Abstract:In order to solve the inhomogeneous component distributions and low combustion efficiency in the preparation process of nano-thermite， the core-shell structured nAl@Cu（BTC）/Fe（BTC） was prepared via a layer by layer assembly technique. The structure， morphology， thermal reaction performance （thermite-reaction temperature） and combustion performance （combustion time， ignition delay time， and combustion temperature， etc.） of nAl@Cu（BTC）/Fe（BTC） were studied. The results show that the thickness and morphology of the coating layer can be regulated during the layer by layer assembly process. As the thickness of the coating layer increases， the nano-thermite gradually changes from rough and loose to smooth and dense. The nano-thermite with alternating 12 layers of Cu（BTC）/Fe（BTC） possesses a severe burning effect with a fast flame propagation rate that reaches the maximum flame within 0.710 seconds. Besides， this sample also achieves a moderate ignition delay time （0.509 s）， the shortest combustion time （2.036 s）， and the highest combustion temperature （1425 ℃）. Meanwhile， its decomposition peak temperature of aluminum oxidation reaction can be reduced to 552.5 ℃ and 735.0 ℃ due to the synergistic effect of Cu（BTC） and Fe（BTC）.

Abstract:1，3，5，5-Tetranitro-hexahydropyrimidine （DNNC） and 1，4，6，6-tetranitro-1，4-diazepane （TNDA） were synthesized from the reaction of 2，2-dinitropropane-1，3-diol with tert-butylamine and ethylenediamine， respectively. Their structures were characterized by nuclear magnetic resonance （NMR）， fourier infrared spectroscopy（FT-IR）， and single crystal X-ray diffraction. Meanwhile， their thermal behaviors and mechanical sensitivities were determined by differential scanning calorimetry-thermogravimetry（DSC-TG） and the BAM methods. Furthermore， isodesmic reactions and EXPLO5 were used to predict detonation parameters. The crystal structures indicate that the cyclohexane skeleton in DNNC and the cycloheptane skeleton in TNDA are both chair conformations. Both of them have extensive intermolecular and intramolecular non-classical hydrogen bonds. The results of DSC-TG show that the phase transition temperatures of DNNC and TNDA are 155.0 ℃ and 154.5 ℃， respectively. Furthermore， their peak decomposition temperatures are 215.3 ℃ and 205.9 ℃. In addition， DNNC and TNDA possess good mechanical sensitivity. Their impact sensitivities are 25 J and 17.5 J， and friction sensitivities are 144 N and 240 N. Besides， their theoretical detonation velocities are 8772 m·s^-1 and 7828 m·s^-1， and detonation pressures are 34.8 GPa and 25.0 GPa.

Abstract:A new energetic iron-oxygen cluster， ［Fe₂^Ⅲ（μ₂-CH₃O）（μ₃-OH）（μ₂-O）（BODTO^2-）（H₂O）］₄ （1）， was synthesized by solvothermal method using 5，5"-｛［3，3"-bis（1，2，4-oxadiazole）］-5，5"-yl｝-bis（1-hydroxytetrazole） as ligand. The structure and thermal stability of compound 1 were studied by single-crystal X-ray diffraction， differential scanning calorimetry and thermogravimetric analysis. The catalytic performance of compound 1 on the thermal decomposition of ammonium perchlorate （AP） was also investigated by differential thermal analyzer. Compound 1 crystallizes in cubic I-43d space group with a density of 1.506 g·cm^-3. In the crystal structure， the nearby Fe³⁺ cations are interconnected to each other by bridging oxygen atoms. Through those connections， the iron（Ⅲ） cluster cages are formed. The peak thermal decomposition temperatures of compound 1 are 513.9， 617.6 K and 669.4 K， respectively. The detonation velocity and detonation pressure of compound 1 are 6.94 km·s^-1 and 19.09 GPa， respectively. In addition， the impact sensitivity and friction sensitivity of compound 1 are 15 J and 360 N， respectively. After adding 10% compound 1 to AP， the high temperature decomposition temperature of AP decreases by 65 K， and the decomposition activation energy decreases by 82.2 kJ·mol^-1， demonstrating the high catalytic activity of compound 1 for the thermal decomposition of AP and the great potential of compound 1 for application in energetic combustion catalysts.

