Abstract:Crystal density is an important parameter for predicting the detonation performance of energetic materials (EMs). Many studies have shown that the theoretical calculation methods are able to figure out accurate densities of CHNO contained EMs. In this work, we overview and categorize some reliable crystal density calculation methods, including isosurface of electron density method, group addition method, molecular surface electrostatic potentials method, crystal packing method and quantitative structure-property relationship method. Among these methods, the effectiveness of molecular volume-based methods depends on its capability to estimate inter- and intramolecular interactions. It is challenging to accurately describe the hydrogen bonding and van der Waals interactions. Due to the huge structure group spaces and highly complex potential energy surface, the crystal packing methods based on empirical forcefields are computationally expensive and lacking accuracy usually. The group addition approach cannot distinguish conformers and polymorphs, and may be unreliable for novel or special energetic materials, which are absent from accurate empirical parameters. The disadvantage of quantitative structure-property relationship method is that it is difficult to give the physical meaning of the equation. The bottleneck of insufficient experimental data and poor model accuracy needs to be solved. Nevertheless, numerous artificial intelligence methods, such as artificial neural networks, genetic algorithm, multiple linear regression, machine learning, have made great achievements in the relationship between properties and structure, facilitating the development of energetic materials based on the materials genome concept and serving as a main tendency in future.

Abstract:In accordance with increasing stringent ammunition safety requirements, the manufacture, transportation and applications of traditional 2,4,6-trinitrotoluene (TNT)-based melt-cast explosives will not fulfill those safety standards. Recently, the melt-cast explosives based on 2,4-Dinitroanisole (DNAN) as substitute for those of TNT has aroused great attentions. In this paper, the research progress of DNAN-based melt-cast explosives in the last ten years were summarized towards their synthesis, physicochemical properties, energetic and sensitive performance, mechanical and rheological performances. Furthermore, the main research hotspots about DNAN-based melt-casting explosives in the future were also prospected in this article.

Abstract:Based on the single degree of freedom model, the dynamic elastic-plastic response of a spherical shell subjected to internal impulse with quasi-static pressure is obtained. Analytical solutions agree well with numerical simulation results. The solutions can be divided into two situations by confirming whether the yield point occurs in first triangle impulse or the duration of quasi-static pressure. Effects of quasi-static pressure can be studied in two different situations. If the yield occurs in the quasi-static pressure phase, the time when yield occurs is affected by the quasi-static pressure and decreases with the increase of the quasi-static pressure. Whenever the yield occurs, the maximum displacement occurs in the quasi-static phase, and the time reaching maximum displacement is quite different. The value of maximum displacement increases significantly with the increase of the quasi-static pressure. Compared with the elastic situation, the quasi-static pressure has a more obvious effect in the elastic-plastic response analysis. Therefore, the elastic-plastic dynamic response analysis is more valuable and instructive for the evaluation of quasi-static pressure.

Abstract:To study the strength properties of Polymer bonded explosive (PBX) under compression -shear stress state, compression-shear test of PBX simulant was carried out by the experimental method of variable angle shear with loading angle θ 0°, 15°, 30°, 45°, 60°, 75°, 90°; The power function Mohr-Coulomb (M-C) criterion of PBX simulant was established, and compression strength under confining pressure was predicted. The mesoscopic failure characteristics of PBX simulant under compression-shear stress state were analyzed by SEM. The results showed that shear fracture pattern was along the compression-shear surface under loading angles 0°, 15°, 30° and 45°, and hybrid fracture pattern of shear and tension occurred under loading angles of 60°, 75° and 90°; For the shear fracture pattern, with the increase of compression stress, the shear strength of PBX simulant showed a trend of non-linear increase, and the mesoscopic damage would gradually develop from particle shear fracture and breakage to the formation and penetration of secondary cracks. The analysis found that the power function M-C criterion could well describe the trend that shear strength of PBX simulant increased nonlinearly with the increase of compression stress, and predict axial compression strength of PBX simulant under different confining pressure more accurately. The increase of internal friction resistance caused by the increase of compressive stress and the decrease of internal friction coefficient caused by particle breakage and secondary cracks are the important reasons for the non-linear increase of shear failure strength of PBX simulant with the increase of compression stress.

