Abstract:

Abstract:

Abstract:To characterize the structure of TATB-based polymer bonded explosives（PBX） on the meso-scale， an automatic granule boundary extraction method based on the two-dimensional（2D） reconstructed CT images with low quality is presented. Binarization was first performed according to the gray level distribution of the original CT images of TATB-based PBX. Then a proposed elastic capsule algorithm was applied to the binary images and an approximate location of the granule boundary was obtained. With a combination of morphological operations and the marker-based watershed algorithm， a more accurate segmentation of TATB-based PBX granules was realized. The present granule boundary extraction method for 2D CT images of TATB-based PBX shows improved accuracy and portability， as compared to Canny algorithm， iterative phase congruency， SLIC superpixels and other feature extraction techniques.

Abstract:In order to study the influence of stoichiometric ratio and oxygen content of oxidant on detonation process of gelled gasoline/gas-phase oxidant， a three-dimensional two-phase detonation model of gelled gasoline and gas-phase oxidant was established， and the internal detonation process of pulse detonation engine was simulated numerically using conservation element and solving element method. The effect of stoichiometric ratio and oxygen content of oxidant on the formation time， formation distance， peak pressure and propagation velocity of detonation wave were analyzed. The numerical results indicated that when the stoichiometric ratio is lower than 1.15， the formation distance and time of detonation wave decrease with increasing of stoichiometric ratio， and the pressure peak and propagation velocity of detonation wave increase at the same time. When the stoichiometric ratio is of 1.15， the formation distance and time of detonation wave are 0.288 m and 278 μs， and the pressure peak and propagation velocity of detonation wave are 1.85 MPa and 1437 m·s^-1， respectively. The pressure peak and propagation velocity of detonation wave increase with increasing oxygen content of oxidant， and when the oxygen content increases from 23% to 48%， the pressure peak and propagation velocity of detonation wave increase from 1.85MPa， 1437 m·s^-1 to 2.85MPa， 1868 m·s^-1， respectively.

Abstract:In order to speed up the development of new energetic materials and reduce the time and resource consumption caused by a large number of experiments， a method for predicting enthalpy of formation of energetic materials is proposed based on the theory of material genetic engineering. Firstly， the collected atomic coordinate data representing the molecular structure of energetic materials were converted into a coulomb matrix representing the cartesian coordinate system in the molecule to eliminate the influence of translation， rotation， index order and other operations on the prediction of enthalpy of formation. Then， the enthalpy of formation of energetic materials was predicted according to the proposed fusion model of Convolutional Neural Network （CNN） and Bi-directional Long Short-term Memory Network （Bi-LSTM） based on Attention mechanism. In this way， not only can the characteristics of the data be extracted effectively， but also the correlation between the data and the lack of long-term dependence can be fully considered. Meanwhile， the influence of important characteristics on the prediction results can be highlighted. The comparison of experimental results shows that the proposed method based on deep learning has the lowest experimental error in the prediction of enthalpy of formation. Its Mean Absolute Error （MAE）， Mean Absolute Percentage Error （MAPE）， Root Mean Square Error （RMSE） and Root Mean Squared Logarithmic Error （RMSLE） are 0.0374， 1.32%， 0.0541 and 0.028， respectively. The prediction goal of "structure-performance" is realized， and a new method is provided for the prediction of enthalpy of formation of energetic materials.

Abstract:In order to explore the influence of the complexity of crack distribution and shape on the particularity of ultrasonic propagation in curved surface components of polymer bonded explosives （PBX）， and optimize the parameters of ultrasonic oblique incidence testing， a numerical model of ultrasonic nondestructive testing of curved PBX components was established， based on the finite element method and typical testing conditions. The surface P under the excitation of transient displacement was calculated and analyzed by COMSOL commercial software. The propagation law of the internal sound field of PBX component was simulated， the ultrasonic detection signals of different angles and cracks were calculated， and the influence of the incident angle and other parameters on the detection results of small angle oblique incidence of ultrasonic water immersion crack of curved PBX component was studied. The numerical simulation results show that when the angle between the beam and the crack is 8°~10°， the small angle oblique incidence ultrasonic detection method has the best detection performance for PBX internal crack defects， and is not affected by the crack depth. At the same time， the curved PBX simulation specimen was designed and manufactured， the small angle ultrasonic testing experiment system was built， and the ultrasonic testing experiments under different incident angles and crack parameters were carried out. The optimal testing angle （8°） obtained from the experiment was consistent with the simulation results （8°~10°）， which verified the rationality of the numerical simulation results and the effectiveness of small angle ultrasonic testing.

