Fluorinated semi-interpenetrating polymer networks for enhancing the mechanical performance and storage stability of polymer-bonded explosives by controlling curing and phase separation rates

Herein, the effect of fluoropolymer binders on the properties of polymer-bonded explosives(PBXs) was comprehensively investigated. To this end, fluorinated semi-interpenetrating polymer networks(semiIPNs) were prepared using different catalyst amounts(denoted as F23-CLF-30-D). The involved curing and phase separation processes were monitored using Fourier-transform infrared spectroscopy, differential scanning calorimetry, a haze meter and a rheometer. Curing rate constant and activation energy were calculated using a theoretical model and numerical method, respectively. Results revealed that owing to its co-continuous micro-phase separation structure, the F23-CLF-30-D3 semi-IPN exhibited considerably higher tensile strength and elongation at break than pure fluororubber F2314 and the F23-CLF-30-D0 semi-IPN because the phase separation and curing rates matched in the initial stage of curing.An arc Brazilian test revealed that F23-CLF-30-D-based composites used as mock materials for PBXs exhibited excellent mechanical performance and storage stability. Thus, the matched curing and phase separation rates play a crucial role during the fabrication of high-performance semi-IPNs;these factors can be feasibly controlled using an appropriate catalyst amount.

Shock-induced energy localization and reaction growth considering chemical-inclusions effects for crystalline explosives

Chemical inclusions significantly alter shock responses of crystalline explosives in macroscale gap experiments but their microscale dynamics origin remains unclear.Herein shock-induced energy localization,overall physical responses,and reactions in a-1,3,5-trinitro-1,3,5-triazinane(a-RDX)crystal entrained various chemical inclusions were investigated by the multi-scale shock technique implemented in the reactive molecular dynamics method.Results indicated that energy localization and shock reaction were affected by the intrinsic factors within chemical inclusions,i.e.,phase states,chemical compositions,and concentrations.The atomic origin of chemical-inclusions effects on energy localization is dependent on the dynamics mechanism of interfacial molecules with free space volume,which includes homogeneous intermolecular compression,interfacial impact and shear,and void collapse and jet.As introducing various chemical inclusions,the initiation of those dynamics mechanisms triggers diverse decay rates of bulk RDX molecules and hereby impacts on growth speeds of final reactions.Adding chemical inclusions can reduce the effectiveness of the void during the shock impacting.Under the shockwave velocity of 9 km/s,the parent RDX decay rate in RDX entrained amorphous carbon decreases the most and is about one fourth of that in RDX with a vacuum void,and solid HMX and TATB inclusions are more reactive than amorphous carbon but less reactive than dry air or acetone inclusions.The lessdense shocking system denotes the greater increases in local temperature and stress,the faster energy liberation,and the earlier final reaction into equilibrium,revealing more pronounced responses to the present intense shockwave.The quantitative models associated with the relative system density(RD_(sys))were proposed for indicating energy-localization mechanisms and evaluating initiation safety in the shocked crystalline explosive.RD_(sys)is defined by the density ratio of defective RDX to perfect crystal after dynamics relaxation and reveals the global density characteristic in shocked systems filled with chemical inclusions.When RD_(sys)is below 0.9,local hydrodynamic jet initiated by void collapse dominates upon energy localization instead of interfacial impact.This study sheds light on novel insights for understanding the shock chemistry and physical-based atomic origin in crystalline explosives considering chemical-inclusions effects.

