Plastic-bonded Explosives Research Articles

A non-isothermal breakage-damage model for plastic-bonded granular materials incorporating temperature, pressure, and rate dependencies

Plastic-bonded granular materials (PBM) are widely used in industrial sectors, including building construction, abrasive applications, and defense applications such as plastic-bonded explosives. The mechanical behavior of PBM is highly nonlinear, irreversible, rate dependent, and temperature sensitive governed by various micromechanical attributions such as grain crushing and binder damage. This paper presents a thermodynamically consistent, microstructure-informed constitutive model to capture these characteristic behaviors of PBM. Key features of the model include a breakage internal variable to upscale the grain-scale information to the continuum level and to predict grain size evolution under mechanical loading. In addition, a damage internal state variable is introduced to account for the damage, deterioration, and debonding of the binder matrix upon loading. Temperature is taken as a fundamental external state variable to handle non-isothermal loading paths. The proposed model is able to capture with good accuracy several important aspects of the mechanical properties of PBM, such as pressure-dependent elasticity, pressure-dependent yield strength, brittle-to-ductile transition, temperature dependency, and rate dependency in the post-yielding regime. The model is validated against multiple published datasets obtained from confined and unconfined compression tests, covering various PBM compositions, confining pressures, temperatures, and strain rates.

Improving the energetic properties of 1,1-diamino-2,2-dinitroethene in PBX mixture

Abstract The new eyesight in the energetic materials focuses on reserving high efficiency together with optimization of safe handling. In this study, a novel nitramine, cis1,3,4,6-tetranitrooctahydroimidazo-[4,5-d]imidazole (BCHMX), is combined with 1,1diamino-2,2-dinitroethene (FOX7), and bound by a styrene-butadiene rubber fabricating an insensitive plastic bonded explosive (PBX) mixture. The obtained PBX was fully characterized in comparison with the familiar explosives; SEMTEX, EPX1 and other PBXs, filled by RDX (1,3,5trinitro-1,3,5-triazinane), HMX (1,3,5,7tetranitro-1,3,5,7-tetrazine). The related individual fillers were also included. Sensitivities to various stimuli and the velocities of detonation were measured for the composites in comparison with the selected explosives. EXPLO 05 has been applied to obtain the detonation properties of the tested explosives. Different relationships (comparing performance with sensitivities) are stated and discussed. The results showed that BC/FOX7 - SBR has very low sensitivity compared with the studied compositions while its performance has larger values.

Structural Support of Aluminum Honeycomb on Cast PBX

As the operating condition for the penetrating missile has been more advanced, the survivability of main charge has been strongly required when the warhead impacts the target. Lots of efforts to desensitize explosives such as the development of insensitive molecular explosives or optimizing plastic-bonded explosives(PBX) systems has been made to enhance the survivability of main charge. However, these efforts face their limits as the weapon system require higher performance. Herein, we suggest a new strategy to secure the survivability of main charge. We applied structurally supportable aluminum honeycomb(HC) structure to cast PBX. The aluminum HC structure reinforces the mechanical strength of cast PBX and helps it to withstand external pressure without the reaction like detonation. In this study, impact resistance character, shock sensitivity and internal blast performance of PBXs reinforced with HC structure were investigated according to the application of aluminum HC structure. The newly suggested aluminum HC structure applied to cast PBX was proved to be a promising manufacturing method available for high-tech weapon systems.

Screening of volatiles from explosive initiators and plastic-bonded explosives (PBX) using headspace solid-phase microextraction coupled with gas chromatography - mass spectrometry (SPME/GC-MS).

