Mechanical behavior and failure mechanism of polyurea nanocomposites under quasi-static and dynamic compressive loading

Polyurea is an elastomeric material that can be applied to enhance the protection ability of structures under blast and impact loading.In order to study the compressive mechanical properties of SiC/polyurea nanocomposites under quasi-static and dynamic loading,a universal testing machine and split Hop-kinson pressure bar(SHPB)apparatus were used respectively.The stress-strain curves were obtained on polyurea and its composites at strain rates of 0.001-8000 s-1.The results of the experiment suggested that increase in the strain rates led to the rise of the flow stress,compressive strength,strain rate sensitivity and strain energy.This indicates that all of the presented materials were dependent on strain rate.Moreover,these mechanical characters were enhanced by incorporating a small amount of SiC into polyurea matrix.The relation between yield stress and strain rates were established using the power law functions.Finally,in order to investigate the fracture surfaces and inside information of failed specimens,scanning electron microscopy(SEM)and micro X-ray computed tomography(micro-CT)were used respectively.Multiple voids,crazes,micro-cracks and cracking were observed in fracture surfaces.On the other hand,the cracking propagation was found in the micro-CT slice images.It is essential to understand the deformation and failure mechanisms in all the polyurea materials.     

Thermodynamics and performance of Al/CuO nanothermite with different storage time

The storage stability of energetic materials is important for its application. Here, the storage stability of Al/CuO nanothermite, which was prepared by electrospray method and stored with different storage time, was systematically researched. The activation energy of Al/CuO nanothermite was calculated by differential scanning calorimetry (DSC). The ignition temperature and the curve pressure history of Al/CuO nanothermite was measured using ignition temperature measuring device and constant-volume pressurization tests, respectively. Further, the thermites were characterized by X-ray Diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and Transmission electron microscopy (TEM). The results show that the morphology of the thermites did not change significantly. The activation energy was decreased from 254.1 kJ/mol to 181.8 kJ/mol after storage for 13 months. When stored for 0, 7 and 13 months, the peak pressures of Al/CuO nanothermite were 685.8 kPa, 626.3 kPa and 625.5 kPa, respectively. In addition to the ignition temperature, it was 775 ℃, 739 ℃ and 754 ℃, respectively. This result indicated that the ignition and combustion properties of Al/CuO nano-thermite are obviously reduced when stored for a long time, at room temperature.     

Effect of metal powders on explosion of fuel-air explosives with delayed secondary igniters

In order to improve the energy level of fuel air explosive(FAE) with delayed secondary igniters, high energetic metal powders were added to liquid fuels mainly composed of ether and isopropyl nitrate. Metal powders' explosive properties and reaction mechanisms in FAE were studied by high-speed video, pressure test system, and infrared thermal imager. The results show that compared with pure liquid fuels, the shock wave overpressure, maximum surface fireball temperature and high temperature duration of the mixture were significantly increased after adding high energetic metal powder. The overpressure values of the liquid-solid mixture at all measuring points were higher than that of the pure liquid fuels. And the maximum temperature of the fireball was up to 1700 ℃, which was higher than that of the pure liquid fuels. After replacing 30％of aluminum powder with boron or magnesium hydride, the shock wave pressure of the mixture was further increased. The high heat of combustion of boron and the hydrogen released by magnesium hydride could effectively increase the blast effect of the mixture. The improvement of the explosion performance of boron was better than magnesium hydride. It shows that adding high energetic metal powder to liquid fuels can effectively improve the explosion performance of FAE.     

Numerical and experimental study on the response characteristics of warhead in the fast cook-off process

The response characteristics of the warhead under thermal stimuli conditions are important to the safety improvement. The goal of this study is to obtain data on the warhead in the fast cook-off process. In this paper, a numerical calculation method is proposed, whose reliability is supported by comparison with experimental results. Through the numerical calculation, the temperature distribution, temperature change, and ignition time are acquired. The numerical results show that the ignition time is 76 s after the warhead started to burn and that the maximum temperature of the explosive's outer surface is 238.3 C at the ignition time. The fast cook-off experiment of the warhead is implemented so as to get the flame temperature and reaction grades that are not available through numerical calculation. The experimental results show that the overpressure fails to reach the preset minimum value which is equivalent to 6 kg of TNT and that the reaction grade is deflagration. The research results have reference value for the design of the warhead and the reduction of detonation risks.     

A reusable planar triggered spark-gap switch batched-fabricated with PCB technology for medium-and low-voltage pulse power systems

Triggered spark-gap switch is a popular discharge switch for pulse power systems. Previous studies have focused on planarizing this switch using thin film techniques in order to meet the requirements of compact size in the systems. Such switches are one-shot due to electrodes being too thin to sufficiently resist spark-erosion. Additionally, these switches did not employ any structures in securing internal gas composition, resulting in inconsistent performance under harsh atmospheres. In this work, a novel planar triggered spark-gap switch (PTS) with a hermetically sealed cavity was batched-prepared with printed circuit board (PCB) technology, to achieve reusability with low cost. The proposed PTS was inspected by micro-computed tomography to ensure PCB techniques meet the requirements of machining precision. The results from electrical experiments demonstrated that PCB PTS were consistent and reusable with lifespan over 20 times. The calculated switch voltage and circuit current were consistent with those derived from real-world measurements. Finally, PCB PTS was used to introduce hexanitrostilbene (HNS) pellets in a pulse power system to verify its performance.     

故障类别的模糊聚类分析

本文通过故障状态-特征的模糊聚类分析,按故障间的相似性对故障进行分类,然后按类别实施故障诊断,可在最少监测点的条件下,获得最多的设备运行故障信息。从而简化故障诊断过程,提高诊断速度和精度。     

时间序列法在军械装备故障预测中的应用

运用时间序列的方法对军械装备使用中的故障进行预测,并以火炮射击的距离偏差、火炮轮胎下沉量为例进行定量的分析和计算,阐述了预测原理和使用方法。     

空投鱼雷最优落水点分析

针对反潜机使用空投鱼雷对潜实施攻击时的最优落水点问题,建立了鱼雷弹道模型、声纳自导系统发现模型、潜艇机动模型、均方差模型,对空投鱼雷对潜攻击过程进行了模拟仿真,得出了相对于不同舷角、距离的鱼雷发现概率,并确定了鱼雷的最优落水点,以期为部队合理使用空投鱼雷提供决策依据.     

基于StarBus的对象事务服务的设计与实现

在分布式计算环境中，对象事务服务（ＯｂｊｅｃｔＴｒａｎｓａｃｔｉｏｎＳｅｒｖｉｃｅ简称ＯＴＳ）对于提高分布式系统的开发效率具有重要意义。设计与实现一个高效的对象事务服务的关键在于克服网络阻塞的问题，本文着眼于一种基于面向对象传值语义的设计方法，可以有效地减少网络阻塞，适合于企业级应用。     

军事文化发展的动力系统浅析

军事文化的发展有一个动力系统,科学技术的不断更新是军事文化发展的根本动力;军事文化体系的内部矛盾是军事文化发展的持久张力;人类普遍的和平理想是军事文化发展的永恒引力;各国之间的文化交流是军事文化发展的强大推力。这些动力交互作用,推动军事文化的不断发展。