Effects of temperature, particle size, and air humidity on sensibility of typical high-energetic explosives

The production and utilization of high-energetic explosives often pose a range of safety hazards,with sensitivity being a key factor in evaluating these risks.To investigate how temperature,particle size,and air humidity affect the responsiveness of commonly used high-energetic explosives,a series of BAM(Bundesanstalt für Materialforschung und-prüfung)impact and friction sensitivity tests were carried out to determine the critical impact energy and critical load pressure of four representative high-energetic explosives(RDX,HMX,PETN and CL-20)under different temperatures,particle sizes,and air humidity conditions.The experimental findings facilitated an examination of temperature and particle size affecting the sensitivity of high-energetic explosives,along with an assessment of the influence of air humidity on sensitivity testing.The results clearly indicate that high-energetic explosives display a substantial decline in critical reaction energy when subjected to micrometre-sized particles and an air humidity level of 45%at a temperature of 90℃.Furthermore,it was noted that the critical reaction energy of high-energetic explosives diminishes with an increase in temperature within 25℃−90℃.In the same vein,as the particle sizes of high-energetic explosives increase,so does the critical reaction energy for micrometre-sized particles.High air humidity significantly affects the sensitivity testing of high-energetic explosives,emphasizing the importance of refraining from conducting sensitivity tests in such conditions.

Research Progress in Detection of Explosives by Chemical Colorimetric Method

This article reviews the current application status and research progress of colorimetric detection methods based on chemical colorimetry in the detection of explosives.It mainly introduced colorimetric sensors,colorimetric sensor arrays,and chemical colorimetric sensors based on novel material substrates.The application prospect of chemical colorimetric method in the field of explosives detection was prospected.

Dinitrophenyl-oxadiazole compounds:Design strategy,synthesis,and properties of a series of new melt-cast explosives

Melt-cast explosives are the most widely used energetic materials in military composite explosives,researchers have been unremittingly exploring high-energy and insensitive melt-cast explosives.In this work,a series of dinitrophenyl-oxadiazole compounds were designed and prepared.These compounds have an ideal low melting point(80-97℃),good detonation performance(detonation velocity D=6455-6971 m/s,detonation pressure P=18-19 GPa)and extreme insensitive nature(impact sensitivity≥60 J,friction sensitivity>360 N).All these compounds were well characterized by nuclear magnetic resonance,fourier transform infrared spectroscopy,elemental analysis.Compounds 2,3 were unambiguously confirmed by X-ray single crystal diffraction analysis.As a result,their overall properties are superior to traditional melt-cast explosives trinitrotoluene(TNT)and dinitroanisole(DNAN)which may have excellent potential applications in insensitive melt-cast explosives.

Assessing the energy release characteristics during the middle detonation reaction stage of aluminized explosives

Afterburning behind the detonation front of an aluminized explosive releases energy on the millisecond timescale,which prolong the release of detonation energy and the energy release at different stages also shows significant differences.However,at present,there are few effective methods for evaluating the energy release characteristics of the middle reaction stage of such explosives,which can have a duration of tens to hundreds of microseconds.The present work demonstrates an approach to assessing the midstage of an aluminized explosive detonation based on a water push test employing a high degree of confinement.In this method,the explosive is contained in a steel cylinder having one end closed that is installed at the bottom of a transparent water tank.Upon detonation,the gaseous products expand in one direction while forcing water ahead of them.The resulting underwater shock wave and the interface between the gas phase products and the water are tracked using an ultra-high-speed framing and streak camera.The shock wave velocity in water and the expansion work performed by the gaseous detonation products were calculated to assess the energy release characteristics of aluminized explosives such as CL-20 and RDX in the middle stage of the detonation reaction.During the middle stage of the detonation process of these aluminized explosives,the aluminum reaction reduced the attenuation of shock waves and increased the work performed by gas phase products.A higher aluminum content increased the energy output while the presence of oxidants slowed the energy release rate.This work demonstrates an effective means of evaluating the performance of aluminized explosives.

