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We have studied the effects of damage caused by compressive loading on the shock sensitivity of the plastic bonded explosive PBX 9501. PBX 9501 consists of 95 wt. % HMX and 5 wt. % nitroplasticized Estane binder. The binder is a mixture of 49 wt. % Estane® 5703 (BF Goodrich), 49 wt. % Nitroplasticizer (a eutectic mixture of bis(2,2‐dinitropropyl)formal and bis(2,2 dinitropropyl)acetal), and 2 wt. % Irganox® 1010 stabilizer. PBX 9501 cubes, 25.4 mm on a side, were compressed to various uniaxial loads in an Instron machine. After loading, 10×10 mm cross‐sections, 3.5 mm thick, were taken from the center of each cube. These slices were then subjected to nearly identical 35 kbar shocks. Transmitted shock wave profiles were measured using interface velocimetry (VISAR). Comparison of shock wave growth is a measure of shock sensitivity. Results on four samples indicate little change in sensitivity caused by compressive loading.

The attenuation of blast waves and fragment velocity caused by an explosion was examined. The blast wave was attenuated by covering an explosive with water based material or sand. The relation between density of the materials for covering the explosive and the attenuation of peak pressure and impulse of the blast wave was studied to reduce the volume and weight of the material. The attenuation effect of the blast wave depended not only on the weight of the barrier materials, but also on the porosity. Reduction of fragment velocity accelerated by a high explosive using a sand or water layer was also evaluated.

The thermal conductivity, diffusivity and heat capacity of the UK PBX EDC37 and its binder system have been measured over a temperature range of ambient to approximately 90 °C. Independent measurements of any two of the above, and knowledge of the density, allows the third to be calculated. Comparisons between the directly measured and calculated values give an indication of the reliability of such data. Thermal conductivity measurements were made using the Lee's disc method, thermal diffusivity via Angstrom's method, and heat capacity via Differential Scanning Calorimetry. Such data are required for the development and validation of PBX thermal models. This paper outlines the current state of research and details the important observations to date.

We assess the accuracy of a recently developed nonlocal density functional in treating van der Waals molecular systems. This new functional contains a non‐empirical treatment of dispersion interactions and exhibits the appropriate behavior in the high‐density limit. We present results for three model noncovalently bonded systems: the methane‐benzene complex, a dimethylnitramine dimer, and a dimer of triaminotrinitrobenzene in its crystalline symmetry. Predicted interaction energies are greatly improved with this new approach as compared to conventional density functionals. Intermolecular distances are also improved, though the degree of improvement varies with the character of the intermolecular interactions, with dispersion dominated systems showing the greatest improvement.

Brillouin scattering is a powerful tool for probing the acoustic properties of materials. Coupled with high pressure environments, such as those accessible using diamond anvil cells, the method can reveal rich materials physics under extreme conditions, in addition to providing fundamental data for the development of equations of state. For the first time, the acoustic properties of two classes of polymers‐rubbery elastomers and semi‐crystalline fluoropolymers‐ have been measured from ambient pressure to ∼12 GPa. From the measured acoustic properties for the elastomers, elastic constants, and moduli were determined as a function of pressure. P‐V isotherms were also constructed, and fit to a range of empirical/semi‐empirical isothermal equation‐of‐state (EOS) forms. From this analysis, the isothermal bulk modulus and its pressure derivative are reported.

Munroe jets are formed by the oblique interaction of detonation products from two explosive charges separated by an air gap. The jet consists of a high velocity jet of low density precursor gases and particles that travel faster than the primary jet which is a high pressure regular reflection. The Los Alamos PHERMEX Data Volumes contain 40 radiographs taken by Douglas Venable in the 1960's of Munroe Jets generated by Composition B explosive charges separated by 5 to 80 mm of air. In several of the experiments the Munroe jets interacted with thin Tantalum foils and with aluminum plates. The PHERMEX experiments were modeled using the AMR Eulerian reactive hydrodynamic code NOBEL. When the detonation arrives at the bottom of the gap, the detonation products expand against the air and precursor gases travel at high velocity ahead of the detonation wave in the explosive. The expanding detonation products from the explosive collide and result in a high pressure shock reflection. Interaction with a metal plate c...