The detection of explosives and explosive devices based on the volatile compounds they emit is a long-standing tool for law enforcement and physical security. Toward that end, solid-phase microextraction (SPME) combined with gas chromatography-mass spectrometry (GC-MS) has become a crucial analytical tool for the identification of volatiles emitted by explosives. Previous SPME studies have identified many volatile compounds emitted by common explosive formulations that serve as the main charge in explosive devices. However, limited research has been conducted on initiators like fuses, detonating cords, and boosters. In this study, a variety of SPME fiber coatings (i.e., polydimethylsiloxane (PDMS), polydimethylsiloxane/divinylbenzene (PDMS/DVB), divinylbenzene/carboxin/polydimethylsiloxane (DVB/CAR/PDMS), and carboxin/polydimethylsiloxane (CAR/PDMS)) were employed for the extraction and analysis of volatiles from Composition C-4 (cyclohexanone, 2-ethyl-1-hexanol, and 2,3-dimethyl-2,3-dinitrobutane (DMNB)) and Red Dot double-base smokeless powder (nitroglycerine, phenylamine). The results revealed that a PDMS/DVB fiber was optimal. Then, an assortment of explosive items (i.e., detonation cord, safety fuse, slip-on booster, and shape charge) were analyzed with a PDMS/DVB fiber. A variety of volatile compounds were identified, including plasticizers (tributyl acetyl citrate, N-butylbenzenesulfonamide), taggants (DMNB), and degradation products (2-ethyl-1-hexanol).

Structural properties of aqueous grown polydopamine thin films determined by neutron reflectometry

In this work, neutron reflectometry (NR) studies of the bio-mimetic polymer, polydopamine (PDA), deposited from differing initial concentrations of precursor material dopamine hydrochloride for a range of polymerization times, is reported. PDA can form a complex and highly versatile polymer film, with many structure studies having been performed previously, but a comprehensive structural determination of PDA by NR is lacking in the literature. It was found that simple box models were incapable of fully explaining the observed data, necessitating the use of a composite model consisting of the weighted average of both the 1 and 2 box models to fully capture the heterogeneous nature of the PDA film structure. Confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM) were performed to capture the surface structure and relative mechanical difference between the separate domains of the PDA. The CLSM results provide evidence that the PDA domains are larger than the coherent scattering length of a neutron used in these measurements, 10μm, supporting the need for a composite model. The AFM measurements show complex structure below the coherence length provide physical justification for the two box model. It was determined that film structure and quality are both heavily impacted by the initial concentration of dopamine hydrochloride and the polymerization time, giving confidence to the highly customizable nature of PDA as an adhesion promoting interface treatment in composite systems, such as plastic bonded explosives (PBX).

Continuum modeling predictions of nonlinear specific heat in phase transition of energetic materials

We propose a chemo-thermal-mechanical model that considers phase transition phenomena, heat generation due to chemical reactions and mechanical deformations, and finite strain elasto-plastic behavior. We implement this highly nonlinear model in a state-of-the-art finite element solver. We study the chemical, thermal, and mechanical processes in the phase change of heterogeneous reactive materials at the microstructural level. The model is calibrated and applied to the HMX β→δ phase transition within plastic-bonded explosives. We present computational results such as chemical heating extrema, highly nonlinear and non-equilibrium specific heat, and accumulated plastic strain in representative unit cells for several volume fractions and heating histories. We show that particle volume fraction and sample heating rate are highly relevant for the pre-ignition response of plastic-bonded explosives to thermo-mechanical loads. We predict highly nonlinear specific heats for a finite system at the continuum level. Moreover, we utilize an analytic expression that estimates with a high degree of accuracy the critical temperature at which the maximum chemical heat release occurs.

Tracing temperature and pressure evolutions in shocked TATB‐based PBX by time‐resolved Raman spectroscopy

AbstractTime‐resolved Raman spectroscopy has been used to simultaneously measure temperature and pressure in the TATB‐based plastic‐bonded explosive (PBX) sample under laser‐driven shock wave. Temperature and pressure have been confirmed according to the ratio of anti‐Stokes to Stokes Raman intensities and the variation of the center wavenumber of the Raman peak under shock loading, respectively. The location of the shock front has been determined according to the ratio of the spectral height of the shifted Raman peak under shock loading to that of the original Raman peak, and the velocity of the shock front has been estimated by linear fit for the locations of the shock front versus delay times. Therefore, the shock propagation in this PBX sample is characterized according to the measured temperature, pressure, and shock velocity. In addition, the correlation between the pressure and the temperature under shock waves is established, and the pressure‐dependence temperature gradient is 10.06 ± 0.67 K/GPa.

