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Abstract:To study the ignition mechanism of charge under the combined action of shock wave and fragment impact, the critical impact velocity of fragment corresponding to the ignition of impacted charge obtained by the experimental method of first compacting charge by shock wave and then impacting damaged charge by fragment was 446.9-449.4 m·s^-1. LS-DYNA program was used to numerically simulate the shock wave damage of charge based on the nodal constraint-separation method. Then, secondary simulation to the ignition reaction process of impact damaged charge under fragment impact was performed by full restart method. The critical impact velocity of fragment corresponding to the ignition of impact damaged charge obtained by “up-down” method is from 452 m·s^-1 to 453 m·s^-1, the experimental and numerical results are in good agreement. Results show that the nodal constraint-separation method and the full restart numerical simulation technology can be used to simulate the ignition of charge under the combined action of shock wave and fragments, the critical velocity of fragments impact ignition of charge damaged by shock wave is lower than that of non-damaged charge, and the damaged state of charge sensitizes the impact sensitivity of fragments. This reduces the critical velocity of fragment impact ignition.

Abstract:To study the multi-factor coupling problem existed in the impact safety of explosive at high temperature, an impact sensitivity testing installation of explosive at high temperature was designed and an impact sensitivity testing method at high temperature was proposed. Combined with the scanning electron microscopy and X-ray diffraction techniques, the response of octogen (HMX) crystal particles under impact process at high temperature was studied by the established test method. Results show that with the increase of temperature, the drop hammer impact sensitivity of HMX crystal particles increases gradually. Meanwhile, the quality of HMX crystal is gradually reduced as temperature increasing. At 140 ℃, a small number of crystals are fragmented, and more crystals are fragmented at 180 ℃. When temperature reaches 200 ℃, all HMX crystals are fragmented. The β→δ phase transition temperature of HMX occurs between 184 ℃ and 186 ℃. After the temperature is reduced to room temperature, δ phase crystal gradually returns to β phase, and the impact process is helpful to the recovery of β phase. The main factors affecting the impact sensitivity of HMX crystal particles before and after thermal loading include temperature increasing, micro cracks and phase transition. The temperature range acted by different influence factors is different.

Abstract:To study the failure and damage behavior of opening mode crack in 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)-based polymer bonded explosive(PBX) under quasi-static loading, a semi-circular bending (SCB) specimen with pre-fabricated crack was designed. The initiation and propagation behavior of cracks in the experiments were studied by digital image correlation method and high speed photography technology of 90000 fps， respectively. Results show that the brittle fracture of sample occurs along the pre-fabricated crack direction, and the strain analysis shows that there is a significant tensile strain concentration region. On the crack propagation path, only the strain evolution of crack tip region has a significant time effect, and the evolution process has a significant inflection point at loading of about 0.85 p_max. The strain concentration effect at the crack tip begins to appear and expand rapidly after the inflection point. There is a significant plastic delaying phenomenon during the crack propagation process. The analyses of strain distribution and evolution characteristics at the crack tip indicate that plastic deformation of TATB-based PBX takes place locally at the crack tip, and the plastic deformation has an obvious influence on the initiation and propagation behavior of the crack.

Abstract:To study the damage characteristics of polymer bonded explosive (PBX) under impact load action, the dynamic impact test of TATB-based PBX was carried out with split Hopkins on pressure bar (SHHB) and X-ray micro-computed tomography(X-μCT) was used to observe and characterize the damage. Based on CT image sequences and combined with digital image processing algorithm, the extraction and 3D reconstruction of damaged cracks was performed and a damage variable evaluation method based on the proportion of defect volume in CT image sequences was proposed. The value of damage variables under different impact velocities of bullet was calculated. Results show that the damaged cracks extends from two ends to the middle along the direction of approximately 60° with the end face. The whole crack exhibits a “hourglass” distribution characteristic. With the increase of the bullet impact velocity, the crack extension direction is unchanged. Because of the existence of initial damage, the value of damage variables does not always increase, while first decreases and then increases, and then shows a sharp increase trend.

