics simulations. Plastic shock waves propagate via dislocation nucleation or growth. With decreasing particle velocity, a remarkable drop in plastic shock wave velocity relative to the linear shock velocity–particle velocity relation is observed in the elastic–plastic two-wave regime for different loading directions. This reduction can be attributed to the changes in the mechanisms of plastic shock wave generation/propagation, from the dislocation nucleation-dominant mode, to the alternating nucleation and growth mode, and to the growth-dominant mode. For weak shocks, the plastic shock advances at the speed of the growth of existing dislocations (below the maximum elastic shock wave speed), considerably slower than the dislocation nucleation front for strong shocks (above the maximum elastic shock wave speed).

Dynamic behavior of PMMA under planar shock conditions

As a non-metallic low wave impedance material, PMMA has been widely used in experiments of blast and shock. But the dynamic performances of different kinds of PMMA vary greatly. In this paper, the plane shock-wave experiments were performed with a 57 mm bore single-stage light gas gun in order to determine the dynamic behavior of PMMA at stress levels between 0.4 and 3.8 GPa. The particle velocity and shock wave velocity were measured with electromagnetic particle velocity sensors embedded into the samples directly, and the velocity of the flyer was measured with a laser velocity measuring system. The typical wave forms of particle velocity and the Hugoniot data of the experiments were presented in this paper. The dynamic stress–strain relations of experiments at different pressure ranges were obtained by the Lagrangian analysis method based on one dimensional strain, and the loading and unloading characteristics of which were discussed.

Interaction of Blast Waves with Multilayer Surfaces and Multiphase Media

The possibilities and methods of attenuation of blast waves when they are reflected on any limiting surface in terms of the peak pressure and momentum of the compression phase are of real practical interest. This interest stems from the need to eliminate or maximally mitigate the harmful effects of accidental and terrorist explosions. Porous materials are widely used in a variety of engineering structures due to their superior energy absorption capacity and other advantages in mechanical and physical properties. But when the porous material was used in protective structures to resist an explosive shock wave or high velocity impact, the protective function of the porous material was questionable. There are data indicating both a weakening and an increase in the explosive load on the protected object, depending on the structure of the porous material, the thickness of the protective layer, the duration of the positive phase of the blast wave pressure.

Building a weak shockwave from linear modes

In shockwave theory, the density, velocity and pressure jumps are derived from the conservation equations. Here, we address the physics of a weak shock the other way around. We first show that the density profile of a weak shockwave in a fluid can be expressed as a sum of linear acoustic modes. The shock so built propagates at the speed of sound and matter is exactly conserved at the front crossing. Yet, momentum and energy are only conserved up to order 0 in powers of the shock amplitude. The density, velocity and pressure jumps are similar to those of a fluid shock, and an equivalent Mach number can be defined. A similar process is possible in magnetohydrodynamics. Yet, such a decomposition is found impossible for collisionless shocks due to the dispersive nature of ion acoustic waves. Weakly nonlinear corrections to their frequency do not solve the problem. Weak collisionless shocks could be inherently nonlinear, non-amenable to any linear superposition. Or they could be non-existent, as hinted by recent works.

RADIATIVE CHARACTERISTICS OF SHOCK HEATED OXYGEN

The emission spectra of oxygen behind the front of a strong shock wave have been studied in the shock wave velocity ranges of 5.7—7.4 and 8.1—10.0 km/s at pressures before the wave front of 1.0 and 0.25 Torr. Time-integrated sweeps of radiation in a wide spectral range of 200—675 nm as well as temporal oscillograms
 of oxygen radiation have been obtained. An analysis of the obtained panoramic spectra shows that at low velocities of the shock wave, the system of Schumann—Runge molecular bands dominates in the emission spectrum. An increase in the shock wave velocity leads to the appearance of intense atomic lines in the emission spectrum. The peculiarities of temporal oscillograms for the most typical spectral lines, such as radiation of molecular oxygen at a wavelength of 213 nm (Schumann—Runge system) and radiation of atomic oxygen at wavelengths of 394 and 645 nm, are highlighted.

Perspectives on Primary Blast Injury of the Brain: Translational Insights Into Non-inertial Low-Intensity Blast Injury.

