Plastic-bonded Explosives Research Articles

AP를 포함한 주조형 복합화약 조성의 열적거동 노화 특성 연구

Purpose: Depending on the explosive effects and purposes, Plastic-Bonded Explosive (PBX) containing molecular explosive powder, metal powder, oxidizer, and other components is developed. Various components have complicated the analysis of thermal properties. Ammonium Perchlorate (AP) is used as an oxidizer for metal oxidation. To analyze the thermal property of PBX, we commonly measured the thermal constant, such as the activation energy, and the reaction rate. In this case of PBX including AP, even Differential Scanning Calorimetry (DSC) measurement, which is widely used for thermal analysis, has become difficult to analyze.BRMethods: PBX including AP is performed by the TGA at different temperature rates. We described the thermal property using Advanced Kinetics and Technology Solutions (AKTS) thermal software program with TGA data.BRResults: Two steps of mass loss were observed in the temperature range 25–450℃. Thermal kinetic parameters were evaluated using the iso-conversional differential method and iso-conversional integral method.BRConclusion: The calculated thermal kinetic parameter demonstrated the prediction of the thermal aging of PBX.

Hot-spot generation and growth in shocked plastic-bonded explosives studied by optical pyrometry

The aggregate behavior of hot spots in shocked plastic-bonded explosives (PBX) was studied by nanosecond optical pyrometry. The averaged thermal emission spectra from at least 25 tiny (50 μg) explosive charges of a pentaerythritol tetranitrate PBX, at several impact velocities from 1.5 to 4.5 km/s, was used to determine average temperatures and emissivities. Individual spectra were analyzed to determine the distribution of hot spot temperatures in individual charges with unique microstructures. Understanding shocks in tiny charges with different microstructures is needed to understand shocks in large PBX charges which sample many microstructures as they propagate. The initial hot spot density was several percent, and the average initial hot spot temperature of 4000 K was, surprisingly, independent of impact velocity. With underdriven shocks, the initial hot spot temperatures clustered around 4000 K, but with overdriven shocks, there were both hotter and colder hot spots. The initial hot spot density increased quadratically with impact velocity. The generation of hot spots was described by a model with a threshold energy to trigger hot spot formation and a distribution of energetic barriers to hot spot formation.

Characterization of Interfacial Micro‐Structures of Explosive‐Binder Composites by Gas Permeation

AbstractThe interface between explosive and binder in plastic‐bonded explosives (PBXs) plays an important role in their properties such as thermal and mechanical stability, and also their performance in detonation processes. However, characterization of their interfacial micro‐structures remains challenging, due to the sensitive nature of the explosive material, and the extremely thin nature of the interface. This work demonstrates a concept of characterizing interfacial structures between explosives and binders by gas permeation. The N2 permeability data of composite films of cyclotetramethylene‐tetranitramine (HMX) particles dispersed in fluororubber binder (copolymers of vinylidene fluoride and chlorotrifluoro‐ethylene, F2311) were tested and fitted by using gas transport mechanism theory, e. g. the Hashemifard‐Ismail‐Matsuura (HIM) model, and the Knudsen diffusion equation. The results indicate the presence of voids of thickness 2.2 nm between HMX and F2311, consistent with the results of neutron reflection and thermal conductivity measurements. These interfacial voids are considered to be related to the surface roughness of HMX particles. This work provides an alternative characterization technique for, as well as a new insight into, the interface between HMX and F2311.

Coating processes towards selective laser sintering of energetic material composites

Abstract This research aims to contribute to the safe methodology for additive manufacturing (AM) of energetic materials. Coating formulation processes were investigated and evaluated to find a suitable method that may enable selective laser sintering (SLS) as the safe method for fabrication of high explosive (HE) compositions. For safety and convenience reasons, the concept demonstration was conducted using inert explosive simulants with properties quasi-similar to the real HE. Coating processes for simulant RDX-based microparticles by means of PCL and 3,4,5-trimethoxybenzaldehyde (as TNT simulant) are reported. These processes were evaluated for uniformity of coating the HE inert simulant particles with binder materials to facilitate the SLS as the adequate binding and fabrication method. Suspension system and single emulsion methods gave required particle near spherical morphology, size and uniform coating. The suspension process appears to be suitable for the SLS of HE mocks and potential formulation methods for active HE composites. The density is estimated to be comparable with the current HE compositions and plastic bonded explosives (PBXs) such as C4 and PE4, produced from traditional methods. The formulation method developed and understanding of the science behind the processes paves the way toward safe SLS of the active HE compositions and may open avenues for further research and development of munitions of the future.

