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Dynamic damage evolution in materials is of growing interest, in particular, the role of defect structure on material strength during a dynamic experiment. Many studies in the past have seen strong correlations between the shockwave profile and the defect structure during dynamic experiments, such as quasi‐elastic release behavior. Bauschinger effect is a microstructurally controlled process in which a material displays a change in stress‐strain characterisitics due to a change in the defect structure. Studies on depleted uranium have revealed indications of Bauschinger effect being a mechanism present during quasi‐static experiments, which could be a result of the large amount of twinning observed in these materials. As work continues to improve strength models, it becomes imperitive to understand the role of defect structure on the properties of materials under dynamic conditions. The study reported here is an observation of the release wave behavior in depleted uranium that first undergoes compressive shock loading followed by a reversal of the loading direction upon release.

We present the possibility of using femtosecond laser‐generated shock waves to effect a new kind of material transformation, a coherent dissociation of a material into two slabs. Coherent dissociation is fundamentally different from fracture. Every atom at the interface would react synchronously, which would greatly enhance our ability to understand fundamental mechanisms and to identify and characterize transition states.

The Deep Impact active space experiment has been done to study a hypervelocity collision of a metal impactor with the nucleus of the comet 9P/Temple 1. In this work we present results of numerical modeling in comparison with corresponding experimental data. The modeling has been done with the use of 3D “finite‐size particle in cell” method. The computational setup corresponded to impact angle of 30 degree with respect to the horizon for different materials forming the surface of the comet nuclei, i.e. ice and sand. Conclusions are made for the possible composition of the comet.

Combined shock and shear loading of explosives has been shown to result in detonation of explosives at input pressures less than those required with a nearly planar shock. In this study, the effect of combined shock and shear loading on PBXN‐110 is investigated. The explosive sample is loaded by a TNT/Octol plane wave lens or a Pentolite pad in contact with a layer of PMMA followed by a cylindrical wave shaper that has one side angled at 45 degrees. The experiment is repeated for different thicknesses of the PMMA layer in order to vary the input pressure. In addition, the experiment is modeled using the Lagrangian finite element hydrocode EPIC, and the results of the experiments are compared with the numerical simulations.

A new, tabular, SESAME equation of state, along with new diamond‐anvil, Hugoniot, and thermal‐expansion data, is presented for Ti‐Beta‐21S (TIMETAL® 21S), a high‐strength, high‐temperature, beta‐stabilized alloy of Ti, Mo, Nb, Al and Si. The new equation of state combines an empirical, Vinet description of the cold curve with the Johnson ionic model and the Thomas‐Fermi‐Dirac model for the thermal electronic contributions. Two coexisting phases, HCP (α) and BCC (β), are observed at room temperature and pressure, with the α phase disappearing above 67 GPa. Predictions for the room‐temperature isotherm, principal Hugoniot, thermal expansion, and heat capacity are compared to new and existing experimental results.

The Isentropic Compression Experiment (ICE) technique has proven to be a valuable complement to the well‐established method of shock compression of condensed matter. However, whereas the high‐pressure compression response of interferometer window materials has been studied extensively under shock loading, similar knowledge of these materials under quasi‐isentropic loading is limited. We present recent experimental results on the quasi‐isentropic compression of the high‐pressure window LiF on the Veloce pulsed power generator. While it is a frequently used window material in quasi‐isentropic loading and unloading experiments, the unloading response of LiF is usually neglected. It will be shown how the strength of LiF may influence the wave profile analysis and thus the inferred compressive strength of the material being studied.