Abstract:In order to explore the feasibility of combining emulsion explosive ink and inkjet printing process， an oil-in-water （O/W） two-component binder system was designed through ethyl acetate solution of fluorocarbon resin （FEVE） as oil phase and polyvinyl alcohol （PVA） aqueous solution as water phase. The micro-nano HMX was selected as the main explosive to prepare O/W suspension explosive ink for the inkjet printing. Furthermore， the density， morphology， mechanical properties， thermal safety performance， impact sensitivity and friction sensitivity of the printed samples were characterized by electron density tester， laser confocal microscope， scanning electron microscope （SEM）， X-ray diffractometer （XRD）， nanoindentation instrument， simultaneous thermal analysis TG-DSC， impact and friction sensitivity tester. The detonation velocity and critical size of the printed samples were tested. The results show that the surface of the inkjet printed sample is relatively flat， the average line roughness is 7.346 μm， and the internal particle distribution is compact. The crystal type of HMX particles would not change during printed process， and the printed samples display good the thermal stability and the mechanical properties. The measured density of the sample is 1.5326 g·cm^-1 （83% theoretical maximum density）. The impact energy and the friction load of the printed sample are 7 J and 144 N， respectively. The detonation velocity of the printed sample with size of 1 mm×1 mm is 7076 m·s^-1 and the critical size is 1 mm×0.087 mm. Therefore， the samples prepared through inkjet printing of HMX based emulsion explosive ink have excellent safety performance and micro-scale detonation performance.

Abstract:The packing structure of energetic crystals is one of the important factors affecting their sensitivity. A crucial mechanism for reducing the sensitivity of energetic materials is buffering external stimuli through the slipping between molecular layers within the crystal. It is very important to understand the inherent relationship between the geometric shape of energetic molecules and their crystal properties for the better design of low sensitivity high energetic materials （LSHEs）. This study used neutral CHNO molecules containing nitro from the Cambridge Structural Database as samples. Hypothesis testing methods （including Z-， t-， and χ² tests） were employed to investigate the correlation between the geometric shape of molecules and their crystal density， packing coefficient， and slipping ability. The study shows that among spherical， planar and linear molecules： spherical molecules have the highest crystal density and packing coefficient， but weaker slipping ability； planar molecules with high planarity achieve a crystal density comparable to spherical molecules by a high packing coefficient， while also exhibiting stronger crystal slipping ability， its confidence level of the χ² test is close to 1； linear molecules perform less well than the former two. Though some crystals with high crystal density and packing coefficient do not have slipping ability， general speaking， the crystal density and packing coefficient of the crystals with slipping ability are higher than those without. Both Z-tests and t-tests indicate a confidence level exceeding 0.95， suggesting that designing crystal structures conducive to intermolecular-layer slipping is not contradictory to reduceing their sensitivity and increasing crystal density. Planar molecules have a higher crystal density than average， and it is strongly associated with crystal slipping ability， making them the preferred choice for designing LSHEs.

Abstract:In order to understand the ignition process of plasma jet in the liquid propellant electrothermal chemical gun， the spreading characteristics of plasma jet in simulative liquid propellant LP1846 were studied. A two-dimensional axisymmetric unsteady mathematical model of plasma jet spreading in the liquid was established， and the model was validateded with the experiments based on the liquid working medium of water. On this basis， the spreading process of plasma jet in the simulative liquid propellant LP1846 was numerically simulated. The morphological changes of plasma jet and the distribution characteristics of pressure， velocity and temperature in the jet field were analyzed. Results show that when the plasma jet expands in the simulative liquid propellant LP1846， there is turbulent mixing phenomenon due to Taylor-Helmholtz instability， and it becomes more and more intense. It is manifested by the protruding head of the jet and the axial elongation to form a tip， and the jet entrains the simulative liquid propellant medium to produce droplets in Taylor cavity， and the number of droplets gradually increases. At the same time， the necking phenomenon occurs near the nozzle hole during the expansion of plasma jet due to the simulative liquid propellant backflow. The jet field fluctuates due to the alternating action of expansion and compression waves， especially near the nozzle hole. The pressure field shows alternating distribution of high and low pressures， and the velocity field also shows similar distribution.

Abstract:To reveal the relationship between the evolutions of polymer chains within the NEPE propellant matrix and the hyperelastic mechanical behavior， a multiscale approach was adopted to investigate the evolution behavior and characterization model of polymer chains under different deformation states. Firstly， based on the microscopic models of components such as matrix adhesives， curing agents， and plasticizers， a dynamic model describing the evolution of cross-linked and free chain configurations under complex deformation states was developed through molecular dynamics simulation of the matrix system Subsequently， the free energy contributed bycrosslinked and free chains was quantitatively characterized based on statistical mechanics， and a hyperelastic constitutive model considering the cross-linking and entanglement effects was established. Finally， the developed constitutive model was validated by using the quasi-static tensile experimental data of NEPE propellant matrix samples. Compared with the classical Arruda-Boyce model， the constitutive parameters in the present model have real physical significances and can be obtained by experimental methods， which enables the present model to better predict the hyperelastic behavior of the propellant matrix under different deformation states， and thus provide model for the regulation of mechanical properties and component optimization of propellant matrix.

