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.