The shock Hugoniot of polymers is known to exhibit a non‐linear US‐UP relationship at relatively low pressures and commonly displays a concave curvature with an initially rapid shock velocity. However, the experimentally measured shock Hugoniot of particle reinforced composites shows an opposite effect displaying a convex curvature with an initially rapid change in particle velocity. Transformation to pressure‐volume space shows an initial expansion that is not related to a low‐pressure phase change or reaction. In contrast, the volume expansion is connected to decohesion of solid particles from the polymer matrix. Equation of state experiments conducted for epoxy‐cast Al+Fe2O3 composites show deviation from ideal Hugoniot behavior as a result of damage evolving at a critical impact stress. Two compositions prepared with significantly different volume fractions of the binder phase show damage occurring at approximately the same critical impact stress. The Burch‐Murnaghan equation of state (BM‐EOS) is used to characterize the composite's compressibility and identify the magnitude of the critical damage stress.The shock Hugoniot of polymers is known to exhibit a non‐linear US‐UP relationship at relatively low pressures and commonly displays a concave curvature with an initially rapid shock velocity. However, the experimentally measured shock Hugoniot of particle reinforced composites shows an opposite effect displaying a convex curvature with an initially rapid change in particle velocity. Transformation to pressure‐volume space shows an initial expansion that is not related to a low‐pressure phase change or reaction. In contrast, the volume expansion is connected to decohesion of solid particles from the polymer matrix. Equation of state experiments conducted for epoxy‐cast Al+Fe2O3 composites show deviation from ideal Hugoniot behavior as a result of damage evolving at a critical impact stress. Two compositions prepared with significantly different volume fractions of the binder phase show damage occurring at approximately the same critical impact stress. The Burch‐Murnaghan equation of state (BM‐EOS) is used...

Small lead zirconate titanate (PZT) discs within commercial piezoelectric probes were impacted by low density foams in a set of gas gun experiments. For each probe the voltage across a 50 Ω load was measured to determine the change in the electrical charge on the piezoelectric disc. Four different foams having densities between 0.1 and 0.35 g/cm3 were driven at velocities up to 1.0 km/s. Impact with the piezoelectric probes was calculated to generate stresses in the range 0.07 to 0.3 GPa. Hydrocode simulations were run to predict the stress history within the piezoelectric element and to interpret the shape of the measured voltage pulse. From the experimental results the piezoelectric charge coefficient d33 was deduced to be around three times the low stress d33 value available for the piezoelectric material. Results for an impact stress of 0.1 GPa followed by pressure release indicate that a large proportion of the initial polarization was recovered on release.

Highly porous samples of tantalum pentoxide (Ta2O5) aerogel were compressed from initial densities of 0.1, 0.15, and 0.25 g/cm3 by shock waves with strengths between 0.3 and 3 Mbar. The compressed material was between 5 and 15 times as dense as the unshocked aerogels with temperatures of ∼5 eV (∼58,000 K). These strong shock loadings were produced by the OMEGA Laser System at the Laboratory of Laser Energetics. The shocked states were diagnosed with the OMEGA velocity interferometer system for any reflector. When the compression measurements are compared to an available high‐energy‐density equation‐of‐state model, it is found that the model underestimates the level of compression achieved by shock loading below a Mbar.

Aluminum oxynitride (AlON) is a polycrystalline transparent ceramic. It is an attractive material as a high strength window material. In this work we analyze the results of four sets of plane shock wave experiments reported to determine the shear strength of AlON. Our analysis indicates that the compression of AlON appears to undergo a shift around 16–20 GPa becoming relatively more compressible. However, AlON continues to retain shear strength at higher stresses. The reason for the observed shift remains to be understood and explained satisfactorily.

3D molecular dynamics calculations of plasticity and fracture in nanocrystalline copper under high strain rate are carried out. Grain boundary sliding and dislocation motion are observed. Flow stress dependence on grain size is obtained. Three general properties of spall process are considered: existence of sites of stress concentration, two step process of microcrack formation and stochastic character of microcrack formation. Spall strength dependences on grain size and strain rate are obtained.

The propagation of detonation in shock‐compressed nitromethane was observed with a high‐speed framing camera. The test explosive, nitromethane, was compressed by a reverberating shock wave to pressures as high as 10 GPa prior to being detonated by a secondary detonation event. The pressure and density in the test explosive prior to detonation were determined using two methods: manganin stress gauge measurements and LS‐DYNA simulations. The velocity of the detonation front was determined from consecutive frames and correlated to the density of the reverberating shock‐compressed explosive prior to detonation. Observing detonation propagation under these non‐ambient conditions provides data which can be useful in the validation of equation of state models.