Research on the quasi-isentropic driving model of aluminized explosives in the detonation wave propagation direction

Taking CL-20(Hexanitrohexaazaisowurtzitane)-based aluminized explosives with high gurney energy as the research object, this research experimentally investigates the work capability of different aluminized explosive formulations when driving metal flyer plates in the denotation wave propagation direction.The research results showed that the formulations with 43 μm aluminum(Al) powder particles(The particle sizes of Al powder were in the range of 2~43 μm) exhibited the optimal performance in driving flyer plates along the denotation wave propagation direction. Compared to the formulations with Al powder 13 μm, the formulations with Al powder 2 μm delivered better performance in accelerating metal flyer plates in the early stage, which, however, turned to be poor in the later stage. The CL-20-based explosives containing 25% Al far under-performed those containing 15% Al. Based on the proposed quasi-isentropic hypothesis, relevant isentropy theories, and the functional relationship between detonation parameters and entropy as well as Al reaction degree, the characteristic lines of aluminized explosives in accelerating flyer plates were theoretically studied, a quasi-isentropic theoretical model for the aluminized explosive driving the flyer plate was built and the calculation methods for the variations of flyer plate velocity, Al reaction degree, and detonation product parameters with time and axial positions were developed. The theoretical model built is verified by the experimental results of the CL-20-based aluminized explosive driving flyer plate. It was found that the model built could accurately calculate the variations of flyer plate velocity and Al reaction degree over time. In addition, how physical parameters including detonation product pressure and temperature varied with time and axial positions was identified. The action time of the positive pressure after the detonation of aluminized explosives was found prolonged and the downtrend of the temperature was slowed down and even reversed to a slight rise due to the aftereffect reaction between the Al powder and the detonation products.

Assessment of portable FTIR and Raman spectroscopy for the detection of 2,3-dimethyl-2,3-dinitrobutane(DMDNB)in plastic explosives

The Marplex Convention was established to prevent the manufacture of unmarked plastic explosives and stipulates that a volatile detection agent must be added at the time of manufacture.However,to-date,laboratory testing remains the internationally accepted practice for identifying and quantifying the taggants stipulated in the Convention.In this project,portable FTIR and Raman instruments were tested for their ability to detect 2,3-dimethyl-2,3-dinitrobutane(DMDNB),the chemical marker incorporated in plastic explosives that are manufactured within Australia.While both FTIR and Raman instruments detected solid DMDNB(98%purity),field analysis of plastic explosives at an Australian Defence establishment showed that both FTIR and Raman spectra were matched the relevant explosive(RDX or PETN),rather than the DMDNB taggant.For all three plastic explosives tested,the concentration of DMDNB was measured by SPME-GC-MS to be between 1.8 and 2%,greater than the minimum 1%concentration stipulated by the Marplex Convention.Additional testing with a plastic explosive analogue confirmed that the minor absorption peaks that would characterize low concentrations of DMDNB were masked by absorption bands from other compounds within the solid.Thus,while both FTIR and Raman spectroscopy are suitable for detection of plastic explosives,neither rely on the presence of DMDNB for detection.It is likely that similar results would be found for other taggants stipulated by the Marplex Convention,given they are also present in concentrations less than 1%.

Nacre-inspired interface structure design of polymer bonded explosives toward significantly enhanced mechanical performance

Realizing effective enhancement to the structure of interface region between explosive crystals and polymer binder plays a key role in improving the mechanical properties of the current polymer bonded explosives(PBXs).Herein,inspired by the structure of natural nacre which possesses outstanding mechanical performance,a kind of nacre-like structural layer is constructed in the interface region of PBXs composites,making use of two-dimensional graphene sheets and one-dimensional bio-macromolecules of cellulose as inorganic and organic building blocks,respectively.Our results reveal that the constructed nacre-like structural layer can effectively improve the interfacial strength and then endow the PBXs composites with significantly enhanced mechanical properties involving of creep resistance,Brazilian strength and fracture toughness,demonstrating the obvious advantage of such bioinspired interface structure design strategy.In addition,the thermal conduction performance of PBXs composites also exhibits noticeable enhancement due to the remarkable phonon transport capability endowed by the asdesigned nacre-like structural layer.We believe this work provides a novel design route to conquer the issue of weak interfacial strength in PBXs composites and greatly increase the comprehensive properties for better meeting the higher requirements proposed to the explosive part of weapon equipment in new era.

