Abstract:To improve the mechanical property of single-based propellant with high nitrogen content, nitrocellulose/2,4-dinitrotoluen/diphenylamine(NC/DNT/DPA), 3% dimethylsulfoxide(DMSO), N,N-dimethylformamide(DMF), cyclohexanone, cyclohexane, chloromethane, ethyl acetateandbutyl acetate were added to alcohol ketone respectively to form ternary mixed solvent, plasticizing high-nitrogen nitrocellulose and obtaining the corresponding single-based propellant. The microstructure of single-based propellant samples were observed by scanning electron microscopy, and the mechanical properties were tested by universal material testing machine and beam impact testing machine. In addition,the energy of single-based propellant samples were studied by closed bomb test. Results show that when the auxiliary solvents are added, the mechanical properties of the high-nitrogen single-based propellant samples are improved. The compressive strength of the sample with 3% butyl acetate at low temperature (-40 ℃), normal temperature (20 ℃) and high temperature (50 ℃) increases by 15.7%, 4.3% and 17.7%, and the impact strength increases by 26.9%, 96.9% and 170.0%, respectively. The addition of the auxiliary solvent has little effect on the combustion of single-based propellant. And compared with the basic single-based propellant, the gunpowder force of the single-based propellant samples prepared by the ternary mixed solvent has a small decrease.

Abstract:In order to solve the problem of high viscosity of high solid content propellants, supercritical carbon dioxide (SC-CO₂) has been used as a plasticizer to improve its rheological behavior. The in-line viscosity of the CA/CaCO₃ solution was measured by a slit die rheometer during the extrusion process assisted with SC-CO₂, and the Power law was used to describe the rheological behavior of CA/CaCO₃ and CA/CaCO₃/SC-CO₂ solutions. Polyflow was utilized to model the dispersive mixing properties of the CA/CaCO₃/SC-CO₂ solutions. Results show that with the presence of SC-CO₂, the viscosity and pressure of the CA/CaCO₃ solution decreases significantly.And the viscosity coefficient of the CA/CaCO₃ solution at 50℃ decreases by 26.00%, while its non-Newtonian index increases by approximately 16.67%. As the extrusion temperature increases, the viscosity of the CA/CaCO₃/SC-CO₂ solution decreases, and its shear viscosity is less sensitive to temperature at higher shear rate. According to this simulation results, when the CA/CaCO₃/SC-CO₂ solution is subjected to the maximum shear stress, the maximum probability density increases by 20.63% at 50 ℃, which confirms that SC-CO₂ improves the dispersion mixing properties of the CA/CaCO₃ solution.

Abstract:In order to investigate the combustion performance of four-hole cuboid gun propellants, a combustion physical model was established according to the structural characteristics of four-hole cuboid gun propellants. The Ψ-Ζ and Γ-Ψ curves were obtained through the Maple software. The theoretical combustion properties of four-hole cuboid gun propellants were compared with that of the cylindrical seven-hole and single-hole gun propellants under the same web size and length-to-diameter ratio. Meanwhile, the web size, length-to-diameter ratio and inner-hole diameter were researched as the main factors to the theoretical combustion properties. The results demonstrated that the four-hole cuboid gun propellant performed a good progressive combustion property when the length-to-diameter ratio was higher than 1.5, which was better than the cylindrical single-hole gun propellants. Although the four-hole cuboid gun propellant performed a worse combustion property than the cylindrical seven-hole gun propellant, it displayed the combustion split points in the latter point. Meanwhile, the four-hole cuboid gun propellant had a better progressive combustion property when the inner web size was the same as the outer, the length-to-diameter ratio was in the range from 1.5 to 3, and the inner-hole diameter was in the range from 0.10 mm to 0.20 mm. The experimental results agreed well with the theoretical analysis results, but the moulding process leaded to the certain deviation of inner hole, resulting in the splitting point reached in advance.

Abstract:In order to study the propagation characteristics of the flame generated by ignition charge combustion in the propellant pellet packed bed under the ignition transmission structure of the central fire tube， a porous media model was used to simulate the gun propellant pellet packed bed in the propellant chamber， the flow and propagation process of high temperature and high speed gas generated by the combustion of ignition charge in the gun propellant pellet bed is simulated by using the N-S equation， the isothermal surface propagation of the temperature field is equivalent to the flame front propagation， and the simulation results were compared with those of experimental data. The results show that in the case of a dense charge bed of propellant， the isothermal surface is equivalent to the flame front in the process of ignition flame propagation， and the simulation value of flame propagation velocity is 91 m·s^-1， which is close to 96 m·s^-1 obtained by experiment；the simulated cloud images of temperature field of high temperature flame gas propagation are consistent with those of the experimental flame propagation images； the pressure data at the three pressure measuring holes in the chamber calculated by the porous media model are in good agreement with those of experimental data.