Previously established Ignition and Growth reactive flow models for the detonating triaminotrinitrobenzene (TATB) based plastic bonded explosives LX‐17 and PBX 9502 are applied to recent experimental detonation propagation/failure experiments using unconfined cones, confined arcs, and unconfined arcs. The conical experiments are initially overdriven by the convergent geometry and then fail to detonate at smaller diameters than do unconfined cylindrical charges when the radial rarefaction wave lowers the shock pressure and temperature and thus decreases the chemical energy release rate. Unconfined TATB arcs detonate more slowly than cylindrical charges on the inner surface and exhibit large phase velocities on the outer surface. Confinement reduces but does not eliminate these effects. The Ignition and Growth model calculations based on parameters normalized to a great deal of one‐, two‐ and three‐dimensional detonation propagation data reproduce these features and agree closely with experimental detonation velocity and arrival time data.

An accurate method for controlling strain rates in dynamic compressions studies involves using the non‐linear elastic property of fused silica to transform an initial shock into a ramp wave of known amplitude and duration. Fused silica when placed between a dry Indiana limestone specimen and a projectile produces strain rates in the range of 104/s. Ramp‐loading strain rates are higher than what can be produced on Hopkinson bars and lower than what shock experiments attain. The strength determined at the elastic limit under ramp loading compared to Hopkinson bar measurements shows a significant strength increase with increasing strain rate.

The TRIDENT laser at Los Alamos has been used to drive small plate impact experiments. Flyers are typically 8 mm in diameter and 0.1 to 1.0 mm thick, while the targets are 10 mm in diameters and 0.2 to 2.0 mm thick. One of the sample materials is copper composed of large columnar grains. These samples can reveal information about damage in single crystals and bi‐crystals. This work will focus on simulating these experiments to reveal the stress loading histories. A phenomenological single crystal plasticity model in the FLAG hyrdocode will be used. At the time of first negative pressure, calculated stress and strain concentrations occur at regions of high damage seen by metallurgical examination of a recovered sample. These calculated concentrations help to reveal the driving conditions that cause damage formation.

Our purpose is to provide the explanation of the successive waves which can occur in the general case when a wave propagates through a material with a non‐convex equation of state. We show that decrease of the sound speed introduces isentropic compression waves (ICW) inside shock waves (SW) and rarefaction shocks (RS) inside isentropic release (IR) fans. After basic phenomena explanations, we illustrate them on the example of a virtual material which gathers all these cases. Hydrocode calculations based on this material show the difficulties of high‐order numerical schemes to reproduce the physical features.

A combination of parallel‐plate impact experiments utilizing stress measurements and mesoscale numerical simulations are used to investigate the effect of particle morphology on the mechanical and chemical response of Ni+Al powder mixtures. The instrumented gas‐gun impact experiments were performed at pressures up to 6 GPa. Based on measured shock velocity increases and shock compressibility changes consistent with the Ballotechnic model, the flake‐based powder mixture was found to exhibit shock‐induced reaction. The particle‐level mechanistic details of deformation, mass‐flow, and mixing, were explored through discrete particle continuum simulations, validated against the experimental results. The micron‐scale spherical and flake mixtures were found to display widely varying configurational changes at several length scales, which give insight into why the flake‐Ni morphology is more susceptible to shock‐induced reactions under the imposed conditions.

Hydrocodes are widely used to predict or simulate highly dynamic and transient events such as blast and impact. Codes such as GRIM, CTH or AUTODYN are well developed and involve complex numerical methods and in many cases require a large computing infrastructure. In this paper we present a simple 1‐D Langrangian hydrocode developed at the University of Cambridge, called CAV_KO written in Visual Basic. The motivation being to produce a code which, while being relatively simple, is useful for both experimental planning and teaching. The code has been adapted from the original KO code written in FORTRAN by J. Borg, which, in turn, is based on the algorithm developed by Wilkins [1]. The developed GUI within MS Excel™ and the automatic generation of x‐t diagrams allow CAV_KO to be a useful tool for quick calculations of plate impact events and teaching purposes. The VB code is licensed under the GNU General Public License and a MS Excel™ spreadsheet containing the code can be downloaded from www.shockphysics.com together with a copy of the user guide.

