Defence Technology(防务技术)最新文献

In this paper, a model order reduction strategy is adopted for the static and dynamic behaviour simulation of a high-speed tracked vehicle. The total number of degree of freedom of the structure is condensed through a selection of interface degrees of freedom and significant global mode shapes, for an approximated description of vehicle dynamic behaviour. The methodology is implemented in a customised open-source software to reduce the computational efforts. The modelled tracked vehicle includes the sprung mass, the unsprung masses, connected by means of torsional bars, and all the track assemblies, composing the track chain. The proposed research activity presents a comprehensive investigation of the influence of the track chain, combined with longitudinal vehicle speed, on statics and vehicle dynamics, focusing on vertical dynamics. The vehicle response has been investigated both in frequency and time domain. In this last case road-wheel displacements are assumed as inputs for the model, under different working conditions, hence considering several road profiles with different amplitudes and characteristic excitation frequencies. Simulation results have proven a high fidelity in model order reduction approach and a significant contribution of the track chain in the global dynamic behaviour of the tracked vehicle.

In this study, we investigated the performance improvement caused by the addition of copper (Cu) nanoparticles to high-density polyethylene (HDPE) matrix material. Composite materials, with filler percentages of 0.0, 2.0, 4.0, 6.0, 8.0, and 10.0 wt% were synthesized through the material extrusion (MEX) 3D printing technique. The synthesized nanocomposite filaments were utilized for the manufacturing of specimens suitable for the experimental procedure that followed. Hence, we were able to systematically investigate their tensile, flexural, impact, and microhardness properties through various mechanical tests that were conducted according to the corresponding standards. Broadband Dielectric Spectroscopy was used to investigate the electrical/dielectric properties of the composites. Moreover, by employing means of Raman spectroscopy and thermogravimetric analysis (TGA) we were also able to further investigate their vibrational, structural, and thermal properties. Concomitantly, means of scanning electron microscopy (SEM), as well as atomic force microscopy (AFM), were used for the examination of the morphological and structural characteristics of the synthesized specimens, while energy-dispersive X-ray spectroscopy (EDS) was also performed in order to receive a more detailed picture on the structural characteristics of the various synthesized composites. The corresponding nanomaterials were also assessed for their antibacterial properties regarding Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) with the assistance of a method named screening agar well diffusion. The results showed that the mechanical properties of HDPE benefited from the utilization of Cu as a filler, as they showed a notable improvement. The specimen of HDPE/Cu 4.0 wt% was the one that presented the highest levels of reinforcement in four out of the seven tested mechanical properties (for example, it exhibited a 36.7% improvement in the flexural strength, compared to the pure matrix). At the same time, the nanocomposites were efficient against the S. aureus bacterium and less efficient against the E. coli bacterium. The use of such multi-functional, robust nanocomposites in MEX 3D printing is positively impacting applications in various fields, most notably in the defense and security sectors. The latter becomes increasingly important if one takes into account that most firearms encompass various polymeric parts that require robustness and improved mechanical properties, while at the same time keeping the risk of spreading various infectious microorganisms at a bare minimum.

This review paper explores the potential of oil palm biomass as a valuable cellulose source for the production of nitrocellulose-based propellants, contributing to the green revolution and sustainable energy solutions. It highlights the availability of the corresponding biomass in Malaysia and in line with global studies, the chemical compositions, as well as a brief description of current technologies for converting biomass of oil palm into value added products specifically cellulose. Steps to achieve maximum utilization of biomass from oil palm industry for cellulose production and prospective source for nitrocellulose-based propellant are also proposed. The methodology section outlines the pre-treatment of lignocellulosic fibres, cellulose extraction, and nitrocellulose production processes. Overall, the review underscores the prospective of palm oil biomass as a sustainable cellulose source for propellant manufacturing, while acknowledging the need for further research and advancements in the field.