Abstract:To study the characteristics of erosive burning and gas flow in internal perforation of a tubular propellant, an interior ballistic model of a closed bomb was established considering the gas phase region inside the tube, gas phase region outside the tube and solid propellant region. The accuracy of the interior ballistic model and calculation method of the closed bomb was verified through comparing the numerical simulation results with the experimental data in the literature. On this basis, the effects of different length, internal diameter and loading density of propellant on the erosive burning of internal perforation were discussed respectively. Results show that for the tubular propellant with d=0.56 mm, l=50 mm, when 0.016≤ψ≤0.80(ψ is the burned percentage), the maximum pressure difference of internal and external perforation increases from 1.23 MPa to 2.00 MPa, the maximum gas velocity on the end face decreases from 430 m·s^-1 to 200 m·s^-1, the erosive burning coefficient on the end face decreases from 1.98 to 1.10, the erosive burning critical point of internal perforation moves from 7mm away from the symmetrical plane to 20 mm, the erosive burning area decreases by 65%. The ratio of burning surface to port area is an important factor affecting the erosive burning of internal perforation. The erosive burning does not occur when the ratio of burning surface to port area is less than 71.4. The erosive burning intensity becomes stronger with the increase of length and decrease of internal diameter, i.e. with the increase of the ratio of burning surface to port area, the erosive burning occurs evidently when the ratio of burning surface to port area is larger than 142.8. The maximum gas velocity on the end face and the erosive burning coefficient decrease slightly as the loading density increases, while the gas pressure difference of internal and external perforation increases obviously.

Abstract:Micro-porous combustible composites of NC/TEGN/RDX were fabricated by the extrusion molding process of solvent method and supercritical carbon dioxide（SC-CO₂） foaming technique using nitrocellulose (NC), triethylene glycol dinitrate (TEGN) and cyclotrimethylenetrinitramine (RDX) as energetic matrix, and thermoplastic elastomer-methyl methacrylate (MMA) as binder. Scanning electron microscopy and impact test of simple supported beam were used to investigate the cell morphology and mechanical property of the composite, respectively. Results show that increasing the saturation pressure is beneficial to reducing the pore size and increasing the pore density. With increasing the foaming temperature, the cell size of the composites gradually increases, and the cell density shows a trend of increasing first and then decreasing. When the content of thermoplastic elastomer increases from 5% to 15%, the impact strength can increase by 37.74%. The impact strength of the micro-porous combustible composites of NC/TEGN/RDX increases from 3.21 kJ·m^-2 to 4.31 kJ·m^-2 when the saturation pressure is in the range of 10 MPa to 25 MPa. However, the impact strength gradually decreases with the increase of foaming temperature. Cell size and cell density are important factors affecting the mechanical properties of NC-based energetic micro-porous composites, and the dense and uniform cell structure can effectively improve the mechanical properties.

Abstract:Aiming at the current situation that gaseous organic solvents are difficult to recover due to the existence of trace amount of nitroglycerin（NG）（0.02-4.83 mg·kg^-1） during the production of tri-base gun propellant, the absorption-degradation method is adopted to absorb and chemically decompose NG via spray liquid. Results show that sodium hydroxide aqueous solution, sodium hydroxide ethanol aqueous solution and sodium sulfide aqueous solution can be used as spray liquid and the explosion-elimination performance is positively correlated with temperature and solution concentration. Taking the initial concentration of gaseous NG, 5 mg·kg^-1, as an example, the removal rate of gaseous NG reaches 99.92% when the concentration of sodium hydroxide aqueous solution is 2.0%, the system temperature is 50 ℃, the gas-liquid contact time is 20 s and the ratio of the liquid to gas is 0.16 L·m^-3.