Previous tests carried out in planar recovery capsules showed that strong shock waves (incident pressures 3–7 GPa), generated by a charge of amine‐sensitized nitromethane and attenuated by a PMMA layer, can initiate reactions in non‐porous equimolar mixtures of manganese and sulfur. The current study focused on the onset of these reactions using time‐resolved temperature measurements. A photomultiplier‐based two‐color pyrometer was used to record sample temperatures shortly after the passage of the shock. An experimental complication encountered when studying shock‐induced reactions in porous energetic materials using pyrometry, i.e. intense light due to large localized heating, can be mostly eliminated if a non‐porous sample is studied. Further, in order to increase the reliability of the pyrometry results, the reactive test mixture (Mn‐S) was chosen to have a high heat of reaction (214 kJ/mol) and thus a high reaction temperature, and baseline tests were performed with inert melt‐cast mixtures of WS2 an...

The longitudinal fracture propagation behavior of explosively loaded cylindrical metal shells in self‐organized shear bands mode is discussed. In this mode fractures can propagate longitudinally tens of mm, while recovery observations show that fracture surface consists of a series of elementary shear fracture cells mm length. These evolve from shear instabilities located approximately along given generatrix where a macro facture surface will ultimately be formed and coalesce longitudinally at some stage of their growth breaking through the shell wall radically. It is shown that up‐stream shear initiations forming earlier have a strong influence on the shear instability sites and orientation selection on the neighboring down‐stream section in self‐organized shear mode. Proper simulation of these processes is important for understanding the high strain‐rate fracture.

Lateral stress gauges have been used to measure the variation of shear strength with longitudinal stress in shock loaded Ti‐6Al‐4V. Results show that lateral stress decreases slightly behind the shock front before reaching a constant level. We believe that this is due to the deformation microstructure not reaching its steady state immediately, but rather evolving over time. We have also observed that the Hugoniot and shear strength of our material is in close agreement to previous work. Recovered Taylor impact specimens show a circular foot print, and x‐ray tomography examination shows no evidence of tensile damage immediately under the impact face.

We report herein a series of ab initio simulations of water under both static and shocked conditions. We have calculated the coherent x-ray scattering intensity of several phases of water under high pressure, using ab initio Density Functional Theory (DFT). We provide new atomic scattering form factors for water at extreme conditions, which take into account frequently neglected changes in ionic charge and electron delocalization. We have also simulated liquid water undergoing shock loading of velocities from 5-11 km/s using the Multi-Scale Shock Technique (MSST). We show that Density Functional Theory (DFT) molecular dynamics results compare extremely well to experiments on the water shock Hugoniot.

Specimens consisting of either spherical or flake aluminum particles saturated with liquid heptane were subjected to reflected shock pressures on the order of 20–30 GPa. Postmortem analysis of the spherical powder shows that while average size does not significantly change, surface morphology is no longer spherical but sharp edged with evidence of shear and particle break‐up. A similar analysis for flakes shows break down to finer particles one order less than the original flake size. This suggests that the oxide layer was damaged and that bare aluminum was exposed, thus increasing aluminum particle sensitivity to reaction.

There is a recent interest in the response of thermoplastics to shock. Previous work on three simple hydrocarbons has indicated that the shear strength increases with the complexity of the side group. Strength values have been calculated using lateral stress measurements with manganin gauges that have been recalibrated for use in the low stress regime. The present work aims to investigate the effect of the configuration of the thermoplastic's chain when side groups are added. Results show that whilst polyethylene has the lowest shear strength, polypropylene and polystyrene have similar values. In all cases the strength of polymer increases with time after the shock has past. As the applied stress increases, polystrene and polypropylene strengthen to a higher degree when compared with polyethylene. Explanations are offered in terms of microstructure and tacticity of the chain.

