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Abstract:The safety issues of weapons and ammunition are essential that they matter the survivability and effectiveness of weaponry. The complex and harsh enviroments faced by ammunition lead to the high requirment of ammunition safety that the development of safe ammunition is the only way. Ammunition safety mainly depends on inherent safety and safety enhancement technology. Using insensitive explosives is the key way to improve the inherent safety of ammunition， while the enhancement and protection of charge and structure are important means to improve ammunition safety . In order to meet the requirements of high damage power and safety of ammunition， it is necessary to balance and coordinate the prominent contradiction between high energy and insensitivity of explosives from the multi-scale structures， such as molecules， crystals and mixed systems of explosives. Safety enhancement technologies such as charge structures， weak link structurse of projectiles and protection enhancements can effectively control the accidental ignition， reaction violence and evolution ammunition charges， and furthermore improve the safety of ammunition under abnormal environment and accident conditions. Therefore， the design ideas and technicalapproches for safety ammunition systems were proposed， including strengthening the foundation of multi-scale material design and performance control of insensitive explosives， complementing the shortcomings of charge structures， protection enhancement， and accidental ignition and reaction control， and exploring and developing the integrated design of material，- structure- and function .

Abstract:The spheroidization of energetic materials can significantly improve the processing and application properties of explosive crystals. Based on the current research on spheroidization technology of typical energetic materials both in China and abroad， the research progress of spherical single crystals， spherical agglomerates and spherical branched crystals are reviewed from the perspective of crystallization strategy. The crystallization process， spheroidization mechanism and desensitization effect of spherical products are emphatically introduced. It is showed that spherical products have the virtues of good flowability， high bulk density and low sensitivity， and have great potential in explosive applications. Combining crystal engineering thinking， it is suggested to construct the crystallization database of typical energetic materials， strengthen online process monitoring， improve model calculations and multidisciplinary cross study， thus providing guidance for precise regulation and industrial production of spherical crystallization process of energetic materials.

Abstract:In order to explore the effect of 3，4-dinitrofurazan （DNTF） on the explosive energy release process of layered composite thermobaric charges， various double-layer composite charges were prepared， with the content of aluminum powder in the outer charge adjusted from 60% to 94%， and the content of DNTF adjusted from 40% to 0. Then， explosion tests were carried out in a closed tank under nitrogen and air environment. Based on the correlation between quasi-static pressure and effective mechanical energy， the released energy of charges at different reaction stages was obtained. Moreover， the afterburning process of aluminum powder from different charges was analyzed according to the evolution of fireball. The results reveal that the dispersed DNTF particles are easy to be ignited and grow rapidly after being shock-dispersed when the mass fractions of DNTF in the outer charge is 40%， which can improve the anaerobic combustion rate of aluminum powder and the aerobic combustion rate of aluminum powder at the edge of the cloud， thus the combined mechanical energy released during detonation and anaerobic combustion is raised 12% than that of the homogeneous charge with same composition. Whereas， when the DNTF in the outer charge is replaced by polytetrafluoroethylene （PTFE） in the same proportion， the combustion rate after dispersal is significantly reduced as well as shock wave overpressure and temperature， and the total mechanical energy released decreased by about 22% than composite charge containing DNTF in its outer layer. Moreover， when the outer charge is all replaced by aluminum powder， intensely aerobic combustion with longer duration will occur in the high-concentration aluminum powder cloud， the total mechanical energy released drops by only 5%， while the combined mechanical energy released by detonation and anaerobic combustion drops by 32%， and the peak shock wave overpressure has a considerable reduction. The above indicates that DNTF in the outer layer of the composite charge plays an important role in enhancing the combustion rate of the aluminum powder cloud and energy release rate in the early explosion stage.

