Abstract:

Abstract:

Abstract:In order to explore the effects of structure on combustion performance of aluminum/polytetrafluoroethylene （Al/PTFE）-based reactive materials and improve combustion performance of fluorine-based thermite， additive manufacturing technology （3D printing） was utilized to prepare Al/PTFE-based reactive materials with solid， hollow， core-shell， and confined hollow structures， as well as Al/CuO-based and Al/Fe₂O₃-based reactive materials with confined hollow structures. The microstructure， thermal performance， combustion rate， and gas production performance were assessed by scanning electron microscope （SEM）， differential scanning calorimetry （DSC）， high speed camera， and constant volume combustion chamber. The results show that each sample exhibits intact structure and uniform components. Under the circumstance of same mass， the samples with core-shell and confined hollow structures display lower heat release than that of samples with solid and hollow structures. The burning rate of samples with hollow， core-shell， and confined hollow structures is 1.44， 1.32， and 2.62 times higher than that of samples with solid structure， respectively. Obvious improvement in gas production performance and pressurization rate appears for samples with hollow and confined hollow structures， especially for samples with confined hollow structure. The burning rate of Al/PTFE， Al/CuO， and Al/Fe₂O₃ materials with confined hollow structure is significantly higher than that of corresponding samples with solid structure， particularly for Al/Fe₂O₃ materials. The approach to regulate combustion performance of lines by preparing materials with hollow structure is expected to provide a novel idea for designing new high-performance weapons.

Abstract:Aluminized explosives have been widely applied due to their high energy density and pressure output. To further enhance the secondary combustion reaction and pressure output of aluminized explosives， graded structure is designed inspired by the microstructure of bamboo. In this work， the radially-graded structured HMX/Al （RGS-HMX/Al） cylinders with three layers containing different sizes and content of Al were prepared through 3D direct writing technology. The effects of Al distribution on combustion and pressure output properties of graded HMX/Al were fully studied. For the RGS-HMX/Al cylinder with Al content of 10%， 20%， and 30% distributed from inner to outer layer， the combustion reaction and flame propagation of inner layer were faster than that of outer layer. And the pressure （2337.61 kPa） was higher than that of RGS-HMX/Al cylinder with Al content in the reverse distribution. For the RGS-HMX/Al cylinder containing Al of 10 μm， 5 μm， and 160 nm distributed from inner to outer layer， a slow combustion process with sparse bright Al droplets was observed. Moreover， the highest peak pressure （1512.65 kPa） was obtained for the RGS-HMX/Al cylinders with nAl in the middle layer， which exhibited much higher pressure output than that homogeneous HMX/Al cylinder. More importantly， bimodal pressure was observed for the RGS-HMX/Al cylinders with Al of 10 μm in the middle layer.

Abstract:In order to prepare gun propellants with complex geometries， the extrusion 3D printing process of double base gun propellants was proposed. Square-shaped， wheel-shaped， star hole-shaped and lace seven hole double base gun propellants were printed by screw extrusion gun propellants 3D printer. The surface structure， size uniformity， density and mechanical property of the printed gun propellants were characterized. The results show that the surface of the printed gun propellants is smooth without obvious defects. The size uniformity of lace seven hole gun propellants reaches the standard of traditional gun propellant preparation process， and the size uniformity of arc thickness for wheel-shaped gun propellant is good， with a standard deviation of 0.026 mm and a relative standard deviation of 0.92%. The density of square-shaped gun propellant is higher （1.567 g·cm^-3） than those of other gun propellants （1.549-1.559 g·cm^-3）. The tensile strength of gun propellant samples with concentric filling path （the filling line direction is parallel to the tensile direction） and straight line （the filling line direction is perpendicular to the tensile direction） are 14.467 MPa and 10.789 MPa， respectively， the former is equivalent to that of gun propellants prepared by traditional extrusion process. The good printing of multi geometry gun propellants with radians and angles provides a basis for the preparation of complex geometry gun propellants.