A series of plate impact experiments were performed using the single stage light gas gun facility at the Cavendish Laboratory, Cambridge University to investigate the shear strengths of a hypabyssal kimberlite, a siltstone and a sandstone. The siltstone and the kimberlite show a linear dependence longitudinally in σ‐up space up to pressures in excess of 10 GPa [l]. The lateral stress data, as measured using manganin gauges, shows Hugoniot elastic limits of 2.2±0.1 GPa for kimberlite and 4.8±0.2 GPa for siltstone. The sandstone does not appear to behave elastically at any point in the experimentally determined Hugoniot, which is expected due to its high porosity. This is reinforced by a lack of measurable elastic behavior in the lateral stress data, and no obvious HEL

The dynamic response of strong polycrystalline ceramics is relatively well documented with high Hugoniot elastic limits (HEL) and very low spall strengths. In contrast, the response of single crystal ceramics is less researched and some of the findings are controversial. In the work presented here we were interested in the extremely high HEL which was reported recently for gallium gadolinium garnet (GGG) as well as in strength of sapphire and magnesium aluminate spinel, on which there are very few reports. The measurements were made with manganin gauges embedded at the back of the specimens, with a thick Plexiglas backing for the gauge. These measured stress‐time histories are very simple to interpret and accurate values for the HEL and spall strength of these materials can be easily extracted. Some of our results (e.g. the HEL of GGG) are quite different than those published by other workers.

This study uses the pressure‐shear plate impact configuration to investigate the rate‐controlling mechanisms of the plastic response of metals at strain rates on the order of 106 s−1 and at temperatures that approach melt. In similar experiments by Frutschy and Clifton [1] on OFHC copper, the flow stress decreases with increasing temperature and increases with increasing strain rate over the full range of temperatures and strain rates examined. No conclusive evidence of a change in rate‐controlling mechanism was obtained. In the current study, temperatures that are larger fractions of the melting temperature are accessible because of the lower melting point of aluminum. So far, the shearing resistance has been measured at temperatures up to 630 °C, which is 81% of the melting temperature at the concurrent pressure. Several approaches are being explored to obtain even higher fractions of the melting temperature, possibly exceeding it.

A Critical Damage Evolution (CDE) model for describing the strength softening process in the dynamic tensile spall has been suggested via a percolation hypothesis. Two physical parameters, named as the critical voids linking damage D1 and the critical fracturing damage Df, are proposed. D1 indicates the critical value of damage for the onset of void coalescence, and Df the critical value for the occurrence of catastrophic fracture. With the measurements of the free‐surface velocity profiles of 20♯ steel from planar impact experiments, we demonstrate that these two critical damage parameters are independent of the impact stress and the tensile strain rate, and they are also applicable to describe the dynamic tensile fracture behavior in imploding metallic cylindrical shell experiments. Therefore, we propose that these two parameters may be regarded as the material constants to identify the intrinsic characteristic of the dynamic tensile fracture in explosion and shock wave events.

Temporal softening that is associated with the passage of a shock wave is investigated along with its effect upon material strength and issues of macroscopic scaling. Specimens are loaded in such a way that a moderate tensile pulse is applied during the temporal window of softening. It is found that strength is reduced as a consequence of temporal softening. It appears that temporal softening contributes to a reversal of typically observed macroscopic scaling effects.

Los Alamos National Lab (LANL) is actively engaged in the development of a model to predict the formation of micron‐scale fragments ejected (ejecta) from shocked metals that have surface defects. The LANL ejecta model considers that the amount of ejecta is mainly related to the material's phase on shock release at the free‐surface. This effort investigates the relation between ejecta production and shock‐breakout pressure for Sn shocked with high explosives to pressures near the solid‐on‐release/partial‐liquid‐on‐release phase transition region. We found that the amount of ejecta produced for shock‐breakout pressures that resulted in partial‐liquid‐on‐release increased significantly compared to that which resulted in solid‐on‐release. Additionally, we found that the amount of ejecta remained relatively constant within the partial‐liquid‐on‐release, regardless of shock‐breakout pressure.

