Defence Technology(防务技术)最新文献

An innovative metallic buffer consisting of series-connected hat-shaped entangled wire mesh damper (EWMD) and parallel springs are proposed in this work to enhance the reliability of engineering equipment. The impact response and the energy dissipation mechanism of hat-shaped EWMD under different quasi-static compression deformations (2–7 mm) and impact heights (100–200 mm) are investigated using experimental and numerical methods. The results demonstrate distinct stages in the quasi-static mechanical characteristics of hat-shaped EWMD, including stiffness softening, negative stiffness, and stiffness hardening. The loss factor gradually increases with increasing compression deformation before entering the stiffness hardening stage. Under impact loads, the hat-shaped EWMD exhibits optimal impact energy absorption when it enters the negative stiffness stage (150 mm), resulting in the best impact isolation effect of metallic buffer. However, the impact energy absorption significantly decreases when hat-shaped EWMD enters the stiffness hardening stage. Interestingly, quasi-static compression analysis after experiencing different impact loads reveals the disappearance of the negative stiffness phenomenon. Moreover, with increasing impact loads, the stiffness hardening point progressively shifts to an earlier stage.

The debris cloud generated by the hypervelocity impact (HVI) of orbiting space debris directly threatens the spacecraft. A full understanding of the damage mechanism of rear plate is useful for the optimal design of protective structures. In this study, the hypervelocity yaw impact of a cylindrical aluminum projectile on a double-layer aluminum plate is simulated by the FE-SPH adaptive method, and the damage process of the rear plate under the impact of the debris cloud is analyzed based on the debris cloud structure. The damage process can be divided into the main impact stage of the debris cloud and the structural response of the rear plate. The main impact stage lasts a short time and is the basis of the rear plate damage. In the stage of structure response, the continuous deformation and inertial motion of the rear plate dominate the perforation of the rear plate. We further analyze the damage mechanism and damage distribution characteristics of the rear plate in detail. Moreover, the connection between velocity space and position space of the debris cloud is established, which promotes the general analysis of the damage law of debris cloud. Based on the relationship, the features of typical damage areas are identified by the localized fine analysis. Both the cumulative effect and structural response cause the perforation of rear plate; in the non-perforated area, cratering by the impact of hazardous fragments is the main damage mode of the rear plate.

This work uses refined first-order shear theory to analyze the free vibration and transient responses of double-curved sandwich two-layer shells made of auxetic honeycomb core and laminated three-phase polymer/GNP/fiber surface subjected to the blast load. Each of the two layers that make up the double-curved shell structure is made up of an auxetic honeycomb core and two laminated sheets of three-phase polymer/GNP/fiber. The exterior is supported by a Kerr elastic foundation with three characteristics. The key innovation of the proposed theory is that the transverse shear stresses are zero at two free surfaces of each layer. In contrast to previous first-order shear deformation theories, no shear correction factor is required. Navier’s exact solution was used to treat the double-curved shell problem with a single title boundary, while the finite element technique and an eight-node quadrilateral were used to address the other boundary requirements. To ensure the accuracy of these results, a thorough comparison technique is employed in conjunction with credible statements. The problem model’s edge cases allow for this kind of analysis. The study’s findings may be used in the post-construction evaluation of military and civil works structures for their ability to sustain explosive loads. In addition, this is also an important basis for the calculation and design of shell structures made of smart materials when subjected to shock waves or explosive loads.

Aiming at the problem of multi-UAV pursuit-evasion confrontation, a UAV cooperative maneuver method based on an improved multi-agent deep reinforcement learning (MADRL) is proposed. In this method, an improved CommNet network based on a communication mechanism is introduced into a deep reinforcement learning algorithm to solve the multi-agent problem. A layer of gated recurrent unit (GRU) is added to the actor-network structure to remember historical environmental states. Subsequently, another GRU is designed as a communication channel in the CommNet core network layer to refine communication information between UAVs. Finally, the simulation results of the algorithm in two sets of scenarios are given, and the results show that the method has good effectiveness and applicability.