Abstract:The dynamic characteristics of unreacted solid explosive PBX-59 under ramp wave compression were studied with a magnetic driven loading experimental technique， and the dynamic response of PBX-59 under a peak pressure up to 18.5 GPa was obtained. The p-V relationship， the acoustic velocity-particle velocity relationship and other dynamic parameters of PBX-59 were obtained by the iterative Lagrange data processing method modified by impedance matching under the ramp wave compression. Combined with the dyamic parameters and isentropic equation of state derived from experimental data， the experimental results were hydrodynamically simulated. The numerical calculation agree well with the experimental results， which verifies the validity of the experimental technology， data processing method， and physical model.

Abstract:The thermal stress fracture of polymer bonded explosive （PBX） was studied by a combined simulated and experimental method using notched PBX cylinders. A 2D axisymmetric finite element model， which contained temperature related material properties， was employed to calculate the thermal elastic-plastic response of PBX cylinders under the condition of the initial cooling temperature of 50 ℃ and cooling rate of 10 ℃·min^-1. Temperature， strain and acoustic emission （AE） measurements were used in an air-cooling test for verification. Simulation results show that there is a temperature boundary layer near the surface and a temperature difference in the cylinder， resulting in tension stress greater than the strength of the PBX. A circular notch in the cylindrical surface distinctly amplifies the thermal stress and the stress gradient. The factor of stress concentration reaches a maximum of 1.6 when the notch radius is 2 mm. The PBX endures brittle broken during thermal shock when thermal stress exceeded its tension strength， accompanied with strong AE signals and a sharply decline on strain-time response. The critical fracture temperature of cylinders with and without a notch determined by simulation are respectively 8.3 ℃ and 12.6 ℃， while the value determined by experiment are respectively 9.2 ℃ and 12.5 ℃.

Abstract:In order to understand the reaction characteristics of azide binder/non-isocyanate bonding system， curing processes of 3，3-bis（azidomethyl）oxetane-tetrahydrofuran copolymer（PBT）/bis-propargyl-succinate（BPS） binding system were investigated by microcalorimetry. The kinetic parameters and characteristic temperatures of PBT/BPS binding system were calculated through Kissinger method and Crane method. The equation between the complete curing time and the curing temperature was also fitted， demonstrating that the apparent activation energy， pre-exponential factor， reaction order and heat for curing reaction of PBT/BPS bonding system are 81.94 kJ·mol^-1， 10^8.48 s^-1， 0.93 and -926.88 J·g^-1， respectively. The values of gelation temperature， curing temperature and post-curing temperature were examined to 319.29 K， 344.52 K and 366.11 K， respectively. Besides， self-catalyzed phenomenon could be witnessed to exist in the curing reaction process of the PBT/BPS bonding system. The equation between the complete curing time and the curing temperature was y＝8.3345×10⁴e^-0.02309x-11.116.

Abstract:As the diffusion and migration of the deterrents affect the service life of gun propellants during the storage period， the molecular dynamics simulation （MD simulation） was applied to compare the diffusion rate of the small molecule dibutyl phthalate （DBP） and polyneopentyl glycol adipate （NA） in gun propellants. Meanwhile， the effect of nitroglycerin （NG） content on the diffusion of DBP and NA in double base gun propellants was explored and the diffusion mechanism was analyzed. The results indicate that the diffusivity of DBP and NA in nitrocellulose （NC） is equivalent at 5 ℃ and the diffusion coefficients are both in the order of 10^-12 m²∙s^-1. The diffusion coefficients of DBP and NA are 1.88×10^-11 m²∙s^-1 and 7.57×10^-12 m²∙s^-1 at 65 ℃， respectively. The diffusion coefficients of DBP and NA are 3.42×10^-11 m²∙s^-1 and 1.11×10^-11 m²∙s^-1 at 85 ℃， respectively. At the same temperature， the order of the diffusion coefficient of the deterrents is DBP>NA， which shows that NA has better anti-migration properties， which are more prominent at high temperatures. Owing to the high temperature， the peak value reduces， thus weakening interaction between DBP， NA and NC， meanwhile， the fractional free volume of system increases， which is conducive to the diffusion of DBP and NA. The diffusion capacity of DBP and NA increases with the increase of NG content. Adding NG weakens the interaction between DBP， NA and NC， so DBP and NA move more actively and the diffusion ability increases. The molecular dynamics simulation method is used to study the diffusion properties of the deterrents in gun propellants， which provides important theoretical guidance for predicting the life of gun propellants.

