Defence Technology(防务技术)最新文献

Investigating natural-inspired applications is a perennially appealing subject for scientists. The current increase in the speed of natural-origin structure growth may be linked to their superior mechanical properties and environmental resilience. Biological composite structures with helicoidal schemes and designs have remarkable capacities to absorb impact energy and withstand damage. However, there is a dearth of extensive study on the influence of fiber redirection and reorientation inside the matrix of a helicoid structure on its mechanical performance and reactivity. The present study aimed to explore the static and transient responses of a bio-inspired helicoid laminated composite (B-iHLC) shell under the influence of an explosive load using an isomorphic method. The structural integrity of the shell is maintained by a viscoelastic basis known as the Pasternak foundation, which encompasses two coefficients of stiffness and one coefficient of damping. The equilibrium equations governing shell dynamics are obtained by using Hamilton's principle and including the modified first-order shear theory, therefore obviating the need to employ a shear correction factor. The paper's model and approach are validated by doing numerical comparisons with respected publications. The findings of this study may be used in the construction of military and civilian infrastructure in situations when the structure is subjected to severe stresses that might potentially result in catastrophic collapse. The findings of this paper serve as the foundation for several other issues, including geometric optimization and the dynamic response of similar mechanical structures.

In the pursuit of advancing imidazolium-based energetic ionic liquids (EILs), the current study is devoted to the synthesis and characterization of 1,3-dibutyl-imidazolium azide ([BBIm][N₃]), as a novel member in this ionic liquids class. The chemical structure of this EIL was rigorously characterized and confirmed using FTIR spectroscopy, 1D, and 2D-NMR analyses. The thermal behavior assessment was conducted through DSC and TGA experiments. DSC analysis revealed an endothermic glass transition at T_g=–61 °C, followed by an exothermic degradation event at T_onset=311 °C. Similarly, TGA thermograms exhibited a one-stage decomposition process resulting in 100% mass loss of the sample. Furthermore, the short-term thermal stability of the azide EIL was investigated by combining the non-isothermal TGA data with the TAS, it-KAS, and VYA/CE isoconversional kinetic approaches. Consequently, the Arrhenius parameters (E_a=154 kJ·mol^-1, Log(A/s^-1))=11.8) and the most probable reaction model g(α) were determined. The observed high decomposition temperatures and the significantly elevated activation energy affirm the enhanced thermal stability of the modified EIL. These findings revealed that [BBIm][N₃] EIL can be a promising candidate for advanced energetic material application.

As a kind of high-efficiency explosive with compound destructive capability, the energy output law of thermobaric explosives has been receiving great attention. In order to investigate the effects of main components on the explosive characteristics of thermobaric explosives, various high explosives and oxidants were selected to formulate five different types of thermobaric explosive. Then they were tested in both open space and closed space respectively. Pressure measurement system, high-speed camera, infrared thermal imager and multispectral temperature measurement system were used for pressure, temperature and fireball recording. The effects of different components on the explosive characteristics of thermobaric explosive were analyzed. The results showed that in open space, the overpressure is dominated by the high explosives content in the formulation. The addition of the oxidants will decrease the explosion overpressure but will increase the duration and overall brightness of the fireball. While in closed space, the quasi-static pressure formed after the explosion is positively correlated with the temperature and gas production. In addition, it was found that the differences in shell constraints can also alter the afterburning reaction of thermobaric explosives, thus affecting their energy output characteristics. PVC shell constraint obviously increases the overpressure and makes the fireball burn more violently.

Heat-resistant energetic materials refer to a type of energetic materials that possess a high melting point, high stability and operational safety. By studying the structures of these energetic materials has showed that the thermal stability can be enhanced by introducing amino groups to form intra/inter-molecular hydrogen bonds, constructing conjugate systems and designing symmetrical structures. This article aims to review the physical and chemical properties of ultra-high temperature heat-resistant energetic compounds and provide valuable theoretical insights for the preparation of ultra-high temperature heat-resistant energetic materials. We also analyze the selected 20 heat-resistant energetic materials with decomposition temperatures higher than 350 °C, serving as templates for the synthesis of various high-performance heat-resistant energetic materials.

In order to improve the overall resilience of the urban infrastructures, it is required to conduct blast resistant design for important building structures in the city. For complex terrain in the city, it is recommended to determine the blast load on the structures via numerical simulation. Since the mesh size of the numerical model highly depends on the explosion scenario, there is no generally applicable approach for the mesh size selection. An efficient method to determine the mesh size of the numerical model of near-ground detonation based on explosion scenarios is proposed in this study. The effect of mesh size on the propagation of blast wave under different explosive weights was studied, and the correlations between the mesh size effect and the charge weight or the scaled distance was described. Based on the principle of the finite element method and Hopkinson-Cranz scaling law, a mesh size measurement unit related to the explosive weight was proposed as the criterion for determining the mesh size in the numerical simulation. Finally, the applicability of the method proposed in this paper was verified by comparing the results from numerical simulation and the explosion tests and was verified in AUTODYN.