Abstract:5,5′-Bis(2,4,6-trinitrophenyl)-2,2′-bi(1,3,4-oxadiazole) (TKX-55), a thermally stable explosive, was synthesized with a total yield of 60.3% from trinitrotoluene via oxidation, chlorination, substitution and cyclization reactions. The chemical structure of TKX-55 was characterized by infrared (IR) spectroscopy, nuclear magnetic resonance (NMR,¹H and ¹³C). Next, we optimized the chlorine and substitution reaction conditions.When SOCl₂ acted as chlorine reagent, the highest yield was up to 88.8%. When THF was used as solvent and the reaction time was 24 h, NaHCO₃ was a better acid-binding agent compared with others (such as NaOH、Et₃N and Na₂CO₃). The decomposition temperature of TKX-55 is 335 ℃. After optimizing the molecularstructure of TKX-55, its detonation velocity (D=8052 m·s^-1) and detonation pressure (p=28.6 GPa) are calculated by Kamlet-Jacob formula, which are better than those of PYX (D=7590 m·s^-1, p=26.2 GPa) and HNS (D=7545 m·s^-1, p=23.6 GPa).

Abstract:Potassium dinitroacetonitrile was synthesized via the reactions of nitrosation and nitration-hydrolysis using ethyl cyanoacetate as raw material with a total yield of 76.93%, and its structure was characterized by NMR, IR and elemental analysis. The samples of potassium dinitroacetonitrile with different crystal morphologies were prepared by adding the different surfactants, changing the cooling rate and stirring speed. The thermal decomposition process of potassium dinitroacetonitrile with different crystal morphologies was studied by DSC and their mechanical sensitivities were tested. Results show that the crystal morphology of potassium dinitroacetonitrile has little effect on the thermal decomposition process of the sample. The sensitivity of potassium dinitroacetonitrile sample obtained after the addition of surfactant polyethylene glycol (400) is the lowest (the impact sensitivity is 8%, the friction sensitivity is 12% and the characteristic drop heights of impact sensitivity H₅₀ is >129.5 cm).

Abstract:The change in crystal structure of α-2,4-dinitroanisole (α-DNAN) under the different conditions of temperatures and pressures was studied by the method of combining theory and experiment, and its application potential in the low velocity layer of plane wave lens was discussed. The results of comprehensive experiments (variable temperature X-ray diffraction, high pressure Raman spectra) and theoretical calculations (density functional theory, molecular dynamics) show that the α-DNAN crystals can exist stably in the range of the studied temperatures（298-358 K） and pressures（0.0001-1.5 GPa）, and the phase transition phenomenon does not occur. Under temperature-pressure coupling, the a-axis direction of the α-DNAN crystal is most easily expanded or compressed due to the large amount of π-π action. The b-axis direction is most difficult to be compressed due to its strong steric hindrance. At lower pressures (0.0001, 0.6 GPa), the density of α-DNAN crystals decreases with temperature increasing. Under the condition of 0.2 GPa, the density of α-DNAN crystals at 313 K is lower than that of at 308 K and 323 K, and the mechanical properties are also correspondingly worse, which indicates that the change of crystal structure is the result of the synergistic effect of pressure and temperature.

Abstract:To establish a simple, efficient and good reproducible method of measuring the content of γ-crystal form impurities in ε-hexanitrohexaazaisowurtzitane(ε-CL-20), the characteristic parameters for the quantitative characterization of γ-CL-20/ε-CL-20 mixed samples were determined by Raman spectroscopy, and then, the characteristic peak area ratio A₂₃₂/A₅₂₈ of two crystal forms was plotted against γ-CL-20 content. The standard curves in the two sets of concentration ranges of 2%-9% and 10%-90% were obtained respectively and compared with the quantitative results obtained by the peak area method. Results show that when the content of γ-CL-20 is 2%-9%, the relative error of A₂₃₂/A₅₂₈ values for three sets of parallel experiments is not more than 2.2%, and the fitting equation is y=0.0062e^0.2512x with a correlation coefficient of 0.9806. When the content of γ-CL-20 is 10%-90%, the relative error of A₂₃₂/A₅₂₈ is not exceed 2.9%, and the fitting equation is y=0.0822e^0.0596x with a correlation coefficient of 0.9816. Data reproducibility and fitting correlation coefficient of A₂₃₂/A₅₂₈ are far better than the peak are method.

