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3-nitro-1,2,4-tri-azol-5-one (NTO) is a high energy insensitive explosive. To study the shock initiation process of NTO-based polymer bonded explosive JEOL-1 (32%octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 32% NTO, 28% Al and 8% binder system), the cylinder test, the gap experiments and numerical simulation were carried out. Firstly, we got the detonation velocity (7746 m/s) and the parameters of Jones-Wilkins-Lee (JWL) equation of state (EOS) for detonation product by cylinder test and numerical simulation. Secondly, the Hugoniot curve of unreacted explosive for JEOL-1 was obtained calculating the data of pressure and time at different Lagrangian positions. Then the JWL EOS of unreacted explosive was obtained by utilizing the Hugoniot curve as the reference curve. Finally, we got the pressure growth history of JEOL-1 under shock wave stimulation and the parameters of the ignition and growth reaction rate equation were obtained by the pressure-time curves measured by the shock-initiation gap experiment and numerical simulation. The determined trinomial ignition and growth model (IG model) parameters can be applied to subsequently simulation analysis and design of insensitive ammunition with NTO-based polymer bonded explosive.

Cadmium sulfide nanorods with a length of 69 nm have been prepared by using Cd(OAc)2.2H2O and S8 at 125 °C in the presence of triethylenetetramine as the template agent and coordination agent and characterized by using X-ray diffraction, transmission electron microscopy, FTIR, photoluminescence, and UV–vis absorption spectroscopic techniques. Photocopolymerization of glycidyl methacrylate (GMA) and sodium acrylate (SA) was carried out using CdS nanorods as a photocatalyst under UV light exposure at 400 nm in the presence of β-cyclodextrin (β-CD). To optimization of the effective parameters on the synthesis of copolymer nanocomposite, the amounts of initiator, monomers, and β-CD, duration of pre-deoxygenation, and light wavelength were evaluated. Ring opening of poly(GMA-co-SA)/CdS nanocomposite with NaN3 afforded poly(HAzPMA-co-SA)/CdS nanocomposite and subsequent mixing with RDX in DMF led to the formation of poly(HAzPMA-co-SA)/RDX/CdS nanocomposite as a polymer bonded explosive. All of the copolymer nanocomposites were characterized using various tools of instrumental analysis.

This work investigates kinetics and thermal decomposition behaviors of pentaerythritol tetranitrate (PETN) and two polymer-bonded explosive (PBX) samples created from PETN (named as PBX-PN-85 and PBX-PP-85) using the vacuum stability test (VST) and thermogravimetry (TG/DTG) techniques. Both model-free (isoconversional) and model-fitting methods were applied to determine the kinetic parameters of the thermal decomposition. It was found that kinetic parameters obtained by the modified Kissinger–Akahira–Sunose method (using non-isothermal TG/DTG data) were close to those obtained by the isoconversional and model-fitting methods that use isothermal VST data. The activation energy values of thermal decomposition reactions were 125.6–137.1, 137.3–144.9, and 143.9–152.4 kJ·mol−1 for PBX-PN-85, PETN, and PBX-PP-85, respectively. The results demonstrate the negative effect of the nitrocellulose-based binder in reducing the thermal stability of single PETN, while the polystyrene-based binder seemingly shows no adverse influence on the thermal decomposition of PETN in our presented PBX compositions.

Thermal stimuli is one of the major external stiumuli resulting from an overheated explosion of a munition. In order to evaluate the influence of external thermal stiumuli on the thermal hazards of JEOL-1 (32 wt% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 32 wt% 3-nitro-1,2,4-triazole-5-one (NTO), 28 wt% Al and 8 wt% binder system) explosive, accelerating rate calorimeter (ARC) is used to study the adiabatic thermal decomposition properties of JEOL-1 molding powders, and the slow cook-off properties of JEOL-1 are studied by experimental test and numerical simulation. The activation energy Ea, pre-exponential factor A, mechanism function f(α) and self-accelerating decomposition temperature (SADT) of adiabatic thermal decomposition of JEOL-1 molding powders are obtained according to ARC results. The response level of JEOL-1 polymer bonded explosive (PBX) columns exposed to an engulfing liquid pool fire is examined by the slow cook-off test. The ignition location, ignition temperature, ignition time and the transient temperature distributions of JEOL-1 PBX columns during the slow cook-off are obtained by numerical simulation. It can be concluded from this study that JEOL-1 is a low vulnerable explosive with high thermal safety.

To satisfy the energy and security requirements of the explosives, it is necessary to develop high-energetic low vulnerable explosive. As the representatives of high-energetic explosives and low vulnerable explosives, hexanitrohexaazaisowurtzitane (HNIW) and 3-nitro-1,2,4-triazole-5-one (NTO) are used to research high-energetic low vulnerable polymer-bonded explosive (PBX) in this study. Based on the formulation of PAX-11 (94 mass% HNIW, 2.4 mass% CAB, 3.6 mass% BDNPA/F), some HNIW is replaced by NTO to reduce the vulnerability of the PBX during this work. Solution−water suspension method was used to prepare a series PBXs with different formulations. The explosion probability method, differential scanning calorimeter and accelerating rate calorimeter are used to evaluate the hazards of different PBX molding powders. And the thermal vulnerabilities, mechanical properties and energy levels of PBX columns are assessed by slow cook-off tests, tensile strengthes and detonation velocities, respectively. Moreover, finite element numerical simulations are adopted to study the transient temperature distributions, ignition time and ignition locations of the PBX columns during slow cook-off. The investigated results show that when the mass fraction of HNIW and NTO is 50% and 44%, respectively, the PBX passes the slow cook-off test and the detonation velocity reaches 8685 m s−1. To balance the energy and vulnerability of the PBXs, we obtain a high-energetic low vulnerable PBX formulation (50 mass% HNIW, 44 mass% NTO, 2.4 mass% CAB, 3.6 mass% BDNPA/F, 0.5 mass% additional graphite) which can be used in the warhead of the high-explosive anti-tank cartridge.