Most traumatic brain injuries (TBIs) during military deployment or training are clinically “mild” and frequently caused by non-impact blast exposures. Experimental models were developed to reproduce the biological consequences of high-intensity blasts causing moderate to severe brain injuries. However, the pathophysiological mechanisms of low-intensity blast (LIB)-induced neurological deficits have been understudied. This review provides perspectives on primary blast-induced mild TBI models and discusses translational aspects of LIB exposures as defined by standardized physical parameters including overpressure, impulse, and shock wave velocity. Our mouse LIB-exposure model, which reproduces deployment-related scenarios of open-field blast (OFB), caused neurobehavioral changes, including reduced exploratory activities, elevated anxiety-like levels, impaired nesting behavior, and compromised spatial reference learning and memory. These functional impairments associate with subcellular and ultrastructural neuropathological changes, such as myelinated axonal damage, synaptic alterations, and mitochondrial abnormalities occurring in the absence of gross- or cellular damage. Biochemically, we observed dysfunctional mitochondrial pathways that led to elevated oxidative stress, impaired fission-fusion dynamics, diminished mitophagy, decreased oxidative phosphorylation, and compensated cell respiration-relevant enzyme activity. LIB also induced increased levels of total tau, phosphorylated tau, and amyloid β peptide, suggesting initiation of signaling cascades leading to neurodegeneration. We also compare translational aspects of OFB findings to alternative blast injury models. By scoping relevant recent research findings, we provide recommendations for future preclinical studies to better reflect military-operational and clinical realities. Overall, better alignment of preclinical models with clinical observations and experience related to military injuries will facilitate development of more precise diagnosis, clinical evaluation, treatment, and rehabilitation.

Liquid temperature effect on the hydraulic shock wave velocity in polyethylene pipes

Introduction. Providing people with high quality drinking water has always come first. However, its transportation through pipeline systems was often associated with some problems, such as the temperature of the water and the environment, as well as the possibility of water hammer on certain pipe sections. This was especially true for systems that use polyethylene pipes. Temperature is a key factor affecting the flexibility properties of polyethylene pipes, and it affects not only the design, but also the investment in the development of water supply networks. The purpose of these studies was to study the effect of water and ambient temperature on the density, properties of the pipe material and the speed of propagation of a hydraulic shock wave in polyethylene pipes.Materials and Methods. In the experiments performed, the method of field research was used, when tests are carried out on specialized equipment on samples specially made for the pursued purposes. Here, samples of high-density polyethylene pipes were used, which were subjected to tensile tests on a tensile testing machine, and each experiment was carried out three times.In the course of the experiments, the samples were exposed to certain temperature regimes (both external and internal), while the influence of the hydrodynamic pressure of the liquid in the pipe was also investigated, as a result of the change in time of the liquid velocity in its sections. To do this, the samples were supplied with liquid under a certain pressure in order to find out the influence on the pipes of an effect known as water hammer.Results. In the course of the research, it was found that the value of the elastic modulus of high-density polyethylene PE100 decreases with increasing water temperature, and the decrease at a temperature of 60° C reaches 60.21% compared to its value at a water temperature of +4° C. Based on the results of experiments to determine the effect of the elastic modulus of polyethylene with increasing temperature, an exponential equation was derived to calculate the value of the polyethylene coefficient as a function of time E = 1.312e-0,01t with the correlation coefficient R2 = 0.988 ; and based on the results of the studies carried out to calculate the value of the propagation velocity of a hydraulic shock wave, an exponential equation was derived as a function of time C = 275.9e-0,01t with the coefficient correlation R2 = 0.987 .Discussion and Conclusions. In the course of the research, it was found that such a phenomenon as water hammer has a harmful effect on the pipe walls, which, if possible, should be avoided even at the design stage of the water supply network. During the experiments, it was found that with an increase in temperature, the values of the elastic modulus of polyethylene decreased with a simultaneous decrease in the values of the propagation velocity of the hydraulic shock wave.