Research on Explosive Hardening of Titanium Grade 2.

In this investigation, three different explosive materials have been used to improve the properties of titanium grade 2: ammonal, emulsion explosives, and plastic-bonded explosives. In order to establish the influence of explosive hardening on the properties of the treated alloys, tests were conducted, including microhardness testing, microstructure analysis, and tensile and corrosion tests. It has been found that it is possible to achieve a 40% increase in tensile strength using a plastic explosive (PBX) as an explosive material. On the other hand, the impact of the shock wave slightly decreased the corrosion resistance of titanium grade 2. The change in corrosion rate is less than 0.1µm/year, which does not significantly affect the overall corrosion resistance of the material. The reduction in corrosion resistance is probably due to the surface geometry changes as a result of explosive treatment.

Multi-aspect simulation insight on thermolysis mechanism and interaction of NTO/HMX-based plastic-bonded explosives: a new conception of the mixed explosive model.

Reactive molecular dynamics (RMDs) calculations were used to determine, for the first time, the process of thermolysis of the mixed explosives, including 3-nitro-1,2,4-triazol-5-one (NTO) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazoline (HMX). Significantly, this is the first time that a layered model for mixed explosives, which is an extreme innovation of mixed explosive models was adopted. It is shown that a large amount of NO2 in the HMX and OH groups generated by the decomposition of HNO2 has a favorable effect on the thermolysis of NTO, as further validated by a reduction in the activation energy of NTO/HMX. The amount of H2O and N2 in the resulting products increased significantly, but the amount of NH3 changed slightly. The analysis results correspond to the change in chemical bonds. Whenever there is an increase in temperature, the time for the maximum number of clusters to appear is shortened accordingly. In addition, the acidity of NTO has been considered. An independent gradient model based on Hirshfeld partition (IGMH) and atoms in molecule (AIM) analysis of NTO/HMX was implemented. The relatively strong hydrogen bonds indicate that HMX can inhibit the acidity of NTO and is beneficial for the wide application of NTO/HMX-based plastic-bonded explosives (PBXs).

Co-agglomerated crystals of 2,2′,4,4′,6,6′-hexanitro -stilbene/-azobenzene with attractive nitramines

Co-agglomerated crystals (CACs) of trans-2,2,4,4′,6,6′-hexanitrostilbene (HNS) and trans-2,2′,4,4′,6,6′-hexanitroazobenzene (HNAB) with RDX, β-HMX, BCHMX and ε-CL-20 have been prepared. Powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), Raman studies and differential thermal analysis (DTA) have confirmed that this process leads to the formation of co-crystals (CCs), in which HMX is present in its δ-form, CL-20 in its β-form and trans-HNS changes its conformation to cis-form. In most cases, these significant structural changes and intermolecular-orientations have improved the impact sensitivities, mainly in some CACs with cis-HNS; for CL-20, on the other hand, the insertion of HNS or HNAB into its crystal lattice is destabilizing. Logical relationships between some FTIR, Raman vibrational modes of the CACs studied and parameters of their initiation and detonation have shown greater information about corresponding molecular structural relationships. The detonation energies of these co-crystals are in most of cases higher than that of correspond to the percentage of the coformers in them. It has been shown that this co-agglomeration can reduce the sensitivity of nitramines (with the exception of CL-20) roughly to the level of the sensitivity of analogous plastic-bonded explosives (PBXs), with the high-performance parameters of the resulting CACs being maintained. From a practical point of view, the combination of HMX and HNS appears to be the most optimal; these CACs at a molar ratio of 1.00/0.11 have exhibited the impact sensitivity of 47 J and the calculated detonation velocity 8.98 km.s−1.

In operando measurements of high explosives.