Learning the initial mechanical response of composite material: structure evolution and energy profile of a plastic bonded explosive under rapid loading.

Plastic bonded explosive (PBX) is a typical composite material used widely in the defense industry and in aerospace engineering. The mechanical behavior of PBX is an important factor to be considered in its formulation design, but the initial mechanical response is not well understood due to the complexities of atomic interactions in a multi-component system. We applied a hybrid force field to investigate the initial mechanical response of cyclotrimethylenetrinitramine(RDX)-based PBX, by molecular dynamics. The structure evolution shows that the initial damage occurs mainly in the binder region, and is caused by conformational stretching and void propagation. The relationship between loading rate and initial damage indicates that lower loading rate is more beneficial to conformation relaxation, and consequently to increasing strain limitation. The energy profile indicates that the variation of non-bonded interaction energy, especially coulomb energy, has a significant influence on the variation of total energy. Therefore, when designing PBX, good mechanical strength can be expected by selecting polymer and explosive formulations with strong electrostatic interaction. Graphical abstract The structure evolution and energy profile of plastic bonded explosive (PBX) under uniaxial tension.

Measuring detonation wave profiles in plastic-bonded explosives using PDV

To obtain reaction zone parameters for several high explosives, experimental measurements of the detonation wave profiles in HMX-, RDX- and PETN-based explosives were performed using photon Doppler velocimetry (PDV). Planar detonations were produced by impacting the explosive with a sapphire flyer in a gas gun. Particle velocity wave profiles were measured at the explosive/window interface. LiF windows with very thin vapor-deposited aluminum mirrors were used for experiments. All measurements show a distinct end to the reaction zone, indicating a Chapman-Jouguet (CJ) point. For HMX-based explosives, the presented measurements show that the fast reaction time is approximately 10±2 ns, whereas for RDX- and PETN-based explosives, the values are 14±3 ns and 7±2 ns, respectively. The reaction times or reaction zone lengths obtained in the present study are smaller than previously reported data but much closer to the estimated values in theory. Additionally, the velocity at the Von Neumann (VN) spike was analyzed using the “beat cycles” method, and the pressure at the VN spike was obtained.

Correlations Between Laser Induced Breakdown Spectroscopy (LIBS) and Dynamical Mechanical Analysis (DMA) for Assessment of Aging Effect on Plastic Bonded Explosives (PBX)

Plastic Bonded Explosives (PBXs) are explosive materials, in which sensitive explosive powders with high detonation performance are bound together in a matrix using small quantities of a synthetic polymer. They provide good thermal stability and improve cook‐off properties with negligible shrinkage. Laser‐induced breakdown spectroscopy (LIBS) has been introduced as a novel method for assessment of thermal aging in PBXs. Thermal aging of fifteen samples of PBXs with the same composition has been studied in two temperatures 60 and 70 °C for 5 period times during 29 d. Dynamical mechanical analysis (DMA) has also been done on different aged samples in order to validate the LIBS results. Among different molecular bands, LIBS data showed that the changes in line intensity in CN and AlO molecular radiations could be used to assess aging effects. Principle component analysis (PCA) chemometric method was also implemented in order to obtain more accurate discrimination between different samples. Since there is a good agreement for the outputs of LIBS data and DMA results, LIBS technique can be introduced a reliable method for assessment of thermal aging of PBXs.

Effect of energy content of the nitraminic plastic bonded explosives on their performance and sensitivity characteristics