Improvement of Accuracy of Temperature Measurement Method around Discharge Field Based on Shock Wave Velocity

The shock wave mitigation technique by using the electromagnetic energy is one of the promising methods. The baroclinic effect has the important role in this method. This effect has the possibility to apply to the generation the vortex phenomena in the compressible flow field. Therefore, the comprehension of the effect is inevitable for exploring the further vortex control- ing application in the supersonic flow field. Until now, the temperature distribution measurement has been conducted in order to the comprehension of the baroclinic effect by the interaction between the shock wave and the temperature modulated field due to the electric discharge energy, based on the shock wave velocity. However, the conventional method depends on the Mach number at the down stream region of the discharged field. This Mach number has a large impact on the temperature determination.Based on this background, in this study, we tried to improve the temperature determination method. As a result, the determination accuracy improved.

Experimental study on the dynamic compression of materials at XGIII facility by laser proton photography

A new method for material dynamic density measurement based on proton photography is developed at XGIII facility. The protons produced by the picosecond laser of XGIII was used as the proton source to diagnose the density distribution of lattice foam under the compression of the nanosecond beam of XGIII. The density of lattice foam was calculated from the photographic results using Monte Carlo simulation method. Benefitting fromn this newly developed method, the images of the compressed lattice foam and the shock front at 5.2 ns is obtained successfully. The density distribution of the lattice foam was obtained from the images and the density of lattice foam increases about 20 times at the shock front due to the compression of the shock. The velocity of shock wave in lattice foam is also given, about 40 km/s. The density and spatial resolution of the method are further calibrated by using diamond step objects, and experimental results show that they are better than 4% and 12 <i>μ</i>m, respectively. In order to further improve the density and spatial resolution of the proton photography at XGIII facility, a new radiogrphy method utilizing quasimonoenergetic proton beams obtained from an energy selector is proposed in this paper, and the resolution of this method is simulated by Monte Carlo program. The simulation results show that the relative density resolution can be improved to more than 1%. Through the above experimental and the simulation results, we demonstrated that diagnostic capability has been established for fast process (nanosecond scale), high pressure (nearly 100 GPa) conditions at XGIII facility.

CONNECTION OF THE INTENSITY OF THE FLUX OF SCR PROTONS WITH THE VELOCITY OF THE CME AND WITH THE FADING OF THE RADIO EMISSION OF THE SUN IN THE DECAMETER RANGE

The relationship between SCR and CME and with fading of the continuum of noise storms and typeIV radio bursts in the decameter range is investigated. It was shown earlier that about 60% of CMEs associated with solar proton events are accompanied by deep fading of the solar radio emission in the decameter range, which coin-cides in time with CME registration. It has also been shown that fading is characterized by fading depth, the frequency bandwidth in which the fading occurs, as well as the duration of the fading and the frequency at which the maximum fading depth is observed. Further detailed studies have shown that for proton events accompanied by fading of the solar radio emission in the decameter range, the relationship between the intensity of the SCR proton flux and the CME velocity is much worse than for events without fading of the solar radio emission in the decameter range. However, it was foundthat for such events, the relationship between the flux of SCR protons and the CME velocity significantly increases if we take into account the fading depth of the solar radio emission in the decameter range.Earlier in (Isaeva, 2019), the results of a study of the relationship between the intensity of fading of the continuum of noise storms with the parameters of X-ray bursts, with the CME velocity and the velocity of coronal shock waves, as well as with the intensity of the SCR proton flux were presented. This paper presents the results of studying the relationship between the intensity of the SCR proton flux withthe parameters of type II and IV radio bursts, as well as with the CME velocity and with the velocity of coronal shock waves, depending on the intensity of fading of the solar radio emission in the decameter range at a frequency of 27 MHz. The frequency of 27 MHz was chosen because in the region of this frequency the maximum fading depth of the solar radio emission in the decameter range is observed.