The current waveform of Ferroelectric ceramics PZT 95/5 depoling under tilted shock wave compression has been studied. An analytic model was established to analyze the effects of incident angle on the rising time, duration and peak amplitude of the depoling current. Experiments were conducted as well to confirm these effects. Results indicated that with the increasing of incident angle, the depoling current rises more slowly, the pulse duration becomes broader and the peak amplitude remains constant until the waveform decays into a triangular form.

Thresholds for shock sensitivity were determined for explosive samples with and without applied fields using a variation of the Navy's modified gap test. Rectangular charges (76 mm wide×12.7 mm long×6 mm thick) confined on two sides by 50.8 mm thick bars of Teflon were shock loaded using the Navy's standard large scale gap test donor system. Particle blow‐off velocity at the opposite end of the sample (12.7 mm from input surface) was measured using a high‐speed camera. Velocity versus input pressure plots highlight thresholds for first reaction, deflagration, and detonation. In addition the use of an intensified high‐speed electronic camera provided a clear differentiation of when the products were self‐luminous, directly confirming initiation. Electric fields were applied transverse to the shock direction via thin foil electrodes. These electrodes were held in place by the Teflon insulation. The data show that higher levels of reaction were obtained in this explosive with less input stress when voltages ...

Accurate predictions of non‐eroding penetration are becoming a problem of increasing technological importance. Sandia's Zapotec (a coupling of Pronto3D and CTH) has been the code of choice for design purposes, but there have been some concerns expressed about relying on a single code methodology. Consequently, LLNL's ALE3D (which uses a slide line based approach) is currently being investigated for applicability. As a benchmark, we choose to model the penetration experiments of steel projectiles against aluminum targets to examine the differences between the two methodologies.

Phase transformations of graphite with various densities and microstructure at shock‐wave loading in steel targets with conic cavities were studied. Graphites GMZ (ρ = 1.70 g/cc), MPG‐7 (ρ = 1.91 g/cc) and MF‐307 (ρ = 2.01 = g/cc) were used in the experiments. The recovered specimens were studied by means X‐ray phase analysis. The maximum degree of graphite‐diamond transformation was estimated. Experimental data were compared to results of 2D numerical calculations. We have found that transition onset pressure and speed of phase transformation decrease with increasing graphite crystallinity.

Complementary gas‐gun and electromagnetic pulse tests conducted in Sandia's Dynamic Integrated Compression Experimental (DICE) Facility have, respectively, probed the behavior of electronic‐grade Kovar® samples under controlled impact and intermediate‐strain‐rate ICE (Isentropic Compression Experiment) loading. In all experiments, velocity interferometer (VISAR) diagnostics provided time‐resolved measurements of sample response for conditions involving one‐dimensional (i.e., uniaxial strain) compression and release. Wave‐profile data from the gas‐gun impact experiments have been analyzed to assess the Hugoniot Elastic Limit (HEL), Hugoniot equation of state, spall strength, and high‐pressure yield strength of shocked Kovar®. The ICE wave‐profile data have been interpreted to determine the locus of isentropic stress‐strain states generated in Kovar® for deformation rates substantially lower than those associated with a shock process. The impact and ICE results have been compared to examine the influence of loading rate on high‐pressure yield strength.

Although reaction can be initiated by shockwaves in titanium and silicon powder mixtures, self‐sustained reactive waves have mainly been observed in a deflagration mode propagating on the order of a few centimeters per second. In the present work, the possibility of faster combustion modes is investigated by observing the propagation of reactive waves in cylindrical charges up to fifteen diameters long. Fine powders below 45 μm in size are mixed and packed into cylindrical containers made of various materials thus providing varying degrees of confinement. The mixture porosity was varied between 47% and 65%. After initiation by a high explosive booster charge, reactive waves were observed using optical and piezoelectric time‐of‐arrival gauges. Rapid reactive waves were observed to propagate at about 2 km/s, then die out after a distance of about two charge diameters. The extended length of propagation of these waves points to a contribution of chemical energy from the powder reaction.

