Defence Technology(防务技术)最新文献

This paper investigates the three-dimensional crack propagation and damage evolution process of metallic column shells under internal explosive loading. The calibration of four typical failure parameters for 40CrMnSiB steel was conducted through experiments and subsequently applied to simulations. The numerical simulation results employing the four failure criteria were compared with the differences and similarities observed in freeze-recovery tests and ultra-high-speed tests. This analysis addressed the critical issue of determining failure criteria for the fracture of a metal shell under internal explosive loads. Building upon this foundation, the damage parameter D_c, linked to the cumulative crack density, was defined based on the evolution characteristics of a substantial number of cracks. The relationship between the damage parameter and crack velocity over time was established, and the influence of the internal central pressure on the damage parameter and crack velocity was investigated. Variations in the fracture modes were found under different failure criteria, with the principal strain failure criterion proving to be the most effective for simulating 3D crack propagation in a pure shear fracture mode. Through statistical analysis of the shell penetration fracture radius data, it was determined that the fracture radius remained essentially constant during the crack evolution process and could be considered a constant. The propagation velocity of axial cracks ranged between 5300 m/s and 12600 m/s, surpassing the Rayleigh wave velocity of the shell material and decreasing linearly with time. The increase in shell damage exhibited an initial rapid phase, followed by deceleration, demonstrating accelerated damage during the propagation stage of the blast wave and decelerated damage after the arrival of the rarefaction wave. This study provides an effective approach for investigating crack propagation and damage evolution. The derived crack propagation and damage evolution law serves as a valuable reference for the development of crack velocity theory and the construction of shell damage evolution modes.

In the realm of military and defence applications, exposure to radiation significantly challenges the performance and reliability of solder alloys and joints in electronic systems. This comprehensive review examines radiation-induced effects on solder alloys and solder joints in terms of microstructure and mechanical properties. In this paper, we evaluate the existing literature, including experimental studies and fundamental theory, to provide a comprehensive overview of the behavior of solder materials under radiation. A review of the literature highlights key mechanisms that contribute to radiation-induced changes in the microstructure, such as the formation of intermetallic compounds, grain growth, micro-voids and micro-cracks. Radiation is explored as a factor influencing solder alloy hardness, strength, fatigue and ductility. Moreover, the review addresses the challenges and limitations inherent in studying the effects of radiation on solder materials and offers recommendations for future research. It is crucial to understand radiation-induced effects on solder performance to design robust and radiation-resistant electronic systems. A review of radiation effects on solder materials and their applications in electronics serves as a valuable resource for researchers, engineers, and practitioners in that field.

The sandwich panel incorporated a honeycomb core, a widely utilized composite structure recognized as a fundamental classification of composite materials. Comprised a core resembling a honeycomb, possessing thickness and softness, and is flank by rigid face sheets that sandwich various shapes and materials. This paper presents an examination of the static and dynamic analysis of lightweight plates made of aluminum honeycomb sandwich composites. Honeycomb sandwich plate samples are 300 mm long, and 300 mm wide, the heights of the core have been varied at four values ranging from 10 to 25 mm. The honeycomb core is manufactured from Aluminum material by using a novel technique namely resistance spot welding (RSW) instead of using adhesive material, which is often used when an industrial flaw is detected. Numerical optimization based on response surface methodology (RSM) and design of experiment software (DOE) was used to verify the current work. A theoretical examination of the crashworthiness behavior (maximum bending load, maximum deflection) and vibration attributes (natural frequency, damping ratio, transient temporal response) of honeycomb sandwich panels with different design parameters was also carried out. In addition, the finite element method-based ANSYS software was used to confirm the theoretical conclusions. The findings of the present work showed that the relationship between the natural frequency, core height, and cell size is direct. In contrast, the relationship between the natural frequency and the thickness of the cell wall is inverse. Conversely, the damping ratio is inversely proportional to the core height and cell size but directly proportional to the thickness of the cell wall. The study indicates that altering the core height within 10–25 mm leads to a significant increase of 82 % in the natural frequency and a notable decrease of 49 % in the damping ratio. These findings are based on a specific cell size value of 0.01 m and a cell wall thickness of 0.001 m. Also, the results indicate that for a given set of cell wall thickness and size values, an increase in core height from (0.01–0.025) m, leads to a reduction of the percentage of maximum response approximately 76 %. Conversely, the increasing thickness of the wall of cell wall, ranging 0.3–0.7 mm with a constant core height equal to 0.015 m, resulted in a de crease of maximum transient response by 7.8 %.