Aluminized Enhanced Blast Explosive Based on Polysiloxane Binder

AbstractDrastic measures are taken in order to improve the properties of enhanced blast explosives. First, a binder with high reactivity as reducing agent is selected. The binder, platinum cure silicone, generates pyrophoric decomposition products in situ during the detonation. Arising problems with curing inhibition of the polymer are solved, as nanosized SiO2 is employed as hardening catalyst carrier. Quantum calculations show specific interactions of the binder and aluminum, forming the backbone of the composition. Furthermore, particle size distribution of the main fuel, aluminum powder, is selected so the Al will have enough time to heat, ignite and burn in the atmosphere, creating the thermobaric effect. Potassium perchlorate is employed as an oxidizer, as it reacts with detonation products faster than the widely used ammonium perchlorate. The resulting enhanced blast explosive is denoted as H‐TBX. High speed camera results show similar shock wave velocity 2.5 m from 2.7 kg TNT charge (2 ms after initiation) and 3.5 m from 2.65 kg H‐TBX charge (3 ms after initiation). In the open field, the H‐TBX generates 1.83 times higher peak pressure and 2 times higher impulse than TNT. These findings are compared with data from the literature for Tritonal, PBXN‐109 and AFX‐757. H‐TBX has improved parameters over the former generations of enhanced blast explosives and is currently used in multiple weapons systems.

Shock Wave Propagation and Flame Kernel Morphology in Laser-Induced Plasma Ignition of CH4/O2/N2 Mixture

The application of laser ignition in the aerospace field has promising prospects. Based on the constant volume combustion chamber, the laser ignition of CH4/O2/N2 mixture with different initial pressure, different laser energy, different equivalence ratio and different oxygen content has been carried out. The development characteristics of the flame kernel and shock wave under different conditions are analyzed. In addition, the Taylor model and Jones model are also used to simulate the development process of the shock wave, and a new modified model is proposed based on the Jones model. The experimental results show that under pure oxygen conditions, the chemical reaction rate of the mixture is too fast, which makes it difficult for the flame kernel to form the ring and third-lobe structure. However, the ring structure is easier to form with the pressure and laser energy degraded; the flame kernel morphology is easier to maintain at a rich equivalence ratio, which is caused by the influence of the movement of hot air flow and a clearer boundary between the ring and the third-lobe. The decrease of the initial pressure or the increase of the laser energy leads to the increase in shock wave velocity, while the change of the equivalence ratio and oxygen content has less influence on the shock wave.

Survival of polycyclic aromatic hydrocarbon knockout fragments in the interstellar medium

Laboratory studies play a crucial role in understanding the chemical nature of the interstellar medium (ISM), but the disconnect between experimental timescales and the timescales of reactions in space can make a direct comparison between observations, laboratory, and model results difficult. Here we study the survival of reactive fragments of the polycyclic aromatic hydrocarbon (PAH) coronene, where individual C atoms have been knocked out of the molecules in hard collisions with He atoms at stellar wind and supernova shockwave velocities. Ionic fragments are stored in the DESIREE cryogenic ion-beam storage ring where we investigate their decay for up to one second. After 10 ms the initially hot stored ions have cooled enough so that spontaneous dissociation no longer takes place at a measurable rate; a majority of the fragments remain intact and will continue to do so indefinitely in isolation. Our findings show that defective PAHs formed in energetic collisions with heavy particles may survive at thermal equilibrium in the interstellar medium indefinitely, and could play an important role in the chemistry in there, due to their increased reactivity compared to intact or photo-fragmented PAHs.

Time-resolved imaging of CaF2 poly-crystal response following 355 nm nanosecond laser irradiation

The evolution of 355 nm nanosecond laser-induced damage to C a F 2 poly-crystals is investigated by using the time-resolved pump-probe shadowgraph technique. The damage morphologies of the front surface, rear surface, and interior of the C a F 2 crystal are imaged by optical microscopy. When the rear surface is focused by one laser pulse throughout the front surface, three shock waves (SWs) and one SW are observed in the air beside the front and rear surfaces, respectively. When the laser energies are 40 mJ and 60 mJ, at delay time of 1000 ns the radii of SW fronts beside the front surface are 2569.8 µm and 2831.7 µm, while those beside the rear surface are 1012.9 µm and 1078.1 µm, respectively. The filamentary channels inside the C a F 2 crystal are established before the end of a laser pulse at energies of 25, 40, or 60 mJ. The average propagation velocities of SWs along the filamentary channel are approximately 8.2 µm/ns. The maximum diameters of channels can reach approximately 53 µm and 128 µm for 25 mJ energy and 40 mJ energy, respectively. The experimental results help to explore the mechanism of laser-induced C a F 2 poly-crystal damage in nanosecond regime.