Abstract:

Abstract:Two new explosives， C₈H₂₄N₄（ClO₄）₄ and C₈H₂₄N₄（NO₃）₄∙2H₂O， were prepared from 1，4，7，10-tetranitrocyclododecane by salt formation with nitric acid and perchloric acid respectively， which are expected to be used as emergency reserve materials of weapons in emergency wartime. The structures， thermal properties， and detonation performances of the target products were studied through single crystal X-ray diffraction， infrared spectroscopy， elemental analysis， differential thermal analysis， thermogravimetric analysis， and EXPLO 5.0 program. Results indicate that C₈H₂₄N₄（ClO₄）₄ crystallizes in the orthogonal crystal system， Pcc2 space group with a crystal density 1.968 g∙cm^-3. The crystal of C₈H₂₄N₄（NO₃）₄∙2H₂O is a dihydrate with a crystal density of 1.642 g∙cm^-3， which belongs to the monoclinic crystal system P2₁/n space group. The thermal decomposition peak temperatures of C₈H₂₄N₄（NO₃）₄∙2H₂O and C₈H₂₄N₄（ClO₄）₄ are 293.2 ℃ and 284.1 ℃， and activation energies are 131.76 kJ·mol^-1 and 195.18 kJ·mol^-1， respectively. Compounds C₈H₂₄N₄（NO₃）₄∙2H₂O and C₈H₂₄N₄（ClO₄）₄ exhibit excellent detonation properties， showing very promising performance values （C₈H₂₄N₄（NO₃）₄∙2H₂O， V=8058 m∙s^-1， p=24.0 GPa； C₈H₂₄N₄（ClO₄）₄， V=8680 m∙s^-1， p=36.2 GPa）. Moreover， the impact sensitivities of C₈H₂₄N₄（NO₃）₄∙2H₂O and C₈H₂₄N₄（ClO₄）₄ are 36 J and 33 J， respectively， and their friction sensitivities are higher than 360 N.

Abstract:Fluoropolymers such as polyvinylidene fluoride （PVDF） can effectively inhibit the agglomeration of aluminum powder and enhance its reactivity. However， the affinity between fluorinated polymers and the surface of Al particles covered by alumina is poor， and the inhibitory effect of fluorinated polymers directly coating the Al surface on Al aggregation is not ideal. In this study， a microwave-enhanced reaction method was used to obtain hydroxylated modified PVDF-OH. PVDF-OH was coated on the surface of aluminum powder by solvent/non-solvent method for preparation Al@PVDF-OH. Subsequently， the prepared Al@PVDF-OH composite fuel is used to prepare composite solid propellants. The molecular structure and elemental composition of PVDF-OH were studied using infrared spectroscopy and X-ray diffraction. Using equipment such as scanning electron microscope， differential scanning calorimeter， high-speed camera， and oxygen bomb calorimeter study the microstructure composition and combustion performance of Al@PVDF-OH composite fuels. The results showed that the PVDF-OH prepared by microwave-assisted preparation had a higher hydroxyl content， and the optimal treatment condition was 1 minute at a microwave power of 240 W. The combustion performance of Al@PVDF-OH composite fuel was superior to that of Al@PVDF composite fuel coated with unmodified PVDF and Al@PVDF-OH（H） composite fuel coated with heat-modified PVDF-OH（H）. The optimal PVDF-OH content was found to be 15%. Compared to pure aluminum， the combustion heat value of Al@PVDF-OH composite fuel with 15% PVDF-OH increased from 19140 kJ·kg^-1 to 24912 kJ·kg^-1. Combustion tests mixed with ammonium perchlorate （AP） showed that the ignition delay time of Al@PVDF-OH composite fuel shortened from 77 ms to 70 ms， and the burning rate increased from 195.7 mm·s^-1 to 225.7 mm·s^-1 compared to pure aluminum. Compared to aluminum-based solid propellants， solid propellants based on Al@PVDF-OH composite fuel exhibited an increase in combustion heat value from 13281 kJ·kg^-1 to 14020 kJ·kg^-1， an increase in burning rate from 1.281 mm·s^-1 to 1.915 mm·s^-1， and a reduction in the particle size D₉₀ of condensed phase combustion products from 74.324 μm to 52.749 μm.