This paper presents the first-ever investigation of Menger fractal cubes' quasi-static compression and impact behaviour. Menger cubes with different void ratios were 3D printed using polylactic acid (PLA) with dimensions of 40 mm × 40 mm × 40 mm. Three different orders of Menger cubes with different void ratios were considered, namely M1 with a void ratio of 0.26, M2 with a void ratio of 0.45, and M3 with a void ratio of 0.60. Quasi-static Compression tests were conducted using a universal testing machine, while the drop hammer was used to observe the behaviour under impact loading. The fracture mechanism, energy efficiency and force-time histories were studied. With the structured nature of the void formation and predictability of the failure modes, the Menger geometry showed some promise compared to other alternatives, such as foams and honeycombs. With the increasing void ratio, the Menger geometries show force-displacement behaviour similar to hyper-elastic materials such as rubber and polymers. The third-order Menger cubes showed the highest energy absorption efficiency compared to the other two geometries in this study. The findings of the present work reveal the possibility of using additively manufactured Menger geometries as an energy-efficient system capable of reducing the transmitting force in applications such as crash barriers.

The phenomenon of a target echo peak overlapping with the backscattered echo peak significantly undermines the detection range and precision of underwater laser fuzes. To overcome this issue, we propose a four-quadrant dual-beam circumferential scanning laser fuze to distinguish various interference signals and provide more real-time data for the backscatter filtering algorithm. This enhances the algorithm loading capability of the fuze. In order to address the problem of insufficient filtering capacity in existing linear backscatter filtering algorithms, we develop a nonlinear backscattering adaptive filter based on the spline adaptive filter least mean square (SAF-LMS) algorithm. We also designed an algorithm pause module to retain the original trend of the target echo peak, improving the time discrimination accuracy and anti-interference capability of the fuze. Finally, experiments are conducted with varying signal-to-noise ratios of the original underwater target echo signals. The experimental results show that the average signal-to-noise ratio before and after filtering can be improved by more than 31 dB, with an increase of up to 76% in extreme detection distance.

In recent years, in order to improve the destructive effectiveness of munitions, the use of new types of destructive elements is an important way to improve destructive effectiveness. As a new type of reactive material, reactive alloy contains a large portion of reactive metal elements (Al, Mg, Ti, Zr, etc.), which breaks up under high-velocity impact conditions, generating a large number of high-temperature combustible fragments, which undergo a violent combustion reaction with air. Compared with traditional metal polymers (Al-PTFE) and other reactive composites, it has higher density and strength, excellent mechanical properties and broader application prospects. Currently, researchers have mainly investigated the impact energy release mechanism of reactive alloys through impact tests, and found that there are several important stages in the process of the material from fragmentation to reaction, i.e., impact fragmentation of the material, rapid heating and combustion reaction. This paper focuses on three problems that need to be solved in the impact-induced energy release process of reactive alloys, namely: the fragmentation mechanism and size distribution law of the fragments produced by the impact of the material on the target, the relationship between the transient temperatures and the size of the fragments, and the reaction temperatures and size thresholds of the fragments to undergo the chemical reaction. The current status of the research of the above problems is reviewed, some potential directions to reveal the impact induced reaction mechanism of reactive alloy is discussed.

High speed photography technique is potentially the most effective way to measure the motion parameter of warhead fragment benefiting from its advantages of high accuracy, high resolution and high efficiency. However, it faces challenge in dense objects tracking and 3D trajectories reconstruction due to the characteristics of small size and dense distribution of fragment swarm. To address these challenges, this work presents a warhead fragments motion trajectories tracking and spatio-temporal distribution reconstruction method based on high-speed stereo photography. Firstly, background difference algorithm is utilized to extract the center and area of each fragment in the image sequence. Subsequently, a multi-object tracking (MOT) algorithm using Kalman filtering and Hungarian optimal assignment is developed to realize real-time and robust trajectories tracking of fragment swarm. To reconstruct 3D motion trajectories, a global stereo trajectories matching strategy is presented, which takes advantages of epipolar constraint and continuity constraint to correctly retrieve stereo correspondence followed by 3D trajectories refinement using polynomial fitting. Finally, the simulation and experimental results demonstrate that the proposed method can accurately track the motion trajectories and reconstruct the spatio-temporal distribution of 1.0×10³ fragments in a field of view (FOV) of 3.2 m×2.5 m, and the accuracy of the velocity estimation can achieve 98.6%.