Abstract:Ultrafine 2，6-diamino-3，5-dinitropyrazine-1-oxide （LLM-105） possesses high safety performance and low impact initiation threshold， showing promising applications in the initiation sequence. Solid-phase ripening is the main aging behavior of ultrafine LLM-105 during the storage process， which leads to the growth of particle size and performance degradation. Temperature and humidity are important environmental factors that affect solid-phase ripening， but the microscopic mechanism is still unclear. In situ small angle X-ray scattering （SAXS）， Scanning electron microscope （SEM） and in situ Atomic force microscopy （AFM） were used to capture the structural evolution of ultrafine LLM-105 particles under different temperature and humidity environments， and the solid-phase ripening mechanism was analyzed. Ultrafine LLM-105 had obvious solid-phase ripening after 30 days at 120 ℃， and its specific surface area （SSA） decreased by 41.6%. The ripening mechanism was dominated by Ostwald Ripening （OR）， accompanied with Smoluchowski Ripening （SR）. Humidity significantly accelerates the solid-phase ripening of ultrafine LLM-105 by promoting OR. After 30 days at 60 ℃ and 90% relative humidity， SSA decreased by 35.8%.

Abstract:In order to explore the thermal safety characteristics of modified double base propellants， the thermal decomposition behaviors of modified double base propellants with RDX content of 0， 18%， 46% and 54.6% were studied by differential scanning calorimetry （DSC） respectively， and the thermal decomposition temperatures at different heating rates （2， 5， 10 and 20 ℃·min^-1）were obtained. The apparent activation energy， activation pre-exponential factor， reaction rate， Gibbs free energy， activation enthalpy and activation entropy were calculated by thermal reaction kinetics analysis， and the influence of RDX content on the double base components and apparent activation energy was also analyzed. The response characteristics of modified double base propellants with different RDX contents were obtained by slow cook-off and 5s burst point temperature tests. Results show that when RDX content is 18%， the apparent activation energy is the highest， and the response temperature and the response intensity of slow cook-off test and 5s burst point temperatures all are the lowest. The first decomposition peak temperature of samples moved backward， the apparent activation energy decreased， the slow cook-off response temperature moved to higher temperature， the thermal sensitivity of the system decreased， but the response level increased with the increase of RDX content. The response level is explosion， which could not pass the slow cook-off test when the RDX content is 46% or above. The 5s burst point temperature moves to high temperature with the increase of RDX content and presents a significant rising trend， and the thermal stability of modified double base propellants is improved.

Abstract:To study the influence of liner offset on the jet forming and armor breaking process of shaped charge， the numerical model verified by pulse radiography and penetration depth tests was used to investigate the evolution of the pressure distribution on the liner surface， molding parameters and penetration depth under different offsets ranging from 0~0.05D_k. The allowable range of liner offset that meets the requirements of good jet performance was obtained. In addition， the variation law of jet shape and lateral velocity under the coupling of liner deflection and deflection was discussed. The results show that the liner offset affects the symmetric distribution of liner surface pressure at 10μs and 12 μs after initiation （middle and late collapse process）， and a negligible effect observed at 10 μs and 12 μs after initiation（early and finally collapse process）. When the liner offset is 0.0125D_k， the jet maintains good collimation and continuity， and the penetration depth decreases by 6.6% compared with the axisymmetric case； When the offset exceeds 0.0125D_k， the jet bends in a bow shape and breaks at severe bending， with the decrease of penetration depth exceeding 10%. When the deflection angle of the liner is -0.015α， and the deflection changes from 0 to -0.0125D_k， the bending direction of jet changes， and the bending degree decreases first and then increases.