Gruneisen equation of state for condensed media in terms of pressure, volume and internal energy is suitable for description of high‐pressure flow problems in condensed media including shock waves. It is shown that thermodynamically formulated Gruneisen equation of state can be regarded as a differential equation for internal energy along an isentrope. The differential equation has a formal but general solution for internal energy as a sum of cold part and thermal part. In this solution, cold internal energy is given by a special solution of the differential equation, while thermal part is a general solution represented as a product of a function of volume and that of entropy. The volume function, Θ(v), can be regarded as a characteristic temperature, whereas the entropy function C(S) is proved to be a conjugate variable of the volume function. The above formulation is possible under the assumption that the Gruneisen parameter is a function only of volume. It is shown that TdS can be replaced by Θ(v)dC(S)...

Failure front (FF) and penetration velocity have been measured for long gold rods impacting and penetrating borosilicate (BS) glass. Data are obtained by visualizing simultaneously FF propagation with a high speed camera and rod penetration with flash X‐rays. Results for BS glass are qualitatively similar to those of DEDF (PbO) glass. FF velocity rapidly decreases from an initial value to a lower, approximately constant value. FF velocity increases with impact velocity, vp. The FF velocity remains significantly lower than the shear velocity, even at the highest impact velocity tested, about 2.5 km/s. The ratio of the FF velocity to the rod penetration velocity, vF/u, decreases with increasing vp and appears to be approaching vF/u = 1 asymptotically, as observed previously for DEDF glass. The separation of the FF and the tip of the rod decreases with increasing impact velocity. Importantly, since vF/u⩾1, the gold rod is always penetrating glass behind the FF.

The velocity history of a shocked free surface has traditionally been measured using established techniques such as VISAR or Fabry‐Perot. In recent years a third type of velocimetry has been developed by LLNL which uses Heterodyne techniques, Photon Doppler Velocimetry (PDV). This technique generates a Doppler beat frequency between light incident on the surface and light internally reflected within the system. Unlike the other two techniques PDV does not use an interferometer, instead it relies upon having the ability to directly record the high beat frequency. The setting up and fielding of PDV is therefore much simpler. A low power (Class 1 laser) system using this principal, locally known as Heterodyne Velocimetry (HetV) has been developed and assembled. A series of experiments has been carried out to investigate the Hugoniot of polyethylene using HetV and embedded stress gauges. The results obtained with HetV have been directly compared with the embedded gauge data from the same experiment.

TNT and TNT‐aluminum composites were experimentally studied in an air‐filled 26 m3 chamber for charge masses ranging from 1.1 to 4 kg. Large aluminum mass fractions (35 to 50%wt.) and particle sizes (36 μm) were combined with TNT in two configurations, whereby the aluminum particles were uniformly mixed in cast TNT or arranged into a shell surrounding a cast TNT cylinder. The results show that improved performance is achieved for the shell configuration versus the mixed version during the early afterburning phase (10–40 ms), while both approach the same quasi‐static explosion overpressure (QSP) after a long duration. The QSP ratios with respect to TNT in nitrogen are in good agreement with equilibrium predictions. Thus, the large aluminum mass fraction improves spatial mixing of hot fuels with oxidizing gases in the detonation products and chamber air, resulting in more efficient afterburning energy release.

Concrete cylinders (170 mm×100 mm diameter) were impacted with half‐inch steel spheres over a range of velocities (100–500 m s−1). Crater growth and debris cloud evolution were observed using high speed cameras aligned perpendicular and parallel to the impact direction. In‐plane displacements of the impact face were tracked using Digital Speckle Photography (DSP). Radial cracking was seen to precede circumferential cracking on the high speed sequences and DSP showed bulk motion of fragments surrounding the impact zone. The profile images revealed no significant out‐of‐plane perturbations, and ejecta speed is seen to increase with impact speed. Final dimensions of craters were also seen to increase with increasing impact velocity.

Plastic Bonded Explosive (PBX) formulations incorporating oxide‐free aluminum nanoparticles passivated with a perfluorinated carboxylic acid (C14/nanoAl) were evaluated for performance using Small‐Scale Shock Reactivity and Internal Blast Tests (SSRT and SSBT) to determine the contribution of the C14/nanoAl in the early and later stages respectively of the reaction. These results show that the volume of the dent of samples containing C14/nanoAl is twice as great as the dent volume of standard formulations, suggesting faster aluminum combustion than conventional Al formulations.

