Abstract:From three aspects of mechanical behavior, application research of protective structures and energy-mitigation mechanism, the research progress in using polyurea elastomer for enhanced structural protective performance under blast and impact loading was reviewed. Polyurea elastomer possesses many desirable properties including ease of application, rapid cure time, adhesive property and excellent quasi-static and dynamic mechanical properties, particularly high strain rate dependence and elongation. It is considered that polyurea elastomer for enhanced structural protective performance including concrete masonry wall, metal structure and nonmetal composite material structure has made important progress. Some regular knowledge including effects of the location and the quality ratio of the polyurea elastomer in the composite structure on the anti-detonation performance, the mechanism of using polyurea elatomer for enhanced anti-detonation performance in various composite structures has been obtained. Also, polyurea elastomer is considered as a great potential material in explosion protection field. Simultaneously, it is pointed out that present research is scattered and lacks unsystematic. In the future, more precise constitutive model, the factors affecting the blast resistance of polyurea elastomer, the micro-energy mitigation mechanism of polyurea elastomer and the dimensional effect of protective structure are needed to be studied further.

Abstract:In order to clarify the effect of multi-modal ammonium perchlorate（AP ）on combustion responses characteristics of AP/Hydroxyl polybutadiene(HTPB) composite propellants, the unsteady combustion response (Rp) model of multi-modal AP composite propellant has been established and calibrated. Under 10 MPa and 25-1000 Hz conditions, more than 10 types of AP-based propellant samples containing AP with four typical average particle sizes (330， 250，110 μm and 50 μm) have been used to calculate the characteristics of the combustion response. The effects of the AP modal and mass ratio on combustion response function have been analyzed. The results show that: 1) the Rp model calculation results are in good agreement with experimental results reported in the literature (pressure >5 MPa), deviation <9%; 2) the AP particle modal and mass ratio have great effects on the combustion response function, and law is basically satisfied, showing that the increased content of small-sized AP or reduced the content of large-size AP could reduce medium and low frequency oscillation, but meanwhile it would drive higher frequency oscillation; 3) Replacement of small-sized AP with medium-sized AP can reduce medium and high frequency oscillation. Conversely, the replacement of the large-size AP with medium-size AP can reduced low frequency oscillation.

Abstract:To further study the blasting mechanism of slotted cartridge, blasting model for slotted cartridge with a charge decouple coefficient 2.0 was established by using coupled SPH-FEM algorithm in AUTODYN. The expansion process of the detonation product in the early stage of the explosion, the velocity of detonation product particles and the damage evolution of rock mass around borehole were analyzed. Results show that the detonation product particles can move forward at high speed due to lack the constraint of slotted tube in the slit direction. The maximum velocity of the detonation product particles can reach 4750 m·s^-1. The front-end product particles reach the borehole wall and the rock mass starts to be damaged at 3.5 μs. With the continuous expansion of detonation product，rock mass is further damaged in the slit direction. In the non-slit direction, the expansion of detonation product particles is hindered due to the restraint of the slotted tube. The maximum velocity of particles is only 800 m·s^-1. At the same time, the slotted tube driven by detonation products moves towards borehole wall slowly. The slotted tube reaches the borehole wall and rock mass starts to be damage at 12.6 μs. However, the small range of damage distribution is only formed, and the borehole wall maintains good integrity in non-slit direction.

Abstract:In order to solve the problem of the application of energetic and insensitive plasticizers in Nitrate Ester Plasticized Polyether(NEPE) propellants, the compatibilities of polymer binder PEG with Trimethylol ethane trinitrate(TMETN), 1,2,4-butanetriol trinitrate(BTTN) and nitroglycerin(NG) were studied. By simulating the solubility parameters (δ) of pure substances, the inter and intra molecular radial distribution function, the order of compatibility was concluded as follows: TMETN/PEG>BTTN/PEG> NG/PEG. The methylene in BTTN and the structure of TMETN weakened the intermolecular interaction and reduced the difference of δ between plasticizer and PEG. The interaction of PEG/plasticizer was clarified by calculating binding energy and inter molecular radial distribution function. Intermolecular interaction included Van der Waals and electrostatic interaction, in which the Van der Waals contributed the most. The better the compatibility between plasticizer and PEG, the greater the proportion of the Van der Waals in the intermolecular interacion. The mesoscale morphologies of blends and the dynamic evolution process of the system were investigated by mesoscopic dynamic simulations. By analyzing isosurface of the density fields, order parameters and free energy density，it was found that phase separation occurred in NG/PEG ,BTTN/PEG and slightly gathering occurred in TMETN/PEG. Due to better compatibility with PEG, TMETN might be a potential plasticizer to replace or partially replace NG in NEPE. Present work provides reference for the development of low-vulnerable tactical weapons.