Through the measurement of Hugoniot parameters, we can get useful information about high‐pressure phase transitions, equations of state (EOS), etc. of solids, without pressure calibration. We have performed the Hugoniot measurement experiments on various kinds of hard materials including chalcogenides, oxides, nitrides, and borides by using a high time‐resolution streak photographic system (inclined‐mirror method). It was found that almost all brittle materials behave as an elasto‐isotropic solid which loses shear strength much above the HEL, unlike metals (elasto‐plastic solid), except TiB2. The phase transitions have been observed for ZnS, ZnSe, TiO2, ZrO2, Gd3Ga5O12, AlN, B4C, etc. Some oxide materials showed virtually incompressible EOS's in the high‐pressure phase region. Here, the Hugoniot compression data are reviewed, and the yield property and phase transitions of these hard materials are discussed, as well as the EOS of the high‐pressure phase.

In reactive flow calculations of detonation in a rod, an unreacted or slow reacting layer is formed at the boundary, affecting the diameter effect outcome. We investigate the origin of this boundary layer, and propose a simple and practical way to eliminate it. We show that it is an artifact of the finite rise time of the shock, caused by artificial viscosity. When the shock reaches a boundary cell, it is released right away, so that pressure and temperature there only reach a fraction of their shock levels, and the reaction rate is slow. We propose to remedy this artifact by delaying the boundary motion for a short while (about 40 ns for a 10 cells per mm mesh) after arrival of the shock. In this way boundary cells can reach the appropriate pressure and temperature and react at the appropriate rate. In the paper we show how this remedy works. We compute detonation in a rod with different values of the boundary motion delay, compare the breakout curve from the far end with data from the literature, and obtain good agreement. This finite rise time effect near a low impedance boundary plays a role also in calculations of corner turning situations. But there the detonation borders with a dead zone, and the boundary contour is not known in advance.

Equimolar mixtures of manganese powder and sulfur were melt‐cast into solid pellets in order to study the mechanism of shock‐enhanced reactivity in non‐porous heterogeneous mixtures. This mixture was selected due to the large exothermic heat release of the manganese‐sulfur reaction (214 kJ/mol), which causes the reaction to be self‐sustaining once initiated. The test samples were placed in planar recovery ampoules and a strong shock was delivered via the detonation of a charge of amine‐sensitized nitromethane. Various shock strengths were achieved by placing different thicknesses of PMMA attenuator discs between the explosive charge and the ampoule. The results confirmed that shock‐induced reactions can be produced in highly non‐porous mixtures. Indeed, the critical shock pressure that caused ignition of the mixture in the ampoule was found to be in the range 2.2–3.0 GPa (pressures were estimated using LS‐DYNA simulations of samples with 100% TMD).

At Sandia National Laboratories, we have coined the term “microenergetics” to describe sub‐millimeter energetic material studies aimed at gaining knowledge of combustion and detonation behavior at the mesoscale. Our approach is to apply technologies developed by the microelectronics industry to fabricate test samples with well‐defined geometries. Substrates have been fabricated from materials such as silicon and ceramics, with channels to contain the energetic material. Energetic materials have been loaded into the channels, either as powders, femtosecond laser‐micromachined pellets, or as vapor‐deposited films. Ignition of the samples has been achieved by simple hotwires, integrated semiconductor bridges, and also by lasers. Additionally, grain‐scale patterning has been performed on explosive films using both oxygen plasma etching and femtosecond laser micromachining. We have demonstrated simple work functions in microenergetic devices, such as piston motion, which is also a relevant diagnostic to examine combustion properties. Detonation has been achieved in deposited explosive films, recorded by high‐speed photography.

In the past few years, a series of papers has examined the shock response of common engineering polymers in terms of their microstructure. In this latest work, the behaviours of two polymers, polyethylene and polyoxymethylene, are investigated under conditions of one‐dimensional strain. The study focuses on the experimentally determined lateral component of stress and, from knowledge of the impact conditions, the shear strength. Variations with impact stress amplitude and pulse duration are discussed in terms of the polymer chain structure.

To gain insight into the high pressure response of energetic crystal of RDX, Raman measurements were performed under hydrostatic compression up to 15 GPa. Several distinct changes in the spectra were found at 4.0±0.3 GPa, confirming the α‐γ phase transition previously observed in polycrystalline samples. Symmetry correlation analyses indicate that the γ‐polymorph may assume a space group isomorphous with a point group D2h with eight molecules occupying the C1 symmetry sites, similar to the α‐phase. It is proposed that factor group coupling can account for the observed increase in the number of modes in the γ‐phase.