To facilitate the pre-estimation and optimization of the prescription design of a multi-component polymer bonded explosive (PBX), a multicomponent mesoscopic reaction rate model (MC-DZK model) is developed to predicate preferably the influence of both the explosive components and the particle size of on the shock initiation. All the parameters in the model are determined directly by the parameters in the DZK model for each explosive component. Furthermore, for the multicomponent insensitive explosive PBXC10 (70% TATB, 25% HMX, and 5% Kel-F800 by weight) with different explosive particle sizes, both shock initiation experiments and corresponding numerical simulations are performed, and there is satisfactory agreement between the numerical results and the available experimental data. It is found that the pressure histories present as a shape of step increase during the whole shock initiation process, which is resulted mainly from the rapid chemical reaction rate just behind the precursory shock wave front. It is also found that the smaller the size of the explosive particulates, the faster the pressure grows on the precursory shock wave front, the shorter the run distance to detonation, and the higher the chemical reaction rate just behind the precursory shock wave front.

Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is one of the most widely used explosives. Problems about phase state and unrecoverable damage are significant in the application of HMX and HMX-based polymer-bonded explosive (PBX). Recently, the acceleration of δ- to β-HMX retransformation in humid atmosphere was reported. However, the function of water was not well understood. In this paper, we studied the mixed phase during δ- to β-HMX-d8 retransformation with neutron diffraction. Evidence of γ-HMX-d8 is specially focused to estimate whether the hydrated phase is part of the δ- to β- phase retransformation. Besides, in situ high-pressure neutron diffraction of HMX-based PBX was performed to study the evolution of intergranular strains in special structures such as twin plane, cleavage planes, and slip systems. We observed an abnormal release of strain on certain planes under applied pressure which had not been reported. This abnormal phenomenon was considered to explain the formation of microcrack...

Mesoscale simulation using the material point method (MPM) was conducted to study the pressure&ndash, volume (PV) variations of Octahydro-1,3,5,7-Tetranitro-1,2,3,5-Tetrazocine (HMX)/Estane polymer-bonded explosive (PBX) under impact loading. The PV isotherms and Hugoniot data were calculated for the different porosities and binder volume fractions. The PV isotherms were used to determine the parameters for the Birch&ndash, Murnaghan equation of state (EOS) for the PBX. From the EOS, the isothermal bulk modulus (K0) and its pressure derivative () were calculated. Additionally, the pseudo particle velocity and pseudo shock velocity variations were used to obtain the bulk wave speed c and dimensionless coefficient s for the Mie&ndash, Gr&uuml, neisen EOS. The simulations provide an alternative approach for determining an EOS that is consistent with experimental observations.

Complexities of heating mechanisms make it difficult to investigate the safety of a polymer bonded explosive (PBX) charge of earth-penetrating-weapons (EPWs) during penetration. In this paper, the dynamic damage and non-shock initiation of PBX1314 (60 wt % hexahydro-1, 3, 5-trinitro-1, 3, 5-s-triazine (RDX), 16 wt % aluminum, 24 wt % hydroxy-terminated polybutadiene (HTPB)) during penetration is investigated through experiments and simulations. In the experiments, steel projectiles filled with PBX1314 are launched to penetrate concrete targets. In the results, non-shock initiations occur on the tail surface of PBX1314 along with mechanical damage of the tail and middle part of PBX1314. A dynamic damage and initiation model is proposed to characterize the effects of microcracks on the mechanical and thermal responses of PBX1314. Investigation based on the model suggests that microcrack interfacial friction plays significant roles in damage, heat generation and localization in PBX1314. A non-shock initiation criterion is developed based on macroscale variables in PBX1314. Numerical simulations of the penetration experiments are performed by using the proposed model and criterion. The mechanical damage and non-shock initiation of PBX1314 in the experiments are successfully predicted. The simulation results indicate that the tail of PBX1314 impacts the projectile repeatedly during penetration. Finally, the initiation criterion is satisfied because of frictional heat localization near microcrack surfaces and initiation is activated in the tail of PBX1314.

Synergetic deformation behavior between crystal particles and polymeric binders dominates the machinability of energetic materials. In the present work, we elucidate cutting mechanisms of HMX-based polymer bonded explosive (PBX) in orthogonal cutting by numerical simulations based on a cohesive finite element framework. The polygonal HMX crystals with a particle volume fraction of 90% are modeled by a linear elasticity model, while the HTPB binders are described by a rate-independent hyperelastic model coupled with a rate-dependent plasticity model. Furthermore, cohesive elements are implemented in both crystal particles and binders to describe thermal-mechanical coupling-induced material failure behavior in the cutting process of PBX. Simulation results reveal different deformation modes of PBX, as well as their correlations with machining results. Furthermore, it is found that depth of cut has a strong impact on the cutting processes of PBX, in terms of material failure mode, subsurface damage and energy dissipation. These findings provide important guidelines for the design and synthesis of energetic materials with high machinability. Keywords: Energetic material, Synergetic deformation, Orthogonal cutting, Finite element simulation, Cohesive zone model