Abstract Information about the forty nine nitraminic plastic bonded explosives (PBXs) and different nitramines were collected. Fillers of these PBXs are nitramines 1,3,5-trinitro-1,3,5-triazinane (RDX) and β-1,3,5,7-tetranitro-1,3,5-tetrazocane (β-HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (bicyclo-HMX, BCHMX) and e-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (e-HNIW, CL-20) which are bonded by polyfluoro-elastomers, polydimethyl-siloxane, poly-glycidyl azide, polyisobutylene, polystyrene-butadiene, poly-acrylonitrile-butadiene and hydroxyl-terminated polybutadiene in addition to a melt cast compositions based on 2,4,6-trinitrotoluene. For thirty two of these PBXs the relationships are specified and analyzed between heats of their combustion and relative explosive strengths; by means of these relationships it might be possible to estimate, which groupings in the macromolecule of binder could be liable to their primary fission in the PBXs initiation. Similarly, for forty two of these explosives, the relationships are described and analyzed between their enthalpies of formation and impact sensitivities; here is especially attention paid to PBXs filled by BCHMX. Specific rate constants from Vacuum Stability Test (VST) of four nitramines and twenty PBXs are introduced into relationships with their enthalpies of formation. Regarding to all the mentioned cases, increasing of energy content of the studied explosives leads to increase of the relative explosive strength or initiation reactivity, respectively. Exception with the opposite trend, the outputs of VST are for BCHMX, where in PBXs are matrices with the esteric plasticizers or the energetic poly-glycidyl azide. Admixture of RDX or HMX, respectively, into the BCHX PBXs gives ternary PBXs whose thermal stability, in the sense of applied VST, is higher comparing to the original binary explosives.

A mesoscopic reaction rate model for shock-to-detonation of PBX explosives having different mean particle sizes

In order to well predict mean explosive particle size effects on the shock-to-detonation transition (SDT) process of a plastic bonded explosive (PBX), some improvements to a previous three-term mesoscopic reaction rate model that consists of a hot-spot ignition term, a hot-spot growth term, and an overall reaction term are made: A set of new switch conditions, which depend on mean explosive particle size, is proposed for the operations of the three terms; a new expression is obtained for the hot-spot growth term by combining an ignition efficiency factor which depends on mean explosive particle size and replacing the original burning topology geometric factor, which merely describes the characteristic of the outward pore surface burning reaction, by a more reasonable one, which combines the characteristic of inward particle surface burning reaction and that of outward pore surface burning reaction. Furthermore, for verification, the improved reaction rate model is incorporated into the DYNA2D code to simulate numerically the SDT process of three formulations of PBXC03 having the same density but different mean particle sizes, and the numerical results of pressure histories at different Lagrangian locations in the explosive are found to be in good agreement with previous experimental data.

Use of a Reverberation Technique to Determine Grüneisen Parameter of Unreacted Plastic bonded Explosive

AbstractGrüneisen parameter plays an important role in describing states of materials, especially for highly condition‐depended detonation process. Herein, this key empirical parameter of unreacted plastic bonded explosive (PBX) is determined by a multiple shock‐reverberated technique. The explosive sample is sandwiched between copper plates, within which, shock waves reverberate and compress explosive continuously. This rapid dynamic process is verified by the stepped pressures measured by embedded PVDF stress gauges. The Mie‐Grüneisen equation of state is utilized to calculate the off Hugoniot reverberated states, which have a better agreement with experiments compared to the impedance match method. Five shots of such explosive produce enough experimental data to fit the most reliable Grüneisen parameter. This work demonstrates the accuracy of the shock‐reverberated technique applied to insensitive explosive to determine Grüneisen parameter and provides reference for further study on unreacted JB‐9014.

Introducing Laser Induced Breakdown Spectroscopy (LIBS) as a Novel, Cheap and Non-destructive Method to Study the Changes of Mechanical Properties of Plastic Bonded Explosives (PBX)

This work introduces laser induced breakdown spectroscopy (LIBS) as a novel, cheap and non-destructive method to study the changes of mechanical properties of plastic bonded explosives (PBX) during their aging. Accelerated aging was used in three different temperatures 60, 70, and 80 °C to obtain different aged samples. The measurements of mechanical properties analysis were also done on the aged samples to validate the resulted data from LIBS spectroscopy. LIBS tests were done in both air and argon atmosphere, in which molecular bands such as CN and C2 radiation were compared for all aged samples. In order to more accurate discrimination between spectra of different samples, principal component analysis (PCA) was used as a suitable chemometric method. All these results represent the changes in the chemical structure of specimens, which are due to increasing time and temperature during their aging processes.

Modelling of the viscoelastic behaviour with damage induced anisotropy of a plastic-bonded explosive based on the microplane approach

In this work, a mechanical constitutive law is proposed for a plastic-bonded explosive (PBX) which is a quasi-brittle energetic aggregate material, submitted to quasi-static loadings. Such material, sensitive to hydrostatic pressure, presents viscoelastic behaviour with damage induced anisotropy and irreversible strains. Previous models developed for this kind of material were mainly devoted for transient dynamic behaviour. The few existing quasi-static models considered the mechanical behaviour either isotropic or only elastoplastic. So, a new viscoelastic Microplane model with the damage induced anisotropy is proposed and implemented in commercial Finite Element software. The viscoelasticity was taken into account using a Maxwell generalized model with Microplane approach. The model consists in implementing the viscoelasticity inside the microplanes defining thus a Maxwell model on every direction. The sensitivity of the model to the strain increment magnitude and to the loading direction was analysed. As main conclusion, the experimental behaviour of the studied material was successfully predicted by this model.