Abstract:In order to develop a scale-up and continuous preparation method， the microchannel crystallization technology based on solvent/non-solvent method has been used to prepare hexanitrohexaazaisowurtzitane/octogen （CL-20/HMX） co-crystal. The field emission scanning electron microanalyzer （FE-SEM）， X-ray powder diffraction （XRD）， Raman spectroscopy， Fourier infrared spectroscopy （FT-IR）， thermal analysis and sensitivity test were applied to characterize and analyze the morphology， structure， thermal performance and sensitivity of samples. Results show that this method has successfully prepared CL-20/HMX co-crystal. Its apparent morphology is the flower clusters with a diameter of 20-30 μm， assembled by platelet crystals with thickness of 200-600 nm， accompanying individual flaky crystals （thickness of 200-600 nm）. The CL-20/HMX co-crystal prepared by microchannal crystallization has only one sharp exothermic decomposition peak during the exothermic process. Its exothermic peak temperature is at 243.4 ℃， which is lower than that of the raw materials CL-20 （250.2 ℃） and HMX （284.7 ℃）. Its temperature range of thermal decomposition is only from 242.7 to 246.0 ℃， much narrower than those of raw CL-20 （230.0-254.6 ℃） and HMX （281.0-290.7 ℃）， which means a higher energy release efficiency. Its apparent active energy is 470.75 kJ·mol^-1，falling between CL-20 （175.04 kJ·mol^-1） and HMX （481.45 kJ·mol^-1）， which is 297.29 kJ·mol^-1 hagher than that of raw CL-20，indicating a good thermal stability. Its impact sensitivity is 18 J， which is 8 J and 3.6 J higher than those of raw CL-20 （10 J） and HMX （14.4 J） respectively， and the friction sensitivity is 20% lower than that of raw CL-20. The sensitivity results show the safety of the CL-20/HMX co-crystal has been improved compared with the raw materials.

Abstract:3，4‐Bis（3'‐aminofurazan‐4'‐yl）furazan（BATF）was synthesized by reduction with stannous chloride in glycerol using 3，4‐bis（3'‐aminofurazan‐4'‐yl）furoxan（BAFF） as raw material. 3，4‐Bis（3'‐nitrofurazan‐4'‐yl）furazan（BNTF） was prepared from BAFF by using hydrogen peroxide as oxidantwith total yield of 59.0%. The structures of BATF and BNTF were characterized by 1H NMR，13C NMR，IR，MS spectra and elemental analysis，and the single crystal structure data of BNTF was obtained successfully. The crystal belongs to orthorhombic system，space group P212121 with crystal parameters a=0.71437（10） nm， b=0.96839（11）nm，c=51555（17）nm，V=1.0484（2）nm3，Z=4，Dc=1.876 g·cm-3，F（000）=592. The influence of molar ratio，reaction time，and reaction temperature on the yield of BNTF was investigated. Results show that the optimum conditions are as follows：n（BATF）∶n（35% H2O2）∶n（98% H2SO4 ）∶n（Na2WO4?2H2O）=1∶60∶40∶0.86，the reaction time is 3 h，the reaction temperature is 30 ℃ and the yield of BNTF is 93.3%. The thermal stability of BNTF was determined by DSC and TG‐DTG methods. Apparent activation energy Ea（147.83 kJ·mol-1），pre‐exponential factor A（9.33×1015 min-1）and decomposition rate constant k （2.18×10-44）of thermal decomposition reaction for BNTF were calculated by Kissinger method，Rogers method and Arrenhis method，respectively. The detonation velocity（8.3 km·s-1）and detonation pressure（31.3 GPa）of BNTF were estimated by Ka‐mlet‐Jacobs equation. Characteristic drop height of impact sensitivity（H50=43.0 cm）and friction sensitivity（36.0%）for BNTF were measured according to GJB772A-1997 methods 601.2 and 602.1，respectively.

Abstract:Six preparation methods of physical mixing， ball milling， vapor deposition， electrostatic spray/spinning， solvent/non-solvent and 3D printing for aluminum-fluoro reactive materials are summarized. Recent research progress of Al-fluoropolymer reactive materials are reviewed from the aspect of product performance and method advantages and disadvantages. The reaction process of aluminum-fluoropolymer reactive materials at slow heating rate and fast heating rate are introduced. The promising research directions in the future are pointed out， including design a new method that combines the advantages of various preparation methods and more attention should be paid to strengthen the research on the reaction mechanism of aluminum-fluoropolymer reactive materials when heated.