Abstract:In order to solve the dilemma of traditional technology to prepare gun propellants with complex structure and explore a new way to improve incremental combustion surface of gun propellants， 3D direct ink-writing was used to design and print nitrocellulose-based gun propellants embedded with multi-cubic pores. The 3D printed nitrocellulose-based gun propellants embedded with multi-cubic pores were characterized by constant volume combustion and internal ballistic properties. The results show that the printed nitrocellulose-based gun propellants embedded with multi-cubic pores， prepared by nitrocellulose， energetic plasticizer， and solvent as printing materials， are in accordance with the expected design of incremental combustion surface. Due to the influence of the diameter of printing needle， the ratio of dissolved cotton， the ratio of alcohol/acetone， and the speed of solvent volatilization， there is a certain deviation between design size and actual size of printed gun propellants. The preliminary ballistic test of 12.7 mm machine gun shows that when the mixed charge of NC-120 and D-4/7 is 16 g and the charge ratio is 1∶1， the bore pressure is 314.2 MPa and the muzzle velocity is 854.1 m·s^-1. The stable and normal combustion of the direct ink-writing printed gun propellants embedded with multi-cubic pores in the chamber is realized. However， for the sake of practical application of printed gun propellants embedded with multi-cubic pores， several parameters need to be further optimized such as shape， web size， and the web size matching between inner and outer layer.

Abstract:In order to investigate the application effect of fluorocarbon resin （FEVE） in explosive ink， a new type of oil-in-water emulsion bonded system was designed by employing polyvinyl alcohol （PVA） aqueous solution as water phase and FEVE/ethyl acetate solution as oil phase. By adding sub-micron CL-20 particles into bonded system， CL-20-based explosive ink was prepared for direct writing. Scanning electron microscope， rheometer， X-ray diffractometer， and impact and friction sensitivity tester were used to characterize morphology and detonation performance of printed samples. The results show that PVA/FEVE oil-in-water emulsion binder system can stably exist for 174 h. The CL-20 explosive ink with 90% solid content exhibits optimal rheological properties and good printability. The obtained direct writing sample with microporous internal structure displays a smooth surface， and the crystal form of CL-20 explosive is still ε type. The impact energy and friction force of printed samples are 216 N and 4.5 J， respectively. Compared with raw ε-CL-20， impact sensitivity and friction sensitivity of printed samples are reduced by 125% and 200%， respectively. The detonation velocity， critical detonation corner turning， critical detonation thickness of 1-mm line width， and critical detonation size of square section of printed samples are 6772 m·s^-1， 160°， 0.039 mm， and 0.4 mm×0.4 mm， respectively， which show excellent micro-scale detonation capability.

Abstract:In order to develop a micro-scale booster for Micro Electro-Mechanical Systems （MEMS） pyrotechnics with excellent mechanical properties. A fully soluble explosive ink was designed with hexanitrohexaazaisowurtzitane （CL-20） as the main explosive， hydroxyl terminated polyether （HTPE）/ nitrocellulose （NC） as the bonding system， ethyl acetate as the co-solvent， and a certain amount of toluene diisocyanate （TDI）. Inkjet printing technology was used to achieve high-precision charge molding， and the cross-linking reaction of isocyanate and hydroxyl group was used to enhance the mechanical properties of micro charge. The density， micro morphology， thermal stability， crystal form and mechanical properties of the samples were characterized by electron densitometer， scanning electron microscope， differential scanning calorimeter， X-ray diffraction and nanoindenter. The results show that the density of the printed sample is 1.70 g·cm^-3， which is 88.54% of the theoretical maximum density. The crystal form of CL-20 in the printed sample is determined by ε type change to β type. The apparent activation energy of thermal decomposition is 173.00 kJ·mol^-1， which is 13.17 kJ·mol^-1 higher than that of the raw material CL-20. The nanoindentation test results show that the elastic modulus of the printed sample is 10.47 GPa and the hardness is 0.22 GPa， showing good mechanical properties. Inkjet printing charge has good detonation transmission ability， and the critical detonation size and detonation velocity are 1 mm×0.18 mm and 8054 m·s^-1， respectively.