Combustion crack-network reaction evolution model for highly-confined explosives

The evolution behavior of combustion crack reaction of highly confined solid explosives after non-shock ignition is governed by multiple dynamic processes,including intrinsic combustion of explosives,crack propagation,and rapid growth of combustion surface area.Here,the pressure increase can accelerate the combustion rate of explosives,and the crack propagation can enlarge the combustion surface area.The coupling between these two effects leads to the self-enhanced combustion of explosive charge system,which is the key mechanism for the reaction development after ignition.In this study,combustion cracknetwork(CCN) model is established to describe the evolution of combustion crack reaction of highly confined solid explosives after non-shock ignition and quantify the reaction violence.The feasibility of the model is verified by comparing the computational and experimental results.The results reveal that an increase in charge structure size causes an increase in the time of crack pressurization and extension of cracks due to the high temperature-generated gas flow and surface combustion during the initial stage of explosive reaction,but when the casing is fractured,the larger the charge structure,the more violent the late reaction and the larger the charge reaction degree.The input pressure has no obvious influence on the final reaction violence.Further,a larger venting hole area leads to better pressure relief effect,which causes slower pressure growth inside casing.Larger reserved ullage volume causes longer lowpressure induction stage,which further restrains the internal pressure growth.Furthermore,the stronger the casing constraint,the more rapid the self-enhanced combustion of the high temperaturegenerated gas,which results in more violent charge reaction and larger charge reaction degree during casing break.Overall,the proposed model can clarify the effects of intrinsic combustion rate of explosives,charge structure size,input pressure,relief area,ullage volume,and constraint strength on the reaction evolution,which can provide theoretical basis for violence evaluation and safety design for ammunition under accident stimulus.

Self-healed microcracks in polymer bonded explosives via thermoreversible covalent bond and hydrogen actions

Polymeric materials used for the polymer bonded explosive(PBX)or other energetic composite materials(ECMs)that simultaneously possess excellent mechanical properties and high self-healing ability,convenient healing,and facile fabrication are always a huge challenge.Herein,self-healing linear polyurethane elastomers(PTMEG2000-IPDI-DAPU,denoted as 2I-DAPU)with high healing efficiency and mechanical properties were facilely fabricated by constructing reversible covalent bonds and dynamic hard domains into polymer chains.Furthermore,a TATB-based PBX using as-prepared 2I-DAPU polymer as the binder was constructed,disclosing an excellent self-healing property to heal cracks generated during fabrication,transportation and storage.The damage healing manner of such a PBX sample was investigated by means of prefabricated damage through mechanical load,heal treatment via heating at high temperature,and CT-scanning the inner structure and mechanical property characterization via Brazilian test.The self-healing mechanism of internal damage in PBX was preliminarily explored.We propose that this 2I-DAPU binder with Diels-Alder bonds could generate plentiful active surface groups resulting from damage and drive self-healing at fitting temperature and increase the slightly packed hard phase via incorporating a small amount of hydrogen bonds.This work may offer a novel strategy for improving mechanical property and healing ability in the field of self-healing material which could help expand its applications with enhanced versatility in mechanical-enhanced functional materials.

Ordered Solidification Technique Under Low Pressures in the Loading of Molten Explosives

In order to improve the quality of loading and make the ammuni- tion safe in use,a new loading technique of ordered solidification has been studied.The study shows that the adoption of this new technique makes the charge more compact and brings about a satisfactory supplement of liquid ex- plosives,thus increasing the charge density,which is most advantageous to the crimination of pores,cavities,gaps at the bottom and in loose struc- tures.The physical mechanical properties of the charge are hence greatly im- proved,and the sensitivity of the charge to environmental stimulations is much lowered.

Thermobaric and enhanced blast explosives(TBX and EBX)

In this review, excerpts from the literature of thermobaric(TBX) and enhanced blast explosives(EBX) that are concentrated on studies that include their compositions, properties, reactive metal components, modeling and computations are presented.

