Defence Technology(防务技术)最新文献

Honeycomb sandwich structures are widely used in lightweight applications. Usually, these structures are subjected to extreme loading conditions, leading to potential failures due to delamination and debonding between the face sheet and the honeycomb core. Therefore, the present study is focused on the mechanical characterisation of honeycomb sandwich structures fabricated using advanced 3D printing technology. The continuous carbon fibres and ONYX-FR matrix materials have been used as raw materials for 3D printing of the specimens needed for various mechanical characterization testing; ONYX-FR is a commercial trade name for flame retardant short carbon fibre filled nylon filaments, used as a reinforcing material in Morkforged 3D printer. Edgewise and flatwise compression tests have been conducted for different configurations of honeycomb sandwich structures, fabricated by varying the face sheet thickness and core cell size, while keeping the core cell thickness and core height constant. Based on these tests, the proposed structure with face sheet thickness of 3.2 mm and a core cell size of 12.7 mm exhibited the highest energy absorption and prevented delamination and debonding failures. Therefore, 3D printing technology can also be considered as an alternative method for sandwich structure fabrication. However, detailed parametric studies still need to be conducted to meet various other structural integrity criteria related to the lightweight applications.

Lug joints are preferred joineries for transferring heavy loads to parent components in aerospace vehicles. They experience corrosion due to environmental conditions, improper surface finishes and rubbing displacement between the pin and lug-hole. This causes damage of different sizes and shapes near the lug-hole. Stiffness degradation due to corrosion-induced damage is modelled as a through-pit at one of the identified critical locations through stress analysis. The effect of this pit on fatigue crack initiation life is estimated. Lug-hole is pre-stressed by cold-working and the benefits of inducing plastic wake on the intended performance of the lug joint during the damages due to corrosion are brought out and compared with non-cold-worked lug-hole. Numerical analysis is performed on this lug joint with press-fit. The results obtained highlight the benefits of cold-working and the methodology can be extended to damage growth and analyse the effect of surface treatments for better structural integrity of components of aerospace vehicles.

Target maneuver recognition is a prerequisite for air combat situation awareness, trajectory prediction, threat assessment and maneuver decision. To get rid of the dependence of the current target maneuver recognition method on empirical criteria and sample data, and automatically and adaptively complete the task of extracting the target maneuver pattern, in this paper, an air combat maneuver pattern extraction based on time series segmentation and clustering analysis is proposed by combining autoencoder, G-G clustering algorithm and the selective ensemble clustering analysis algorithm. Firstly, the autoencoder is used to extract key features of maneuvering trajectory to remove the impacts of redundant variables and reduce the data dimension; Then, taking the time information into account, the segmentation of Maneuver characteristic time series is realized with the improved FSTS-AEGG algorithm, and a large number of maneuver primitives are extracted; Finally, the maneuver primitives are grouped into some categories by using the selective ensemble multiple time series clustering algorithm, which can prove that each class represents a maneuver action. The maneuver pattern extraction method is applied to small scale air combat trajectory and can recognize and correctly partition at least 71.3% of maneuver actions，indicating that the method is effective and satisfies the requirements for engineering accuracy. In addition, this method can provide data support for various target maneuvering recognition methods proposed in the literature, greatly reduce the workload and improve the recognition accuracy.

An in-depth understanding of the fracture behavior and mechanism of metallic shells under internal explosive loading can help develop material designs for warheads and regulate the quantity and mass distribution of the fragments formed. This study investigated the fragmentation performance of a new high-carbon silicon-manganese (HCSiMn) steel cylindrical shell through fragment recovery experiments. Compared with the conventional 45Cr steel shell, the number of small mass fragments produced by the HCSiMn steel shell was significantly increased with a scale parameter of 0.57 g fitted by the Weibull distribution model. The fragmentation process of the HCSiMn shell exhibited more brittle tensile fracture characteristics, with the microcrack damage zone on the outer surface being the direct cause of its high fragmentation. On the one hand, the doping of alloy elements resulted in grain refinement by forming metallographic structure of tempered sorbite, so that microscopic intergranular fracture reduces the characteristic mass of the fragments; on the other hand, the distribution of alloy carbides can exert a "pinning" effect on the substrate grains, causing more initial cracks to form and propagate along the brittle carbides, further improving the shell fragmentation. Although the killing power radius for light armored vehicles was slightly reduced by about 6%, the dense killing radius of HCSiMn steel projectile against personnel can be significantly increased by about 26% based on theoretical assessment. These results provided an experimental basis for high fragmentation warhead design, and to some extent, revealed the correlation mechanism between metallographic structure and shell fragmentation.

Foam concrete is a prospective material in defense engineering to protect structures due to its high energy absorption capability resulted from the long plateau stage. However, stress enhancement rather than stress mitigation may happen when foam concrete is used as sacrificial claddings placed in the path of an incoming blast load. To investigate this interesting phenomenon, a one-dimensional difference model for blast wave propagation in foam concrete is firstly proposed and numerically solved by improving the second-order Godunov method. The difference model and numerical algorithm are validated against experimental results including both the stress mitigation and the stress enhancement. The difference model is then used to numerically analyze the blast wave propagation and deformation of material in which the effects of blast loads, stress–strain relation and length of foam concrete are considered. In particular, the concept of minimum thickness of foam concrete to avoid stress enhancement is proposed. Finally, non-dimensional analysis on the minimum thickness is conducted and an empirical formula is proposed by curve-fitting the numerical data, which can provide a reference for the application of foam concrete in defense engineering.

