Abstract:Aiming at the unclear issues of charge deformation and ignition mechanisms in the spigot safety evaluation tests of cast explosives， a viscoelastic-viscoplastic deformation and multi-hotspot competitive ignition model for cast PBXs was developed. This model considers multiple hotspot mechanisms， including microcrack friction， microvoid collapse， and localized viscous shear flow heating. Simulations of macro-mesoscopic rheological-ignition response under spigot were conducted， obtaining the pressure， shear flow， and ignition response characteristics of explosive charges under different drop heights， spigot lengths， and spigot shapes. The results indicate that the ignition response process of the charge under spigot is driven by both pressure and shear strain rate. When these two factors overlap at high levels， the resulting localized viscous shear flow becomes the dominant hotspot mechanism. For the same spigot diameter， a larger aspect-ratio spigot induces higher pressure and shear flow in the charge above the spigot， coupled with a longer spigot action time and higher impulse， leading to an easier ignition with a reduced critical ignition height. Compared to a flat-head spigot， an oval-head spigot significantly reduces the critical ignition height of the charge. These findings provide technical support for interpreting the ignition response and mesoscopic mechanisms of cast explosives under low-speed long-pulse penetrating mechanical stimulation， as well as for constructing safety evaluation and numerical characterization methods for projectile drop with foreign object penetration.

Abstract:To promote the resource utilization of retired HTPB propellants， composite gel explosives were prepared by compounding them with energetic gels： the three-component propellant-containing composite explosive 1-PxDyϕz， the quaternary propellant-containing composite explosive 2-PxDyϕz that contains 9% RDX， the propellant-containing composite explosive 3-PxDyϕz that contains 15% RDX， and the propellant-containing composite explosive 4-PxDyϕz that contains 20% HMX. （x represents the content of propellant P， x=30%， 40%， 50%， y is particle size， y=5， 10， 15 mm； z denotes the charge size， z=40， 50， 65 mm）. Tests on detonation velocity， witness plate damage， and underwater explosion energy were conducted to investigate the energy characteristics of these composite gel explosives with varying propellant content， particle size， and charge diameter. The results indicate that an increase in the propellant content in 1-PxDyϕz and 2-PxDyϕz composite explosives reduces the detonation velocity and brisance of the composite explosives， whereas increasing the propellant content in 3-PxDyϕz and 4-PxDyϕz increases both detonation velocity and brisance. The decrease in propellant particle size from 1-PxDyϕz to 4-PxDyϕz contributes to the increase of detonation velocity and brisance， and the increase in charge diameter significantly increases the damage capability. Results of underwater explosion tests show that an increase of propellant content in 1-PxDyϕz and 2-PxDyϕz reduces the total underwater energy output， while 3-PxDyϕz has a relatively constant total energy with an increase in propellant content， and 4-PxDyϕz has an increasing total underwater energy with an increased of propellant content. Additionally， the total underwater energy from 1-PxDyϕz to 4-PxDyϕz increases with the decrease of propellant particle size.

Abstract:To investigate the damage effects of focused discrete rod warheads， a typical cylindrical target structure perforated by the focused discrete rod was designed. Through Abaqus^TM finite element simulation and statics experimental tests， the damage effectiveness of the focused discrete rod warhead on the structure was simulated and experimentally validated. The results indicate that under tensile loading， the ultimate load of the cylindrical structure perforated by the focused discrete rod is 19.22% of that of the unperforated cylinder， while the traditional fragment-perforated cylinder reaches 91.08%. Consequently， the ultimate load of the focused discrete rod-perforated cylinder is reduced by 71.86% compared to the traditional fragment-perforated cylinder. Under compressive load conditions， the cylindrical structure shows coupled buckling and fracture failure， with reduced stress concentration around the perforation. The ultimate load of the focused discrete rod-perforated cylinder is 68.76% of that of the unperforated cylinder， whereas the traditional fragment-perforated target cylinder reaches 93.84%. The structural ultimate load of the focused discrete rod-perforated cylinder is decreased by 25.08% compared to the fragment-perforated target， highlighting the differences in damage effects under various loading modes. The numerical simulation results and experimental data show good consistency in load response magnitude and failure trends， with the maximum relative error controlled within 15%， validating the reliability of the research method.

Abstract:To address the limitations of traditional velocity measurement techniques in reusability， a fragment velocity measurement method based on the depolarization characteristics of PVDF film was proposed. By analyzing the composition of the response signal of PVDF film under fragment impact and the frequency response characteristics of each signal component， a criterion for identifying fragment impact time using the depolarization signal as the characteristic component was established. In response to the acquisition requirements of the high impedance， low amplitude， and high-frequency response depolarization signal， a depolarization signal acquisition scheme based on a source follower was designed according to the PVDF film voltage source equivalent model. Each module of the conditioning circuit was designed， selected， theoretically calculated， and simulated. Finally， a ballistic gun test was conducted using a single PVDF film with dimensions of 210 mm×150 mm×0.05 mm to verify the feasibility and accuracy of the proposed method. The test results show that the proposed velocity measurement method can effectively measure fragment impact velocity and exhibits certain reusability. Compared with fragment velocity results obtained via high-speed photography， the velocity measurement deviation is less than 3.47%.

