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Abstract:To study the microscale combustion characteristics of ammonium perchlorate/hydroxyl-terminated polybutadiene (AP/HTPB) composite propellant particle, a 2D steady state combustion model of a periodic sandwich unit was established based on gas-solid coupling, using simplified two-step global chemical reaction kinetic mechanism. The microscale combustion characteristics of AP/HTPB were numerically analyzed by FLUENT software. Results show that under the condition of volume fraction of AP as 0.75, at the low pressure of < 0.4 MPa, the overall flame of AP/HTPB combustion is a premixed combustion and the burning rate of AP is lower than that of HTPB. With increasing the pressure, when the pressure is more than 2.5 MPa, the flame reveals in a diffusion structure and the burning rate of AP is higher than that of HTPB. The higher the pressure, the stronger the thermal feedback from gas phase to solid phase, and the higher the temperature and burning rate on coupled surface. The volume release rate in the gas phase increases with increasing the pressure, the exothermic region contracts and the two connected exothermic core regions split to two independent core regions.When the combustion pressure is constant (2.5 MPa) and the volume fraction of AP changes from 0.7 to 0.95, the smaller the AP content, the relatively larger the binder HTPB width in a periodic sandwich unit, the flame surface tends to split into two narrow and long strip flame surface, and the temperature increases with splitting.

Abstract:To study the fatigue properties of hydroxyl terminated polybutadiene (HTPB) propellant at different temperatures, the constant stress control fatigue cyclic loading tests at different temperatures were carried out. Taking peak strain as damage factor, based on damage mechanics and viscoelastic theory, a three-stage model of fatigue damage with temperature effect of HTPB propellant was established. The results show that with increasing temperature, the fatigue life of materials decreases, the fracture strain increases. The peak strain in the process of fatigue obviously has three stages of evolution: initial deformation stage, stable development stage and acceleration stage, which is the macro-behavior of material damage. The three-stage model established overcomes the shortcomings of two-phase model that can′t consider macroscopic crack propagation. By fitting the model parameters, the theoretical results of 213 K and 333 K are predicted by linear regression method, which are in good agreement with the experimental results, therefore it can be used to characterize the damage evolution law of materials very well.

Abstract:To study the effect of environment oxygen content (oxygen volume fraction) at different altitudes on the combustion characteristics of aluminum-magnesium fuel-rich propellant, the laser radiation ignition was used. The ignition and combustion process of the propellant was recorded by a high-speed camera, and the surface temperature and flame temperature of the propellant were measured by an infrared thermometer. The effect of environment oxygen content and pressure on the ignition process, flame temperature and burning rate of the propellant was investigated. The results show that gas phase reaction of propellant ignition occurs mainly in the diffusion zone of propellant thermal decomposition products and environment gas, and the first flame is away from the propellant surface when the environment oxygen content is higher than oxygen content in thermal decomposition products, but the distance between the diffusion zone and the propellant surface decreases as the pressure increases. The flame temperature is in linearly positive proportion with the environment oxygen content and pressure. The burning rate of aluminum-magnesium fuel-rich propellant increases with the increase of pressure and environment oxygen content and the effect of them on burning rate is accord with B-number theory, the pressure is the main factor affecting the burning rate, however, as the pressure increases, the effect of pressure on the burning rate is relatively reduced. The burning rate sensitivity coefficient ratio of pressure and environment oxygen content is decreased from 200 to 40 when pressure is increased from 0.1 MPa to 1.5 MPa.

Abstract:In order to improve the mechanical property of single-base propellant, the single perforation cylinder modified single-base propellant containing glycidyl azide polymer (GAP)-base energetic thermoplastic elastomer were prepared. The thermal stability was evaluated by methyl violet method and vacuum stability test. The thermal decomposition process of the sample was investigated by using differential scanning calorimetry method (DSC). The impact and compression properties of the sample were studied. The results show that when increasing the content of GAP-ETPE, the thermal stability of the modified single-base propellant improve, the exothermic peak temperature, enthalpy of thermal decomposition and density gradually decrease; the impact strength and compression ratio of modified single-base propellant sample under the temperature of-40 ℃, 20 ℃ and 50 ℃ all gradually increases, while the compressive strength decreases. Compared with the blank sample, the impact strength of the sample containing 30% of GAP-ETPE at low temperatures, room temperature and high temperature increases by 161.4%, 160.1% and 164.0%, respectively; compressive strength decreases by 23.6%, 28.8% and 33.1%, respectively; compression ratio increases by 246.4%, 233.9% and 266.0%, respectively.