Abstract:In order to study the interaction between igniting pyrotechnics and packaging cellulose materials during the working process of traditional igniters for rocket engines and the influence of the structure of igniting pyrotechnics on flame propagation characteristics， igniting pyrotechnics/cellulose composite samples were prepared. The effects of cellulose shell on the thermal reaction performance of igniting pyrotechnics were studied by simultaneous thermal analysis （DSC-TG） and Fourier transform infrared spectroscopy （FTIR）. On this basis， the influence of charge structure， charge amount and formula composition on flame propagation process and combustion temperature distribution was studied by using simulated combustion chamber. The flame structure and flame temperature distribution of different igniters were obtained by high-speed camera and high-speed infrared thermal imager， and correlated with the collected pressure data. The results show that the cellulose shell reduces the total heat release of the condensed phase reaction of the black powder and the Mg/PTFE ignition powder. When the cellulose content is 33.33%， the total heat release of the two igniting pyrotechnics is reduced by 66.36% and 29.98%， respectively. However， the heat release of B/KNO₃ increased by 2.39 times. The analysis of gas phase decomposition products and combustion condensed phase products showed that cellulose did not change the thermal reaction path of black powder and Mg/PTFE. The simulation of ignition process shows that the pre-ignition phenomenon will occur in the ignition and combustion process of the black powder igniter with a cylindrical charge of 10 g. The igniting pyrotechnics generates a large amount of gas to carry some unburned particles to break the shell before ignition. The cellulose shell has a certain pressurization effect， which lays a pressure foundation for the establishment of the initial flame. The charge structure and charge quantity have no significant effect on the combustion temperature of the igniter， and the difference of the combustion temperature does not exceed 50 ℃. However， the working time of the igniter of the square and annular igniter cartridges is shorter， which is about 42.4% shorter than that of the small cylindrical and shaped igniter cartridges， which is beneficial to improve the ignition efficiency. In terms of formula influence， Mg/PTFE has the highest combustion temperature and the shortest working time， while the combustion temperature of large particle size black powder is higher than that of small particle size， so the former works longer.

Abstract:In order to study the morphology evolution of 1， 1-diamino-2， 2-dinitroethylene （FOX-7） particles under thermal stimulus and its influence on mechanical properties and mechanical sensitivities， four kinds of FOX-7 particles with typical size and morphology differences were selected. By controlling heating time and temperature， the morphology， mechanical properties and mechanical sensitivities evolutions of FOX-7 particles after heating were studied by scanning electron microscope， compressive stiffness experiment and mechanical sensitivities tests. The results show that the surface cracks of FOX-7 particles appear after heating and returning to room temperature. With the increase of heating temperature or heating time， the surface cracks of large-size particles （>100 μm） grow and break through ， thus the particles crack in layers and exfoliate. While， the surface cracks of small-sized particles （<100 μm） do not grow with the increase of heating temperature or heating time. Kawakita equation was used to fit the compaction curves of FOX-7 particles before and after heating. It is found that the modulus of FOX-7 particles increase after heating， and the increase is even greater for small particle size. Under the condition of larger particle size， FOX-7 has relatively low mechanical sensitivities， and still maintains low mechanical sensitivities after being heated and returning to room temperature. When the particle size is small， the mechanical sensitivities of FOX-7 are relatively high， and after heating and returning to room temperature， the mechanical sensitivities increase significantly， which may be related to the greater increase of modulus.

Abstract:In order to understand the effect of initial free cavity on the violence of confined octogen （HMX）-based PBX-3 in slow cook-off， the weak restricted test setup was designed with initial free cavity volume ratios of 1.0% and 7.4%， respectively， referring to Sandia instrumented thermal ignition（SITI）. The confined HMX-based PBX-3 explosives were heated at the same rate in slow cook-off tests. The temperatures of different locations at the center plane of explosive and shell surface were acquired using small-sized K type thermocouples， the shell velocity after thermal explosion was measured using the heat-resistant probe of photonic-Doppler-velocimeter（PDV）， and the wreckage of test setup was recycled in the slow cook-off chamber. The results show that the confined PBX-3 explosives are ignited in the center region for the same restricted strength and heating process， no matter with the initial free cavity volume. When the initial free cavity volume ratio is 1.0%， the shell surface temperature and the overall temperature of the explosive are higher when thermal explosion occurs， the shell accelerates faster and the maximum velocity is higher after thermal explosion， the wreckage fragments of test setup are smaller， and the reaction violence is higher. It is analyzed when the initial free cavity volume ratio is 1.0%， the stress of explosive is larger before thermal explosion， resulting in more serious damage. When thermal ignition occurs at the center of the explosive， the larger thermal stress causes a higher pressure induced by the gas accumulation， and the burning rate of explosive is higher. The high-temperature gas generated by the combustion is easier to enter the microcracks， resulting in stronger convective burning， faster pressure growth rate and more violent reaction.

