Plastic-bonded Explosives Research Articles

Experimental study on surface ignition reaction evolution of pressed PBX-A under inertial mass confinement

An experimental apparatus was designed to study the non-shock initiation reaction evolution process of a HMX (cyclotetramethylenete-tranitramine)-based pressed PBX (Plastic Bonded Explosive)-A column under the main constraint of the inertial mass of the explosive bulk, with strong bottom and circumferential confinements and with the strength of a PMMA plate cover as the threshold to control the internal reaction pressure. The HMX-based pressed PBX-A column was ignited by black powder. The experimental results show that the reaction violence was quite mild, and the estimated amount of explosive consumed at the time of the PMMA plate cracking was only 1.8% of the thickness. The velocity curve of the constrained surface shows that the internal reaction pressure at the initial stage of the structural deformation shows the “quasi-isobaric” characteristic, and the estimated reaction pressure at this stage was about 157.41 MPa.

Cis‐1,3,4,6‐Tetranitrooctahydroimidazo‐[4,5‐d]Imidazole (BCHMX) as a Part of Low Sensitive Compositions based on DATB or HNAB

AbstractA new focus in the fields of energetic materials is on preserving high performance while enhancing manipulation safety. In this work, a special type of plastic‐bonded explosive (PBX) mixture has begun to be developed by combining a new nitramine, cis‐1,3,4,6‐tetranitrooctahydroimidazo‐[4,5‐d]imidazole (BCHMX), with the thermally stable explosives 1,3‐diamino‐2,4,6‐trinitrobenzene (DATB) and 2,2’,4,4’,6,6’‐hexanitroazobenzene (HNAB) bonded by a styrene‐butadiene rubber (SBR) binder. The studied PBXs prepared are insensitive explosives. They have been compared with Czech plastic explosives (SEMTEX 10 and SEMTEX 1H), a new Egyptian plastic explosive (EPX‐1), a Swedish plastic explosive (Sprängdeg m/46) and with analogous PBXs, filled by 1,3,5‐trinitro‐1,3,5‐triazinane (RDX), β‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane (β‐HMX), and cis‐1,3,4,6‐tetranitrooctahydroimidazo‐[4,5‐d]imidazole (BCHMX). The individual explosives, PETN, BCHMX, β‐HMX and RDX, have been studied as well. Thermal behavior of the pure active components has been investigated. The impact and friction sensitivities have been obtained along with the measured detonation velocities. The detonation characteristics have also been calculated using the EXPLO5 code. The relationship between performance and sensitivity to mechanical impulses has been investigated. The results have shown that DATB has a significant influence on the reduction of the sensitivity of BCHMX to a level close to TNT and much lower than all the other studied plastic explosives. In addition, the new PBX based on BCHMX and DATB has higher detonation characteristics than the commercial PBXs and TNT. The influence of DATB on BCHMX is a promising topic requiring more research for its application.

Microcomputed X-Ray Tomographic Imaging and Image Processing for Microstructural Characterization of Explosives

Microstructural characterization of composite high explosives (HEs) has become increasingly important over the last several decades in association with the development of high fidelity mesoscale modeling and an improved understanding of ignition and detonation processes. HE microstructure influences not only typical material properties (e.g., thermal, mechanical) but also reactive behavior (e.g., shock sensitivity, detonation wave shape). A detailed nondestructive 3D examination of the microstructure has generally been limited to custom-engineered samples or surrogates due to poor contrast between the composite constituents. Highly loaded (>90 wt%) HE composites such as plastic-bonded explosives (PBX) are especially difficult. Here, we present efforts to improve measurement quality by using single and dual-energy microcomputed X-ray tomography and state-of-the-art image processing techniques to study a broad set of HE materials. Some materials, such as PBX 9502, exhibit suitable contrast and resolution for an automatic segmentation of the HE from the polymer binder and the voids. Other composite HEs had varying levels of success in segmentation. Post-processing techniques that used commercially available algorithms to improve the segmentation quality of PBX 9501 as well as zero-density defects such as cracks and voids could be easily segmented for all samples. Aspects of the materials that lend themselves well to this type of measurement are discussed.