Abstract:To gain a comprehensive understanding of the properties changes of TNT crystals under strong magnetic field radiation， the morphological changes， the lattice constants and the thermal decomposition characteristic were explored using the scanning electron microscope， X-ray diffraction， Raman spectroscopy and differential scanning calorimeter （DSC）， respectively. Moreover， the variations of lattice constants， molecules distributions， mechanical properties and theoretical impact sensitivity of TNT under magnetic field radiation were investigated by molecular dynamics simulations. The experimental results， with the application of 6 T magnetic field， showed that the microscopic morphology was changed from the scale-needle structure to the irregular block structure， and the exothermic peak temperature of thermal decomposition was increased from 289.6 ℃ to 304.1 ℃. However， the crystal phase structure and lattice constants of the TNT remained unchanged. Furthermore， theoretical investigations indicated that the TNT lattice constant not affected by magnetic field radiation， but the magnetic field did change the molecules distribution in the TNT crystal. The 8 T magnetic field radiation significantly improved the ductility of TNT. However， it simultaneously increased the impact sensitivity of TNT by comparing the ratio for the longest trigger bonds.

Abstract:The planetary motion of impeller in the vertical mixer can effectively promote the dispersed circulation and homogeneous distribution of different material components， which has been employed in the preparation procedure of solid propellant slurry. However， the mixer involves complex interfaces and motions that it is difficult to study the mixing mechanism and rheological property of slurries by traditional methods. Based on the smoothed particle hydrodynamics （SPH）， the continuum was discretized into the conserved particles with physical quantities for simulating the interaction between the propellant slurry and blades under laminar flow. A meshless method for the mixing process of propellant slurries in non-Newtonian fluid state was developed by combining the Herschel-Bulkley （HB） constitutive model. The numerical simulations were compared with the experiments to verify the accuracy of the proposed model. The correlations of the blade motion parameters and power consumption were explored. The effects of geometric configurations and rotation modes on the mixing uniformity of slurries and the torque loads of impellers were analyzed. Research findings indicate that the simulation and literature experiment results have a good agreement that the average relative error between them is around 4.98% in the non-Newtonian fluid with shear rate index n=0.47. The mixing uniformity index of planetary impellers increased by 8.9% and 7.3% respectively than those of central and eccentric impellers after stirring for 2.65 s. The maximum amplification in torque can reach 38.4% within the revolution radius range of 0.11D_w-0.23D_w at Reynolds number Re=1.

Abstract:As an important thermodynamic parameter of explosives， thermal conductivity significantly affects the ignition response characteristics of explosive charge. In order to quickly and effectively obtain the thermal conductivity of explosives without tests， an axisymmetric heat conduction theoretical model of typical cylindrical charge structure is established， and its steady-state analytical solution is derived. Also， a method for calculating the thermal conductivity of explosives is proposed based on the slow cook-off experimental data. The thermal conductivity of a new type of insensitive explosive， GOL-1（HMX/Al/AP/Binder）， is determined. The numerical simulation results of the ignition response of small-size charge structure under typical cook-off conditions shows that the calculated results of the charge center temperature-time curves at different heating rates are basically consistent with the experimental results， and the deviations of ignition temperature at charge center and ignition time between the calculated and experimental results are 2.27% and 1.12% at most， which indicates the effectiveness of the thermal conductivity of the GOL-1 and the feasibility of the numerical simulation method. The established calculation method reveals the thermal conductivity characteristics and rules based on the temperature-time curves of slow cook-off experiments， which is more suitable for calculating the thermal conductivity of explosives compared with volume-weighted method and string or parallel heat conduction model. In the absence of experimental data for determining the thermal conductivity of new explosives， this method is an effective determination method， providing a basic parameter for the design and evaluation of thermal safety of ammunition and promoting the development of digital design and quantitative evaluation of safe ammunition.

Abstract:To investigate the cook-off response characteristics of JEO explosive （NTO/HMX/additives）， an experimental system for multi-point temperature and pressure measurements during the cook-off process of explosive was devised. The cook-off experiments of JEO explosive were conducted at two different heating rates of 5 ℃·min^-1 and 2 ℃·min^-1 to obtain the ignition time， ignition temperature， temperature history at different positions within the explosive， and pressure evolution inside the device. The effect of heating rates on temperature and pressure variations and reaction intensity during the cook-off process of JEO explosive was analyzed. Furthermore， based on the experimental research， a multiphase flow species transport model for explosive cook-off was adopted considering the influence of pressures on the thermal decomposition reaction of explosive， and numerical simulations were conducted to investigate the thermal decomposition process of JEO explosive under different heating rates using Fluent software. The results indicate that the thermal decomposition reaction of JEO explosive proceeds slowly before phase transition， while it accelerates significantly afterwards， leading to a rapid increase in temperature and an exponential growth in pressure until ignition. The ignition temperature of JEO explosive is approximately 220 ℃， and its response level is deflagration under the constraint conditions of this experiment， demonstrating excellent thermal safety. As the heating rate decreases， the ignition time of JEO explosive prolongs， and the ignition location shifts from the edge of the charge towards the center， resulting in an increased intensity of the reaction. During the thermal decomposition process before ignition， only a small portion of the explosive undergoes reaction， with the majority of the reaction occurring during the combustion stage after ignition.