Using Raman spectroscopy, a novel submicron‐sized HMX (sm‐HMX) was determined to be both the gamma polymorph and stable with respect to conversion to beta‐HMX under ambient conditions for at least a year. Pressing of sm‐HMX powder in a small diameter pellet press at pressures from 10,000 psi to 31,000 psi and 1 to 5 minute hold times was found to promote the gamma to beta polymorphic phase transition. The fraction converted and rate of conversion versus time after pellet removal from the press, measured using Raman spectroscopy, fit a sigmoidal curve, indicating nucleation and growth as a possible polymorphic transition mechanism.

This paper presents results on the dynamics of damage in copper under incipient spall conditions for multicrystalline specimens. Specimens were annealed from polycrystalline material to reduce the number of grain boundaries the shock wave traverses in passing through the specimen. The specimens incorporated unique fiducials that permit accurate correlation of pre‐shot characterization of the grain orientations, grain size etc. with the location of the dynamic diagnostics and with post‐shot metallography. The dynamic diagnostics—Transient Imaging Displacement Interferometry (TIDI), point VISAR, line VISAR—were all precisely aligned on the specimen surface to view regions of interest revealed in the pre‐shot characterization. Initial analyses demonstrate the wealth of information obtained from this experimental approach. Examples include observation that regions in the surface microstructure most likely to be damaged based on pre‐shot characterization show some of the largest displacements during the shock‐...

In this work, we present evidence for how strong radial confinement can result in aligned macro‐scale crack opening. We damage cylinders in a tight‐fitting quartz sleeve, open on both ends, and observe the occurrence of aligned cracks opening normal to the longitudinal axis. This geometry and confinement is common in experimental arrangements such as strand burners and DDT tubes. Further, we observe, with high‐speed photography, how this non‐random crack opening affects combustion, and propose mechanisms, garnered from time‐lapse photography and elastic stress analysis, for how it occurs.

Shock states are generally obtained from shock velocity (D) and material velocity (u) measurements. In this paper, we propose a hydrodynamical method for estimating the (D‐u) relation of Nitromethane from easily measured properties of the initial state. The method is based upon the differentiation of the Rankine‐Hugoniot jump relations with the initial temperature considered as a variable and under the constraint of a unique nondimensional shock‐Hugoniot. We then obtain an ordinary differential equation for the shock velocity D in the variable u. Upon integration, this method predicts the shock Hugoniot of liquid Nitromethane with a 5% accuracy for initial temperatures ranging from 250 K to 360 K.

Work with conventional high explosives shows that the initiation thresholds for a variety of projectile types can be mapped onto a single curve. This curve is distinct from, although parallel to, the Pop Plot curve. In contrast for an insensitive high explosive, the location of the initiation thresholds appear divided between those forming a distinct threshold curve and those that appear to be a continuation of the Pop Plot. Projectile diameters larger than the failure diameter still form a distinct threshold, but smaller projectile diameters lie on the Pop Plot curve. Impacts lying on the threshold curve produce non‐divergent detonations which in many cases appear likely to remain non‐divergent or even fade. Those initial conditions that lie on the Pop Plot only need sufficient run distance in the explosive before a diverging detonation is achieved.

We report the first experimental observation of highly nonlinear signals propagating in a two dimensional system composed of granular chains. In this system one of the chains contacts two others to allow splitting and redirecting the solitary-like signal formed in the first chain. The system consists of a double Y-shaped guide in which high- and low-modulus chains of spheres are arranged in various geometries. We observed fast splitting of the initial pulse, rapid chaotization of the signal and sharp bending of the propagating acoustic information. Pulse and energy trapping was also observed in composite systems assembled from hard- and soft-particles in the branches.

The failure thickness of neat nitromethane in aluminum confinement was measured using a novel experimental technique. The thickness was approximated in an annular geometry by the gap between a concentric aluminum tube and rod. This technique was motivated by the desire to have a periodic boundary condition in the direction orthogonal to the annulus thickness, rather than a free surface occurring in typical rectangular geometry experiments. This results in a two‐dimensional charge analogous to previous failure thickness setups but with infinite effective width (i.e. infinite aspect ratio). Detonation propagation or failure was determined by the observation of failure patterns engraved on the aluminum rod by the passing detonation. Analysis of these engraved patterns provides a statistical measurement of the spatial density of failure waves. Failure was observed as far as 180 thicknesses downstream. The failure thickness was measured to be 1.45 mm±0.15 mm.