Surface engineering has been widely implemented in materials science for multipurpose functionalization. However, the rational design of surface structure with both adhesiveness and toughness remains a huge challenge. Herein, a facile and general strategy has been demonstrated for coating of energetic crystal 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) via in situ copolymerization of catechol and amino functionalized monomers. The design principle is on the basis of bioinspired supramolecular chemistry, providing the synergistic effect of covalent and noncovalent interactions. Compared with the pristine HMX crystal, the coated HMX crystals exhibited significantly improved phase-transition stability and reduction of impact/friction sensitivity owing to the reinforced interfacial strength and coating roughness. Moreover, thanks to incorporation of the catechol–containing synthetic polymer (CSP) interlayer, the interfacial interaction between HMX crystal and fluoropolymer binder was noticeably enhanced, leading to markedly improved mechanical strength (both tensile and compression strength were improved by over 40%), as well as creep resistance (the creep strain was decreased by over 55%) for the resulted polymer bonded explosive (PBX) composite. Therefore, the present work provides an effective and universal method for the construction of environmental adaptive energetic materials on account of their reduced sensitivity, enhanced mechanical strength and thermal stability, which were favorable for their practical applications.

Polymer bonded explosive (PBX) is a particle-matix composite consisting of explosive particles, polymer matrix/binder, and the interface between the particles and the binder, and the particle volume fraction (PVF) in the PBX is extremely high. To simulate the meso-scale deformation and damage behaviors of PBX with the numerical manifold method (NMM), a bilinear cohesive contact relationship (BCCR) model with three parameters is incorporated in the NMM to describe the particle-binder interface, a visco-elastic constitutive model of prony series with 22 parameters is incorporated in the NMM to describe the polymer binder, and a fracturing algorithm based on the maximum tensile stress criterion and the Mohr–Coulomb criterion is employed to describe the fracturing failures of the particles as well as the binder. The PBX meso-scale deformation and damage process of microcrack initiation, crack propagation and formation of crack bands under tensile or compressive conditions are studied through NMM simulations, and the influenes of the PVF and the explosive particle geometrical distribution (PGD) on PBX mechanical performaces are specially investigated. This work enables and proves the NMM to be an promissing roubust numerical tool for further simulation studies of the meso-scale mechanical performances of PBX, as well as other particle-fillled polymer composites.

A micromechanical model for the thermoelasticity of polymer-bonded composites is presented. The model is particularly aimed at describing materials where the polymeric binder phase undergoes non-negligible thermal expansion affecting the overall thermoelastic response. Constitutive choices for modeling a mixed binder-void interphase layer are proposed, and an associated decomposition of total eigenstrains into classical, elastic imperfection (damage), and binder thermal expansivity parts is examined within the context of imperfect inter-particle interfaces. A novel temperature dependent modified Eshelby tensor is identified, making possible the development of a temperature dependent modified self-consistent homogenization scheme—what we call the M $\theta$ -SCH model. A method for distinguishing between dispersed and isolated parts of the binder and void phases in the model is also provided, along with a description of particle coating (or interphase) thickness derived from particle morphology and mesoscale effective properties. Although the theory is general, its development is motivated by the need to model anisotropic and highly nonlinear observed thermal expansion behavior of the polymer bonded explosive PBX 9502, for which model simulations are performed and compared with existing measurements.

The application of in situ structural health monitoring in polymer bonded explosive materials through the introduction of carbon nanotubes into the binder phase is investigated through piezoresisti...

Nano-fillers have attracted a large amount of attention in enhancing the mechanical properties of polymer bonded explosive (PBX), due to the strong interfacial interactions. However, the addition of inert components reduces the energy output and makes the processing, recycling and re-utilization of energetic composites quite unfavorable. To improve the mechanical properties while maintaining detonation performance, a novel self-reinforced PBX was constructed with very low content of nano-1,3,5-triamino-2,4,6-trinitrobenzene (TATB) served as modifiers. The incorporation of nano-TATB particles into PBX evidently increased the storage modulus, strength, and toughness. The enhanced mechanism could be ascribed to the nano effect of nanoparticles and “interlocking block” formed on the rough surface of nano-TATB, which provided stronger interfacial interaction. This work demonstrates the successful application of nano-energetic crystals to self-reinforce PBXs, thereby opening up new perspectives in structure design and modification of mechanical properties for energetic composites without changing the intrinsic components of energetic composites.

Polymer bonded explosives (PBX) are kind of particulate-reinforced composite materials in which interface interaction is of great significance to its structural and mechanical features. In this work, effect of temperature and strain rate on the microstructure, mechanical properties and fracture damage mechanism of TATB-F2314 are studied using molecular dynamics simulations. The TATB layers at the TATB-F2314 interface are deformed, leading to a rough and undulate surface that facilitates the formation hydrogen bonds between TATB and F2314. Intermixing phase is characterized for the first time at the TATB-F2314 interface. The interfacial structures and mechanical properties of TATB-F2314 depend strongly on temperature and strain rate. F2314 experiences a ductile-to-brittle transition at its glass transition temperature, which exerts great influence on the structural evolution and failure mechanism of TATB-F2314. The fracture mainly appears on F2314 under a quasi-static or low strain rate tension but transfers to TATB layers near to the interfacial intermixing phase at a high strain rate. Our simulations reveal the effect of temperature and strain rate on the microstructure, mechanical behavior and fracture damage mechanism of TATB-F2314 interface, which is useful for the design, preparation and safe use of PBX.