In operando studies of high explosives involve dynamic extreme conditions produced as a shock wave travels through the explosive to produce a detonation. Here, we describe a method to safely produce detonations and dynamic extreme conditions in high explosives and in inert solids and liquids on a tabletop in a high-throughput format. This method uses a shock compression microscope, a microscope with a pulsed laser that can launch a hypervelocity flyer plate along with a velocimeter, an optical pyrometer, and a nanosecond camera that together can measure pressures, densities, and temperatures with high time and space resolution (2ns and 2 µm). We discuss how a detonation builds up in liquid nitromethane and show that we can produce and study detonations in sample volumes close to the theoretical minimum. We then discuss how a detonation builds up from a shock in a plastic-bonded explosive (PBX) based on HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane), where the initial steps are hotspot formation and deflagration growth in the shocked microstructure. A method is demonstrated where we can measure thermal emission from high-temperature reactions in every HMX crystal in the PBX, with the intent of determining which configurations produce the critical hot spots that grow and ignite the entire PBX.

A mathematical model for estimating the Gurney velocity of chemical high explosives

The Gurney velocity is an important performance parameter that characterizes the metal pushing capability of conventional chemical explosives. Herein, this study proposes a mathematical model that aims to provide a simple and effective means by which the Gurney velocity of pure and mixed CHNO-based explosives can be accurately determined using as input information the volumetric heat of detonation, the parameter psi (Ψ) and an adjustable parameter (λ) that accounts for the type of the explosive being studied. The new model proved adequate for evaluating the Gurney velocity of sensitive and insensitive explosives of military interest, including melt-castable and plastic-bonded explosives (PBXs) and showed superior predicting performance compared to benchmark models. It is believed that the Gurney velocity obtained by the new method along with the Gurney-type equations would be very helpful for ordnance engineers for calculating the peak fragment deployment velocity from various warhead geometries, including omnidirectional and directed energy warheads for use in various weapons systems.

Comprehensive study on thermal decomposition mechanism and interaction of 3-Nitro-1,2,4-Triazol-5-One/Poly-3-nitromethyl-3-methyloxetane plastic bonded explosives

In this paper, the thermal decomposition process of 3-Nitro-1,2,4-Triazol-5-One (NTO)/Poly-3-nitromethyl-3-methyloxetane (Poly-NIMMO) based Plastic Bonded Explosives (PBXs) at five temperatures from 2500 K to 3500 K was simulated based on the reactive molecular dynamics, and some related analysis contents were supplemented and verified by first-principles and quantum chemistry methods. In particular, given the strong acidity of NTO explosive, the interaction between NTO and Poly-NIMMO was analyzed. The analysis results of the atoms in molecules (AIM) method and Independent gradient model based on Hirshfeld partition (IGMH) method show that there are some relatively strong hydrogen bonds between them. The activation energies of the initial decomposition stage and the intermediate decomposition stage of the mixed system are 60.37 kJ∙mol−1 and 98.37 kJ∙mol−1. Compared with the pure NTO system, the activation energies of the two stages decrease to a different extent. Poly-NIMMO in the mixed system brings a lot of NO2 and OH groups, these molecular fragments and groups will have chemical reactions with NTO and decomposition products of NTO, resulting in the reduction of the number of hydrogen transfer reactions between NTO molecules. By comparing the quantity of products, it can be found that the content of H2O is greatly increased. The curve reaches the peak in a shorter time, and the decomposition reaction rate of the system is faster. The amount of CO2 did not increase too much, and more C atoms gathered to form clusters. The changes of the number of bonds verify the above analysis. In addition, in a certain temperature range, the relationship between the maximum number of clusters and temperature is positively correlated, but the excessive temperature can inhibit the maximum number of clusters. The ratio of O, N, H atoms to C atoms in the cluster after equilibrium at five temperatures is H/C > N/C > O/C. There is no doubt that Poly-NIMMO will reduce the acidity of the system, but it will promote the thermal decomposition of NTO and reduce the insensitivity of PBXs to thermal stimulation.