Detonation Shock Dynamics (DSD) describes the evolution of a two‐ or three‐dimensional detonation wave in a way that accounts for the finite detonation reaction zone thickness as long as it is sufficiently small compared to the radius of curvature of the detonation wave front. The current DSD solver obtains its input parameters by superimposing a rectangular Cartesian grid over the high explosive (HE) regions, determining the signed normal distance from each grid point to the nearest point on the HE boundary (negative on the inside of HE and positive on the outside) and assigning a material identification to each grid point. It has been shown previously to work well with a Lagrangian geometric description where the mesh entities, particularly cell faces, are contiguous and therefore distances to the HE boundary are precisely defined. In this paper a new scheme for the DSD driver code is presented that allows the HE boundary to be represented in a noncontiguous fashion, such as is obtained from a Youngs‐type material interface reconstruction, as often used in Eulerian hydrodynamics codes.

The sensitivity and mechanical behavior of energetic material is highly dependent on its constituents. Cast and cast‐cured explosives have mechanical properties significantly different from metals and the assumption of isotropic behavior may not be valid beyond a finite strain. While Split Hopkinson Pressure Bar (SHPB) can be successfully used to obtain mechanical properties of these soft and compliant explosives, ignition conditions are seldom achieved in SHPB tests. If ignition occurs in very small sample at extremely high strain rates, it would be very difficult to calculate the energy and energy rate that led to successful ignition. In contrast to the SHPB test, the standard drop‐weight test to measure the sensitivity of explosives, is intended to obtain ignition at impact, but is only a go‐no go test. Due to lack of quantifiable parameters, the result from this test is not suitable for modeling, which is important in development of new explosive formulation. In order to overcome this barrier and allow evaluation of the susceptibility of the different formulations to ignition, a new test was recently developed. This method is now applied to test hydroxy‐terminated poly butadiene (HTPB) bonded explosives.

Phase transition behavior of FeMnNi alloy with α‐e phase transition threshold in range of 6 GPa–7 GPa and corresponding spall phenomena in symmetric impact were studied experimentally. Impact of z‐cut sapphire flyer on specimen with z‐cut sapphire window and reverse impact by using specimen driven as flyer on z‐cut sapphire and LiF window were used for loading and release wave profile measurement by VISAR. Experiments were conducted in velocity range 500 m/s–2000 m/s. Pulse X‐ray was used for spallation verification by reason of difficulty in specimen recovery. Spallation phenomena were observed as impact stress far exceeds α‐e transition threshold. Observed spall phenomena should be related to special release wave configuration formed during reverse phase transition when impact stress slight exceeds phase transition threshold and even typical rarefaction shock wave formation is not observed.

In a recent series of papers, we have made a study of the shock response of a number of polymers, whilst systematically changing their structure, for example pendent side group size (polyethylene, polypropylene and polystyrene) or degree of halogenation (polyethylene, polyvinylidene difluoride and polytetrafluoroethylene). In this study, we examine a single polymer, polyethylene in two structural forms—high density weight and cross‐linked. Results show that overall, the shear strengths of these two variants of polyethylene are similar. However, we note that the rate of change of shear strength with applied shock stress is greater in the cross linked material. We have suggested that this be due to the crosslinking restricting the ability of the polymer chains to move relative to each other.

A specific dual functional material that consists of a mixture of nickel, aluminum and a binder is characterized. This is a mixture and not an alloy or a compound. The potential dual functions offered by this material consist of the strength and energetic characteristics. A first step in characterizing the material is the determination of the thermodynamically complete equation of state P = P(ρ,T) from first principles, without the binder. A supercell approach, similar to the virtual crystal approximation, and first principle methods are used first to obtain the EOS of the mixture. Then, the question of failure criteria is addressed. The dual functional materials have dual branches of failure criteria: mechanical and chemical reaction based failure criteria. In this paper, the chemical reaction based failure criterion is discussed using an ab initio molecular dynamics approach.