Modern conflicts demand substantial physical and psychological exertion, often resulting in fatigue and diminished combat or operational readiness. Several exoskeletons have been developed recently to address these challenges, presenting various limitations that affect their operational or everyday usability. This article evaluates the performance of a dual-purpose passive ankle exoskeleton developed for the reduction of metabolic costs during walking, seeking to identify a force element that could be applied to the target population. Based on the 6-min walk test, twenty-nine subjects participated in the study using three different force elements. The results indicate that it is possible to reduce metabolic expenditure while using the developed exoskeleton. Additionally, the comfort and range of motion results verify the exoskeleton's suitability for use in uneven terrain and during extended periods. Nevertheless, the choice of the force element should be tailored to each user, and the control system should be adjustable to optimise the exoskeleton's performance.

A critical challenge of any blast simulation facility is in producing the widest possible pressure-impulse range for matching against equivalent high-explosive events. Shock tubes and blast simulators are often constrained with the lack of effective ways to control blast wave profiles and as a result have a limited performance range. Some wave shaping techniques employed in some facilities are reviewed but often necessitate extensive geometric modifications, inadvertently cause flow anomalies, and/or are only applicable under very specific configurations. This paper investigates controlled venting as an expedient way for waveforms to be tuned without requiring extensive modifications to the driver or existing geometry and could be widely applied by existing and future blast simulation and shock tube facilities. The use of controlled venting is demonstrated experimentally using the Advanced Blast Simulator (shock tube) at the Australian National Facility of Physical Blast Simulation and via numerical flow simulations with Computational Fluid Dynamics. Controlled venting is determined as an effective method for mitigating the impact of re-reflected waves within the blast simulator. This control method also allows for the adjustment of parameters such as tuning the peak overpressure, the positive phase duration, and modifying the magnitude of the negative phase and the secondary shock of the blast waves. This paper is concluded with an illustration of the potential expanded performance range of the Australian blast simulation facility when controlled venting for blast waveform tailoring as presented in this paper is applied.

In this study, a series of hypervelocity impact tests were carried out based on a two-stage light gas gun, and the sequence spectrum and radiation evolution data of the impact products under different impact conditions were obtained. The diameter of the projectile is 3–5 mm, the impact velocity is 3.13–6.58 km/s, and the chamber pressure is 0.56–990 Pa. The spectrum of ejected debris cloud in the 250–310 nm band were obtained using a transient spectral measurement system and a multi-channel radiometer measurement system. The test results reveal that the flash radiation intensity increases as a power function with the kinetic energy of the impact. Furthermore, the peak value of the line spectrum decreases as the chamber vacuum degree increases, while the radiation width gradually expands. The line spectrum in the spectral characterization curve corresponds to the ejected debris clouds splitting phase, which does not produce significant line spectrum during material fragmentation and is dominated by the continuum spectrum produced by blackbody radiation. There will appear one or three characteristic peaks in the flash radiation time curve, the first and second peaks correspond to the penetration phase and the third peak corresponds to the expansion phase of the ejected debris clouds on the time scale, the first and second peaks are more sensitive to the chamber vacuum degree, and when the pressure is higher than 99 Pa, the first and second characteristic peaks will disappear. The radiant heat attenuation of the flash under different impact conditions is significantly different, the attenuation exponent has a power function relationship with the impact velocity and the chamber vacuum degree, while the attenuation exponent has a linear relationship with the diameter of the projectile, the specific expression of the attenuation exponent is obtained by fitting. The findings from this research can serve as a valuable reference for remote diagnostic technologies based on flash radiation characteristics.