Release Wave Research Articles

Tests of Unconfined Single Fragment Generators

A single fragment cannot be accelerated very well and undisturbed by an unconfined high explosive charge. The converging shock and release waves eject a higher number of very small spall debris of the fragment in the firing and target direction. This means, the fragment is considerably deformed and looses some mass. In addition, the release waves reduce the high pressure zone after the fragment very fast. Therefore, only moderate velocities are achieved. Generator für einen einzelnen Splitter ohne Verdämmung Ein einzelner Splitter kann nicht sehr gut unbeschädigt mit einer Sprengladung ohne jegliche Verdämmung beschleunigt werden. Die einlaufenden Schock- und Verdünnungswellen stoßen eine größere Anzahl von feinen Splittern von der Splitterachse in die Spreng- bzw. Zielrichtung aus. Hierdurch wird der Splitter deformiert und verliert auch an Masse. Der Abbau der detonativen Hochdruckzone hinter dem Splitter durch die vom Rand des Splitters einlaufenden Verdünnungsfächer ergibt verringerte Splittergeschwindigkeiten. Générateur pour un éclat individuel sans confinement Un éclat individuel ne peut être accéléré sans dommage avec une charge explosive sans aucun confinement. Les ondes de choc et de détente qui arrivent éjectent un grand nombre d'éclats fins à partir de l'axe dans la direction de l'explosion ou de la cible. l'éclat est ainsi déformé et sa masse est également réduite. La réduction de la zone de détonation de haute pression derrière l'éclat résultant des faisceaux de détente arrivant du bord de l'éclat donne des vitesses d'éclat réduites.

A model for penetration by very low aspect ratio projectiles

Summary As the aspect ratio (L/D) of a projectile decreases and the projectile becomes more disk like, the penetration mode changes. A model for the penetration of low L/D projectiles has been developed to explain and predict the low L/D penetration event. The model divides the penetration into two phases: first a flyer plate type impact, and second, a crater growth phase. Calculations provided insight into the physical mechanism involved. Shortly after impact, the projectile enters a long period of constant velocity penetration. This behavior leads to the depth of penetration scaling with projectile diameter. A large crater grows in the target, and the projectile travels into a debris filled crater as a free body. The velocity is “frozen” in when release waves arrive from the free surface. In the model, the crater in the target is analyzed by assuming plastic constitutive response, with the motion caused by an impulsive load due to the impact. The final depth of penetration is obtained by combining a one-dimensional depth of penetration and a plastic target cratering response. The model compares well with both large scale numerical simulations and experimental data.

Fire-diffuse-fire model of dynamics of intracellular calcium waves.

When Ca2+ is released from internal stores in living cells, the resulting wave of increased concentration can travel without deformation (continuous propagation) or with burst-like behavior (saltatory propagation). We analyze the "fire-diffuse-fire" model in order to illuminate the differences between these two modes of propagation. We show that the Ca2+ release wave in immature Xenopus oocytes and cardiac myocytes is saltatory, whereas the fertilization wave in the mature oocyte is continuous.

Effect of irreversible phase change on shock-wave propagation

New release adiabat data for vitreous GeO 2 are reported up to ∼25 GPa using the VISAR technique. Numerical modeling of isentropic release wave induced dynamic states achieved from one dimensional strain–stress waves is consistent with a phase change that induce an increase in zero-pressure density from 3.7–6.3 Mg/m 3 starting at ∼8 GPa. The first release adiabat data for SiO 2 ( fused quartz) are presented (obtained with immersed foil technique) . Above 10 GPa, the SiO 2 release isentropes, in analogy with GeO 2, are steeper than the Hugoniot in the volume-pressure space, indicating the presence of an irreversible phase transition (to a stishovite-like phase) . We simulate propagation of shock-waves in GeO 2, in spherical and planar symmetries, and predict enhanced attenuation for shock pressures ( p) above the phase change initiation pressure (8 GPa) . The pressure from a spherical source decays with propagation radius r, p ∼ r x, where x is the decay coefficient. Modeling hysteresis of the phase change gives x = −2.71, whereas without the phase change, x = −1.15. An analytical model is also given.