Material characterization at high strain rates under simultaneous compression and shear loading has been a challenge due to the differing normal and shear wave speeds. An experimental technique utilizing the compression Kolsky bar apparatus was developed to apply dynamic compression and shear loading on a specimen nearly simultaneously. Synchronization between the compression and shear loading was realized by generating the torsion wave near the specimen which minimizes the time difference between the arrival of the compression and torsion waves. This modified Kolsky bar makes it possible to characterize the dynamic response of a material to combined compression and shear impact loading. This method can also be applied to study dynamic friction behavior across an interface under controlled loading conditions. The feasibility of this method is demonstrated in the dynamic characterization of a simulant polymer bonded explosive material.

The thermal decomposition kinetics of the interesting polycyclic nitramine cis-1,3,4,6- tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX) and its polymer bonded explosive (PBX) based on polyurethane matrix, have been investigated using different thermal analysis techniques and methods. The used polyurethane matrix is based on hydroxyl-terminated polybutadiene (HTPB) cured by hexamethylene diisocyanate (HMDI). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used nonisothermally, whereas the vacuum stability test (VST) was used isothermally. Kinetic parameters were determined by using isoconversional (model-free) methods. Furthermore, the Advanced Kinetics and Technology Solution (AKTS) software was used to determine the kinetic parameters of the studied samples in order to provide a comparison. It was found that the decomposition temperature of BCHMX/HTPB is lower than that of pure BCHMX. All the applied techniques as well as computational results showed that BCHMX/HTPB has a lower activation energy than pure BCHMX. The different methods used, Kissinger, Ozawa, Flynn, and Wall (OFW) and Kissinger-Akahira-Sunose (KAS) methods presented activation energies in the same range of the AKTS software results. Also the results proved that VST technique could be a useful tool to present results suitable for calculation of the kinetic parameters of explosives.

In this work, inspired by the strong chemical adhesion of mussels, a facile and noncovalent in situ polymerization of dopamine approach has been employed to coat 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) crystals. The resultant polydopamine (PDA) coated TATB (pTATB) core–shell particles are subjected to in-depth characterizations. It has been demonstrated that a dense graphite-like structure PDA is uniformly coated on the surfaces of TATB crystals. By optimization of the reaction time, pH value and temperature, the morphology and thickness of the PDA layer on TATB crystals were finely controlled on a nanometer scale. Then, the pTATB was further used as the solid filler of a typical polymer bonded explosive (PBX). It has been shown that the PBX containing pTATB exhibited significantly improved tensile and compression strength or strain, and creep resistance, due to the strong interfacial interactions at the PDA interlayer. Moreover, the mechanical properties could be further improved by using more PDA content. This work demonstrates an effective and fundamental surface modification method to enhance the interfacial interaction between crystalline particles and binders, resulting in improved mechanical properties.

Material Point Method (MPM) mesoscale simulation was used to study the constitutive relation of a polymer bonded explosive (PBX) consisting of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and a fluorine polymer binder F2314. The stress-strain variations of the PBX were calculated for different temperatures and different porosities, and the results were found to be consistent with experimental observations. The stress-strain relations at different temperatures were used to develop the constitutive equation of the PBX by using numerical data fitting. Stress-strain data for different porosities were used to establish the constitutive equation by fitting the simulation data to an improved Hashion-Shtrikman model. The equation can be used to predict the shear modulus and bulk modulus of the PBX at different densities of the sample. The constitutive equations developed for TATB/F2314 PBX by MPM mesoscale simulation are important equations for the numerical simulations of the PBX at macroscale. The method presented in this study provides an alternative approach for studying the constitutive relations of PBX.

The ultrasonic attenuation coefficient is sensitive to the internal constituent components of the material, and the effective entry of ultrasonic waves into the material is of great significance for the development of non-destructive testing. In this paper, based on DIGIMAT/FE, a mesoscopic model of materials is built, covering two phases of explosive particles and binder, using ABAQUS/EXPLICT to load ultrasonic loading of materials, extracting internal unit stress-time curves and stress wave propagation clouds, and establishing the relationship between the ultrasonic attenuation coefficient of the bonded explosive and the different mass ratio of the explosive particles. Taking the RDX/Estane composite adhesive as an example, the volume fraction of explosive particles RDX and the influence of ultrasonic frequency on the sound attenuation coefficient were studied. The numerical simulation results of the model were compared with the real experimental data to verify the validity of the model. This numerical model method can effectively guide the acoustic experimental process of the material and provide a theoretical basis for the non-destructive testing of materials.

Using Digimat-FE, a representative volume element (RVE) model was constructed that reflects the true mesostructure of PBX explosives. The model consists of three phases of explosive particles, binder and pores. Through Digimat-MF, various factors affecting the effective elastic modulus of PBX explosives were investigated, including the elastic modulus, volume fraction, morphology, gradation, porosity and pore diameter of the explosive particles. The calculation results show that the higher the volume fraction of explosive particles, the larger the effective elastic modulus of PBX, and the increase of the effective elastic modulus of PBX is obviously increased when the volume fraction exceeds 60%. The morphology of the explosive particles has little effect on the effective elastic modulus of the PBX explosive, while the grading of the explosive particles has a great influence. The existence of pores makes the effective elastic modulus of PBX explosives significantly reduced, and the increase of porosity makes the effective elastic modulus decrease exponentially; the increase of pore diameter makes the effective elastic modulus of PBX explosives decrease.