Abstract:The crystal morphologies of β-HMX (octahydro-1,3,5,7-tetranitro-1, 3, 5, 7-tetrazocine) in eight pure organic solvents were predicted based on the modified attachment energy (AE) model by using molecular dynamics (MD) method. Results demonstrate that the morphological dominant crystal faces of β-HMX in vacuum are: (0 1 1), (1 1 -1), (0 2 0), (1 0 0) and (1 0 -2), respectively. The (1 0 0) face is the most polar crystal face and has the largest interaction energy with the solvent molecules, which results in a slow growth rate and appears as dominant face in the final crystal morphology. The (1 0 -2) and (0 2 0) faces have the small interaction energies with the solvent molecules, which appear as small areas or even disappear in the final crystal morphology. The order of the aspect ratio of the crystal morphology is: cyclopentanone>cyclohexanone>N, N-dimethylacetamide (DMAC)>pyridine>acetone>triethyl phosphate>propylene carbonate>Dimethyl sulfoxide (DMSO), which indicates that DMSO and propylene carbonate are more favorable for the spheroidization of β-HMX in crystallization experiments. The experimental crystal morphologies of β-HMX in eight pure organic solvents were investigated using a natural cooling recrystallization method. Results show that the predicted morphologies are in good agreement with the experimental results. The attached energy (AE) model is suitable for predicting the crystal morphology of β-HMX, which may serve as a guide in β-HMX recrystallization experiments.

Abstract:A new zwitterionic energetic compound N-(2,2-dinitroethyl)-aminoguanidine can be obtained through two-step reactions (degradation reaction and substitution reaction) using 2,2-dinitro-1,3-propanediol as raw material in a total yield of 65%. Its structure was characterized by single-crystal X-ray diffraction，FT-IR, NMR (¹H NMR and ¹³C NMR) and elemental analyses. Its thermal decomposition temperature was confirmed by differential scanning calorimetry and thermogravimetry (DSC-TG), and energetic parameters were calculated using the method of isodesmic reactions and K-J formula. The results show that the crystal of zwitterionic N-(2,2-dinitroethyl)-aminoguanidine belongs to monoclinic system and P2₁/n space group with cell parameters of a=8.8613(10) Å，b=6.4568(6) Å，c=13.4134(16) Å，α= 90°，β=95.093(4)°，γ=90°, V=764.43(14) nm³，Z=4，D_c=1.670 g·cm^-3，F(000)＝400. The decomposition temperature locates at 183.8 ℃, and calculated detonation velocities and pressures are 8333 m·s^-1, 29.4 GPa, respectively. The measured impact and friction sensitivities are low (IS=20 J,FS=120 N)。

Abstract:Various preparation methods have been widely explored to improve the combustion performance of nanothermites in recent years. In this work, two kinds of Fe₂O₃-containing nanothermites were successfully prepared by in-situ ball milling method and conventional ultrasonic blending method respectively. The morphologies and performance of as-prepared products have been fully characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), contact angle tests, scanning electron microscopy (SEM), high-speed imaging experiments and infrared temperature measurement. The results show that the Fe₂O₃-doped nanothermites via in-situ ball milling method exhibit better performance than that made by ultrasonic blending method. The optimal nanothermites with 17% Fe₂O₃ doped amount possess the maximum mass gain percentage of 13.1% per 100 ℃. Compared with the products made by ultrasonic blending method, the heating voltage and initial combustion temperature of in-situ ball milled nanothermites decrease to 12 V and 600 ℃, respectively. In addition, the combustion flame of in-situ ball milled nanothermites is more stable and homogeneous than the corresponding one.