Shear strength of aluminum in shock waves

Two series of experiments are conducted for determining the shear strength of shockcompressed aluminum (type AD1) at pressures of 4–16 GPa, including in loading and release waves. A saturated water solution of ZnCl2 serves as a control material. Previous data on the shear strength of materials based on measuring the two principal stresses are refined. It is confirmed that tangential stresses in aluminum and its alloys relax in the shock front for shock amplitudes exceeding 10 GPa. The reasons for discrepancies in previous determinations of the shear strength of metals in shock waves are clarified.

Prediction of fragment number and size distribution in dynamic fracture

The present study is focused on predicting fragment number and size distribution in dynamic fragmentation processes. Because of the unloading effect of release waves arising from fracture nucleations, we consider there to be a minimum value for fragment size. Combined with the assumption that the sites of fracture nucleation are distributed randomly in the sample, we have deduced a set of equations with which the fragment number and size distribution curve could be calculated. Different from previous work, the parameters in this work are all physically determined but not fitted. Comparison with expanding cylindrical shell and ring experiments has been made, showing that the theory has a good predictive capability.

Fibre Optic Shock Velocity Sensor for Solids

This paper reports a fibre optic sensing technique for the measurement of shock velocity in solid materials. The shock-induced changes in the light transmission properties of an optical fibre are employed as the principal transduction mechanism. A polycarbonate flyer plate generated shock waves by impacting a perspex target. The shock velocity was determined from the difference in arrival times of the shock front at the spatially separated optical fibres embedded in the target. The main advantage of this sensor system lies in its simplicity and immunity to optical and radio frequency (RF) noise. Consideration is also given to the effect of release waves on the uniform shock pressure region generated by the ˚yer impact which can degrade the accuracy of the velocity measurement.

Index of refraction and mechanical behavior of soda lime glass under shock and release wave propagations

This article reports a set of experiments designed to measure change in the refractive index of transparent material under both planar shock and release wave propagations. Information about both mechanical and optical properties of transparent material were obtained simultaneously through the measurement of particle velocity at or near the impact surface and the free surface velocity. Data thus obtained is used to determine shock and release wave velocities and the Hugoniot elastic limit (HEL) of the material. Shock wave velocity in soda lime glass remains unchanged at 5.83±0.04 km/s, i.e., equal to the measured ultrasonic longitudinal wave velocity, when it is shock compressed to less than or equal to 4.3 GPa. The value of shock wave velocity begins to decline when the impact stress in the glass exceeds this value. The release wave velocity, however, remains equal to the measured ultrasonic longitudinal wave velocity to only 3 GPa, it begins to decline at higher stresses. The variation in the refractive index of the glass shows a cusp at 3.04–3.14 GPa. Additionally, up to and including the impact stress of 3.14 GPa, the refractive index after shock compression and release is within 1% of its ambient value, but at higher stresses it differs by larger percentage points. The HEL of the glass is determined to be 3.10±0.06 GPa although it lacks the classic well defined cusp in all the recorded wave profiles of soda lime glass.

Dynamic compression of an Fe–Cr–Ni alloy to 80 GPa

Wave profiles were measured in an Fe–Cr–Ni alloy (stainless steel 304) shock compressed to Hugoniot stresses between 7 and 80 GPa. A single-stage propellant gun was used to generate shock states and time histories were recorded by velocity interferometry. The particle velocity measurements are generally consistent with impedance match calculations to ±2%. Unloading wave velocities were obtained from analysis of the release wave profiles. Using Eulerian finite strain theory and under the assumption of fully elastic initial release, the first and second pressure derivatives of the longitudinal modulus are given by: 7.9(0.5) and −0.16(0.06) GPa-1, where the numbers in parentheses are one standard deviation uncertainties. The first and second pressure derivatives of the adiabatic bulk modulus are: 6.4(1.0) and −0.17(0.08) GPa-1. The unloading wave velocities are generally consistent with extrapolated trends from low-pressure ultrasonic data as well as with higher stress shock measurements on an alloy of similar composition. From 1 bar to 80 GPa, Poisson’s ratio, ν, increases with Hugoniot stress, σ (in GPa), according to the relation: ν=0.29 + 0.0008σ. The Hugoniot elastic limit of 304 steel was found to be 0.35(0.12) GPa, and the initial yield stress is 0.21(0.07) GPa. The elastic precursor velocity was 5.8(0.1) km/s. Numerical simulations of the wave profiles using a constitutive model that incorporates a Bauschinger effect and stress relaxation reproduced the main features observed in the profiles. Release adiabats were also calculated from the measured wave profiles. The shear stress at unloading was determined to vary with stress according to the relation: τ0+τc=0.149+0.018σ, where σ is given in GPa.