Abstract:Compared with traditional casting method， composite solid propellant manufactured by additive manufacturing （commonly known as “3D printing”） technology exhibits a series of technical advantages， such as arbitrary grain configuration without mold limitation and continuously controllable formulation as well as performance. In order to improve printing effect， printing formulation and technical parameters of composite solid propellant based on light-curing molding were studied， and the performance of printed propellant samples was evaluated. In addition， comprehensive additive manufacturing of composite solid propellant and resistive temperature sensor was achieved by integrating resistive temperature sensor into the printed propellant samples， and the resistance values of temperature sensor at different temperatures were examined. The results show that solid propellant slurry with 83% solid content displays a good pre-curing effect by adding no less than 3% ultraviolet （UV）-curable resin. The slurry with 77% or 80% solid content can be extruded through a 0.26 mm diameter needle， while solid content reaching 81% or above requires a 0.5 mm diameter needle. The printed propellant sample comprising 81% solid content possesses good dimensional stability and unconspicuous appearance defects， but computed tomography （CT） results reveal the existence of lamellar pores inside the sample. The tensile strength and elongation at break of printed propellant sample are equal to 0.94 MPa and 15.63% at 20 ℃， respectively. At 60 ℃， the tensile strength and elongation at break of sample are 0.70 MPa and 14.63%， respectively. The printed propellant owns comparable tensile strength and reduced elongation at break compared to conventional casting propellant. The bonding strength between temperature sensor and propellant is 0.21 MPa， showing favourable bonding effect. The resistance of temperature sensor varies linearly with temperature within testing temperature range （20-60 ℃）， demonstrating good temperature monitoring capability.

Abstract:Inkjet printing technology is an advanced micro-manufacturing technology based on ink droplets， which integrates jetting technology， discrete stacking numerical control manufacturing， and computer-aided design. It is one of the important loading approaches for micro-structured energetic devices such as MEMS pyrotechnics. In the ink-jet printing process， the precise control of droplets is the key to improving the printability and accuracy of the targeted materials. Based on the systematic investigation of the inkjet printing forming mechanism， the physical characteristics of ink and the influence of printing process parameters on the formation of ink droplets were discussed， and the reason and control methods for the "coffee ring" effect were also summarized. The controlling strategies of droplet formation and deposition in the ink-jet printing process were described. At the same time， the application of ink-jet printing technology in booster， nano-thermite， etc. was reviewed， and the development direction of inkjet printing technology in energetic materials was prospected. The drop-on-demand and control with picoliter of ink-jet printing technology provides a prerequisite for the precise charging of micro-nano-structured energetic agents and has good application prospects in MEMS pyrotechnics and special-shaped energetic devices.

Abstract:The structural integrity evaluation of the metal-explosive bonding interface is of great importance and engineering value. To realize high sensitivity detection of interfacial debonding defects in the metal-explosive structure， the ultrasonic detection and imaging methods based on multiple pulse-echoes was proposed. The acoustic impedance and reflection characteristics at bonding interface of aluminum， shellac， and RDX were calculated and analyzed. For specimens with different adhesive layer thickness and artificial prefabricated debonding defects， debonding information were extracted from the captured multiple echoes. The influence of adhesive layer with different thickness on the amplitude of multiple echoes was discussed and analyzed. Results show that dramatical amplitude difference exists in the reflected waves between the aluminum-adhesive and the aluminum-water interface. Both the first echo and multiple echoes could effectively distinguish the area with and without adhesive layer. The acoustic attenuation caused by the aluminum-adhesive interface keeps accumulating in high order echoes. As the thickness of the adhesive layer increases， the cumulative effect of the acoustic attenuation difference in the multiple ultrasonic echoes between aluminum-adhesive and aluminum-water interfaces gradually weakens. Experimental results show that the minimum debonding defects with Φ1.5 mm circular and 1 mm wide rectangular shape could be detected using multiple ultrasonic echoes method.