In order to investigate the mechanical response behavior of the gas obturator of the breech mechanism, made of polychloroprene rubber (PCR), uniaxial compression experiments were carried out by using a universal testing machine and a split Hopkinson pressure bar (SHPB), obtaining stress-strain responses at different temperatures and strain rates. The results revealed that, in comparison to other polymers, the gas obturator material exhibited inconspicuous strain softening and hardening effects; meanwhile, the mechanical response was more affected by the strain rate than by temperature. Subsequently, a succinct viscoelastic damage constitutive model was developed based on the ZWT model, including ten undetermined parameters, formulated with incorporating three parallel components to capture the viscoelastic response at high strain rate and further enhanced by integrating a three-parameter Weibull function to describe the damage. Compared to the ZWT model, the modified model could effectively describe the mechanical response behavior of the gas obturator material at high strain rates. This research laid a theoretical foundation for further investigation into the influence of chamber sealing issues on artillery firing.

Laser driven flyer plate technology offers improved safety and reliability for detonation of explosives in industrial applications ranging from mining and stone quarrying to the aerospace and defense industries. This study is based on developing a safer laser driven flyer plate prototype comprised of a laser initiator and a flyer plate subsystem that can be used with secondary explosives. System parameters were optimized to initiate the shock-to-detonation transition (SDT) of a secondary explosive based on the impact created by the flyer plate on the explosive surface. Rupture of the flyer was investigated at the mechanically weakened region located on the interface of these subsystems, where the product gases from the deflagration of the explosive provide the required energy. A bilayer energetic material was used, where the first layer consisted of a pyrotechnic component, zirconium potassium perchlorate (ZPP), for sustaining the ignition by the laser beam and the second layer consisted of an insensitive explosive, cyclotetramethylene-tetranitramine (HMX), for deflagration. A plexiglass interface was used to enfold the energetic material. The focal length of the laser beam from the diode was optimized to provide a homogeneous beam profile with maximum power at the surface of the ZPP. Closed bomb experiments were conducted in an internal volume of 10 cm³ for evaluation of performance. Dependency of the laser driven flyer plate system output on confinement, explosive density, and laser beam power were analyzed. Measurements using a high-speed camera resulted in a flyer velocity of 670 ± 20 m/s that renders the prototype suitable as a laser detonator in applications, where controlled employment of explosives is critical.

This paper investigates the attitude tracking control problem for the cruise mode of a dual-system convertible unmanned aerial vehicle (UAV) in the presence of parameter uncertainties, unmodeled uncertainties and wind disturbances. First, a fixed-time disturbance observer (FXDO) based on the bi-limit homogeneity theory is designed to estimate the lumped disturbance of the convertible UAV model. Then, a fixed-time integral sliding mode control (FXISMC) is combined with the FXDO to achieve strong robustness and chattering reduction. Bi-limit homogeneity theory and Lyapunov theory are applied to provide detailed proof of the fixed-time stability. Finally, numerical simulation experimental results verify the robustness of the proposed algorithm to model parameter uncertainties and wind disturbances. In addition, the proposed algorithm is deployed in a open-source UAV autopilot and its effectiveness is further demonstrated by hardware-in-the-loop experimental results.

Flame temperature and spectral emissivity were the important parameters characterizing the sufficient degree of fuel combustion and the particle radiative characteristics in the Rocket Based Combined Cycle (RBCC) combustor. To investigate the combustion characteristics of the complex supersonic flame in the RBCC combustor, a new radiation thermometry combined with Levenberg-Marquardt (LM) algorithm and the least squares method was proposed to measure the temperature, emissivity and spectral radiative properties based on the flame emission spectrum. In-situ measurements of the flame temperature, emissivity and spectral radiative properties were carried out in the RBCC direct-connected test bench with laser-induced plasma combustion enhancement (LIPCE) and without LIPCE. The flame average temperatures at fuel global equivalence ratio (α) of 1.0b and 0.6 with LIPCE were 4.51% and 2.08% higher than those without LIPCE. The flame combustion oscillation of kerosene tended to be stable in the recirculation zone of cavity with the thermal and chemical effects of laser induced plasma. The differences of flame temperature at α = 1.0b and 0.6 were 503 K and 523 K with LIPCE, which were 20.07% and 42.64% lower than those without LIPCE. The flame emissivity with methane assisted ignition was 80.46% lower than that without methane assisted ignition, due to the carbon-hydrogen ratio of kerosene was higher than that of methane. The spectral emissivities at 600 nm with LIPCE were 1.25%, 22.2%, and 4.22% lower than those without LIPCE at α = 1.0a (with methane assisted ignition), 1.0b (without methane assisted ignition) and 0.6. The effect of concentration in the emissivity was removed by normalization to analyze the flame radiative properties in the RBCC combustor chamber. The maximum differences of flame normalized emissivity were 50.91% without LIPCE and 27.53% with LIPCE. The flame radiative properties were stabilized under the thermal and chemical effects of laser induced plasma at α = 0.6.