Abstract:In order to enhance the thermal decomposition property of nitrocellulose (NC), an energetic combustion catalyst nitrated graphene oxide (NGO) was introduced to NC and NGO/NC energetic composites were prepared. Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM) were used to investigate the structure and morphology of NGO/NC energetic composites, respectively. The thermal decomposition properties of NC in the presence of NGO were characterized through thermogravimentry-differential scanning calorimetry (TG-DSC). With the NGO addition amount of 1%, the structure of NC does not obviously change and NGO/NC energetic composition possesses a porous three-dimensional network structure. The apparent decomposition heat of NC enhances from 339 J·g^-1 to 2132 J·g^-1 with a mass loss of 96% and the exothermic peak temperature increases from 201 ℃ to 213 ℃, indicating that the addition of NGO can enhance the apparent decomposition heat and thermostability of NC.

Abstract:A new energetic material dirubidium 5, 5′-bis (tetrazole-1-oxide) (BTORb) was synthesized by using 1H, 1′H-5, 5′-bistetrazole-1, 1′-diolate (BTO) as the original material. The monocrystal of target salt was first cultivated by the method of gradual evaporation, and the single crystal structure was menstruated by single X-ray diffraction. It is found that the Rb⁺ and BTO^2- formed a dissymmetrical structure. In different layers, they are alternately arranged and connected with each other, forming a three-dimensional reticular structure. Its thermal decomposition behavior was investigated through DSC and TG-DTG technologies, indicating a good thermal stability with a decomposition temperature beginning at 292 ℃. Its kinetic parameters of non-isothermal reaction was calculated by Kissinger and Ozawa methods with the equation of Arrhenius is lnk=13.51-186.3×10³/RT. Its standard heat of formation was calculated with the result of 274.91 kJ·mol^-1. Its critical temperature of thermal explosion T_b is 356.7 ℃, indicating that the salt has a good thermal stability. The impact sensitivity (H₅₀) of BTORb is 34.8 cm, with the drop hammer of 800 g. The friction sensitivity is 36%, under the condition of 70°, 1.23 MPa. The 50% fire energy of electrostatic spark sensitivity is 0.34 J.

Abstract:3, 5-Dimethyl-4-hydroxy aniline hydrochloride was synthesized with a total yield of 75% from p-aminobenzene sulfonic acid via diazotization, condensation and hydrolysis reaction. 3, 5-Dimethyl-4-hydroxy phenyl-pentazole, which is stable at-50 ℃ was synthesized from 3, 5-dimethyl-4-aniline hydrochloride, and the yield was 66.7%. A small amount of pentazole anion was synthesized from 3, 5-dimethyl-4-hydroxy phenyl-pentazole by using methanol as solvent, ferrous salts as reductant, and m-chloro-peroxybenzoicacid as oxidant to break the C—N bond. Pentazole anion was characterized by MS and NMR. According to the isotope labeling experiments, nitrogen atoms in pentazole anion are in the same chemical environment, which means pentazole anion may possess aromaticity.

Abstract:The large smooth ε-CL-20 particle was prepared by adding CL-20 filtrate to anti-solvent, precipitated a small amount of crystal of playing a similar role of seed crystal, and the secondary faster adding a lot of anti-solvents, made the crystal grow along the seed crystal. The effect of solvent volume and stirring rate on the morphology and size of ε-CL-20 was analyzed. The performances of ε-CL-20 after crystallization were characterized. Results show that compared with the raw material, the crystal particles of ε-CL-20 prepared by this method have the characteristics of smooth surface, no sharp edge angle, high density and narrow size distribution. The characteristic drop height H₅₀ of ε-CL-20 increases from 25 cm to 40 cm, the friction sensitivity decreases from 96% to 32%, the density increases from 2.0367 g·cm^-3 to 2.0384 g·cm^-3.

Abstract:In order to study the blast power of RDX-based thermobaric explosive (TBE), the cylinder test with diameter 25 mm and static explosion experiment were carried out. The parameters of Jones-Wilkins-Lee (JWL) equation of state were obtained by simulating the cylinder test with ANSYS/LS-DYNA. JWL-Miller model was introduced to simulate the propagation process of shock waves of TBE. The parameters of secondary reacting rate of Aluminums powder were determined by adjusting the calculated results according to the test results. Results indicate that the parameters of shock waves from numerical simulation with modified JWL-Miller model can fit the experiments in free field with an average relative error less than±5%.

Abstract:To research the temperature adaptation performance of cast polymer bonded explosive (PBX) under the condition of shell restriction, explosive of component as HMX/HTPB/TDI was prepared, and five specimens were charged with the size of Ф20 mm×20 mm, Ф15 mm×65 mm, Ф100 mm×200 mm, Ф150 mm×300 mm and Ф200 mm×400 mm, respectively. In which, the latter three specimens of larger size were divided into two forms of "without defect" and with "pre-prepared defect". The change in internal damage, temperature and strain of shell external, and size, density, mechanical properties of the explosive was studied by temperature impact test and temperature cycle test of-55-70 ℃. Results show that after temperature impact test and temperature cycle test, there is not obvious thermal damage in the cast PBX and the original damage does not extend obviously. With the increase of specimen size, the time required to reach temperature equilibration via heating and cooling is prolonged and the change in high and low temperature strain reveals a trend of decrease after tests, the density of the explosive increases by 0.001 g·cm^-3 and the tensile strength and compressive strength increase by 0.12, 0.55 MPa, respectively.