Abstract:To improve the ignition reliability of firearm firing-ignition systems， the Lagrangian-Eulerian fluid-structure coupling method （ALE） was used to establish the ignition model of the firing-ignition systems， and a parametric simulation platform was built. The pressure start time was used as the ignition output performance characteristic parameter to establish the ignition reliability proxy model of the firearm firing-ignition system. The reliability of the firing-ignition systems under the influence of changes in structure and assembly parameters was simulated and studied. At the same time， based on small-caliber rifle firing-ignition system， an ignition system simulation test device was designed， and experimental research on the ignition performance and reliability of the ignition system was carried out to verify the ignition model. The results show that the error between the calculation results of the firearm firing-ignition reliability analysis model and the experimental results is 0.72%， indicating that the model has good accuracy. The influence rule of the average change of each factor on the system reliability is as follows： striking pin protrusion> locking gap> fire table head diameter> primer shell thickness> primer loading depth> firing pin head diameter. The standard deviation change has little impact on system reliability. This study provides theoretical and technical guidance for the reliability design of firearm firing-ignition systems.

Abstract:Energetic materials serve as the energy source for munition damage， directly impacting the strike range and effectiveness of munitions. With the increasing strategic requirements of modern weapon systems for high energy， high efficiency and high security， research on the thermal properties of energetic materials has gained more attention. The thermal properties of energetic materials not only directly affect the energy output， control and regulation of energetic materials， but also are related to the safe transportation， storage and use. In order to provide a reference for the research methods of thermal properties of energetic materials， this paper systematically reviews the thermal performance characterization techniques and theoretical prediction models applied to energetic materials in recent years， involving the analysis of thermal decomposition reaction mechanism， combustion performance test， detonation performance evaluation and safety performance prediction， and analyzes and compares the characteristics and application scope of each characterization technology. Finally， it proposes that the experimental characterization technology in future research should be developed in the direction of high integration， high spatiotemporal resolution， small dose non-contact interference， and real-time monitoring and analysis. In the computational simulation research， it is necessary to co-construction and share the standard database according to the actual production of energetic materials， in order to obtain a high-precision and high-efficiency performance prediction model.

Abstract:The morphology and structure of energetic materials have significant impact on their various properties. In order to improve the inherent performance of existing energetic materials and meet the different application requirements of weapon， the assembly of energetic materials is an effective technology. Based on the relevant works of domestic and foreign scholars， the current methods of energetic materials assembly and the effects on performances were summarized from two perspectives： the directly affecting the structure of single-component energetic materials through assembly and regulating their performance， and the assembly components and composite structure of multi-component composite energetic materials synergistically regulating the performance. The enlightenment of other functional materials assembly for energetic material was elaborated. Currently， the assembly of single-component energetic materials can achieve new crystal morphology， while multi-component assembly can compensate for the inadequacy of available performance control， and achieve synergistic improvement of energy and safety performance. However， the development of energetic material assembly still faces problems such as monotonous assembly methods， difficult process control， unclear assembly mechanisms， and insufficient research on multi-components. Future research may focus on three perspectives： the improvement of crystal assembly theory for energetic materials， the development of mesoscopic characterization techniques， and the exploration of new assembly technologies.

Abstract:The solidification process of melt-cast explosive is a significant step during its research and manufacture. Solidification， and related charge quality play key roles in the detonation performance and safety of explosives. Based on domestic and foreign research works， the development of solidification techniques of the melt-cast explosive is systematically summarized from three aspects： finite element simulation， solidification process and on-line detection methods. The application of the finite element simulation in flow -temperature-stress field simulation during casting and solidification process of the melt-cast explosive is reviewed. The formation of defects during the solidification process and the effects of different techniques on solidification are elucidated. Furthermore， the application of on-line detection of temperature， stress-strain， viscosity， and internal structure in the high-quality precision forming techniques of melt-cast explosive is discussed. The development of numerical simulation， solidification process optimization and on-line detection technique in melt-cast explosive can provide vital theoretical and technical guidance for the design and development of the solidification equipments and the quality improvement of solidified charges. In the future， the improvement of the charge and solidification technique requires further development and application in aspects such as model construction of equipment-material， safety of process equipment， precise control of process conditions， real-time information monitoring， on-line detection and adaptive regulation.