An experimental technique in which an explosive charge induces sliding between two metals has been developed as part of a study of dry friction at very high sliding velocities and pressures. Aluminium alloy/stainless steel and pure aluminium/pure copper tribo‐pairs have been investigated. Optical studies of cross‐sections of the aluminium samples have shown that, depending on the stress/sliding velocity conditions, the sub‐surface deformation is either deep, suggesting high friction, or concentrated near the surface suggesting low friction. Recent further studies of the microstructures near the surface of the samples are described. Transmission electron microscopy reveals that a clearly delineated layer of nanocrystalline material ∼1 μm thick is created at the surface of the aluminium samples. Spectroscopic analysis shows evidence of inter‐penetration of the two materials with mixing occurring at a very fine scale. The observations support the contention that, in a mechanism akin to adiabatic shear, therm...

Constitutive models for brittle materials such as glass can be very complex as they are dependent on strains, strain rates, pressures, temperatures, damage and other parameters. There may also be significant (pressure‐dependent) strength after failure such that the constitutive response is much different for intact material and failed material. A large number of laboratory tests is required to develop a comprehensive constitutive model. Another approach is to develop simple models by using penetration‐velocity data obtained from ballistic experiments. Here various functional forms of simple models (with a limited number of constants) can be used to (computationally) match the penetration velocity over a range of impact velocities. This allows for the determination of the most important parameters and it provides an approximation of the stresses that occur during penetration. This article presents several simple computational models for borosilicate glass, including single‐state models and dual‐state models (that include an intact strength and a failed strength).

We report on large-scale non-equilibrium atomistic simulations of shock-induced transformations in poly crystalline iron samples. These simulations show that, depending on the crystallographic orientation of the body-centered-cubic (bcc) parent phase grains with respect to the shock direction, a significant fraction of the product phase can be face-centered-cubic (fcc) instead of the expected hexagonal-close-packed (hcp) structure. This observation is explained by the existence of different transformation mechanisms for shocks along different crystallographic directions. We conclude that the observation of different product phases can be explained by simple geometric considerations of the involved transformation mechanisms between the parent bcc structure and the product hcp and fcc structures. Ultrafast high-energy laser-based experiments are underway to further investigate this subject. © 2007 American Institute of Physics.

A technique has been developed to measure the time‐resolved position of a laser‐driven shock wave and the subsequent material flow. Ultrafast dynamic ellipsometry, using a chirped femtosecond laser pulse, probes picosecond material dynamics in a single shot by capitalizing on the refractive index changes in the shocked material. For transparent materials, the shock velocity, the particle velocity, and the shocked material's refractive index are extracted. Hugoniot data for poly(chlorotrifluoroethylene‐co‐vinylidene fluoride) (Kel‐F 800) was obtained using ultrafast dynamic ellipsometry, and the data agrees well with previous data on macroscopic samples obtained in plate impact gas gun experiments.

This paper examines phase transitions in cerium during shock compression using PVDF gauges. A two‐wave structure was observed with loading pressures of 4 GPa⩽P

Hugoniot of C60 fullerite and sound velocity in shock‐compressed fullerite were experimentally studied at the pressure range up to P∼60 GPa. The results of the shock‐wave measurements were used for the semi‐empirical description of thermodynamic properties of simple cubic phase of C60 fullerite.

In the framework of density functional theory, static properties and phonon spectra of beryllium have been calculated under high compression (for pressures up to 4 Mbar) for two solid phases: hexagonal compact (hcp) and body‐centered cubic (bcc). The melting curve and some isotherms in the liquid phase have been calculated using quantum molecular dynamics. The coupling of these theoretical data to a quasi‐harmonic approach (phonon moments) allows us to suggest a new theoretical phase diagram and to build a multiphase equation of state (EOS) valid in a large range of pressure and temperature. The resulting Hugoniot curves as well as the evolution of the longitudinal sound speed with both pressure and temperature are in good agreement with available experimental data.