The regulation of the burning rate pressure exponent for the ammonium perchlorate/hydroxyl-terminated polybutadiene/aluminum (AP/HTPB/Al) composite propellants under high pressures is a crucial step for its application in high-pressure solid rocket motors. In this work, the combustion characteristics of AP/HTPB/Al composite propellants containing ferrocene-based catalysts were investigated, including the burning rate, thermal behavior, the local heat transfer, and temperature profile in the range of 7–28 MPa. The results showed that the exponent breaks were still observed in the propellants after the addition of positive catalysts (Ce-Fc-MOF), the burning rate inhibitor ((Ferrocenylmethyl)trimethylammonium bromide, FcBr) and the mixture of FcBr/catocene (GFP). However, the characteristic pressure has increased, and the exponent decreased from 1.14 to 0.66, 0.55, and 0.48 when the addition of Ce-Fc-MOF, FcBr and FcBr/GFP in the propellants. In addition, the temperature in the first decomposition stage was increased by 7.50 °C and 11.40 °C for the AP/FcBr mixture and the AP/FcBr/GFP mixture, respectively, compared to the pure AP. On the other hand, the temperature in the second decomposition stage decreased by 48.30 °C and 81.70 °C for AP/FcBr and AP/FcBr/GFP mixtures, respectively. It was also found that FcBr might generate ammonia to cover the AP surface. In this case, a reaction between the methyl in FcBr and perchloric acid caused more ammonia to appear at the AP surface, resulting in the suppression of ammonia desorption. In addition, the coarse AP particles on the quenched surface were of a concave shape relative to the binder matrix under low and high pressures when the catalysts were added. In the process, the decline at the AP/HTPB interface was only exhibited in the propellant with the addition of Ce-Fc-MOF. The ratio of the gas-phase temperature gradient of the propellants containing catalysts was reduced significantly below and above the characteristic pressure, rather than 3.6 times of the difference in the blank propellant. Overall, the obtained results demonstrated that the pressure exponent could be effectively regulated and controlled by adjusting the propellant local heat and mass transfer under high and low pressures.

The primary goal of this study is to develop cost-effective shield materials that offer effective protection against high-velocity ballistic impact and electromagnetic interference (EMI) shielding capabilities through absorption. Six fiber-reinforced epoxy composite panels, each with a different fabric material and stacking sequence, have been fabricated using a hand-layup vacuum bagging process. Two panels made of Kevlar and glass fibers, referred to as (K-NIJ) and (G-NIJ), have been tested according to the National Institute of Justice ballistic resistance protective materials test NIJ 0108.01 Standard-Level IIIA (9 mm × 19 mm FMJ 124 g) test. Three panels, namely, a hybrid of Kevlar and glass (H–S), glass with ceramic particles (C–S), and glass with recycled rubber (R–S) have been impacted by the bullet at the center, while the fourth panel made of glass fiber (G-S) has been impacted at the side. EMI shielding properties have been measured in the X-band frequency range via the reflection-transmission method. Results indicate that four panels (K-NIJ, G-NIJ, H–S, and G-S) are capable of withstanding high-velocity impact by stopping the bullet from penetrating through the panels while maintaining their structural integrity. However, under such conditions, these panels may experience localized delamination with variable severity. The EMI measurements reveal that the highest absorptivity observed is 88% for the K-NIJ panel at 10.8 GHz, while all panels maintain an average absorptivity above 65%. All panels act as a lossy medium with a peak absorptivity at different frequencies, with K-NIJ and H–S panels demonstrating the highest absorptivity. In summary, the study results in the development of a novel, cost-effective, multifunctional glass fiber epoxy composite that combines ballistic and electromagnetic interference shielding properties. The material has been developed using a simple manufacturing method and exhibits remarkable ballistic protection that outperforms Kevlar in terms of shielding efficiency; no bullet penetration or back face signature is observed, and it also demonstrates high EMI shielding absorption. Overall, the materials developed show great promise for various applications, including the military and defense.