Effects of Al/O on pressure properties of confined explosion from aluminized explosives

Pressure histories were tested in a 500-L chamber to identify the pressure load in confined explosion from aluminized explosives. Different aluminized explosives with Al/O, ranging from 0.25 to 1.23, were used. The recorded pressure curves could express the reflection of initial shock wave and the after burning combustion of aluminum. As there is no objective way to gain quasi-static pressure(P_(QS)),method of multipoint averaging was used in smoothing the original pressure curves to gain the P_(QS). The P_(QS),rising time of pressure(t_(QS)) which stands for the duration of the initial reflected shock wave, and attenuation coefficient(ω) which stands for the supportive effects of the combustion of aluminum to the P_(QS) are used to characterize the pressure load in the confined explosion from aluminized explosives. The research results showed that the Al/O significantly affected the three characteristic quantities. With the increase of Al/O, the P_(QS) increased at first and decreased later, gaining maximum at Al/O=0.99; the t_(QS)sustained growth and the ω decreased at first and increased later, gaining minimum at AI/O=0.99.

Thermal decomposition and kinetics of plastic bonded explosives based on mixture of HMX and TATB with polymer matrices

This work describes thermal decomposition behaviour of plastic bonded explosives(PBXs) based on mixture of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane(HMX) and 2,4,6-triamino-1,3,5-trinitrobenzene(TATB)with Viton A as polymer binder. Thermal decomposition of PBXs was undertaken by applying simultaneous thermal analysis(STA) and differential scanning calorimetry(DSC) to investigate influence of the HMX amount on thermal behavior and its kinetics. Thermogravimetric analysis(TGA) indicated that the thermal decomposition of PBXs based on mixture of HMX and TATB was occurred in a three-steps. The first step was mainly due to decomposition of HMX. The second step was ascribed due to decomposition of TATB, while the third step was occurred due to decomposition of the polymer matrices. The thermal decomposition % was increased with increasing HMX amount. The kinetics related to thermal decomposition were investigated under non-isothermal for a single heating rate measurement. The variation in the activation energy of PBXs based on mixture of HMX and TATB was observed with varying the HMX amount. The kinetics from the results of TGA data at various heating rates under non-isothermal conditions were also calculated by Flynn—Wall—Ozawa(FWO) and Kissinger-Akahira-Sunose(KAS)methods. The activation energies calculated by employing FWO method were very close to those obtained by KAS method. The mean activation energy calculated by FWO and KAS methods was also a good agreement with the activation energy obtained from single heating rate measurement in the first step decomposition.

Nitro-tetrazole based high performing explosives:Recent overview of synthesis and energetic properties

Heterocyclic skeleton(Azoles)and different energetic groups containing high performing explosives are highly emerged in recent years to meet the challenging requirements of energetic materials in both military and civilian applications with improved performance.For this purpose tetrazole(Azole)is identified as an attractive heterocyclic backbone with energetic functional groups nitro(-NO_(2)),nitrato(-ONO_(2)),nitrimino(-NNO_(2)),and nitramino(eNHeNO_(2))to replace the traditionally used high performing explosives.The tetrazole based compounds having these energetic functional groups demonstrated advanced energetic performance(detonation velocity and pressure),densities,and heat of formation(HOF)and became a potential replacement of traditional energetic compounds such as RDX.This review presents a summary of the recently reported nitro-tetrazole energetic compounds containing poly-nitro,di/mono-nitro,nitrato/nitramino/nitrimino,bridged/bis/di tetrazole and nitro functional groups,describing their preparation methods,advance energetic properties,and further applications as highperforming explosives,especially those reported in the last decade.This review aims to provide a fresh concept for designing nitro-tetrazole based high performing explosives together with major challenges and perspectives.