Abstract:The apparent fracture toughness K_c is an important material property that characterizes the ability to resist crack initiation and propagation in the polymer bonded explosive （PBX）， investigating the size effect of apparent fracture toughness K_c is of great significance for predicting the crack initiation and failure behavior of PBX at different scales. This study examines the size effect characteristics of the apparent fracture toughness K_c of PBX surrogates by cracked straight through Brazilian disk （CSTBD） tests. Fracture tests were conducted on CSTBD specimens to investigate the influence of pre-existing crack lengths （2， 4， 6， 8， 10 mm） on the apparent fracture toughness K_c. The size effect of the apparent fracture toughness K_c of PBX surrogates was explained using the traditional maximum tangential stress （MTS） criterion and the modified maximum tangential stress （MMTS） criterion， which considers the higher-order coefficients of Williams series and the length estimation model of fracture process zone （FPZ）. Results show that， as the crack length increases， K_c increases from 0.139 MPa·m^0.5 to 0.251 MPa·m^0.5， and K_c tends to stabilize with the increase in crack length. With the use of the A₃ term-corrected FPZ length estimation model， the modified maximum tangential stress （MMTS） criterion can effectively explain the size effect of the apparent fracture toughness K_c of PBX surrogates compared to the traditional maximum tangential stress （MTS） criterion.

Abstract:A green non-toxic， easy and accuracy analysis method of the nitrogen content in nitrocellulose （NC） was investigated by using ultraviolet spectrophotometer， which was based on a linear relationship between the nitrogen content of NC and the molar ratio of nitrite-to-nitrate ions released after alkaline hydrolysis. Under the same reaction condition， five NC standard samlpes with known nitrogen contents were hydrolyzed. The concentrations of NO₂^- and NO₃^- in the hydrolysate were measured by the ultraviolet spectrophotometer， and the reaction condition of measuring system was optimized. The linear relationship between the nitrogen content of NC standards （x） and the molar ratio of nitrite-to-nitrate ions （y） was determined by the least squares method. Finally， three NC samples were used to evaluate the proposed method. Results show that the concentration of NO₂^- and NO₃^- in alkaline hydrolysate can be measured simultaneously by ultraviolet spectrophotometer， and the most suitable reaction condition is as follows： the concentration of sulfamic acid of 20 g·L^-1， and the process time of 30 min. Under the optimal reaction condition， the linear relationship between x and y is obtained， and the R² is 0.9893. The verification results of NC_A， NC_B and NC_C reveal that the nitrogen content determined by ultraviolet spectrophotometer and actual nitrogen contents are in good agreement. The relative standard deviation （n=4） values are all less than 0.150%.

Abstract:The performance and dependability of PBX are significantly impacted by internal cracks. Accurate crack identification and quantitative analysis are crucial to evaluate the performance of PBX. Currently， the ability to identify and quantitatively analyze internal cracks of PBX needs to be further improved. Consequently， research on a deep learning-based method for PBX crack identification was conducted. Based on the popular deep learning networks， five different deep learning network structures were designed. This study aimed to compare the effects of network type， connection style， and pre-trained models on the recognition of PBX cracks. Internal crack images of PBX were obtained by CT technique. The training dataset of network was constructed using these crack images. The crack dataset was used to train five different types of networks. The performance of five networks was assessed based on Accuracy， F₁， and MIoU. Select an outstanding network for PBX crack recognition and training based on the findings. The results indicate that， U-Net outperforms Seg-Net in pixel-level crack recognition and the Concatenate operation preserves more features compared to the Pooling Indices method. The pre-trained model （MobileNet and ResNet） can improve the training speed of the network， but its crack pixel-level recognition performance is reduced. The proposed method was applied to identify PBX crack， achieving pixel-level recognition. The results include a crack detection rate of 0.9570， a single pixel recognition accuracy of 0.9936， an MIoU of 0.9873， and a relative crack area of 0.7585， demonstrating superiority over traditional image segmentation methods.

Abstract:As one of the mechanically vulnerable components in the structure of solid rocket motors， it is extremely important to clarify the physical and chemical properties of the interface for solid propellants， damage evolution patterns， and the effect of dewetting on the integrity of the propellant grain structure. Compared with experiments， numerical simulation can quickly and efficiently study the different physicochemical properties of various interface systems， and has good application prospects. From the microscale molecular dynamics that can reveal the mechanism of experimental phenomena from a molecular perspective， the mesoscale finite element numerical simulation considering the microstructure of complex filler particles and other materials in solid propellants， and the macroscopic numerical simulation closely related to the macroscopic mechanical response， the research progress of various interface mechanical properties for composite solid propellants was reviewed， the driving effect of numerical simulation for composite solid propellant interfaces at multiple scales on solid propellant engineering design at multiple scales and the current shortcomings were discussed， and the future development directions were also put forward.