Modern additive manufacturing processes enable fabricating architected cellular materials of complex shape, which can be used for different purposes. Among them, lattice structures are increasingly used in applications requiring a compromise among lightness and suited mechanical properties, like improved energy absorption capacity and specific stiffness-to-weight and strength-to-weight ratios. A dedicated modeling strategy to assess the energy absorption capacity of lattice structures under uni-axial compression loading is presented in this work. The numerical model is developed in a non-linear framework accounting for the strain rate effect on the mechanical responses of the lattice structure. Four geometries, i.e., cubic body centered cell, octet cell, rhombic-dodecahedron and truncated cuboctahedron 2+, are investigated. Specifically, the influence of the relative density of the representative volume element of each geometry, the strain-rate dependency of the bulk material and of the presence of the manufacturing process-induced geometrical imperfections on the energy absorption capacity of the lattice structure is investigated. The main outcome of this study points out the importance of correctly integrating geometrical imperfections into the modeling strategy when shock absorption applications are aimed for.

The present work investigates higher order stress, strain and deformation analyses of a shear deformable doubly curved shell manufactures by a Copper (Cu) core reinforced with graphene origami auxetic metamaterial subjected to mechanical and thermal loads. The effective material properties of the graphene origami auxetic reinforced Cu matrix are developed using micromechanical models cooperate both material properties of graphene and Cu in terms of temperature, volume fraction and folding degree. The principle of virtual work is used to derive governing equations with accounting thermal loading. The numerical results are analytically obtained using Navier's technique to investigate impact of significant parameters such as thermal loading, graphene amount, folding degree and directional coordinate on the stress, strain and deformation responses of the structure. The graphene origami materials may be used in aerospace vehicles and structures and defence technology because of their low weight and high stiffness. A verification study is presented for approving the formulation, solution methodology and numerical results.

Melt-cast explosives are the most widely used energetic materials in military composite explosives, researchers have been unremittingly exploring high-energy and insensitive melt-cast explosives. In this work, a series of dinitrophenyl-oxadiazole compounds were designed and prepared. These compounds have an ideal low melting point (80–97 °C), good detonation performance (detonation velocity D = 6455–6971 m/s, detonation pressure P = 18–19 GPa) and extreme insensitive nature (impact sensitivity ≥60 J, friction sensitivity >360 N). All these compounds were well characterized by nuclear magnetic resonance, fourier transform infrared spectroscopy, elemental analysis. Compounds 2, 3 were unambiguously confirmed by X-ray single crystal diffraction analysis. As a result, their overall properties are superior to traditional melt-cast explosives trinitrotoluene (TNT) and dinitroanisole (DNAN) which may have excellent potential applications in insensitive melt-cast explosives.

This study systematically examines the energy dissipation mechanisms and ballistic characteristics of foam sandwich panels (FSP) under high-velocity impact using the explicit non-linear finite element method. Based on the geometric topology of the FSP system, three FSP configurations with the same areal density are derived, namely multi-layer, gradient core and asymmetric face sheet, and three key structural parameters are identified: core thickness (t_c), face sheet thickness (t_f) and overlap face/core number (n_o). The ballistic performance of the FSP system is comprehensively evaluated in terms of the ballistic limit velocity (BLV), deformation modes, energy dissipation mechanism, and specific penetration energy (SPE). The results show that the FSP system exhibits a significant configuration dependence, whose ballistic performance ranking is: asymmetric face sheet > gradient core > multi-layer. The mass distribution of the top and bottom face sheets plays a critical role in the ballistic resistance of the FSP system. Both BLV and SPE increase with t_f, while the raising t_c or n_o leads to an increase in BLV but a decrease in SPE. Further, a face-core synchronous enhancement mechanism is discovered by the energy dissipation analysis, based on which the ballistic optimization procedure is also conducted and a design chart is established. This study shed light on the anti-penetration mechanism of the FSP system and might provide a theoretical basis for its engineering application.