An experimental investigation of phase transition (PT) from hexagonal silicon nitride β‐phase to cubic c‐phase in porous samples was conducted in the range of pressure of 15–50 GPa. In that range the Hugoniot of porous β–Si3N4 samples was constructed. The loading of the samples was made through Al and Cu shields by Al impactors accelerated with explosive products. The boundary velocity between the sample surface and water window was registered by laser Doppler velocimeter VISAR. One of the main goals of the research was to observe two‐wave front configuration caused by the phase transition for more accurate PT pressure definition from the profile and the second wave front diffusion which takes information about PT kinetics. The registered profiles shown the absence of two‐wave configuration on the shock wave front which probably caused by high porosity of the samples (∼15%). Moreover, there was no any diffusion in the wave front which perhaps connected with fast PT kinetics. The presence of PT was found f...

Shock‐induced phase transitions of C70 fullerite with hexagonal close‐packed structure were experimentally studied with use of recovery assemblies of planar geometry at pressures 8 to 36 GPa. It was found that C70 fullerite undergoes a series of polymorphic transitions in conditions of step‐like shock compression. Hexagonal close‐packed structure of C70 fullerite remained practically unchanged at shock pressure 8 GPa. Shock‐induced transformation of the hexagonal structure into face centered cubic structure was fixed at pressures in the range 8 to 23.5 GPa. Depth of this transformation was increasing with growth of shock pressure. With further growth of shock pressure the destruction of C70 molecules occurs. This destruction is accompanying with a formation of graphite‐like carbon.

Hexanitrohexaazaisowurtzitane (CL‐20) is one of the few ingredients developed since World War II to be considered for transition to military use. Five polymorphs have been identified for CL‐20 by FTIR measurements (α, β, γ, e, ζ). As CL‐20 is transitioned into munitions it will become necessary to predict its response under conditions of detonation, for performance evaluation. Such predictive modeling requires a phase diagram and basic thermodynamic properties of the various phases at high pressure and temperature. Therefore, the epsilon and gamma phases of CL‐20 at static high‐pressure and temperature were investigated using synchrotron angle‐dispersive x‐ray diffraction experiments. The samples were compressed and heated using diamond anvil cells (DAC). Pressures and temperatures achieved were around 5 GPa and 240 °C, respectively. The epsilon phase was stable to 6.3 GPa at ambient temperature. When heated at ambient pressure the epsilon phase was sustained to a temperature of 120 °C then underwent a tr...

This article proposes a two‐scale finite element approach for the dynamic response of heterogeneous materials. While common two‐scale Finite Element Method (FEM) formulations consider the Representative Volume Element (RVE) much smaller than the finite element mesh, the present paper extends the formulation for the cases when RVE becomes comparable with the finite element in the mesh. The new two‐scale equations and their FEM implementation, are presented together with an example.

The feasibility and reliability of small dimension specimen SHPB tests were investigated by numerical simulation and experiments of 2024 aluminium alloy with series of dimension. Also an attempt is made to get curves of strain rate over 104 s−1 by small dimension specimens. Accuracy of transmitted signal in eccentric compression tests of small specimen was analyzed and discussed by experiments and numerical simulation. Results showed that the distortion of signals can be eliminated by mounting strain gages in series or far away from the specimen‐bar interfaces.

Pressure‐shear plate impact experiments and soft recovery experiments were performed for 92.93 wt% aluminas with 75‐mm‐diameter compressed‐gas gun. The in‐material longitudinal and transverse particle velocities were traced by the embedded electromagnetic velocity gauges. The decoupled transverse particle velocities show an attenuation of shear waves with decreasing of material shear rigidity. SEM analysis of the intact samples shows heterogeneous meso‐structures, and that of recovered samples shows the transit of intergranular microcracks to transgranular microcracks with increasing shock loading. The transverse shear promotes the microcracks nuclearing and expanding, and these microcracks result in remarkable dilation of alumina samples after unloading.

Shock‐compression research began in the 1940s for reasons of national defense. While military‐related research will continue to be a major motivator of shock research, war between nations is not as probable today as it was in the last century. Today other issues are gaining national and international importance. This situation raises the possibility of redistribution of federal funding into fields other than those related directly to military research. It is timely to consider possible future directions that would put us in a position to obtain support to address emerging needs of society, while maintaining traditional expertise. Possibilities for future research at national and military laboratories and at universities are suggested in the context of ideas and questions posed in a recent report of the National Research Council of the National Academies. Dynamic‐compression research is positioned to play a prominent role in general scientific research and such results are needed to enhance probabilities of achieving present and emerging technological goals of national importance.