Acceleration–deceleration process of thin foils confined in water and submitted to laser driven shocks

An experimental, numerical, and analytical study of the acceleration and deceleration process of thin metallic foils immersed in water and submitted to laser driven shocks is presented. Aluminum and copper foils of 20 to 120 μm thickness, confined on both sides by water, have been irradiated at 1.06 μm wavelength by laser pulses of ∼20 ns duration, ∼17 J energy, and ∼4 GW/cm2 incident intensity. Time resolved velocity measurements have been made, using an electromagnetic velocity gauge. The recorded velocity profiles reveal an acceleration–deceleration process, with a peak velocity up to 650 m/s. Predicted profiles from numerical simulations reproduce all experimental features, such as wave reverberations, rate of increase and decrease of velocity, peak velocity, effects of nature, and thickness of the foils. A shock pressure of about 2.5 GPa is inferred from the velocity measurements. Experimental points on the evolution of plasma pressure are derived from the measurements of peak velocities. An analytical description of the acceleration–deceleration process, involving multiple shock and release waves reflecting on both sides of the foils, is presented. The space–time diagrams of waves propagation and the successive pressure–particle velocity states are determined, from which theoretical velocity profiles are constructed. All characteristics of experimental records and numerical simulations are well reproduced. The role of foil nature and thickness, in relation with the shock impedance of the materials, appears explicitly.

Shock-melting pressures from non-planar impacts

A pulsed high-power proton beam is used to ablatively accelerate flier foils of several tens of micrometers thickness to hypervelocities. The power density profile (8 mm diameter FWHM) results in a radially dependent acceleration and a velocity profile that generates, upon impact on a planar target, a radially symmetric pressure distribution covering a certain pressure interval. Using a line-imaging laser-Doppler velocimeter allows us to measure simultaneously the velocity distribution of the flier and the emergence of the shock wave at the rear side of the target. If the material in the release wave is in a melting state the reflectivity of the target is reduced due to material spraying and causes a loss of the velocimeter signal. By selecting the initial distance between flier and target the impact velocity and the pressure interval, respectively, can be adjusted such that it contains the threshold pressure for melting after shock release.

On the collapse of vapour cavities in a thin liquid layer under high pressure transient

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Me-Bar Y. 1996On the collapse of vapour cavities in a thin liquid layer under high pressure transientProc. R. Soc. Lond. A.452757–768http://doi.org/10.1098/rspa.1996.0038SectionRestricted accessArticleOn the collapse of vapour cavities in a thin liquid layer under high pressure transient Y. Me-Bar Google Scholar Find this author on PubMed Search for more papers by this author Y. Me-Bar Google Scholar Find this author on PubMed Search for more papers by this author Published:09 April 1996https://doi.org/10.1098/rspa.1996.0038AbstractAn apparatus was built in conjunction with the transparent anvils drop weight machine to view the events occurring during the formation, growth, and collapse of vapour cavities in thin liquid layers. During the collapse phase, several mechanisms operate, namely: proportional shrinkage, volume jetting, surface jetting and secondary cavitation, which can be attributed to features of the liquid flow under compression. Localized flow in the bodies of the liquid surrounding the cavities drives the proportional shrinkage (in which the cavities roughly retain their shapes); the pressure or shock waves propagation and reflection at the cavity interfaces drive the volume jets; the interaction of the release or rarefaction waves with the pressure/shock wave itself seems to initiate the secondary cavitation and the surface jets seem to be caused by the variations of the vertical distribution of the horizontal flow velocity during the transition from the tensile to the compression phase. A simple model which considers the liquid a perfectly plastic material and assumes a very rapid rate of vapour condensation fits the experimental results throughout most of the collapse process. It seems that in the final stages of the collapse the rate of condensation is not fast enough and the model is not valid there. Further studies should be carried out to better quantify the various mechanisms observed.FootnotesThis text was harvested from a scanned image of the original document using optical character recognition (OCR) software. As such, it may contain errors. Please contact the Royal Society if you find an error you would like to see corrected. Mathematical notations produced through Infty OCR. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Cawkwell M, Ferreira S, Lease N and Manner V (2022) Ranking explosive sensitivity with chemical kinetics derived from molecular dynamics simulations Molecular Modeling of the Sensitivities of Energetic Materials, 10.1016/B978-0-12-822971-2.00007-3, (347-367), . Cawkwell M and Manner V (2019) Ranking the Drop-Weight Impact Sensitivity of Common Explosives Using Arrhenius Chemical Rates Computed from Quantum Molecular Dynamics Simulations, The Journal of Physical Chemistry A, 10.1021/acs.jpca.9b10808, 124:1, (74-81), Online publication date: 9-Jan-2020. Walley S, Field J, Biers R, Proud W, Williamson D and Jardine A (2015) The Use of Glass Anvils in Drop‐Weight Studies of Energetic Materials, Propellants, Explosives, Pyrotechnics, 10.1002/prep.201500043, 40:3, (351-365), Online publication date: 1-Jun-2015. Balzer J, Siviour C, Walley S, Proud W and Field J (2004) Behaviour of ammonium perchlorate–based propellants and a polymer–bonded explosive under impact loading, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 460:2043, (781-806), Online publication date: 8-Mar-2004.Walley S, Balzer J, Proud W and Field J (2000) Response of thermites to dynamic high pressure and shear, Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 456:1998, (1483-1503), Online publication date: 8-Jun-2000. Agrawal J, Walley S and Field J (1997) High-Speed Photographic Study of the Impact Response of Ammonium Dinitramide and Glycidyl Azide Polymer, Journal of Propulsion and Power, 10.2514/2.5207, 13:4, (463-470), Online publication date: 1-Jul-1997. This Issue09 April 1996Volume 452Issue 1947 Article InformationDOI:https://doi.org/10.1098/rspa.1996.0038Published by:Royal SocietyPrint ISSN:1364-5021Online ISSN:1471-2946History: Manuscript received12/08/1994Manuscript accepted16/01/1995Published online01/01/1997Published in print09/04/1996 License:Scanned images copyright © 2017, Royal Society Citations and impact