Abstract:To study the action rule of laser initiation driven by super capacitor, a time-domain model of laser output driven by super capacitor was established and a laser initiation device driven by super capacitor was designed. The output waveforms of laser under different capacitance values and discharge voltages were obtained. The test data were basically consistent with the numerical simulation data. The initiation rule of laser detonator of teteraamnine bis(5-nitrotetrazoleto) cobalt(Ⅲ) perchlorate (BNCP) as the primary charge and JH-14 as the output charge was studied by the laser initiation device driven by super capacitor. Results show that the laser initiation time driven based on super capacitor decreases rapidly with the increase of discharge voltage, and the maximum decreasing amplitude reaches 71%, and the laser initiation time decreases slightly with the increase of the capacitance value, the decreasing amplitude is about 32.1%. The initiation energy is between 0.037 mJ and 0.057 mJ. The initiation energy utilization rate decreases with the increase of discharge voltage and the capacitance. Under the test conditions of discharge voltage of 13.5 V and capacitance of 120 mF, the initiation action time is as fast as 14.8 μs, which realizes the rapid laser initiation. driven by super capacitor.

Abstract:To explore the application in smoke interference at the middle and far infrared wave-bands of 3-5 μm and 8-14 μm, the CNT/grapheme/carbon composite was prepared by a liquid phase method. Scanning electron microscopy was used to compare and analyze the microscopic morphology of graphene, carbon nanotubes and composite. The static infrared absorption ability of the three materials was compared and analyzed by Fourier transform infrared spectroscopy. Based on the smoke box experiment, the transmittances of graphene, carbon nanotube and composite for 3-5 μm and 8-14 μm in the middle and far infrared were measured, and the average mass extinction coefficient of the smoke screen was calculated according to the Lambert-Beer law. The results show that after bituminous carbonization, bituminous carbon is used as the skeleton, the smoke-screen interference composite material of the complex network structure formed by carbon nanotube and graphene inhibits the agglomeration of CNT and the stacking phenomenon of graphene, and improves the suspension properties. For the 3-5 μm wave-band, the average transmittance of carbon nanotube, graphene and CNT/grapheme/carbon composite obtained by calculated is about 9%, 10% and 5% respectively. The effective shielding time of the composite increases by about 13% and 21% respectively compared with that of CNT and graphene. The average transmittance at the 8-14 μm infrared wave-band is about 3%, 5% and 4%, respectively and the effective shielding time of the composite is about 28% and 13% higher than that of CNT and graphene. The CNT/grapheme/carbon composites improve the suspension performance and infrared absorption performance of the single carbon material, enhance the interference performance at the middle infrared wave-band, decrease the interference performance at the far infrared wave-band, but the effective interference time is still improved, and its far infrared interference time needs further improvement.

Abstract:Laser-driven flyer is an efficient shock loading method, which has essential safety as a method of initiating explosives by laser. The reliability of initiating explosives by laser-driven flyer is closely related to the flight characteristics of flyer. The flying velocity and apparent morphology (planarity and integrity) of flyer are two important parameters for a successful initiation. Therefore, in this paper, the research progresses of laser-driven flyer technique were reviewed from two aspects of characterization means and influencing factors of flight properties of flyer. Focusing on laser-driven single layer foils, the methods of observation, characterization and reception were introduced. The research findings for the function law of influencing factors of flight performance in recent years were analyzed and discussed. The deficiencies existing in current researches were hackled and summarized and the future development directions, including the systematic physical model of flight process of laser-driven flyer and quantitative parameters of planarity and integrity of laser-driven flyer, were pointed out.

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