Mechanisms of shock-induced initiation at micro-scale defects in energetic crystal-binder systems

Crystals of energetic materials, such as HMX, embedded in plastic binders are the building blocks of plastic-bonded explosives. Such heterogeneous energetic materials contain microstructural features such as sharp corners, interfaces between crystal and binder, intra- and extra-granular voids, and other defects. Energy localization or hotspots arise during shock interaction with the microstructural heterogeneities, leading to the initiation of PBXs. In this paper, high-resolution numerical simulations are performed to elucidate the mechanistic details of shock-induced initiation in a PBX; we examine four different mechanisms: Shock-focusing at sharp corners or edges and its dependency on the shape of the crystal, and the strength of the applied shock; debonding between crystal and binder interfaces; collapse of voids in the binder located near an HMX crystal; and the collapse of voids within HMX crystals. Insights are obtained into the relative contributions of these mechanisms to the ignition and growth of hotspots. Understanding these mechanisms of energy localization and their relative importance for hotspot formation and initiation sensitivity of PBXs will aid in the design of energetic material-driven systems with controlled sensitivity, to prevent accidental initiation and ensure reliable performance.

Compressive strength of the plastic-bonded explosive surrogate idoxuridine under quasistatic and dynamic compression

Inert simulant materials, or “mocks”, are often used as surrogates for plastic-bonded explosives (PBX) in non-detonative tests in order to mitigate hazards. Mocks should reproduce as many non-detonative properties of the explosive as possible, including structural behavior in a variety of thermal and mechanical environments. Recently, the molecular crystal idoxuridine (IDOX) has been identified as an ideal mock for the main component in the explosive polymer-matrix composite PBX 9501, and has performed favorably under quasistatic loading conditions. Here, in order to assess robustness over a range of mechanical environments, plastic-bonded IDOX was compression tested from 0.001/s to 2000/s strain rates and compared to PBX 9501 historical data. Plastic-bonded IDOX showed good agreement to PBX 9501 across these strain rates, justifying continued development and production as a mock.

Shock ignition and deflagration growth in plastic-bonded TATB (1, 3, 5-trinitro-2, 4, 6-triaminobenzene) microstructures

TATB (1,3,5-triamino-2,4,6-trinitrobenzene) plastic-bonded explosives (PBX) were shocked with laser-launched flyer plates. The spectral radiance of the emitted light from a small portion of the microstructure (a “microenvironment”) containing a small number of TATB particles with an estimated mass of 150 ng was measured every 0.8 ns from 1 ns to 200 μs and was analyzed to give radiance and time-dependent graybody temperatures. By fabricating an array with 186 PBX charges, we could obtain ≥15 shots at each of 12 velocities between 1.8 and 4.7 km/s. We found that every microenvironment generated a unique radiance fingerprint. Some of these microenvironments were much more reactive than average. The radiance has two peaks around 20 ns and 5 μs, associated with shock ignition and deflagration growth. In our interpretation, the shock creates an ensemble of hot spots of various sizes and temperatures. Of those hot spots that ignite, only a small portion, at about 2200 K, was large enough and hot enough to survive long enough (>100 ns) to ignite individual TATB particles, leading to deflagration. Integrating various time intervals of the radiance can quantify the strength of the shock–PBX interaction, and the decay and growth of the hot spot ensemble and the deflagration.

ReaxFF/lg molecular dynamics study on thermolysis mechanism of NTO/HTPB plastic bonded explosive

3-nitro-1,2,4-triazol-5-one (NTO), a very promising high-energy density energy material, has been extensively used in plastic bonded explosive (PBX). However, the potential mechanism of thermal decomposition of PBX systems composed of NTO and the ordinary binder Hydroxyl-terminated polybutadiene (HTPB) is not yet understood. Therefore, in this paper, the mechanism of thermal decomposition of the NTO/HTPB hybrid system was investigated at five temperatures in the range of 2500–3500 K using a reactive molecular dynamics approach (ReaxFF/lg). The results show that the intermolecular reaction paths of NTO in the hybrid system are still reactions such as dehydrogenation and denitrification reaction, etc. The incorporation of HTPB introduces a large amount of H and OH into the hybrid system, and these radicals react with NTO and the decomposition products of NTO. For example, A large amount of chemical reaction with HNO2 promote the thermal decomposition of NTO. The number of hydrogen transfer reactions between NTO molecules is all reduced to different degrees in the mixed system. The comparison of the number of products is shown that the content of H2O increases greatly and the curve reaches the peak in a shorter time, and the decomposition reaction rate of the system is faster, while the content of N2 decreases substantially. The changes of clusters at five temperatures were analyzed, and the maximum number of clusters increased with the increase of temperature in a certain temperature range, and the high temperature played a certain degree of inhibition on the formation of clusters. The ratio of the number of H, O and N atoms to C atoms in the clusters at each temperature was O/C > H/C > N/C. In addition, The natural logarithm of pre-exponential factor (lnA) of the initial and intermediate decomposition stages of the hybrid system were 24.25 and 28.10, respectively, and the activation energies (Ea) were 68.3786 KJ/mol and 59.6588 KJ/mol, respectively. Comparing the activation energy of NTO-only monoplasmic systems, both were reduced to varying degrees. Therefore, the incorporation of HTPB would contribute to the thermal decomposition of NTO and reduce the insensitivity of the system to thermal stimuli.