Liquid-jet impact on liquid and solid surfaces

Experiments were conducted to investigate the mechanisms of the liquid-jet impact on liquid and solid surfaces associated with cavitation damage and rain erosion. In this work, a liquid jet of 3 mm diameter, generated using a single impact jet apparatus, was impacted at ca. 600 m s −1 on the surface of water and polymethyl-methacrylate (PMMA) placed 15 mm below the nozzle exit. The various phenomena which occurred were photographed using an image-converter high-speed camera. These include (i) the shock wave generated at the moment of the liquid-jet impact on the surface, (ii) shock waves reflected at the liquid/air or solid/air interfaces, as release waves, (iii) the damage to the PMMA, (iv) the overlap of release waves on the central axis, causing central damage in PMMA and cavitation in liquids. The cavitation behaviour and the process of the damage is directly related to the behaviour of the compressive wave caused by the impact of the liquid jet.

Long-rod impact phenomena: role of wave interaction on crack propagation

Long-rod impact experiments were performed at high velocity (about 1500 m/s) against two different transparent targets: PMMA and glass. Early penetration phenomena of wave and crack propagation have been observed by means of high-speed camera. Microcracks always occur behind the shock wave front. Release waves reflected from the side boundaries of target can result in secondary cracking in front of main fracturing. The wave interaction due to different impedance on the target boundaries affects crack propagation. Thus, size of target and confining materials may play important roles of protection capability against the penetrator.

Dynamic compaction of AlLiX powder obtained by a rotating electrode process

The microstructures of dynamically compacted AlLiX powders obtained by the rotating electrode process were studied. Dynamic compaction was carried out using a LEXAN projectile whose velocity was 1520 m s −1 and the dynamic pressure obtained in the area of the (pseudo) planar shock wave was 7.1 GPa. Strong bonding between AlLiX particles with a thin melted contact zone was observed after dynamic compaction. Coarse particles had fewer interparticle contacts, but the contacts were stronger than for small particles. In the first layer of the sample in the area of (pseudo) planar shock wave the presence of 0.44 pores mm −2 and a total porosity of 4.6% were detected by quantitative metallography. Interparticle bonding was not detected in the first particle layer in the area affected by the release wave.