ARC(Heat-wait-search method)와 Isothermal 조건을 이용한 압축형 복합화약의 열적 특성 및 노화 예측 연구

ARC(Heat-wait-search method)와 Isothermal 조건을 이용한 압축형 복합화약의 열적 특성 및 노화 예측 연구

Mesoscopic effects on shock initiation of multi-component plastic bonded explosives

A series of one-dimensional Lagrangian tests have been performed to examine model parameters in the mesoscopic reaction rate model for shock initiation of multi-component plastic bonded explosives (PBXs) for two multi-component plastic bonded explosives PBXC03 (87% HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazoncine), 7% TATB (triaminotrinitrobenzene), and 6% binder by weight) and PBXC10 (25% HMX, 70% TATB, and 5% binder by weight). As the numerical results are in good agreement with experimental data, the model parameters have been used to predict the effects of variations in mesoscopic properties (the particle size, initial density, binder strength, and content) on the shock initiation characteristics of PBXC03 and PBXC10. It is found that the time to detonation for PBXC03 increases with all these mesoscopic properties, while the time to detonation for PBXC10 is basically independent of its mesoscopic properties. Thus, PBXC03 is sensitive to mesoscopic properties, but PBXC10 is not. Moreover, it is also found that the pressure-history curves behind the initial shock wave in PBXC03 have different trends from PBXC10, which implies different chemical reaction mechanisms. Further analysis reveals that it arises from the different hot spot ignition processes due to their different threshold initiation pressures. The hot spots are ignited gradually and almost simultaneously in PBXC03 and PBXC10, respectively.

Novel High-Nitrogen Content Energetic Compounds with High Detonation and Combustion Performance for Use in Plastic Bonded Explosives (PBXs) and Composite Solid Propellants

Novel High-Nitrogen Content Energetic Compounds with High Detonation and Combustion Performance for Use in Plastic Bonded Explosives (PBXs) and Composite Solid Propellants

Reactive Energetic Plasticizers Utilizing Cu-Free Azide-Alkyne 1,3-Dipolar Cycloaddition for In-Situ Preparation of Poly(THF-co-GAP)-Based Polyurethane Energetic Binders.

Reactive energetic plasticizers (REPs) coupled with hydroxy-telechelic poly(glycidyl azide-co-tetrahydrofuran) (PGT)-based energetic polyurethane (PU) binders for use in solid propellants and plastic-bonded explosives (PBXs) were investigated. The generation of gem-dinitro REPs along with a terminal alkyne stemmed from a series of finely designed approaches to not only satisfy common demands as conventional energetic plasticizers, but also to prevent the migration of plasticizers. The miscibility and rheological behavior of a binary mixture of PGT/REP with various REP fractions were quantitatively determined by differential scanning calorimetry (DSC) and rheometer, respectively, highlighting the promising performance of REPs in the formulation process. The kinetics on the distinct reactivity of propargyl vs. 3-butynyl species of REPs towards the azide group of the PGT prepolymer in terms of Cu-free azide-alkyne 1,3-dipolar cycloaddition (1,3-DPCA) was studied by monitoring 1H nuclear magnetic resonance spectroscopy and analyzing the activation energies (Ea) obtained using DSC. The thermal stability of the finally cured energetic binders with the incorporation of REPs indicated that the thermal stability of the REP/PGT-based PUs was maintained independently of the REP content. The tensile strength and modulus of the PUs increased with an increase in the REP content. In addition, the energetic performance and sensitivity of REP and REP triazole species was predicted.