Abstract:In order to further improve the progressive combustion of 37-well propellant, a 37-well nitroguanidine propellant was coated by two-layer coating process. The effects of coating, compatibility of the coating layer and the base propellant, the content and layers of the coating on the combustion performance were investigated by Three-dimensional video microscopy, Scanning electron microscope, DSC and constant volume combustion test. The thickness of the double coated propellant was relatively uniform. The compatibility between coating layer and the propellant was good. When the coating content was 8%, the combustion enhancement value of the double-layer coated propellant was significantly higher than that of the single-layer coated propellant. The combustion enhancement value ΔL of the double-coated propellant increased at first and then decreased with the increasing of the outer coating layer. When the content of inner and outer coating layer was 5%, the progressive combustion was the largest, with ΔL of 0.1431 MPa^-1·s^-1, which increased by 43.53%, compared with the 37-well propellant.

Abstract:In order to improve the performance of burning progressivity and low temperature sensitive coefficient effect of high-energy azidonitramine gun propellant, three insensitive high-energy azidonitramine gun propellants was prepared by the two-stepprocess with polymer composite materials plugging and energetic composite materials desensitization” (called plugged and insensitive gun propellant in this study), whose inner hole was blocked by polymer composite materials and surface was desensitized. The energetic and static combustion performance of plugged and insensitive gun propellant was investigated by heat of explosion and closed-bomb tests. Results show that compared with the untreated gun propellant, with the increase of the content of plugged and insensitive materials, the heat of explosion of three types of plugged and insensitive gun propellants (WCBF-1/18, WCBF-2/18, WCBF-3/18) decrease by 2.6%, 3.6%, 4.3%, and P_r values increase from 0.471 to 0.552, 0.563, 0.576 respectively. The average absolute values of temperature coefficient of relative combustion activity at high temperature for three types of plugged and insensitive gun propellants WCBF-1/18, WCBF-2/18, WCBF-3/18 are 2.87%, 1.89%, 1.56%, respectively, which are all lower than that of untreated gun propellant, it shows that the low temperature sensitivity coefficient effect in the high and normal temperature ranges for plugged and insensitive gun propellant can be improved.

Abstract:To study the interior ballistic performance of charge for partially cut multi-perforated stick propellant, a interior ballistic simulation model of charge for partially cut multi-perforated stick propellant was established based on the classical interior ballistic theory. The calculation of interior ballistic performance of charge was performed using the partially cut multi-perforated stick propellant with high energy nitramine propellant formulations. The experimental validation were carried out on 30 mm artillery. The effect of incision intervals, incision web and incision depth on the interior ballistic performance of partially cut multi-perforated stick propellant was analyzed. The results show that the maximum bore pressure calculated by the established interior ballistic model of partially cut multi-perforated stick propellant is 430.2 MPa. The calculated error of the maximum bore pressure is 5.0% compared with average value of testing maximum bore pressure of 409.7 MPa. The calculated muzzle velocity is 1378.2 m·s^-1, and the calculated error is 2.2% compared with average value of testing muzzle velocity of 1409.6 m·s^-1. The maximum bore pressure and muzzle velocity decrease with the increase of incision intervals. When the incision intervals increase from 5 mm to 50 mm, the maximum bore pressure reduces by 12.0%. And the muzzle velocity reduces by 3.1%. The effect upon the interior ballistic performance is gradually reduced when the numerical value of incision intervals is greater than 20 mm. The value of maximum bore pressure and muzzle velocity increases with the increase of incision depth and incision web. The effect of incision depth upon the maximum bore pressure is more significant than that upon the muzzle velocity. The interior ballistic performance of the propellant is insensitive to the change of incision web′s value.

Abstract:To prevent accidents and assess the risk of static disasters in propellant mixing process, we designed devices to test electrostatic parameters such as resistivity, dielectric constant and charge accumulation. 11/7 single-base propellant was chosen to be tested as a typical product. It shows that the volume resistivity, surface resistivity and dielectric constant of 11/7 single-base propellant are 1.87×10¹⁰ Ω·m，1.06×10¹² Ω, and 1.88, respectively, and the saturated charge-to-mass ratio at friction state of chute is -1.85 μC·kg^-1. ANSOFT MAXWELL software was used to simulate the electrostatic field in mixing silo of 11/7 propellant, obtaining the change curve of the maximum field strength with powder′s height in 1000 mm diameter mixing silo. Results show that the electric field strength increases with the increase of powder′s height. When the powder′s height is 40 mm, the air breakdown field strength is reached and there is a risk of electrostatic discharge. In addition, the critical discharge powder′s heights at different diameters of mixing silos were simulated, and the corresponding change curve was also obtained. It shows that the critical discharge powder′s heights are 81, 46, 42, 41 mm and 40 mm when the diameters of material silo are 100, 200, 300, 400 mm and 500 mm, respectively. However, when the diameter is greater than 500 mm, the critical discharge powder′s height reasonably maintains at 40 mm.