The impact transformations of plagioclase (Pl)—hornblende (Hbl) schist with garnet (Southern Urals) and clinopyroxene–Hbl–Pl schist (Anabar Shield) have been studied with use of recovery assemblies of planar geometry. In the specimens, shock pressures were ranged from 26 to 52 GPa. It was found that an increase of content of F, Ti, and K in a composition of Hbl, as well as a decrease of content of Ca in a composition of Pl, make these minerals more stable to action of shock waves. In experiments with the stepwise shock compression of polymineralic rocks the isotropization of Pl begins at lower pressures than in analogous experiments with monomineralic specimens. Under relatively low pressures, Pl isotropization is caused by its fragmentation on a microscopic scale and is associated with the origin of maskelynite—a typical mineral of meteorites and astroblemes. At higher pressures, Pl isotropization is related to amorphization by means of melting.

The classical thermal explosion theory of D. A. Frank‐Kamenetskii (F‐K) is analytic with respect to charge size but numerical with respect to charge shape. The numerical determination of criticality for a general shape is non‐trivial, and is therefore not often performed in practice. For estimation purposes it would be useful to avoid computations by finding an approximate correlation relating the critical state to the relevant generic attributes of the charge shape. I present such a correlation that accurately does so for bodies of near‐unity aspect ratio; however, the result breaks down for extended aspect ratio bodies.

The conventional spacecraft meteoroids and orbital debris shielding system is the Whipple shield. In general there is a threshold velocity that is just sufficient to shatter the projectile for each system consisting of a projectile and bumper. This velocity is known as the fragmentation onset velocity. To determine the fragmentation onset velocity experimentally, a number of experiments have been conducted with different projectile/bumper configuration. The numerical simulations of fragmentation onset velocity of different material projectile hypervelocity impacts on bumpers with different combination of impact velocities and bumper‐thicker‐to‐projectile‐diameter ratios (t/D) have been performed using the SPH technique of AUTODYN. The spherical projectile materials are aluminum, steel and copper. All bumper material is aluminum alloy 6061‐T6. The simulation velocities were in the range of 1 km/s∼7 km/s. The ratios of t/D were varied from 0.01 to 0.8. The material model contains Mie‐Gruneisen (shock) equat...

The spatial and temporal evolution of aluminum and aluminum monoxide produced during laser ablation of an aluminum sheet were tracked by way of emission and absorption spectroscopy. Atomic Al and molecular AlO temperatures were deduced from the emission spectroscopy data at several distances from the Al sheet surface. The atomic Al temperature was found to increase as a function of distance from the Al sheet surface and decrease over time. The molecular temperature of AlO remained approximately constant near the burning temperature of Al as a function of distance and time. The concentration of atomic Al was measured using absorption spectroscopy with peak concentrations ranging from 2.0×1018–1.2×1019 atoms/m3 as a function of distance from the Al sheet.

As particle size becomes smaller, finite size effects become important and thermo‐mechanical properties of nanoparticles, such as the bulk modulus, deviate from the values of larger size particles. The change in properties from the bulk values is important from an applied standpoint as nanoparticles are used in various applications. The deviation in properties is also important for testing fundamental theories of atomic interactions in finite size systems. A first principles model has been developed that allows the prediction of all thermomechanical effects that will be generated from any laser pulse incident on a nanoparticle. This theoretical work also predicts the thermo‐mechanical effects transmitted to he surrounding transparent medium that the nanoparticles is immersed in, such as water or a solid polymer. The use of short enough pulses produces a train of shock fronts in the surrounding medium. We show that measurements of these shock fronts out in the medium generated by particles of decreasing size allow the determination of the size at which a nanoparticle is small enough to deviate from its bulk behavior and manifest finite size effects. Because the measurements can be made in the surrounding medium, they are easier to perform experimentally.

A proposed nominal/generic (N/G) CP (specific heat at constant pressure) for CHNO energetic materials is employed to predict the specific heat CP for FOX‐7, (1,1‐diamino‐2, 2‐dinitro ethylene).