Abstract:The structure of an integrated initiator assembly， where the flyer is directly integrated onto the surface of the bridge foil， represents one of the optimization directions for Explosive Foil （EF）， and this structure can address the issue of assembly consistency in the split-type EF component. However， the differences in the motion patterns of flyer resulting from the integrated method remain unknown， and there is no experimental data to show the impact of these differences on the performance of products， which hinders the development and optimization of integrated EF technology. Based on this， we focuse on the differences in the motion patterns of flyer between integrated and split-type EF， aiming to reveal the extent to which the differences affect performance. The motion patterns of flyer under the two structures were analyzed and their generation mechanisms were elucidated by using numerical simulation methods. The simulation conclusions were verified through non-charged firing experiment and an up-and-down method experiment was used to compare the working performance of the products. The research results indicate that the integrated structure makes flyer be cut into a flat and round shape quickly， and is less prone to cracking during its motion. The flyer collection experimental results also show that the rate complete flyer under the integrated structure can exceed 75%. The results of the up-down method experiment reveal that the minimum full-firing voltage of the integrated product is reduced by 52 V， with the voltage standard deviation decreasing from 8.01 V to 6.08 V. This confirms that the stable motion behavior of the integrated flyer enhances ignition reliability. The study demonstrates the feasibility of the integrated structure and its optimizing effect on flyer motion behavior.

Abstract:To evaluate the plasticization behavior of nitrocellulose， machine learning was employed with impact strength selected as the performance index. Plasticization temperature， nitrogen content， plasticization time， solvation ratio， and alcohol–ether ratio were used as independent variables to build a multi-factor quadratic regression model. Response surface methodology analyzed the main effects and interactions among these factors. Significant interaction effects are observed among the five variables. To address the limited performance of traditional linear models under small-sample and nonlinear conditions， a random forest model was combined with a nonlinear correction layer. Gaussian-noise data augmentation improved the robustness of the training set. The combined RF+GBR model achieves an R² of 0.98 and an MSE of 0.0341 （kJ·m^-2）² on the training data. Five-fold cross-validation yields an average R² of 0.95 and an MSE of 0.63 （kJ·m^-2）². These results indicate high fitting accuracy and strong generalization capability. Feature-importance analysis identifies nitrogen content as the dominant factor affecting impact strength， followed by solvation ratio. The study provides a quantitative basis for evaluating plasticization reliability and optimizing process parameters.

Abstract:In response to the higher demands for progressive combustion and reduced erosion in small and medium-caliber rapid-fire weapons， a coating system based on stearic acid/silica/polyurethane （SA/SiO₂/PU） phase change material was designed， and the oblate-gun propellants were prepared by combining with fluidized bed technology. The compatibility， thermal decomposition， microstructure， combustion performance and storage stability of the propellants were investigated using differential scanning calorimetry， Raman spectroscopy， scanning electron microscopy， and a closed bomb. Results indicate that the SA/SiO₂/PU coating system exhibits Grade 1 compatibility with the propellant. The enthalpy of melting （ΔH_m） and crystallization （ΔH_c） of the coating system are 39.02 J·g^-1 and 39.46 J·g^-1， respectively， indicating a reversible phase transition process and good chemical stability. Microstructural analysis reveals that the propellant surface is densely and uniformly coated， with a coating thickness of approximately 13 μm under the coating time of 20 min. Compared with the uncoated propellant， the initial dynamic vivacity （L₀） and maximum dynamic vivacity （L_m） of the coated propellants decrease by respectively 48.0% and 44.7%， while the dynamic vivacity difference （ΔL） increases to 0.22 MPa^-1·s^-1， demonstrating high progressive combustion characteristics. In terms of storage stability， the average gas evolution of the coated propellant is 1.04 mL·g^-1， and the methyl violet test shows a 6.25% extension in discoloration time， suggesting that the coating process contributes to an improved storage stability of the oblate-gun propellant.

Abstract:To address the issues of insufficient mechanical properties and high sensitivity in high-energy gun propellants caused by the addition of large amounts of solid high-energy fillers， by using nitrocellulose as the raw material， isophorone diisocyanate as the coupling agent， and polyethylene glycol as the flexible segment， the ladder-like nitrocellulose （LNC） was prepared via a two-step grafting reaction. LNC was then used as an energetic binder to partially replace nitrocellulose， and a semi-solvent method was adopted to prepare LNC-based double-base gun propellants. LNC formed a double-stranded molecular structure according to the designed reaction pathway. The compatibility， thermal decomposition and sensitivity of LNC-based double-base gun propellants were investigated. Results show that there is good compatibility between LNC and nitrocellulose. The LNC-based double-base gun propellants exhibit enhanced thermal stability with the initial decomposition temperature increased from 190.20 ℃ to 200.89 ℃. The impact sensitivity is reduced with the characteristic drop height value increased from 15.4 cm to 28.2 cm.

Abstract:To investigate the evolution of the internal structure and mechanical properties of double-base flake gun propellant during pressing， samples from four typical processing stages—raw materials， thin pressing （1， 3， 5， and 7 passes）， thick pressing （1， 3， 5， 7， and 10 passes）， and finishing pressing （1 and 2 passes）—were systematically characterized. A combination of analytical techniques， including scanning electron microscopy （SEM）， micro-computed tomography （μ-CT）， Fourier transform infrared spectroscopy （FTIR）， tensile testing， dynamic mechanical analysis （DMA）， and linear expansion coefficient measurements， was employed to elucidate microstructural evolution， component interactions， and macro-property variations under thermomechanical coupling. The results indicate that thin pressing constitutes the main dehydration phase， reducing the water content from 22.6% to 0.46% and increasing the density from 1.474 g·cm^-3 to 1.611 g·cm^-3. At this stage， the nitrocellulose （NC） fibrous framework becomes clearly visible， and initial plasticization occurs. Thick pressing is identified as the critical period for plasticization， during which nitroglycerin （NG） molecules penetrate between NC molecular chains， disrupting the original hydrogen-bond network and forming new intermolecular interactions. This process significantly enhances the elongation at break to over 50%， eliminates internal pores and defects， and results in a homogeneous and dense structure. In contrast， fine pressing mainly serves to adjust the propellant sheet to its final thickness， with no notable changes in internal structure or fundamental mechanical properties.