Polymer-bonded explosives are solid high-explosive particles that exhibit brittle behavior in uniaxial tension, quasi-brittle in uniaxial compression, and ductile when subjected to high confining pressure. Tension cracking is the primary failure mode of polymer-bonded explosives quasi-brittle solid, which will lead to overall failure of structural integrity. One characteristic of brittle or quasi-brittle solids, such as polymer-bonded explosives, is that when subjected to overall compressive loading, the tensile cracks will initiate inside the material due to existence of imperfection within the materials. In this study, extended finite element method is applied to analyze the cracking failure mechanism in the PBX 9502 plate-like specimen with cavity subjected to overall compression. The nonlinear constitutive behaviors and failure of polymer-bonded explosives under complex stress states were described by means of stress state–dependent strength surface, non-associated flow rule, and cohesive failure model. Analysis indicates that the tensile stress around the cavity arises in the specimen under overall compression, and this local tensile stress will lead to cracking initiation. The comparison between simulation results and the experimental data reported by Liu and Thompson shows that they are in agreement with each other on some aspects of crack behaviors, including overall development of crack history and inflection, crack initiation moment, and crack initial speed.

We investigate the effects of porosity and chemical reactivity on the shock initiation of an HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine)-based polymer bonded explosive due to thin flyer impact using two-dimensional mesoscale simulations. Microstructural samples are computationally generated, and the calculated shock response is compared to experiments. The sample dimensions are 0.1 × 1.05 mm2, and each sample accounts for grain scale heterogeneities, including randomized grain morphology and pore spacing. Simulations are performed using the Lawrence Livermore National Laboratory (LLNL) arbitrary Lagrangian–Eulerian multi-physics code ALE3D. Chemistry and equation of states are handled with LLNL's thermochemical code Cheetah. We employ a modified Arrhenius-based chemical kinetics model that scales the temperature exponent fitting parameter with flyer shock conditions. This new model is calibrated to the mean response of experimental shock initiation thresholds for three separate Kapton flyer thicknesses. A simplified shock initiation criterion is proposed, which classifies the macroscale initiation response based on cross-sectional temperature profiles of the shocked sample. This criterion is used to further investigate the probabilistic response of the sample to variations in the mean porosity and chemical kinetics rate, and we find an inverse correlation between the shock pressure and the confidence interval of the experimental threshold velocity. The methodology presented in this work for quantifying the probabilistic nature of shock initiation is material agnostic. These mesoscale studies may be used to inform continuum scale models and expedite the development of future, tailored energetic formulations.

To improve thermal stability and security of energetic materials, the core–shell structured FOX-7 (1,1-diamino-2,2-dinitroethylene)/F2602 (fluoroelastomer) PBX (polymer bonded explosive) was prepared from recrystallized FOX-7 by a spray drying strategy. The morphology and crystal form of the recrystallized FOX-7 were retained, and the mean particle size of the FOX-7/F2602 PBX was apparently reduced from 39.72 µm of raw FOX-7 to 1.50 µm. SEM, TEM, and XPS analysis showed that F2602 was deposited on the surface of FOX-7 to form a core–shell structured composite. The formation mechanism of the core–shell composite was proposed. Compared with the recrystallized FOX-7 grains, the prepared FOX-7/F2602 PBX had higher apparent Ea and Tb, which signifies improved thermal stability and thermal safety. The impact sensitivity test showed that the critical height value (H50) of the FOX-7/F2602 composite had remarkable enhancement, indicating better mechanical security. This work provides a simple and effective method to prepare the core–shell structured energetic composite with enhanced safety performance.

In order to study the crack formation mechanism of an aluminized polymer-bonded explosive (PBX) under tensile stress, a Brazilian test was carried out on the aluminized PBX grains with different densities. In addition, the microscopic morphologies of the samples after the Brazilian test were characterized. The experimental results show that the process of crack formation includes initiation, propagation, and final formation; the cracks are generated by the accumulation of microscopic defects and they expand gradually from the interior to the end surface of grains. With increasing grain density, as well as the curing process, the critical stress values could be significantly improved during the formation of cracks. The formation mechanism of the cracks is not transcrystalline fracture but interfacial debonding, which was observed using scanning electron microscopy.

The influence of an explosion-driven deformation on the defect structure in RDX crystals embedded in a polymer-bonded explosive was investigated by means of confocal scanning laser microscopy. The images were compared to the defect structure in the as-received RDX grades, embedded

The β→δ phase transition (PT) of cyclotetramethylene tetranitramine (HMX) plays an important role in the safety of explosives when they are exposed to heat. In this work the effect of HMX content on the PT of HMX in Polymer Bonded Explosive (PBX) is reported. Using in situ X-ray diffraction (XRD) test combined with quantitative analysis, the dependence of the PT temperature and dynamic behavior of HMX in PBX formulations [HMX+triaminotrinitrobenzene (TATB)+Olefin] on the content of HMX is investigated. The results show that the β→δ PT temperature gradually increases with the reduction of HMX content and with the increase of TATB content. Additives of TATB and olefin in high concentration can form compact coatings on the HMX crystals. Such coatings can delay the nucleations of δ-HMX by inhibiting the volumetric expansion during PT. Moreever, these coatings separate the HMX crystals and build up a heat conduction obstacle. As a result the growths of δ-HMX are also suppressed by the coatings. In contrast, fewer additives lead to larger free surface area of HMX, which accelerates the PT.