Based on the system dynamic model, a full system dynamics estimation method is proposed for a chain shell magazine driven by a permanent magnet synchronous motor (PMSM). An adaptive extended state observer (AESO) is proposed to estimate the unmeasured states and disturbance, in which the model parameters are adjusted in real time. Theoretical analysis shows that the estimation errors of the disturbances and unmeasured states converge exponentially to zero, and the parameter estimation error can be obtained from the extended state. Then, based on the extended state of the AESO, a novel parameter estimation law is designed. Due to the convergence of AESO, the novel parameter estimation law is insensitive to controllers and excitation signal. Under persistent excitation (PE) condition, the estimated parameters will converge to a compact set around the actual parameter value. Without PE signal, the estimated parameters will converge to zero for the extended state. Simulation and experimental results show that the proposed method can accurately estimate the unmeasured states and disturbance of the chain shell magazine, and the estimated parameters will converge to the actual value without strictly continuous PE signals.

Boron has been considered a promising powdered metal fuel for enhancing composite propellants' energy output due to its high energy density. However, the high ignition temperature and low combustion efficiency limit the application of boron powder due to the high boiling point of the boron oxide layer. Much research is ongoing to overcome these shortcomings, and one potential approach is to introduce a small quantity of metal oxide additives to promote the reaction of boron. This study prepared boron-rich fuels with 10 wt% of eight nano-metal oxide additives by mechanical ball milling. The effect of metal oxides on the thermo-oxidation, ignition, and combustion properties of boron powder was comprehensively studied by the thermogravimetric analysis (TG), the electrically heated filament setup (T-jump), and the laser-induced combustion experiments. TG experiments at 5 K/min found that Bi₂O₃, MoO₃, TiO₂, Fe₂O₃, and CuO can promote thermo-oxidation of boron. Compared to pure boron, T_onset can be reduced from 569 °C to a minimum of 449 °C (B/Bi₂O₃). Infrared temperature measurement in T-jump tests showed that when heated by an electric heating wire at rates from 1000 K/s to 25000 K/s, the ignition temperatures of B/Bi₂O₃ are the lowest, even lower than the melting point of boron oxide. Ignition images and SEM for the products further showed that the high heating rate is beneficial to the rapid reaction of boron powder in the single-particle combustion state. Fuels (B/Bi₂O₃, B/MoO₃, and B/CuO) were mixed with the oxidant AP and ignited by laser to study the combustion performance. The results showed that B/CuO/AP has the largest flame area, the highest BO₂ characteristic spectral intensity, and the largest burn rate for powder lines. To combine the advantages of CuO and Bi₂O₃, binary metal oxide (CBO, mass ratio of 3:1) was prepared and the test results showed that CBO can very well improve both ignition and combustion properties of boron. Especially B/CBO/AP has the highest burn rate compared with all fuels containing other additives. It was found that multi-component metal-oxide additive can more synergistically improve the reaction characteristics of boron powder than unary additive. These findings contribute to the development of boron-rich fuels and their application in propellants.

The interfacial interaction between HMX molecules and coating materials is the key to the safety performance of explosives and has received extensive attention. However, screening suitable coating agents to enhance the interfacial effect to obtain high-energy and low-sensitivity explosives has long been a major challenge. In this work, HMX-PEI/rGO/g-C₃N₄ (HPrGC) composites were innovatively prepared by a multi-level coating strategy of two-dimensional graphite rGO and g-C₃N₄. The g-C₃N₄ used for desensitization has a rich π-conjugated system and shows outstanding ability in reducing friction sensitivity. The hierarchical structure of HPrGC formed by electrostatic self-assembly and π-π stacking can effectively dissipate energy accumulation under heat and mechanical stimulation through structural evolution, thus exhibiting a prominent synergistic desensitization effect on HMX. The results show that rGO/g-C₃N₄ coating has no effect on the crystal structure and chemical structure of HMX. More importantly, the perfect combination of g-C₃N₄ and rGO endows HPrGC with enhanced thermal stability and ideal mechanical sensitivity (IS: 21 J, FS: 216 N). Obviously, the new fabrication of HPrGC enriches the variety of desensitizer materials and helps to deepen the understanding of the interaction between explosives and coatings.