Abstract:To study the characteristics of erosive burning and gas flow in internal perforation of a tubular propellant, an interior ballistic model of a closed bomb was established considering the gas phase region inside the tube, gas phase region outside the tube and solid propellant region. The accuracy of the interior ballistic model and calculation method of the closed bomb was verified through comparing the numerical simulation results with the experimental data in the literature. On this basis, the effects of different length, internal diameter and loading density of propellant on the erosive burning of internal perforation were discussed respectively. Results show that for the tubular propellant with d=0.56 mm, l=50 mm, when 0.016≤ψ≤0.80(ψ is the burned percentage), the maximum pressure difference of internal and external perforation increases from 1.23 MPa to 2.00 MPa, the maximum gas velocity on the end face decreases from 430 m·s^-1 to 200 m·s^-1, the erosive burning coefficient on the end face decreases from 1.98 to 1.10, the erosive burning critical point of internal perforation moves from 7mm away from the symmetrical plane to 20 mm, the erosive burning area decreases by 65%. The ratio of burning surface to port area is an important factor affecting the erosive burning of internal perforation. The erosive burning does not occur when the ratio of burning surface to port area is less than 71.4. The erosive burning intensity becomes stronger with the increase of length and decrease of internal diameter, i.e. with the increase of the ratio of burning surface to port area, the erosive burning occurs evidently when the ratio of burning surface to port area is larger than 142.8. The maximum gas velocity on the end face and the erosive burning coefficient decrease slightly as the loading density increases, while the gas pressure difference of internal and external perforation increases obviously.

Abstract:To investigate the effect of mold inner flow channel structure on the forming process of nitroguanidine gun propellant, the mold inner flow channel model of 11/7 nitroguanidine gun propellant was established. The numerical simulation of nine schemes of different combinations of shrinkage angle as 30°, 45° and 60° and forming section length as 25, 30 mm and 45 mm was performed. The effect of shrinkage angle and forming section length on the shear rate, pressure and velocity distribution in the extrusion process were analyzed. Results show that the shrinkage angle has similar effects on the interfaces of different contraction sections and forming section and nearing-outlet etc.sections, and it shows that the shear rate of the propellant dough near the center of mold needle and the wall surface is higher than that of the surrounding pare. The sectional pressure distribution is uniform and the flow velocity distribution of the dough has the characteristics of large middle parts and small two sides. The length of forming section has a great influence on the shear rate distribution during the extrusion process of dough. The smaller the length of the forming section, the more likely the sudden change of shear rate, which may lead to the unsteady flow. At the same time, it can be determined that the optimal inner flow channel parameter scheme is the shrinkage angle of 45° and the forming section length of 30 mm.

Abstract:The wall slip is one of the important factors affecting the quality of gun propellant extrusion molding. To improve the accuracy of numerical simulation of the seven-hole nitroguanidine gun propellant extrusion molding, the wall slip mechanism of nitroguanidine gun propellant dough was studied, the mathematical model of gun propellant flow considering the wall slip correction was established. The finite element method was used to simulate the forming process of seven-hore nitroguanidine gun propellant. The pressure field, the velocity field and the velocity vector distribution at the junction of the segment and the forming section were compared and analyzed at cases whether considering the wall slip. The simulation was validated by the gun propellant extrusion test. Results show that the wall slip reduces the forming pressure of gun propellant and improves the uniformity of gun propellant exit rate, which is beneficial to the forming of gun propellant. The error between the actual size and the simulation size of the gun propellant is less than 2.0% in which, the outer diameter error is 0.59%, and the outer arc error 0.36%, the inner arc error 1.80%, the aperture error 1.67%, and the center aperture error 1.72%. The simulation process is in line with the actual processing.

Abstract:To improve the mechanical properties of high-energy TEGDN gun propellants, based on high-energy TEGDN gun propellant formulations, adding a small amount (mass fraction of 0.5%, 1.0%, 1.5%, 2.0%) of cellulose nanofibers (CNFs) obtained from lignocellulose, high-energy TEGDN gun propellants containing CNFs were prepared. The surface structure and thermal decomposition property of high-energy TEGDN gun propellants before and after adding CNFs were studied by scanning electron microscopy, thermogravimetric analyzer and differential scanning calorimeter. The impact strength and energy performance of high-energy TEGDN gun propellants containing CNFs were studied by the Charpy impact testing machine and closed bomb vessel test. The results show that adding a small amount of CNFs can obviously improve the low-temperature impact strength of high-energy TEGDN gun propellants and very little on thermal decomposition performance. Compared with the original high-energy TEGDN gun propellant (reference sample), the impact strength of high-energy TEGDN gun propellant of adding 0.5% CNFs increases by 30.4% under the low temperature of -40 ℃ and increases by 8.9% under the room temperature of 20 ℃. With increasing the content of CNFs, the powder force decreases gradually, the covolume increases gradually, the burning rate decreases gradually, and the pressure exponent increases slightly. When the dosage of CNFs is 0.5%, the powder force, covolume and pressure exponent of high-energy TEGDN gun propellant are 1191.91 kJ·kg^-1, 0.870 L·kg^-1 and 1.06, respectively, compared with the reference sample, they have a reduce of 1.9%, an increase of 5.1% and an increase of 4.2%. respectively