Ignition and growth modeling of shock initiation using embedded particle velocity gauges in the plastic bonded explosive LX-14

ABSTRACT Recently Vandersall et al. [1] reported a series of shock initiation experiments using embedded manganin pressure gauges in the plastic bonded explosive (PBX) LX-14 (95.5% HMX and 4.5% Estane by weight) plus Ignition and Growth (I & G) simulations of all the gauge records. Jones et al. [2] reported a study of LX-14 using embedded particle velocity gauges in a similar shock strength range. It is prudent to test the ability of a reactive flow model to predict both types of gauge results. The I & G LX-14 model parameters based on the pressure records are compared to five sets of particle velocity gauge records. Excellent agreement was obtained with all five particle velocity experiments, implying that the two types of gauges yield equivalent results and that either technique can be used with the I & G model.

Modeling of the deformation and damage of plastic-bonded explosive in consideration of pressure and strain rate effects

The present study deals with numerical modeling of strain rate- and pressure-related deformation and damage of plastic-bonded explosives (PBXs). A mechanical constitutive model that combines a porosity model and a recently developed viscoelastic–viscoplastic damage model (Liu et al., 2019) [1] with necessary modifications is presented. The model is calibrated for 1,3,5-triamino-2,4,6-trinitrobenzene-based PBX by using available experimental data under hydrostatic cyclic compression, uniaxial compression at various strain rates, and triaxial compression with hydrostatic confining pressure. The complex behaviors of PBXs, such as irreversible volumetric compaction and coupled effects of strain rate and pressure on mechanical strength and failure mechanism, are investigated through several single-element tests at typical loading conditions and split Hopkinson pressure bar (SHPB) tests with lateral confinement. The model properly captures these behaviors and is able to accurately restitute the loading and reloading process of the confined SHPB test.

Quasistatic mechanical behavior of HMX- and TATB-based plastic-bonded explosives

Data on the macroscopic quasistatic mechanical behavior of pressed HMX- and TATB-based plastic-bonded explosives (PBXs) are listed in this paper. This review shows that (1) few characterizations are available for TATB-based PBXs. This gap is filled in this paper. An extensive database is detailed for the CEA M2 explosive composition. The HMX and TATB database then enables selection of the deformation mechanisms to be considered: viscoelasticity, damage-induced anisotropy and its effectivity (i.e.: whether or not the damage is influenced by the loading direction), plasticity with kinematic and isotropic hardenings, pressure and temperature dependencies and asymmetric failure threshold. The review also shows that (2) HMX- and TATB-based materials share close elastic and ultimate properties when the compositions (binders, solid volume fractions) and the mechanical behavior of the two crystals differ. The constitutive laws proposed in the literature are reiterated. In our opinion, a universal law could be proposed in the near future, each material being considered by its own set of parameters. The objective of this paper is to draw up the guidelines for model improvement.

Structure–property–performance linkages for heterogenous energetic materials through multi-scale modeling

In porous solid energetic materials, the mechanical processing technique (e.g. casting, pressing) creates defects such as voids, cracks, interfaces, and inclusions; these defects in the microstructure strongly influence the sensitivity of the material to imposed loading. Energy localization at defects causes hotspots; the ignition and growth of hotspots in the microstructure (i.e. the meso-scale) play a crucial role in the macroscale initiation of the material. Predictive models of shock response of energetic materials must connect the meso-scale heterogeneities (structure) and hotspot physics (properties) to macro-scale response (performance and safety). To achieve this structure–property–performance (S–P–P) linkage, SEM-imaged samples of neat pressed HMX are obtained, and morphometry is performed to quantify the microstructure. Since the microstructure is stochastic, the aleatory uncertainties in the morphological parameters are quantified. The link between the microstructure and the key meso-scale quantity of interest—the hotspot ignition and growth rates—is established using reactive meso-scale computations to construct meso-informed surrogate models for energy localization. The surrogate models are used to close homogenized macro-scale governing equations. The performance of the HE at the macro-scale, i.e. its sensitivity to shock loading, is measured via run-to-detonation distances (in Pop plots) and the critical energy required for initiation (in James plots). The predicted critical energy for the material is compared with experimental data. The methods established in this paper can be useful not only for establishing structure–property–performance (S–P–P) linkages for pressed energetic materials, but also for other heterogenous reactive composites such as propellants and plastic-bonded explosives.