Abstract:In order to investigate the dynamic behavior and ignition mechanism of Al/polytetrafluoroethylene（PTFE） reactive material under dynamic loading, a Split Hopkinson Pressure Bar (SHPB) was used to conduct the dynamic compression experiment on reactive materials with different molding pressure. Experimental results show that the Al/PTFE reactive material exhibits typical elastic-plastic mechanical behavior under dynamic loading at strain rate ranging from 2960 s^-1 to 5150 s^-1. The yield strength and hardening modulus of Al/PTFE reactive materials do not show strain rate effect when the molding pressure is 50-150 MPa. The velocity ignition threshold increases slowly from 28.77 m·s^-1 to 29.22 m·s^-1 with the molding pressure. When the molding pressure increases to 100 MPa, the velocity ignition threshold drops significantly to 26.60 m·s^-1. With the increase of the impact velocity, the ignition delay time for reactive materials with the molding pressure of 100-150 MPa decreases from 1000-1100 μs to 600-700 μs, while that of reactive materials with the molding pressure of 30-80 MPa maintains at 600-700 μs. Combining with results of Scanning Electron Microscopy, it is found that the local larger pores inside the reactive materials with higher molding pressure is the main factor for the sudden drop of the velocity ignition threshold. Therefore, the impact ignition characteristics of Al/PTFE reactive materials are mainly related to the external loading form and the internal micro-morphology.

Abstract:In order to study the propagation law of blast shockwaves in a square tunnel, TNT charges with different mass of 1.00 kg, 3.25 kg and 10.28 kg were detonated separately in the tunnel. The shock wave pressure-time curves at different distances were recorded and the parameters of shock waves such as the arrival time, the peak overpressure and the impulse were obtained. Results show that the propagation of shockwaves in tunnel is divided into three stages: the free-field spherical wave propagation, the one-dimensional planar wave propagation and the transition between them. The peak overpressures fit the Hopkinson-Cranz scaling law well except near the explosion center. An empirical formula for calculating peak overpressures was fitted, and the deviation between fitting results and measured values was not more than 10%. However, the impulse does not agree with Hopkinson-Cranz scaling law.

Abstract:To investigate the sensitivity characteristics of an perchlorate-based ECSP containing aluminum, metallic and non-metallic perchlorate-based ECSP with various Al content (0%, 5%, 10%, 15% and 20%) and particle size (0.05, 5, 25, 65 µm and 105 µm) were prepared by means of the casting process; the impact, friction, electrostatic spark, and flame sensitivities of the perchlorate-based ECSP were investigated according to the national military standard methods. The results show that the impact sensitivity of the perchlorate-based ECSP increases with the increase of the aluminum content and decreases with the increase of the particle size of the aluminum powder in the propellant. The metallic and non-metallic perchlorate-based ECSP show low friction sensitivity. The changes of the Al content and particle size have some influence on the friction sensitivity, but the effect is slightly presented. The flame sensitivity of the perchlorate-based ECSP decreases with the increase of the particle size of the aluminum powder. Under the test voltage of 10 kV, the changes of content and particle size of the aluminum powder do not result in obvious combustion of perchlorate-based ECSP. The impact sensitivity is larger for nano-ECSP (H₅₀=33.9 cm) than in the perchlorate-based ECSP with the micro-aluminum powder (H₅₀≥33.9 cm).

Abstract:To investigate the influence of chemical structure of curing agent on the mechanical property of 3, 3-diazidomethyloxetane-tetrahydrofuran copolyethers (PBT) elastomer, N100, the addition product of hexamethylene diisocyanate (HDI) and H₂O, and the mixture of trimethylolpropane and HDI (TMP/HDI), were used as curing agent respectively to produce two type of cross-linked PBT elastomer. Results show that in the same chemical crosslinking network, the tensile strength, tensile strain at break and initial modulus of PBT-N100 elastomer S0 are (0.983±0.03) MPa, (110±7) % and (1.80±0.02) MPa, respectively, while the PBT-TMP/HDI elastomer S4 are (1.43±0.08) MPa, (336±6) % and (1.26±0.01) MPa, respectively. The tensile modulus of elastomer S0 is higher than that of elastomer S4, as its elongation at break and tensile strength poorer than that of S4. Low field NMR reveals that the physical crosslinking strength of PBT-N100 elastomer S0 network chains is higher than that of S4. The strong hydrogen bonding between urea carbonyl group and amidogen in N100 enhances the physical interaction among PBT elastomer network chains, resulting in the tensile modulus of elastomer S0 higher than that of S4, while its elongation at break lower than that of S4.