Abstract:The matrix explosives in cast explosives are molten when being ignited under thermal stimulation， thus the hot gas released by reaction expands and reacts in liquid explosives in the physical form of bubble clouds. Considering the scale distribution and activated developing mechanism of burning-bubble clouds， a regulation model for the evolution of burning-bubble clouds after ignition of cast explosives is established. This model well reflected the dependence of reaction evolution and final reaction violence on intrinsic burning rate， shell confinement strength， charging structure size， reserved air-gap volume and pressure relief venting area. Furthermore， the flexibility of this model was verified by comparing the calculated results with the experimental data. Results show that with the increase of shell confinement strength and charge size， the self-sustaining enhanced combustion and reaction violence level increase. Moreover， with the combined design of pressure relief structure venting threshold and pressure relief venting area， the reaction violence of the charge is controlled. Under the charging condition in this paper， when the ratio of pressure relief venting area to shell surface area is up to 8.6‰， the charge reaction violence level is controlled as burning. This work provides a theoretical basis for the thermal safety design and reaction violence evaluation of explosives.

Abstract:In order to obtain the thermal decomposition properties and melting crystallization kinetic parameters of the lowest eutectic mixture of 3-amino-2，4，6-trinitroanisole （ANTA）/N-methyl-2，4，6-trinitroanisole （TNA）， the thermal decomposition properties of the lowest eutectic mixture of ANTA/TNA were studied by differential scanning calorimetry （DSC）， and the thermal decomposition kinetic parameters were calculated. The effects of additives （HMX and RDX） on the melting process and crystallization process of the lowest eutectic mixture of ANTA/TNA were studied by microcalorimetry. The non-isothermal melting and crystallization behaviors of the eutectic mixture were analyzed by Šatava-Šesták method and Avrami method， respectively. Results show that the lowest eutectic mixture has good thermal stability， and the thermal decomposition kinetic parameters are close to that of ANTA and TNA. The melting process of eutectics conforms to the first-order reaction kinetics， and the heating rate has a great influence on the melting kinetic parameters. Additives can reduce the dependence of melting kinetic parameters on the heating rate to a certain extent. The crystallization process of the lowest eutectic mixture gradually shifts to the low temperature region with the increase of cooling rate， and the crystallization rate decreases with the increase of crystallinity. In HMX medium， the crystallization rate is less affected by crystallinity， and the crystallization rate in RDX increases with the increase of crystallinity.

Abstract:In order to increase the density and detonation energy of the explosive， hydroxyl-terminated fluorine-containing binder （HTFB， 1.40 g·cm^-3） was applied to the formulation of casting PBX explosive （polymer bonded explosive）. The effects of toluene diisocyanate （TDI）， isophorone diisocyanate （IPDI）， hexamethylene diisocyanate （HDI） and hexamethylene diisocyanate trimer （3HDI） on the viscosity and curing process of the binder system were studied， and the effects of curing agents on curing and mechanical properties were also investigated. Results show that the curing agent can significantly reduce the viscosity of the binder system. In the temperature range of 25-70 ℃， the higher the temperature， the lower the viscosity of the binder system was. Above 60 ℃， the viscosity of HTFB binder system changed gently and the difference of each system was small. As curing agent， the viscosity， opening time and gel time of trifunctional isocyanate are more suitable for the preparation process of casting PBX explosive. Based on the formulation of aluminum-containing casting explosive with 88% solid content and the preparation process of pinch-vacuum injection-curing， the influence of HTFB binder on the preparation process and properties of explosive was studied in comparison with HTPB. The HTFB based PBX explosive show decent casting rheological properties and curing quality， and the density and detonation heat are 1.96 g·cm^-3 and 7790 J·g^-1， which are 6.52% and 6.55% higher than that of HTPB based PBX explosive， respectively.

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