Abstract:In order to study thermal shock damage characteristics of small-size polymer bonded explosive （PBX） hemispheres， 0-100 ℃ water-bathed thermal shock test was carried out for Φ10 mm TATB based and HNS based PBX hemispheres. 3D morphology and distribution characteristics of the damages in the PBX hemisphere were studied by X-ray micro-computed tomography，and the thermal conduction and thermal stress of the sample during the thermal shock process were simulated and analyzed by using the 2D axisymmetric thermal elastoplastic model. The CT results show that the two kinds of samples both started to crack from hemisphere corner， in which the cracks in TATB based PBX hemisphere propagate in a circumferential direction along the edge， with tortuous shape and characteristics of tearing and brittle fracture； The cracks in HNS based PBX hemispheres basically penetrate along the axial direction， with the morphology of straight and characteristics of brittle fracture. The simulation results show that strong tensile stress is generated in the in the hemisphere of TATB based PBX during temperature. And the tensile stress from hemisphere corner to hemisphere center region successively exceeds tensile strength， resulting in the initiation of the main cracks from the edge of hemisphere and propagated inward. The damage characteristics of the sample is consistent with the stress distribution characteristics and the temperature characteristics of the binder under temperature shock. This study lays a foundation for the analysis of temperature shock damage mechanism of TATB-based and HNS-based PBX.

Abstract:Aiming at the difficulty in purification of metal pentazolates， the separation and purification of metal pentazolates were studied by precipitation method based on the aqueous solution of sodium pentazolate， which was obtained via C—N cleavage reaction of arylpentazole. Results show that the aqueous solution of sodium pentazolate contains a lot of organic acid salts， as well as inorganic salt impurities such as sodium nitrate and sodium chloride. Compared with N₅ anions， the organic acid salts prefer to precipitate with metal ions in aqueous solution， thus affecting the precipitation of metal pentazolates. Cobalt pentazolate was precipitated from the aqueous solution of sodium pentazolate via acidification， removal of organic acid salts by extraction， and then addition of cobalt chloride. The lower the pH value is， the higher the removal efficiency of organic acid salts is and the higher the purity of cobalt pentazolate is. The optimized separation conditions of cobalt pentazolate are as follows： the pH value is 3， and the molar ratio of cobalt chloride to 4-amino-2，6-dimethylphenol （1） is 0.26∶1. The purity of cobalt pentazolate is up to 97.9% after simple recrystallization as shown by ion chromatography. The applicability of this precipitation method to other metal pentazolates was also studied. Results show that it is also suitable for the separation and purification of iron， ferrous and copper pentazolates.

Abstract:In order to verify the applicability of time-temperature-stress principle in tensile creep of TATB-based PBX and realize the evaluation calculation of long-term uniaxial tensile creep deformation， the conventional tensile creep experiment under constant stress but different temperatures and multistep tensile creep experiment under constant temperature of a TATB-based PBX were carried out. The tensile creep curves under constant temperature but different stresses were obtained by decomposing the multistep creep curve following Chen"s method. The coupled creep compliance master curves under reference temperature and stress （30 ℃ and 3.0 MPa） and parameters of Willianms-Landel-Ferry equation considering temperature and stress were obtained by translating and assembling the creep compliance curves using dichotomy calculation program based on the time-temperature-stress equivalence of nonlinear viscoelastic materials. The results show that the tensile creep behavior of TATB-based PBX is well described by the time-temperature-stress equivalent principle in the analyzed temperature range from 30 ℃ to 50 ℃ and stress range from 1.0 MPa to 5.5 MPa， which could be used to predict the long-term tensile creep deformation under low temperature and low stress through the short-term tensile creep tests at high temperature and stress.