A Solubility Comparison of Cyclotetramethylenetetranitramine (HMX) and Potential Mock-HMX Candidates in Solvents Relevant to Slurry Formulating Polymer-Bonded Materials

Understanding solubility behavior of organic crystalline materials is critical in the development of slurry-formulated plastic bonded composites. In the field of high explosives (HE), a common method for obtaining high density, greater than 95% theoretical maximum density, is to encapsulate HE in a polymer matrix resulting in the formation of plastic bonded explosive (PBX) prills which can then be pressed to high density parts. Prill formation is highly nuanced and requires understanding of particle size distributions, solvent, antisolvent, and binder system as well as interactions thereof. In an effort to create mock-HE that mimics HE in density and mechanical strength, solubility of candidate molecules was compared to cyclotetramethylenetetranitramine (HMX) in binder solvents relevant to prill formation. The results indicate that the mock candidates chosen for this study have different solubilities compared to HMX in water and both organic solvents, 2-butanone and ethyl acetate, investigated. With these solubility differences known, prills to match PBXs based on HMX can be formulated, pressed and tested.

Observing Hot Spot Formation in Individual Explosive Crystals Under Shock Compression.

The formation of hot spots in dynamically compressed, plastic-bonded explosives is known to be the primary mechanism by which these materials ignite and initiate, but hot spots are small, fleeting, and hard to observe. Using a microscope equipped with laser-launched, miniflyer plates, we have studied hot spots in small grains of cyclotetramethylene-tetranitramine (HMX) embedded in a polyurethane binder, shocked to about 20 GPa. A nanosecond video with 4 μm spatial resolution is used to observe hot spot formation and growth, while nanosecond optical pyrometry measured temperature. Using individual ∼200 μm nominally single crystals of HMX (HMX-SC), we observed hot spots forming preferentially on corners or edges. These hot spots are about 4000 K. When there are multiple hot spots, the flame propagated along crystal edges, and the crystal is mostly combusted after about 300 ns. Using polycrystalline grains (HMX-PC), 6000 K hot spots are created near internal defects or crystal junctions. However, the thermal mass of the material at 6000 K is quite small, so after those hot spots cool down, the HMX combustion is similar to the single crystals. Comparing a HMX-based polymer-bonded explosive (PBX) to the individual polymer-bonded HMX-SC and HMX-PC grains shows that the myriad hot spots in the PBX are hotter than HMX-SC and colder than HMX-PC, but they persist for a longer time in PBX than in the individual grains.

Shock Initiation Microscopy with High Time and Space Resolution

AbstractWe describe studies of shock initiation and shock‐to‐detonation transitions in energetic materials using a tabletop shock compression microscope with nanosecond time resolution and micrometer spatial resolution. Planar input shocks with durations of 4–20 ns are produced using 0–4.5 km/s laser‐launched flyer plates. Emphasis is on measurements of temperature, velocities, pressure, and microstructure using photon Doppler velocimetry (PDV), optical pyrometry and high‐speed videography. Techniques are discussed for fabricating disposable shock target arrays of tiny plastic‐bonded explosives (PBX), liquid and powder explosives, and single‐crystal explosives for high‐throughput studies. Optical temperature measurements of shocked triaminotrinitrobenzene (TATB) are discussed. Since TATB is yellow, we developed methods to correct for the blue absorption to obtain more accurate temperatures. Hot spots in shocked polymer‐encased HMX (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine) crystals are observed in real‐time, showing a hot spot produced in a collapsing void that ignites a deflagration. Despite the small dimensions of our explosive charges (typically 1 mm diameter and 250 μm length), we produced reproducible detonation states in solid and liquid explosives using short‐duration shocks near the von Neumann spike (VNS) pressure. We show the VNS pressure is associated with a transition to high‐efficiency gas production from the explosives. In studies of NM, prior to detonation, we see reaction originating at hot spots which coalesce to form a superdetonation.