The effect of initial cooling temperatures on the thermal shock behavior of cylindrical polymer bonded explosive (PBX) was investigated by using a combined acoustic emission (AE) and strain gauge technique in fast air-cooling tests. Dissimilarity was observed below and above the viscous flow temperature (Tf) where the PBX exhibited brittle-ductile transition and temperature dependence on material properties. We found that cooling below Tf would lead to fracture with strong AE signals and a linear strain-time response followed by a sharply decline, while above Tf would generate weaker AE events and a non-linear strain history with soften response. A segmented characterization was proposed for the calculation of thermal shock resistance and the corresponding critical fracture temperature difference. This estimation fits well with our experimental and simulation results.

Dynamic damage response of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX) based polymer bonded explosive (PBX) is investigated by using recently developed three dimensional Peridynamic (PD) method, allowing natural evolution of defects such as cracks or voids. An in-house PD codes are developed and verified by comparing with published results on Kalthoff-Winkler (KW) and crack branching benchmark tests. Numerical modeling of PBX is constructed via random micro-modulus approach, capable of capturing inherent microstructural heterogeneity of PBX materials. The simulation results indicate that damage process depends on both impact speed and interfacial property. Damage mode index (DMI), defined as the ratio of HMX-HMX damage to the summation of Binder-Binder and HMX-Binder damage, is proposed to quantify competitive damage mechanisms between trans- and inter-granular damage. The analyses of DMI exhibit that the inter-granular damage is dominant for the low adhesive strength of interface. However, the trend of trans-granular damage increases with increasing impact speed. The trans-granular damage mode becomes dominant for the high adhesive strength of interface. But the trend of inter-granular model increases with increasing impact speed. The current research highlight the competitive mechanisms of two typical damage modes as a function of material property and external loading conditions in a quantitative manner, providing additional insight into the damage mechanisms of PBX under impact loading.

Polymer bonded explosive (PBX) is a composite consisting of the polymer binder and embedded explosive particles, along with a large number of the particle/binder interfaces as the third constituent. The particle volume fraction is often higher than 90%. In the present work, a visco-elastic constitutive model, an elastic visco-plastic constitutive model and a bilinear cohesive contact relationship model are implemented into the numerical manifold method (NMM) program, an open source code programmed with C language, to describe the deformations of the polymer binder, the explosive particles and the particle/binder interfaces, respectively. The fracturing of the polymer binder and explosive particles is described based on the maximum tensile stress and the Mohr-Coulomb criteria. Three categories of initial defects, including the initial interfacial debonding, initial voids in the polymer binder, and initial micro-cracks in the explosive particles, are considered in the PBX meso-structures under both uniaxial tensile and compressive conditions. The tension-compression asymmetry, the influence of the initial defects on the meso-structure failure modes/patterns and the macroscopic effective tensile/compressive strength of PBXs are investigated. The factors that cause the differences between the NMM results and other numerical or experimental results are analyzed and discussed. This work enables and proves the NMM to be an robust numerical tool for further simulation studies of the mechanical performances of PBXs, as well as other particle-filled composites, at the meso-scale.

The chemical compatibility and the adhesion of energetic materials and additive materials exert a strong influence on the sensitivity, safety and performance of a polymer-bonded explosive (PBX). In this study, the chemical compatibility of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), pentaerythritol tetranitrate (PETN) with several polymers were evaluated using the vacuum stability test (VST) and the differential scanning calorimetry (DSC), while the adhesion between RDX or PETN and each binder based on these polymers was determined through interfacial characteristics using contact angle measurement. The experimental results demonstrate that RDX and PETN are compatible with polystyrene (PS), nitrocellulose (NC) and fluoroelastomer (FKM) according to the STANAG 4147. Therefore the two polymers can be used as adhesives in PBX composition. Moreover, based on interfacial characteristics such as interfacial tension and work of adhesion, the adhesion between RDX and each binder was predicted to be better than that of PETN.

The adhesion energy between the polymer binder and granular crystals strongly influence the mechanical properties of granular composites under different loading conditions. Thus, the accurate measurement of interfacial adhesion is necessary for the accurate description of the mechanical behavior and failure of granular composites. In the current work, an experimental setup capable of performing a peel test at different displacement rates (10 nm/s–1 mm/s) and peel angles (45°–135°) has been developed to experimentally quantify interfacial adhesion between soft elastomer (binder) and hard substrates (crystals). Since the elastomeric binder in many granular composites materials can be viscoelastic in nature, a time-dependent mathematical framework was adopted to calculate interfacial adhesion for these viscoelastic peel test experiments. Thus, the framework allows for the quantification of interfacial adhesion between different combinations of viscoelastic binders and crystals as a function of peel rate and angle. High-resolution optical microscope and digital image correlation was employed to capture the displacement and strain fields of both linear elastic and viscoelastic material under different conditions.

To study the three-dimensional (3D) morphological evolution of damage of the polymer bonded explosive (PBX) during compression process, the damage process of the PBX at the mesoscopic scale was analyzed. Furthermore, the damage evolution of the PBX was also deduced. The 3D deformation behavior and devolution of the internal microstructure of PBX during the in situ compression process were systematically investigated by integrating micro computed tomography (CT) imaging and digital volume correlation (DVC) method. The displacement and strain inside the PBX during the loading of down load were obtained through the DVC method. The results revealed that the strain concentration always appeared at binders between the granules before failure and led to granule internal cracking or granule edge cracking. The results further indicated that integration of micro CT and DVC technique can provide a more practical and effective method for investigating the structural features, strain, and damage mechanism of PBXs during compression process. This study has significant meaning for comprehensive investigation of the damage mechanical behavior of PBX.