Abstract:In the preparation of new heat-resisting energetic materials, two new polynitroazobenzene energetic compounds,2,2′,4,4′,6,6′-hexachloro-3,3′,5,5′-tetranitroazobenzene (HCTNAB) and 4,4′-dichloro-2,2′,3,3′,5,5′-hexanitro-6,6′-dimethoxy- azobenzene (DCHNDOCAB), were prepared and their structures were determined by elemental analyses, FTIR, single-crystal X-ray diffraction analysis. Meanwhile, the thermal decomposition temperature was determined by differential scanning calorimetry (DSC) and TG-DTG, the thermal decomposition temperature of HCTNAB is 266.8 ℃, and the thermal decomposition temperature of DCHNDOCAB is 269 ℃. To accomplish the performance prediction of DCHNDOCAB, we used the calculations that based upon the B3LYP (Becke three-parameter Lee-Yang-Parr)/6-311++G^** method gain optimized structure using Gaussian 09. Our research shows that HCTNAB can be seen as a vital energetic intermediate containing active chlorine. The calculated detonation velocity of DCHNDOCAB is 7117 m·s^-1, and the detonation pressure is 21.0 GPa, show that the DCHNDOCAB is hopeful to become a new heat-resisting azo aromatic energetic materials.

Abstract:In order to solve the problems of low efficiency(direct tension test method (GJB772A-1997)) and poor test accuracy (indirect Brazilian test method) intraditional tensile strength testing of polymer bonded explosive (PBX), we independently established a test plat form based on the hydraulic fracturing method (HFM), developed a novel test method of PBX tensile strength, and achieved accurate testing of PBX tensile strength. To further verify the validity of the test method, the tensile strength of the same PBX dumbbell samples was obtained through direct tension test method and HFM, and the test results were compared. It showed that the relative error between the tensile strength by HFM ((9.49±0.24) MPa) and the tensile strength by direct tension test method ((9.24±0.43) MPa) was only 2.70%, showing the high accuracy. Moreover, the HFM can obtain at least four effective tensile strength data on the on the single dumbbell remnant samples. Compared with the direct tension test method, HFM has the characteristics of less material consumption, high efficiency, and good stability for PBX tensile strength testing. It indicates that the HFM has the advantages of the high accuracy in the direct tension method and high efficiency in the Brazilian test. Therefore, HFM can be widely applied in the in-situ test method for formulation development and tensile strength test of different positions of PBX structural components.

Abstract:To explore the process and safety of emptying ammunition charge by submerged cavitation water jet, relative experimentalresearchwas carried out with A-Ⅸ-Ⅱ explosive as the experimental object. The split Hopkinson pressure bar (SHPB) device was applied to obtain stress-strain mechanical properties of A-Ⅸ-Ⅱ. The emptying experimental system was set up to investigate the impact crushing effect and mechanism of cavitation water jet on A-IX-II. Scanning electron microscope (SEM) was used to characterize the morphology of broken particles and gain the mesoscopic breakup mode of A-Ⅸ-Ⅱ. The internal temperature of A-Ⅸ-Ⅱ during the impact process of cavitation water jet was measured with a self-designed thermocouple temperature measurement device, and the experimental safety was discussed by combining the results of differential scanning calorimetry (DSC) of A-Ⅸ-Ⅱ. The results show that stress-strain curves of A-Ⅸ-Ⅱ include three stages: brittle-elastic stage, nonlinear elastoplastic stage and strain softening stage, and the damage under dynamic loading shows strain rate effect. It is greatly available to use cavitation water jet to empty A-Ⅸ-Ⅱ explosive in fifteen minutes and the maximum particle size of the collected A-Ⅸ-Ⅱ explosive is no more than 3 cm. The damage of A-Ⅸ-Ⅱ is mainly caused by the strong impact of micro-jet and shock wave when the cavitation bubble collapses. The mesoscopic breakup mode is mainly the intercrystalline separation of crystals from binder and aluminum powder, accompanied by a small amount of transgranular phenomenon, and no crystal breakup is found. It is safe to empty A-Ⅸ-Ⅱ explosive by using submerged cavitation water jet as the highest temperature in the experiment is 50 ℃, which is lower than the temperature required for thermal initiation (160 ℃).

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