Experimental investigation of the behaviour of a simulant material for plastic-bonded explosives and modelling of the effectivity and damage induced anisotropy

This paper presents an original experimental investigation and modelling of the behaviour of a simulant material for Plastic-Bonded Explosives (PBXs). The conducted tests are tension, compression, alternated tension/compression, confined compression, channel-die, and DMA. The experimental dispositive and protocols are presented and detailed. Monotonic and cyclic tests are conducted in addition to alternated and non-proportional tests. The obtained results are presented and discussed. A special focus was put on the damage induced anisotropy and the effectivity in the material behaviour. Also, hydrostatic pressure and strain rate dependencies and the presence of hysteresis loops and irreversible strains, are highlighted.Based on the experimental results, damage evolution laws and novel effectivity functions are proposed to model the material behaviour in the quasi-static domain.

Decomposition of Irganox 1010 in plastic bonded explosives

AbstractDegradation pathways of Irganox 1010 in aged plastic bonded explosive (PBX) 9501 were investigated using ultrahigh performance liquid chromatography coupled to quadrupole time of flight mass spectrometry (UHPLC‐QTOF). Using a targeted approach, a total of 44 Irganox 1010 decomposition products were discovered. These decomposition products were formed through hydrolysis, scission, and/or oxidation of Irganox 1010. The hydrolytic decomposition of Irganox is a straightforward process resulting in the cleavage of the ester group(s) while oxidation and scission are more complicated and can happen at multiple locations on the Irganox 1010 molecule. Moreover, due to the symmetric nature of Irganox 1010, multiple decomposition reactions can occur. Indeed some decomposition products exhibited hydrolysis, oxidation, and scission. In order to probe any trends in the aged PBX 9501 samples, principal component analysis (PCA) was implemented. The greatest chemical differences between the aged PBX samples was hydrolysis of the ester functional groups on Irganox 1010. Despite the negative connotations of hydrolysis, the Irganox 1010 decomposition products are still able to function as a radical scavenger in PBX 9501 as intended.

Hot spot ignition and growth from tandem micro-scale simulations and experiments on plastic-bonded explosives

Head-to-head comparisons of multiple experimental observations and numerical simulations on a deconstructed plastic-bonded explosive consisting of an octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine crystal embedded in a polymeric binder with a 4 ns duration 20 GPa input shock are presented. Hot spots observed in high-resolution direct numerical simulations are compared with micro-scale shock-induced reactions visualized using nanosecond microscope imaging and optical pyrometry. Despite the challenges and limitations of both the experimental and simulation techniques, an agreement is obtained on many of the observed features of hot spot evolution, e.g., (1) the magnitude and time variation of temperatures in the hot spots, (2) the time to fully consume the crystals (∼100 ns) of size (100–300 μm) employed in this study, and (3) the locations of hot spot initiation and growth. Three different mechanisms of hot spot formation are indicated by simulations: (1) high-temperature hot spots formed by pore collapse, (2) lower temperature hot spots initiated at the polymer–crystal interface near corners and asperities, and (3) high-temperature reaction waves leading to fast consumption of the energetic crystal. This first attempt at a head-to-head comparison between experiments and simulations not only provides new insight but also highlights efforts needed to bring models and experiments into closer alignment, in particular, highlighting the importance of distinctly three-dimensional and multiple mechanisms of the hot spot ignition and growth.