In order to study the fracture behavior and structure evolution of 1,3,5-Triamino-2,4,6-Trinitrobenzene (TATB)-based polymer bonded explosive in thermal-mechanical loading, in-situ studies were performed on X-ray computed tomography system using quasi-static Brazilian test. The experiment temperature was set from −20 °C to 70 °C. Three-dimensional morphology of cracks at different temperatures was obtained through digital image process. The various fracture modes were compared by scanning electron microscopy. Fracture degree and complexity were defined to quantitatively characterize the different types of fractures. Fractal dimension was used to characterize the roughness of the crack surface. The displacement field of particles in polymer bonded explosive (PBX) was used to analyze the interior structure evolution during the process of thermal-mechanical loading. It was found that the brittleness of PBX reduced, the fracture got more tortuous, and the crack surface got smoother as the temperature rose. At lower temperatures, especially lower than glass transition temperature of binders, there were slipping and shear among particles, and particles tended to displace and disperse; while at higher temperatures, especially above the glass transition temperature of binders, there was reorganization of particles and particles tended to merge, disperse, and reduce sizes, rather than displacing.

We present a multiscale experimental investigation of polymer bonded sugar, a mechanical simulant of polymer bonded explosive, subjected to impact loading. The experiments are conducted by shooting a projectile onto the specimen at an impact velocity of 56 m/s using a modified split Hopkinson bar apparatus. Images at two different scales are captured for macroscale and mesoscale deformation measurement during the loading at a rate of 2 million frames/second. The local deformation measurement is conducted using a newly developed high speed-high spatial resolution image based diagnostic technique. Based on the macroscale full-field deformation, the compression wave velocity and the compression wave thickness are calculated. Further, the stress in front and behind the compression front is calculated. It is observed that the compression wave width is not constant, instead, increases as it propagates towards the support end of the specimen. The change in compression wave width could be due to energy dissipation during the propagation of the compression wave. The meso-scale measurement provided much insight into the dissipation mechanism involved during the compression wave propagation. The plastic deformation of a binder and local damage such as grain fracture and relative sliding of crystals have been observed that could have contributed to the energy dissipation in the material.

An explosive composition, derived from AFX-757, was systematically varied by using three different qualities of Class I RDX. The effect of internal defect structure of the RDX crystal on the shock sensitivity of a polymer bonded explosive is generally accepted (Doherty and Watt, 2008). Here the response to a mechanical non-shock stimulus is studied using an explosion-driven deformation test as well as the ballistic impact chamber. No correlation between RDX crystal quality and deformation sensitivity is observed. The DDT behavior (Deflagration to Detonation Transition) of the three plastic bonded explosives, although similar in composition, is distinct regarding the rate of diameter increase in the explosion-driven deformation test. Recovered polymer bonded explosive from the explosion-driven deformation test responds equally fast or slower in the ballistic impact chamber. Based on our experimental results the shear rate threshold as a single parameter describing mechanical

Explosive determination is of great importance in national defense and security fields. Simple, quick and reliable analytical techniques have been highly demanded in the field. In this work, we proposed a novel method for simultaneous determination of pentaerythritol tetranitrate (PETN), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and 2,4,6-trinaitrotolunene (TNT) in binary-component polymer bonded explosive (PBX) samples by means of a combination of ultraviolet (UV) spectrophotometry with multivariable calibration methods. An orthogonal array design (DAD) was employed to construct the calibration set, which contains 27 reference samples. The calibration models were constructed using Partial Least Square regression (PLS-1) and Multiple Linear Regression (MLR). The variables were selected by the Successive Projection Algorithm (SPA) in MLR model. The predictive ability of the optimized models was validated by a test set including 18 samples. Finally, the two optimized models were successfully applied to simultaneously determine the content of PETN, RDX and TNT in five real binary-component PBX samples. Satisfactory results were obtained for the two models, in which the recovery yields were close to 100% for all the analytes. The computed elliptical joint confidence region (EJCR) further shows that the two models have no proportional and constant errors in the predicted concentrations. In addition, the statistical analysis indicates that MLR model with reasonable variable selection (SPA-MLR) could exhibit a slight superiority toward PLS-1 in the system. In a word, UV-spectroscopy in combination with multivariable calibration techniques has high potential to be a simple, quick and accurate analysis method for explosive determination in practice.

Polymer matrix particulate composites comprise the majority of solid-phase high explosives, and most show considerable deterioration in mechanical properties when damaged. We have quantified this effect in three RDX–HTPB composites by measuring four damage metrics; the change in compressive strength, modulus, thermal conductivity and porosity, with increasing impact strain (the causal metric). This approach was applied to three RDX–HTPB composites containing (a) coarse, (b) fine and (c) both coarse and fine particles. Damage was applied by compression to predetermined levels of strain at strain-rates of the order of 103 s−1. All three materials exhibited deterioration in strength and storage modulus, but only the composites containing coarse particles showed significant changes in porosity or thermal conductivity with increasing specific impact energy. This is because the fine-particle composites mask internal damage by recovering their initial form, the resultant cracks are closed, whereas the coarse particles underwent grain reorientation when impacted and are left open. This last point highlights the difference between active and passive assessments of damage since the former do not change the density or thermal conductivity of the material. The deterioration of secant modulus that results from damage can also be predicted using a simple energy-activation model.