CREST is a new reactive burn model that uses entropy‐dependent reaction rates to model shock initiation and detonation behaviour in plastic bonded explosives. To date the model has been successfully applied to a wide range of one‐dimensional shock initiation data obtained from explosive gas‐gun experiments. In this paper, to provide a more rigorous test of CREST's predictive capability, the model is applied to two‐dimensional explosive detonation propagation experiments. The calculated results show that the CREST reaction rate model, fitted only to one‐dimensional data of the shock to detonation transition, can accurately simulate two‐dimensional explosive data from detonation experiments. This gives confidence in the ability of the model to accurately predict a wide range of shock initiation and detonation phenomena.

This paper considers a multi‐phase equation of state for bismuth. At a phase transition there are changes in volume, energy, and properties of a material that should be included in an accurate model. Modifications are made to a previously published EoS[1] with the aim of extending the pressure and temperature range of the EoS and producing a reasonable estimate of shock melt. This new EoS contains five solid phases and a liquid phase. Comparisons are shown between experimental data and the modified and unmodified EoS.

When a shock‐loaded target is melted on compression or on release, the tensile stresses generated upon reflection of the pressure pulse from a free surface are induced in a liquid state. Instead of the well‐known spallation process occurring in solid targets, cavitation takes place in the melted material and liquid fragments are ejected from the free surface. Although increasing interest is manifested on the subject, related data are still scarce. In a recent paper, we have reported an exploratory investigation of liquid spall in tin targets submitted to intense laser shocks. Here, we present new results obtained over a lower pressure range, where we focus on the progressive transition from the ductile fracture behaviour of solid tin to the cavitation expected above melting. Both time‐resolved free surface velocity measurements and post‐test examination of the recovered samples clearly indicate this transition. Incipient melting produces a decrease in tensile strength that can be evaluated from the veloci...

Several experiments will be presented that are part of a phased plan to understand the evolution of detonation in a detonator from initiation shock through run to detonation, to full detonation, to transition, to booster and booster detonation. High‐speed multiframe schlieren imagery has been used to study several explosive initiation events, such as exploding bridgewires (EBWs), exploding foil initiators (EFIs or “slappers”), direct optical initiation (DOI), and electrostatic discharge. Additionally, a series of tests has been performed on “cut‐back” detonators with varying initial pressing heights. We have also used this diagnostic to visualize a range of EBW, EFI, and DOI full‐up detonators. Future applications to other explosive events, such as boosters and insensitive high explosives booster evaluation, will be discussed. The EPIC finite element code has been used to analyze the shock fronts from the schlieren images to solve iteratively for consistent boundary or initial conditions to determine the temporal‐spatial pressure profile across the output face of the detonator.

Proton radiography (pRad) is a powerful new diagnostic with the potential of producing accurate (1%) direct density measurements from dynamically loaded materials. Experiments have been performed to investigate the feasibility of using proton radiography (pRad) to obtain dynamic radiographs of shock‐compressed materials during plate impact experiments. This work has involved the design, construction, and testing of a new 40 mm single‐stage, powder driven gun, the development of methods to synchronize the shock event generated with the gun to proton output, and initial proof‐of‐principle experiments in Area C at LANSCE. To date, four symmetric impact experiments on aluminum and copper have been performed with successful synchronization. The method used to attain synchronization of the shock event to proton beam output will be discussed and the results of our initial experiments will be presented.

CREST is a new reactive‐burn model for explosives that is able to reproduce a range of shock initiation behaviour in coventional plastic bonded explosives. This is accomplished by using entropy rather than pressure‐dependent reaction rates. In this paper, a CREST model for the insensitive high explosive PBX9502 is tested against a wide range of one‐dimensional experimental data.

Operation of a two‐stage implosion‐driven hypervelocity launcher in which the launch tube is imploded behind the projectile is examined. In particular, techniques to generate a high phase velocity of implosion are explored, and the technique of using a variable thickness flyer plate with a constant thickness layer of explosive is selected for further investigation. An analytic model, based on the Gurney analysis for flyer plate acceleration, is developed to determine the thickness profile necessary to deliver the desired phase velocity. Finite element simulations and experimental implementation of this approach results in the correct increase in phase velocity along the launch tube, however, the velocity profile does not generate the desired constant acceleration profile.