In this study, austenitic stainless steel (ASS) was additively fabricated by an arc-based direct energy deposition (DED) technique. Macrostructure, microstructure, mechanical characteristics at different spatial orientations (0°, 90°, and 45°), and wear characteristics were evaluated at the deposited structure top, middle, and bottom regions. Results show that austenite (γ) and delta-ferrite (δ) phases make up most of the microstructure of additively fabricated SS316LSi steel. Within γ matrix, δ phase is dispersed both (within and along) grain boundaries, exhibiting a fine vermicular morphology. The bottom, middle, and top regions of WAAM deposited ASS exhibit similar values to those of wrought SS316L in the tensile and impact test findings. Notably, a drop in hardness values is observed as build height increases. During SEM examinations of fractured surfaces from tensile specimen, closed dimples were observed, indicating good ductility of as-built structure. Wear test findings show signs of mild oxidation and usual adhesive wear. By depositing a mechanically mixed composite layer, an increase in the oxidation percentage was discovered to facilitate healing of worn surfaces. The findings of this study will help in design, production and renovation of products/components that are prone to wear. WAAM-deposited ASS has remarkable strength and ability to withstand impacts; it can be used in the production of armour plates for defence applications, mainly military vehicles and aircraft.

This paper presents a systematic methodology for analyzing and optimizing an innovative antenna mount designed for phased array antennas, implemented through a novel 2-PSS&1-RR circular-rail parallel mechanism. Initially, a comparative motion analysis between the 3D model of the mount and its full-scale prototype is conducted to validate effectiveness. Given the inherent complexity, a kinematic mapping model is established between the mount and the crank-slider linkage, providing a guiding framework for subsequent analysis and optimization. Guided by this model, feasible inverse and forward solutions are derived, enabling precise identification of stiffness singularities. The concept of singularity distance is thus introduced to reflect the structural stiffness of the mount. Subsequently, also guided by the mapping model, a heuristic algorithm incorporating two backtracking procedures is developed to reduce the mount's mass. Additionally, a parametric finite-element model is employed to explore the relation between singularity distance and structural stiffness. The results indicate a significant reduction (about 16%) in the antenna mount's mass through the developed algorithm, while highlighting the singularity distance as an effective stiffness indicator for this type of antenna mount.

The practical application of energetic materials, particularly 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), is frequently impeded by phase transition challenges. In this study, we propose a novel strategy to enhance the stability of CL-20 by employing a thermo-sensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), to modulate its phase transitions. Our approach involves the use of an in-situ polymerized polydopamine (PDA) shell as a platform for surface grafting through atom transfer radical polymerization, yielding a core-shell structured CL-20@PDA-PNIPAM. Through comprehensive characterization, the successful grafting of PNIPAM is confirmed, significantly enhanced the phase stability of CL-20. Notably, our core-shell structure exhibits a 13 °C increase in phase transition temperature compared to raw CL-20, thereby delaying the ε→α phase transition by over 80 min under combined thermal and solvent conditions. The enhanced stability is attributed to the hydrophobic nature of PNIPAM above its low critical solution temperature in water, which effectively shields the CL-20 crystal. These findings provide new insights into enhancing the stability and safety of energetic materials in complex environments, highlighting the potential of our molecular switch mechanism.

In the process of launching guided projectile under the conventional system, it is difficult to effectively obtain the precise navigation parameters of the projectile in the high dynamic environment. Aiming at this problem, this paper describes a new system of guided ammunition based on tail spin reduction. After analyzing the mechanism of the ammunition's tail spin reduction, a navigation method of large scale difference tail control simple guided ammunition based on speed constraint is proposed. In this method, the corresponding navigation constraints can be carried out by combining the rotation speed state of the ammunition itself, and the optimal solution of navigation parameters during the flight of the missile can be obtained by Extended Kalman Filter (EKF). Finally, the performance of the proposed method was verified by the simulation environment, and the hardware-in-the-loop simulation test and flight test were carried out to verify the performance of the method in the real environment. The experimental results show that the proposed method can achieve the optimal estimation of navigation parameters for simple guided ammunition with large-scale difference tail control. Under the conditions of simulation test and hardware-in-loop simulation test, the position and velocity errors calculated by the method in this paper converged. Under the condition of flight test, the spatial average error calculated by the method described in this paper is 6.17 m, and the spatial error of the final landing point is 3.50 m. Through this method, the accurate acquisition of navigation parameters in the process of projectile launching is effectively realized.

The search for new green and efficient stabilizers is of great importance for the stabilization of nitrocellulose (NC). This is due to the shortcomings of traditional stabilizers, such as high toxicity. In this study, reduced polyaniline (r-PANI), which has a similar functional structure to diphenylamine (DPA) but is non-toxic, was prepared from PANI based on the action with N₂H₄ and NH₃–H₂O, and used for the first time as a potential stabilizer for NC. XPS, FTIR, Raman, and SEM were used to characterize the reduced chemical structure and surface morphology of r-PANI. In addition, the effect of r-PANI on the stabilization of NC was characterized using DSC, VST, isothermal TG, and MMC. Thermal weight loss was reduced by 83% and 68% and gas pressure release by 75% and 49% compared to pure NC and NC&3%DPA, respectively. FTIR and XPS were used to characterize the structural changes of r-PANI before and after reaction with NO₂. The 1535 cm⁻¹ and 1341 cm⁻¹ of the FTIR and the 404.98 eV and 406.05 eV of the XPS showed that the –NO₂ was generated by the absorption of NO₂. Furthermore, the quantum chemical calculation showed that NO₂ was directly immobilized on r-PANI by forming –NO₂ in the neighboring position of the benzene ring.