Jones-Wilkins-Lee Unreacted and Reaction Product Equations of State for Overdriven Detonations in Octogen- and Triaminotrinitrobenzene-Based Plastic-Bonded Explosives.

The Jones-Wilkins-Lee (JWL) equation of state (EOS) is used to calculate expansion of detonation reaction products from the chemical equilibrium Chapman-Jouguet (C-J) state to large volumes. Overdriven detonation waves with shock pressures higher than C-J are created by high-velocity impacts or converging detonation waves. Reflection from high-impedance materials, multiple shock impacts, and Mach stem wave interactions creates similar pressures. When overdriven states were first measured experimentally, the original reaction product JWL EOSs predicted excess compression. This problem was resolved by modifying the JWL EOS to produce less compression at high pressures while still correctly calculating expansion from the C-J state. Zeldovich-von Neumann-Doring (ZND) reactive flow models, which include the measured reaction zone momentum, explained experimental observations that lower C-J pressures are required to smoothly connect the C-J state to overdriven states on the product Hugoniot curve. Experimental data on overdriven detonation waves for two octogen (HMX)-based plastic-bonded explosives (PBXs), PBX 9501 and PBX 9404, and for two triaminotrinitrobenzene (TATB)-based PBXs, LX-17 and PBX 9502, are compared to various JWL reaction product EOSs, including ones generated by the CHEETAH chemical equilibrium code. Excellent agreement is obtained using JWL EOSs for overdriven shock pressures and densities up to 130 GPa and 3.8 g/cm3 for both HMX- and TATB-based PBXs.

Shock to Detonation Transition of Plastic Bonded Aluminized Explosives

AbstractAluminum particles are usually added to plastic bonded explosives (PBX) in order to increase blast efficiency thanks to their post‐combustion with detonation products and air. These particles modify the shock to detonation (SDT) process of PBX. Their role has not been well understood. That is why, in this paper we proposed a review of the main hypotheses concerning aluminum particles effects on SDT. The main issue of thermal and mechanical equilibrium is discussed with the estimation of their impact on the Euler equations. This study also sums up the experimental data registered on RDX and HMX aluminized explosives. A comparison with a reference PBX is proposed and a new light on the mechanism of shock to detonation transition is given.

Glycidyl Azide Polymer and its Derivatives-Versatile Binders for Explosives and Pyrotechnics: Tutorial Review of Recent Progress.

Glycidyl azide polymer (GAP), an energetic binder, is the focus of this review. We briefly introduce the key properties of this well-known polymer, the difference between energetic and non-energetic binders in propellant and explosive formulations, the fundamentals for producing GAP and its copolymers, as well as for curing GAP using different types of curing agents. We use recent works as examples to illustrate the general approaches to curing GAP and its derivatives, while indicating a number of recently investigated curing agents. Next, we demonstrate that the properties of GAP can be modified either through internal (structural) alterations or through the introduction of external (plasticizers) additives and provide a summary of recent progress in this area, tying it in with studies on the properties of such modifications of GAP. Further on, we discuss relevant works dedicated to the applications of GAP as a binder for propellants and plastic-bonded explosives. Lastly, we indicate other, emerging applications of GAP and provide a summary of its mechanical and energetic properties.