Experimental studies were conducted on the fracture phenomena of HR‐2 steel and LY12 aluminum alloy cylinder under explosive imploding. Optical and flash X‐ray photography showed that thermo‐plastic instability in the form of shear fracture occurs during the imploding process. Shear initiation and propagation processes on the inner wall was directly observed by high‐speed photography. The two kinds of experimental records and examination of recovered fragments showed that shear cracks initiate from the inner surface of the cylinder at a very early stage and propagate along the maximum shear stress paths radically outward and longitudinal along the detonation direction to form shear fracture surfaces. Under imploding conditions there is a strong tendency to form self‐organized shear fractures in comparison to exploding fracture of identical cylinder material and loading intensity.

Throughout the years a variety of tests have been designed which provide insight into the sensitivity of high explosives (HE) to non‐shock initiation. Various standard tests such as the LANL drop weight impact, LLNL drop hammer, drop tower and skid tests have been developed to measure energetic response of explosives subjected to a combination of friction and oblique impact. In addition, the BAM test (for HE powders on roughened ceramic) and ABL friction test (powders or solids on roughened metal) have been developed for testing HE under frictional loading. In an effort to understand first principles of non‐shock initiation, we have designed a series of tests to try to isolate friction and impact during the insult of HE. An initial series of tests have been completed with PETN, HMX, and as‐pressed pellets of PBX 9501 (95 wt% HMX, wt% inert binder), PBX 9502 (95 wt% TATB, 5 wt% inert binder), Cyclotol (75 wt% RDX/25, wt% TNT), and Comp B3 (60 wt% RDX, 40 wt% TNT). The results suggest that some types of high explosives are relatively insensitive to pure impact and pure friction but relatively sensitive to insults involving a combination of impact and friction.

The eXtended Finite Element Method (X‐FEM) is a finite‐element based discretization technique developed originally to model dynamic crack propagation [1]. Since that time the method has been used for modeling physics ranging from static meso‐scale material failure to dendrite growth. Here we adapt the recent advances of Vitali and Benson [2] and Song et al. [3] to model dynamic loading of a polycrystalline material. We use demonstration problems to examine the method's efficacy for modeling the dynamic response of polycrystalline materials at the meso‐scale. Specifically, we use the X‐FEM to model grain boundaries. This approach allows us to i) eliminate ad‐hoc mixture rules for multi‐material elements and ii) avoid explicitly meshing grain boundaries.

Enhanced heating from shock compression of a porous material can potentially suppress or delay cracking of the material on subsequent expansion. In this paper we quantify the expected enhanced heating in an experiment in which a sector of a thin cylindrical shell is driven from the inside surface by SEMTEX high explosive ({approx}1 {micro}s FWHM pressure pulse with peak pressure {approx}21.5 GPa). We first derive an analytical equation of state (EOS) for porous metals, then discuss the coupling of this EOS with material elastic-plastic response in a 2D hydrocode, and then discuss the modeling of the HE experiment with both fully dense and 10% porous Ta and a Bi/Ta composite. Finally, we compare our modeling with some recent experimental data.

This paper presents a computational experiment of microstructure effects on shock sensitivity of solid explosives, using a recently developed HE burn model [1]. This model includes specific surface area and the hot spot evolution that is based on an exponential size distribution. Experimentally, Khasainov et al. [2] summarized the effects of specific surface area, and showed that both the run distance to detonation and critical diameter have a linear relationship with the reciprocal of specific surface area. Computational experiments are carried out using a pressed RDX model with various initial specific surface areas that are determined by the average explosive particle size. The results show that both Pop‐plots and critical diameters follow the linear relationship observed by Khasainov.

We have applied Transient Imaging Displacement Interferometry (TIDI) to copper targets loaded by laser‐launched flyers. TIDI captures the full‐field out‐of‐plane surface displacement map single‐shot with the time resolution of the illumination pulses (180 ps). Displacement sensitivity of ∼10 nm with lateral spatial resolution of ∼5 microns is achieved over our ∼1 mm2 field‐of‐view. A framing camera allows capture of up to eight displacement maps for a single loading event, allowing the evolution of the surface motion to be tracked. Point and line VISARs are used as complementary diagnostics that provide a temporally continuous record of the velocity history of the sample, and also provide time stamps for the TIDI displacement maps. The rich heterogeneity in the surface displacement due to the grain structure of the sample is readily measured.