Coating modification is an important way to enhance the reactivity of aluminum powder. In this paper, ammonium perchlorate and aluminum powder were assembled into energetic microunits by liquid deposition method. Spherical particles with AP as shell and ultrafine aluminum powder as the core (Al@AP) were gained. The micromorphology results show that the coated particles are about 5 μm, and the coating layer is evenly distributed on the outer surface of aluminum powder, indicating a complete coating. The energetic microunits were implanted into the nitrate ester plasticizing adhesive system (NEPE) as solid phase fillers. The effect of filler on the rheological properties, safety, mechanical properties, thermal reaction and energy properties of the system was analyzed by comparing with the raw aluminum filler. The test results show that the rheological properties, mechanical properties and pressure index of NEPE containing system Al@AP meets the requirements of solid propellant charging. Compared with Al based propellant, the mechanical sensitivity and thermal sensitivity are decreased, the safety is better, and the explosion heat of the propellant is increased by $7.8\%$. The engine test shows that the specific impulse is increased by 1.2 s. Al@AP can improve the energy output and safety of NEPE propellant, and has potential application prospects in high-energy propellants.

An innovative multi-layer composite explosion containment vessel (CECV) utilizing a sliding steel plate-aluminum honeycomb-fiber cloth sandwich is put forward to improve the anti-explosion capacity of a conventional single-layer explosion containment vessel (SECV). Firstly, a series of experiments and finite element (FE) simulations of internal explosions are implemented to understand the basic anti-explosion characteristics of a SECV and the rationality of the computational models and methods is verified by the comparison between the experimental results and simulation results. Based on this, the CECV is designed in detail and a variety of FE simulations are carried out to investigate effects of the sandwich structure, the explosive quantity and the laying mode of the fiber cloth on anti-explosion performance and dynamic response of the CECV under internal explosions. Simulation results indicate that the end cover is the critical position for both the SECV and CECV. The maximum pressure of the explosion shock wave and the maximum strain of the CECV can be extremely declined compared to those of the SECV. As a result, the explosive quantity the CECV can sustain is up to 20 times of that the SECV can sustain. Besides, as the explosive quantity increases, the internal pressure of the CECV keeps growing and the plastic deformation and failure of the sandwich structure become more and more severe, yielding plastic strain of the CECV in addition to elastic strain. The results also reveal that the laying angles of the fiber cloth's five layers have an impact on the anti-explosion performance of the CECV. For example, the CECV with fiber cloth layered in 0°/45°/90°/45°/0° mode has the optimal anti-capacity, compared to 0°/0°/0°/0°/0° and 0°/30°/60°/30°/0° modes. Overall, owing to remarkable anti-explosion capacity, this CECV can be regarded as a promising candidate for explosion resistance.

A ternary system of PTFE/Al/Bi₂O₃ is constructed by incorporating PTFE-based reactive material and thermite for enhancing the energy release of the PTFE-based reactive material. The effects of Bi₂O₃ in the PTFE/Al/Bi₂O₃ on both mechanical properties and the energy release were investigated through various tests such as thermogravimetry-differential scanning calorimetry, adiabatic oxygen bomb test and split Hopkinson pressure bar test. The microstructure observed through scanning electron microscope and X-ray diffraction results are used to analyze the ignition and reaction mechanism of PTFE/Al/Bi₂O₃. The results indicate that the PTFE/Al/Bi₂O₃ are capable of triggering the exothermic reaction of molten PTFE/Bi₂O₃ and Al/Bi₂O₃ over the PTFE/Al reactive materials, thereby promoting reactions. The excessive aluminum in the ternary system is beneficial for increasing energy release. The ignition of shock-induced chemical reactions in PTFE/Al/Bi₂O₃ is closely related to the material fracture. The dominant mechanism for hot-spot generation under Split Hopkinson Pressure Bar test is the frictional temperature rise at the microcrack after failure.

The evolution of threats and scenarios requires continuous performance improvements of ballistic protections for armed forces. From a modeling point of view, it is necessary to use sufficiently precise material behavior models to accurately describe the phenomena observed during the impact of a projectile on a protective equipment. In this context, the goal of this paper is to characterize the behavior of a small caliber steel jacket by combining experimental and numerical approaches. The experimental method is based on the lateral compression of ring specimens directly machined from the thin and small ammunition. Various speeds and temperatures are considered in a quasi-static regime in order to reveal the strain rate and temperature dependencies of the tested material. The Finite Element Updating Method (FEMU) is used. Experimental results are coupled with an inverse optimization method and a finite element numerical model in order to determine the parameters of a constitutive model representative of the jacket material. Predictions of the present model are verified against experimental results and a parametric study as well as a discussion on the identified material parameters are proposed. The results indicate that the strain hardening parameter can be neglected and the behavior of the thin steel jacket can be described by a modeling without strain hardening sensitivity.

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.