Influence of the octogen quality and production scale on characteristics of granulated plastic bonded explosive

The compositions of granulated plastic bonded explosive (PBX), based on octogen (HMX) and Estane polymer were prepared by aqueous/solvent slurry coating tehnique, on a laboratory and industrial scale. Scale-up was done in an environmentally friendly and cost-effective way: with provided recyclage and reuse of the used organic solvent. The quality of the obtained granulated PBX samples was observed trough the following analyses: the quality of polymer coating layer on HMX crystals was examined by microscopic analysis; the phlegmatizer content in PBX samples was determined; granulometric analysis and the tests of sensitivity to friction and impact were carried out. Compressibility of granulated PBX was determined by pressing. Measured detonation velocities of pressed PBX charges were compared. The obtained properties of the examined pressed PBX indicated that it may find application as a promising main explosive charge in cumulative warheads.

Spatial Heterodyne Raman Spectrometer (SHRS) for In Situ Chemical Sensing Using Sapphire and Silica Optical Fiber Raman Probes.

A spatial heterodyne Raman spectrometer (SHRS), constructed using a modular optical cage and lens tube system, is described for use with a commercial silica and a custom single-crystal (SC) sapphire fiber Raman probe. The utility of these fiber-coupled SHRS chemical sensors is demonstrated using 532 nm laser excitation for acquiring Raman measurements of solid (sulfur) and liquid (cyclohexane) Raman standards as well as real-world, plastic-bonded explosives (PBX) comprising 1,3,5- triamino- 2,4,6- trinitrobenzene (TATB) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) energetic materials. The SHRS is a fixed grating-based dispersive interferometer equipped with an array detector. Each Raman spectrum was extracted from its corresponding fringe image (i.e., interferogram) using a Fourier transform method. Raman measurements were acquired with the SHRS Littrow wavelength set at the laser excitation wavelength over a spectral range of ∼1750 cm-1 with a spectral resolution of ∼8 cm-1 for sapphire and ∼10 cm-1 for silica fiber probes. The large aperture of the SHRS allows much larger fiber diameters to be used without degrading spectral resolution as demonstrated with the larger sapphire collection fiber diameter (330 μm) compared to the silica fiber (100 μm). Unlike the dual silica fiber Raman probe, the dual sapphire fiber Raman probe did not include filtering at the fiber probe tip nearest the sample. Even so, SC sapphire fiber probe measurements produced less background than silica fibers allowing Raman measurements as close as ∼85 cm-1 to the excitation laser. Despite the short lengths of sapphire fiber used to construct the sapphire probe, well-defined, sharp sapphire Raman bands at 420, 580, and 750 cm-1 were observed in the SHRS spectra of cyclohexane and the highly fluorescent HMX-based PBX. SHRS measurements of the latter produced low background interference in the extracted Raman spectrum because the broad band fluorescence (i.e., a direct current, or DC, component) does not contribute to the interferogram intensity (i.e., the alternating current, or AC, component). SHRS spectral resolution, throughput, and signal-to-noise ratio are also discussed along with the merits of using sapphire Raman bands as internal performance references and as internal wavelength calibration standards in Raman measurements.

Development of comprehensive two-dimensional liquid chromatography for investigating aging of plastic bonded explosives

The feasibility of measuring the aging and degradation of PBX 9501 via online two dimensional liquid chromatography (LC × LC) is investigated, and a preliminary instrumental setup and method is developed. Plastic-Bonded eXplosive (PBX) 9501 is nominally composed of 94.9 wt% HMX, 2.5 wt% Estane® 5703 (poly (ester urethane)), 2.5 wt% BDNPA/F (nitroplasticizer), 0.1 wt% Irganox 1010 and PBNA (N-phenyl-naphthylamine) at low concentrations. When exposed to various environmental conditions, PBX 9501 will degrade through different pathways. Because PBX 9501 is composed of both low molecular weight compounds (BDNPA/F, Irganox 1010, PBNA, and potential degradation products) and high molecular weight compounds (Estane® 5703), analysis is normally performed via two independent analyses. The low molecular weight species are analyzed via high pressure liquid chromatography (HPLC) and the high molecular weight species via size exclusion chromatography (SEC). While these individual techniques yield information about the aging of PBX 9501, the combination of HPLC and SEC (i.e. HPLC × SEC) can simplify and streamline the analyses while also providing additional chemical information. A simplified sample preparation method is proposed for LC × LC analysis. Various SEC columns and HPLC column selection, flow rate, and gradient ramps were investigated for their application of measuring aged PBX 9501. Finally, two LC × LC separations of a library standard of PBX 9501 and a sample of aged PBX 9501 are compared.