Abstract:In order to study the effect of dynamic shock on solid propellant during the ignition process of solid rocket motor, a simulation setup based on quenched combustion was designed. The setup is composed of an ignition bolt, a combustion chamber, and a releasing pressure bolt. The metal burst disk is installed in the shear hole of the releasing pressure bolt and controls the ignition pressure precisely during the ignition shock process. Poly(BAMO-THF)/AP/Al solid propellant samples,molded into hollow cylinder, were used to evaluate the simulation shock process in setup. The p-t curves show that the blow-out pressure of burst disk is corresponding to the measured blow-out pressure in strong ignition mode and the pressure deviation is less than ±6%. The calculated pressurization rate according to the collected p-t curves can reach 7000 MPa·s^-1 at 10 MPa ignition and 12000 MPa·s^-1 at 15 MPa ignition, which are much more than the pressurization rate for actual ignition process of solid rocket. After simulation ignition shock experiment, filler particles implanted in the end face of propellant samples are damaged, while the inside surface basically keeps an intact condition. Compressive strength generally increases after ignition shock process, while the strain value at the point decreases when the compressive strength begins to rise. It is included that propellants with unstable structure are easier to be damaged and the mechanical properties would be changed during simulation ignition shock process.

Abstract:Reducing the adhesion between the cast polymer bonded explosive (PBX) slurry and the contact material is one of the key factors to improve the preparation technology level and efficiency of the casting solidified PBX. Constructing micro-nano hierarchical composite bioinspired structure on the metal surface of contact container by solution etching method makes the static contact angles of high-viscosity HTPB and casting PBX slurries be all higher than 130°. The surface has well anti-wetting properties and forming the bioinspired flower micro-nano composite structures on the metal surface by adjusting the etching time for 120 minutes can make the adhesion force between the metal surface and HTPB、HTPB/Al and HTPB/Fox-7 slurry decrease to 29.4, 46.0 μN and 12.7 μN， respectively, with a decrease range of 57%~82%. At the same time, the bioinspired structure is coated on the inner surface of the die, and the non-adherence property of PBX slurry is realized macroscopically.

Abstract:In order to explore the optimal formulation of multi-spectral composite interfering agents and improve their interference performance in multiple wavelengths such as visible light, infrared and millimeter wave, carbon nanotube/ grapheme /carbon lightweight composites were prepared by the combination of material modification technology. The compound dispensing technology is used to prepare the multi-spectral composite interfering agents of “carbon nanotube/graphene/carbon composite material+carbon fiber”. Taking the sum of mass extinction coefficients of each band as the evaluation indicator，the different particle sizes of nanotubes/ grapheme /carbon composite materials （A）, different states of carbon fiber（B）, different mass ratios of carbon fiber（C）, and the different mixed solutions（D） as factors, the effects of various factors on the performance of the interfering agents were analyzed by the orthogonal experiment method. Based on the smoke box experiment, the mass extinction coefficient of the smoke screen was calculated according to the "Lambert-Beer" law. Results show that the extreme differences of factor A and factor C are 1.48 and 1.43, respectively, which are the main influencing factors on the overall shielding performance of composite interfering agents. The extreme differences of factor B and factor D are 0.32 and 0.52, respectively, which are the secondary influencing factors. The optimal preparation conditions are as follows: a carbon nanotube/graphene/carbon composite material having a particle diameter D₅₀ of 4.2 μm and a carbon fiber calcined at 800 ℃, which are mixed at a mass ratio of 85∶15 in an ethanol solution. The multi-spectral composite interfering agent prepared under those conditions has a transmittance of visible, near-infrared, mid-infrared and far-infrared light of less than 5% with an effective shielding time being more than 300 s, and an attenuation value of up to -14 dB and -15.65 dB on 3 mm and 8 mm wavebands with an effective masking time being greater than 30 s. The composite interfering agent prepared under those conditions has a better multi-spectral shielding performance.

Abstract:Both thermal decomposition behaviors and non-isothermal decomposition reaction kinetics of propyl-nitroguanidine (PrNQ) were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) method. Its decomposition mechanism was stuied through in-situ FTIR spectroscopy technology and the compatibilities of PrNQ with 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX), hexanitrohexaazaisowurtzitane (CL-20) and 5,5′-bistetrazole-1,1′-diolate (TKX-50) were also achieved by DSC experiment. The results show that the melting point of PrNQ is around 99 ℃, which is very suitable for the application of melt-cast technology. The thermal stability of PrNQ is good and the difference between the melting point and decomposition temperature of PrNQ is about 137 ℃, which is large enough to guarantee the safety of the melt-cast process. The compatibilities between PrNQ and HMX or TKX-50 are also excellent, with ΔT_p of -0.3 K and 1.36 K， respectively.

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