Elastic moduli as determined by shock-release experiments

The relationship between release-wave velocity and longitudinal elastic modulus in the state following shock compression is examined. The shocked state is characterized by the density of pinned dislocation segments, their pinning separation, and the viscous drag coefficient, in addition to lattice strains representing volumetric and deviatoric stress components. Release from the shock-compressed state is similar to ultrasonic-wave propagation in metals containing pinned dislocation segments. The exceptions are that release-wave amplitudes are greater, dislocation displacement is larger (the restoring force is nonlinear), and frequency content of the release waves is broader. For FCC metals, in which the Peierls stress is low and provides little lattice resistance to dislocation motion, dislocation segments can undergo motion at low applied stress and thus contribute to anelastic deformation unless the driving frequency is very high or special precautions are taken to pin them by various point defects. It is well known that, without such precautions, the ultrasonically determined modulus can be much lower than the true elastic modulus of the crystal lattice. Shock compression can create dislocation segments of density ~10 9−10 10 cm −2 and pinning separation of 500 b. For materials with viscous drag coefficients on the order of 1–100 × 10 −3 dynes cm −2 in the shock-compressed state, the influence of shock-wave-generated dislocation segments is to reduce the effective elastic modulus and thus reduce the observable releasewave speed. This is due to the very short time scale for reverse dislocation motion making ideally elastic deformation unobservable in any practical sense. As a consequence, the modulus based on the release-wave speed in an FCC metal serves only as a lower limit to the fully elastic modulus in the shock-compressed state.

Optical probing of hot expanded states produced by shock release.

The angle and polarization dependence of optical emission and reflection from dense aluminum plasmas produced in the release wave of a strong shock is investigated theoretically. It is shown that with high-speed measurements (few-picosecond resolution), optical probing of the unloading plasma can be used to examine transport properties and ionization balance of thermodynamic states in the vicinity of the liquid-vapor critical point. The calculations were performed using data from two wide-ranging theoretical models of plasma conductivity, a semianalytical model due to Lee and More [Phys. Fluids 27, 1273 (1984)] and a partial-wave analysis due to Rinker [Phys. Rev. B 31, 4207 (1985); 31, 4220 (1985)]. The models predict substantially different values for the conductivity close to the liquid-vapor critical point (more than a factor of 10 for the electron-ion collison time); the different results obtained for the two models suggest that experimental measurements could provide new information for improving the current understanding of dense plasma properties.

Air entrapment during a high-speed liquid jet entry in a deep water surface

The fluid dynamic phenomena of a high speed liquid jet impact on a deep water surface have been studied using Imacon high-speed photography. Both framing and streak techniques are applied to investigate the initial impact stage and penetration velocity. The cavitation caused by air entrapment between two colliding liquid surfaces has been found. The bubble collapse experiences different stages in relation to the contact area, liquid shock wave, release wave and fluid convection.

Performance of the star-shaped flyer in the study of brittle materials: Three dimensional computer simulations and experimental observations

A three dimensional finite element computer simulation has been performed to assess the effects of release waves in normal impact soft-recovery experiments when a star-shaped flyer plate is used. Their effects on the monitored velocity-time profiles have been identified and their implications in the interpretation of wave spreading and spall signal events highlighted. The calculation shows that the star-shaped flyer plate indeed minimizes the magnitude of edge effects. The major perturbation to the one-dimensional response within the central region of the target plate results from spherical waves emanating from the corners of the star-shaped plate. Experimental evidence of the development of a damage ring located in coincidence with the eight entrant corners of the flyer plate is reported. Microscopy studies performed in the intact recovered samples revealed that this damage ring eliminates undesired boundary release waves within the central region of the specimen. Consequently, the observed damage in compression and tension within this region can be attributed primarily to the conditions arising from a state of uniaxial strain.

Failure waves in glass under dynamic compression

Abstract Plate impact (I-d strain) and bar impact (I-d stress) experiments were performed on soda lime glass and pyrex glass. Embedded manganin gauges were used to monitor stress-time profiles in both types of experiments. In the plate impact experiments we found that glass not only fails through inelastic (or densification) deformation, but also through a unique failure process which gives rise to a failure wave first observed by Kanel et al. in the Soviet Union in 1990. In the present work three independent observations were made that support the existence of failure wave in glass: (i) the spall strength below and above the HEL is zero behind the failure wave, (ii) a small recompression is present in the longitudinal gauge (embedded between glass and PMMA) profile due to the reflections of release waves from the advancing failure wave, and (iii) transverse stress (measured by transverse gauge) increases on the arrival of the failure wave. The transverse stress increases because the glass loses its shear...