Investigation on energy output structure of explosives near-ground explosion

In order to give the energy output structure of typical explosives near-ground explosion in real ground conditions,the free-field shockwave,ground reflection shockwave and Mach wave overpressure time history of composition B explosive,RDX explosive and aluminized explosive were measured by air pressure sensors and ground pressure sensors.The shape of the free-field shock wave,ground reflection shock wave,and Mach wave and explosion flame were captured by high-speed camera.The experimental results show that,at the same horizontal distance from the initiation point,the peak overpressure of explosive shock wave of composition B explosive,both in the air and on the ground,is less than that of RDX and aluminized explosives.At a distance of 3.0 m from the initiation point,the peak overpressure of aluminized explosives is slightly less than that of RDX explosives.Owing to the exothermic effect of aluminum powder,the pressure drop of aluminized explosives is slower than that of RDX explosives.At 5.0 m from the initiation point,the peak overpressure of aluminized explosives is larger than that of RDX explosives.At the same position from the initiation point,among the three kinds of explosives,the impulse of aluminized explosives is the maximum and the impulse of composition B explosives is the minimum.With the increase of the horizontal distance from the initiation point,the height of Mach triple-points(Mach steam)of the three explosives increases gradually.At the same horizontal distance from the initiation point,there is poorly difference in the height of Mach triple-points between aluminized explosive and RDX explosive,and the height of Mach triple-points of composition B explosive is much smaller than that of other two explosives.The maximum diameter and duration of the fireball formed by aluminized explosives are the largest,followed by composition B explosive,and the maximum diameter and duration of the fireball formed by RDX explosive are the smallest.

Effect of hydrogen-storage pressure on the detonation characteristics of emulsion explosives sensitized by glass microballoons

In this study,hydrogen-storage glass microballoons were introduced into emulsion explosives to improve the detonation performance of the explosives.The effect of hydrogen-storage pressure on the detonation characteristics of emulsion explosives was systematically investigated.Detonation velocity experiments shows that the change of sensitizing gas and the increase of hydrogen pressure have different effects on the detonation velocity.The experimental parameters of underwater explosion increase first and then decreases with the increase of hydrogen pressure.The decrease of these parameters indicates that the strength of glass microballoons is the limiting factor to improve the detonation performance of hydrogen-storage emulsion explosives.Compared with the traditional emulsion explosives,the maximum peak pressure of shock wave of hydrogen-storage emulsion explosives increases by 10.6%at 1.0 m and 10.2%at 1.2 m,the maximum values of shock impulse increase by 5.7%at 1.0 m and 19.4%at 1.2 m.The stored hydrogen has dual effects of sensitizers and energetic additives,which can improve the energy output of emulsion explosives.

Estimating the metal acceleration ability of high explosives

The Gurney method is widely used in the conceptual design stage of explosive fragmentation warheads employed in various weapons systems.This method states that the peak fragment velocity(V_0) is a function of the Gurney velocity((2E_G)^(1/2)) and the charge-to-metal weight ratio(C/M).The current study is concerned with finding a practical approach for computing the Gurney velocity of pure and mixed high explosives which will eventually help warhead designers to select the best explosive to fulfill the needs of a particular mission.Using multiple regression analysis technique,a four-variable model was derived and used thereafter to estimate the Gurney velocity of aluminized and non-aluminized explosive formulations.The results show that the new model is particularly accurate in predicting the Gurney velocity of combined effects explosives,which are relatively a new class of high blast,high metal acceleration capability explosive compositions.

Ultrasonic Evaluation of the Impact Damage of Polymer Bonded Explosives

The damage properties of polymer bonded explosives under dynamic loading were studied by using ultrasonic evaluation. Explosive samples were damaged by a low-velocity gas gun at different impact velocities. Ultrasonic examination was carried out with a pulse through-transmission method. Spectra analyses were carried out by using fast Fourier transform. Characteristic ultrasonic parameters, including ultrasonic velocities, attenuation coefficients, spectra area and master frequency, were obtained. The correlation between the impact damage and ultrasonic parameters was analyzed. A damage coefficient D was defined by considering a combination of ultrasonic velocity and amplitude. The results show that ultrasonic parameters can be used to quantitatively assess the damage extent in impacted plastic bonded explosives..