Characterizing the response of composite materials to high strain rate deformation is of great importance for a range of applications; however, the experiments required to do this are challenging. In order to be fully representative, specimens must be large, making it difficult to achieve mechanical equilibrium; furthermore diagnostic tools such as X-ray tomography and electron microscopy cannot be used on the required timescales of ca 10 μs. Many composites consist of a rate and temperature dependent polymer binder, with a filler that is independent of these parameters. In this paper, a simulation technique is applied, in which the high rate mechanical response of a composite is experimentally reproduced in low strain rate experiments by making use of the polymer time–temperature superposition principle. This is a novel application of time–temperature superposition to composite materials in order to experimentally replicate the high-rate response. In order to demonstrate this method on a model composite material, a particulate composite (polymer bonded sugar) and its binder are extensively characterized in compression, and the composite in indirect tension (Brazilian) tests, over a range of strain rates and temperatures. It is then shown that by reducing the temperature, low rate experiments can be performed which faithfully replicate the high rate data, opening up the opportunity for more extensive research programs combining mechanical testing and microstructural characterization of these materials.

In this paper, a test projectile with a recessed hole and an initially sealed vented test chamber were designed to investigate the impact initiation and energy release characteristics of the polymer bonded explosive (PBX) materials. Through a thin aluminum cover plate, the test projectile filled with PBX materials was launched into an infinitely rigid impact anvil on the interior. As the initiation takes place on the interior, great amounts of thermo-chemical energy gases were vented through a hole formed by the penetration process. The maximum pressure inside the chamber was used to evaluate the initiation characteristic of PBX materials. The experimental results suggest that the impact pressure has a significant effect on the initiation characteristic and reaction efficiency. It reveals the critical impact-initiated pressure and critical impact pressure of the maximum reaction efficiency. Combining with the theoretical analysis, a relationship between the maximum pressure and the energy deposited into gas inside the chamber is explored to analyze the energy release behavior.

Frictional heating of high-melting-point grit particles during oblique impacts of consolidated explosives is considered to be the major source of ignition in accidents involving dropped explosives. It has been shown in other work that the lower temperature melting point of two frictionally interacting surfaces will cap the maximum temperature reached, which provides a simple way to mitigate the danger in facilities by implementing surfaces with melting points below the ignition temperature of the explosive. However, a recent series of skid testing experiments has shown that ignition can occur on low-melting-point surfaces with a high concentration of grit particles, most likely due to a grit–grit collision mechanism. For risk-based safety engineering purposes, the authors present a method to estimate the probability of grit contact and/or grit–grit collision during an oblique impact. These expressions are applied to potentially high-consequence oblique impact scenarios in order to give the probability of striking one or more grit particles (for high-melting-point surfaces), or the probability of one or more grit–grit collisions occurring (for low-melting-point surfaces). The probability is dependent on a variety of factors, many of which can be controlled for mitigation to achieve acceptable risk levels for safe explosives handling operations.

Leakage of paraffin wax (PW) is a major concern in the development of polymer bonded explosive (PBX) systems because it relates to the amount of PW that can be used as a desensitizer or a fuel, which, in turn, affects the mechanical performance and tolerance of PBX in high-temperature environments. Hydroxyl-terminated polybutadiene (HTPB) binders significantly contribute desirable polymer features to PBX. Thus, a three-dimension (3D) high-temperature non-flowing diurea–paraffin wax (DU–PW) composite was synthesized and creatively employed to a HTPB binder. DU–PW/PW/HTPB composites with different contents of the 3D DU–PW phase change material (PCM) were prepared through a cast molding process. The differential scanning calorimetry (DSC) results demonstrate that these composites can show high phase-change enthalpies and good thermal reliability. As observed from the scanning electron microscope (SEM) photographs, adding DU–PW can clearly reduce the number of holes caused by the leaked PW on the fracture surface of DU–PW/HTPB. Moreover, the addition of DU–PW can remarkably reduce the leakage of PW and improve the thermal stability as well as mechanical properties of the PW-based HTPB. These observations present the potential of utilizing form-stable PCM (FSPCM) to solve the problem of PW leakage in PBX systems.

Dihydroxylammonium 5,5′- bistetrazole-1,1′-diolate (TKX-50) was used to prepare TKX-50-based polymer bonded explosive (PBX) for the first time in this study. The thermal stabilities and the kinetic parameters of TKX-50 and TKX-50-based PBX were compared via Differential Scanning Calorimetry (DSC), Thermal Gravity-Differential Thermal Gravity (TG-DTG) and Accelerating Rate Calorimeter (ARC). Furthermore, in order to know about their thermal safeties comprehensively, an advanced thermal analysis program based on Friedman method was employed to calculate the thermal safety parameters for TKX-50 and its PBX. With its help, two important safety parameters (time to maximum rate under adiabatic conditions (TMRad) and self-accelerating decomposition temperature (SADT)) for the two energetic materials were calculated and discussed. Finally, based on the safety parameters, effects of storage conditions and ambient temperatures on the thermal explosions of TKX-50 and TKX-50-based PBX were further studied by using finite element analysis (FEA).

It has been shown experimentally that under many circumstances the strength limiting factor of Polymer Bonded Explosives (PBXs) is the adhesion which exists between the filler crystals and the polymer matrix. Experimental measurements of the Work of Adhesion between different binders and glass have been conducted using the JKR experimental technique, a reversible axisymmetric fracture experiment, during which the area of contact and the applied force are both measured during loading and unloading of the interface. The data taken with this technique show a rate dependence not present in the analytical JKR theory which is normally used to describe the adhesive contact of two elastic bodies, and which arises from the viscoelastic properties of the bulk polymer. The data is intended to inform the development, and validate the predictions of, microstructural models of PBX deformation and failure.