Abstract:Aluminum foams are multifunctional materials possessing excellent energy absorption properties, and the sandwich composed of multi-layers aluminum foam and steel panels possesses excellent resisting blast ability.In order to study the effect of arrangement sequence of aluminum foam with different densities on the resisting blast ability of sandwich panels, the three aluminum foams which relative densities were 13.0%, 16.7%, 20.4% respectively were selected to compose nine kinds of arrangement modes with different structures. The numerical simulation of blasting process was performed by LS-DYNA softwar, the blast action experiments for parts of the structure were carried out. The results show that the results of experiment and simulation are in accordance with each other. Under the action of blast loading, the deformation of aluminum foam can be divided into three kinds of modes, namely elastic deformation, plastic deformation and densification deformation with cell wall rupture. Transverse deflection of the baseplate of aluminum foam density decreasing structure is smaller than that of the baseplate of aluminum foam density increasing structure, and the trasmission wave strength of aluminum foam density decreasing structure is only 31.6% of the density increasing structure under the same blast loading action, which indicates that the aluminum foam arranged in order of density decreasing can improve the blast-resistance ability of the whole structure.

Abstract:In order to improve the combustion performance of the oblate spherical propellants, the microcellular oblate spherical propellants with layered structure were prepared by supercritical carbon dioxide though temperature-rising method under certain saturation condition and foaming time (t_f). The effects of desorption time (t_d) and foaming temperature (T_f) on the thickness of unfoamed skin were investigated by analyzing the formation mechanism based on classical nucleation theory and proved by the scanning electron microscope (SEM) images. Results show that different thickness corresponding to different combustion properties. The closed bomb tests indicate that t_d=2 min, T_f=85 ℃ and t_f=20 s with 20 μm unfoamed skin shows excellent progressive combustion performance, which is undetected in the samples with thicker unfoamd skin or the samples completely foamed.Therefore, the microcellular oblate spherical propellants with appropriate unfoamed skin thickness and progressive combustion performance can be obtained through controlling the desorption time and foaming temperature.

Abstract:In order to accurately measure the transient high temperature of propellant combustion, the measurement method of broadband thermal radiation temperature for propellant combustion was studied on the thermal radiation theory. The high temperature transient measurement system was integrated; the validity and reliability of the temperature measurement system were verified by single-base propellant combustion test under free-field conditions. Results show that the flame temperatures are between 1500 ℃ and 1800 ℃ when the samples of propellant are placed 3 m away, and the data are repeatable and coincide with theory.

Abstract:Nitroguanidine (NQ) is usually suggested add water as stabilizer before transport and storage. To investigate the thermal decomposition characteristic of the mixture, differential scanning calorimetry (DSC) was used to test the thermal decomposition behaviors of NQ under dynamic and isothermal conditions. The specific heat generation of the decomposition reaction were about 311 and 305 J·g^-1 for dynamic and isothermal DSC. The activation energy of NQ solution under dynamic DSC (E_α=84-78 kJ·mol^-1) and isothermal DSC (E_α=86-78 kJ·mol^-1) obtained by Friedman method was very close, and the value of it did not show much variation; indicated the reaction could be expressed as single step mechanism. And the bell-shaped curves under isothermal DSC indicated the autocatalytic character of it. Then a more accurate autocatalytic model was chosen to describe it, nonlinear fitting was used to calculate the kinetic parameters, the model function equation was expressed as dα/dt=exp (18.03) exp (-92170/RT)(1-α)^1.111 +exp (18.00) exp (-76400/RT)(1-α)^1.111α^1.995. And the dynamic data well fitted with the model curves, verified the correctness of the single autocatalytic model.

Abstract:Using 4, 6-dinitrobenzotriazol-3-ium-1-oxide (DNBTO) as starting material, 4, 6-dinitrobenzotriazol-3-dinitromethyl-1-oxide (TNBTO) was firstly designed and synthesized via the reactions of metathesis, substitution and nitration-hydrolysis. The structures of all compounds were characterized by ¹H NMR, ¹³C NMR, IR and element analysis. Based on the theoretical values of densities and heat of formation, the detonation parameters were calculated using Gaussian 09 program and Kamlet-Jacobs equations. Results show that the density of TNBTO is 1.81 g·cm^-3, and the heat of formation is 143.7 kJ·mol^-1, the detonation velocity and detonation pressure are 8161.2 m·s^-1 and 30.2 GPa, respectively. However, thin layer chromatography shows that TNBTO easily decomposes at room temperature, indicating that its stability is relatively poor.

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