Numerical simulations of the damage evolution for plastic-bonded explosives subjected to complex stress states

A viscoelastic–viscoplastic damage model is developed to describe the inelastic stress–strain responses and fracture processes of plastic-bonded explosives (PBXs) under complex stress states. This model improves the viscoelastic cracking constitutive model called ViscoSCRAM in two respects. (1) The growth rate factor of pressure-dependent tensile damage is incorporated into microcrack evolution equations, and the tension–compression asymmetry feature of quasi-brittle solids can be more reasonably described than the previous one. (2) The viscoplastic property, which is essential to PBXs, especially 1,3,5-triamino-2,4,6-trinitrobenzene-based explosives, is introduced into the framework through an additive decomposition of the total strain rate based on Bodner–Partom viscoplasticity. An efficient numerical scheme in the framework of large inelastic strains is developed. Several single-element tests under various loading paths and a specimen containing a cavity under compression are used to illustrate the main features and predictive capabilities of the proposed model. The numerical simulation can accurately capture the tensile cracks and diffuse shear-dominated material damage of the PBX 9502 perforated plate in comparison with the test conducted by Los Alamos National Laboratory (Liu and Thompson, 2014).

Electron Properties and Thermal Decomposition Behaviors for HMX/HTPB Plastic-Bonded Explosives

We study the microscopic structure properties and early thermal decomposition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)/hydroxyl-terminated polybutadiene (HTPB) composites on the ba...

Theoretical and experimental study of underwater explosion performance of selected explosive compositions

Measurements of underwater explosion parameters and their effects are still the major problem for naval designer. In this study, thermo-chemical calculations have been carried out using EXPLO5 code to determine the underwater explosion parameters for different selected explosive mixtures. Preparation of the different types of explosive mixtures based on melt cast explosive (TNT) and plastic bonded explosives (PBXs) based on polyurethane binder system were presented. The effect of different aluminum weight percentage for the selected explosive mixture has been investigated with respect to the impulse and the resulted deformation. Underwater experimental measurements of the prepared explosive mixtures based on steel plate’s deformation were determined and compared. It was concluded that PBX based on RDX in addition to 25 wt% aluminum and 30wt% ammonium perchlorate produces the highest underwater explosion performance from all the tested samples. This explosive mixture is candidate to replace the traditional well known TNT in the underwater explosive applications.

Involving PETN explosive into polyurethane polymer matrix for reactive armour applications

This paper describes some formulations of plastic bonded explosives (PBXs) in the form of flexible material (sheet explosive) for military and civilian applications. Different compositions based on (70 wt%, 75 wt%, 78 wt%, 80 wt%) of PETN as high explosive filler were prepared by casting technique using HTPB polyurethane binder material. The production technique of the prepared explosive sheets was described in this research. Sensitivity to impact and friction were also measured. In addition, heat of combustion was determined. Besides, the detonation velocity was measured experimentally and the detonation characteristics were calculated using EXPLO 5 thermodynamic code. For comparison, standard commercial available plastic explosives such as EPX-1 and Datasheet C were studied. By comparing the obtained results, several relationships based on the results were observed. A good agreement between the measured and the calculated results was confirmed. Sample containing 78 wt% of PETN bonded by the polyurethane matrix is an optimum for the application of reactive armours.