Quantitative analysis for the determination of aluminum percentage and detonation performance of aluminized plastic bonded explosives by laser-induced breakdown spectroscopy

The aluminized plastic-bonded explosive (PBX) is a composite material in which solid explosive particles are dispersed in a polymer matrix, which includes three major components, i.e. polymeric binder, metal fuel (aluminum) and nitramine explosive. This work introduces a new method on the basis of the laser-induced breakdown spectroscopy (LIBS) technique in air and argon atmospheres to investigate the determination of aluminum content and detonation performance of aluminized PBXs. Plasma emissions of aluminized PBXs are recorded where atomic lines of Al, C and H as well as molecular bands of AlO and CN are identified. The experimental results demonstrate that a good discrimination and separation between the aluminized PBXs is possible using LIBS and principle component analysis, although they have similar atomic composition. Relative intensity of the AlO/Al is used to determine aluminum percentage of the aluminized PBXs. The obtained quantitative calibration curve using the relative intensity of the AlO/Al is better than the resulting calibration curve using only the intensity of Al. By using the LIBS method and the measured intensity ratio of CN/C, an Al content of 15% is found to be the optimum value in terms of velocity of detonation of the RDX/Al/HTPB standard samples.

Experimental investigation of 50 MPa reinforced concrete slabs subjected to blast loading

This paper presents results from blast tests conducted on four 50 MPa concrete slabs with reinforcement ratios of 0,175% and 0,37%. Two of the slabs were retrofitted with 50 mm thick foam in order to investigate the potential of using the foam as a strengthening option. The slabs were simply supported on two sides. Non-confined PBX (Plastic bonded explosive) was molded with the form of a cylinder measuring 20 cm in height and 10,5 cm in diameter. The explosive was detonated at 2 m stand-off distance. The equivalent TNT mass of the explosive ranges from 2,58 to 2,72 kg for the four tests. Accelerometers, displacement and pressure gages were used to measure blast wave parameters and global response of the slabs. A high-speed digital camera in conjunction with a rugged notebook recorded images. Qualitative and quantitative results are included. Slabs retrofitted with foam showed a different pressure pattern as recorded by the sensors and resulted in higher displacement, acceleration and linear momentum.

Explosive Properties of a High Explosive Composition Based on Cis‐1,3,4,6‐tetranitrooctahydroimidazo‐[4,5‐d]imidazole and 1,1‐Diamino‐2,2‐dinitroethene (BCHMX/FOX‐7)

AbstractIn this work, preparation and characterization of a plastic bonded explosive (PBX) based on a mixture of cis‐1,3,4,6‐tetranitrooctahydroimidazo‐[4,5‐d]imidazole (BCHMX) and 1,1‐diamino‐2,2‐dinitroethene (DADNE or FOX‐7) bonded by poly‐dimethyl siloxane binder (PDMS) were investigated. Impact and friction sensitivities were determined. Detonation velocity was measured and the detonation characteristics were determined by the EXPLO 5 thermodynamic code. Relative explosive strength was determined using the ballistic mortar test. For comparison, four individual cyclic nitramines, RDX (1,3,5‐trinitro‐1,3,5‐triazinane), β‐HMX (β‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocane), BCHMX and ϵ‐CL20 (ϵ‐2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane, ϵ‐HNIW) in addition to their PBXs bonded by the same polymeric matrix were studied. Also traditional plastic explosives such as Czech plastic explosive (SEMTEX 10) and Egyptian Plastic Explosive (EPX‐1) were included in the study. The results confirmed that BCHMX/FOX7‐Sil has the lowest impact and friction sensitivity of all the studied samples and its detonation velocity and pressure are higher than the traditional PETN plastic explosives.

Influence of Graphene Oxide on the Sensitivity Parameters of 1,3,5,7-tetranitro1,3,5,7-tetraazacyclo-octane

1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) is one of the most powerful energetic materials which has several applications. Decrease the sensitivity of HMX is a goal for the researchers. In this work, the influence of graphene oxide (GO) on the sensitivity parameters of HMX has been studied. Graphene oxide has been prepared in our laboratories and it was used to prepare a composite based on GO-HMX by solvent-antisolvent slurry method. The prepared samples have been studied by X-ray diffractometer (XRD). Scanning electron microscope (SEM) has been used to check the crystal morphology of each sample. Selected types of plastic bonded explosives (PBXs) based on HMX have been studied for comparison. Impact and friction sensitivities of GO-HMX and the selected PBXs were measured, and the ignition temperature was determined by deflagration test. It was concluded that the crystals of HMX have been coated by layers of GO and the shapes of the crystals have been modified. GO-HMX has lower impact sensitivity than the individual HMX and the studied PBXs while the friction sensitivity are in the same level. The GO layers caused accumulation of the heat inside the crystals during the heating process and decreased the ignition temperature of GO-HMX. GO successfully decreased the sensitivity parameters of HMX and its effect on the detonation parameters should be studied.