The effect of annular multi-point initiation on the formation and penetration of an explosively formed penetrator

Using LS-DYNA software, this paper studies the problem of an annular multi-point initiation circuit applied to an EFP charge, and the effects on the penetrator formation parameters, such as velocity and length-diameter ratio, by examining the number of initiation points, the initiation position, and the synchronized initiation deviation of the annular multi-point initiation circuit. It reaches the conclusion that when there are six or more initiation points, the formed EFP of a multi-point initiation project is similar to the result of a peripherally initiated charge. It also finds that the change of across velocity gradient is the main cause of bending distortion of the penetrator, and that the formed penetrator cannot bend if the multi-point synchronized initiation deviation is less than 200 ns. The simulation results were validated through X-ray imaging experimentation. Both results are in good agreement. It was found that, with the increase of the initiation annular radius, the EFP velocity improves by 24%, and the length-diameter ratio increases by more than 5 times.     

A fuzzy model of the penetration resistance of concrete targets

The penetration resistance of a concrete target varies greatly with the strike velocity of the projectile from low and intermediate impact velocities to high impact velocities. A fuzzy model of the penetration resistance of a concrete target is proposed to describe this characteristic. A complete analysis is conducted of the penetration process during which a rigid projectile penetrates a semi-infinite concrete target based on the proposed fuzzy model. Good agreement is observed between the experimental and predicted results based on the proposed fuzzy model.     

正硅酸乙酯为无机组分前驱体的聚碳酸酯耐磨涂层

以正硅酸乙酯(TEOS)作为无机组分的前驱体,甲基三甲氧基硅烷(MTMS)水解聚合产物作为有机组分,通过溶胶-凝胶法在聚碳酸酯(PC)表面形成耐磨涂层。红外光谱分析表明该涂层具有Si—O—Si的交联网络结构。研究了MTMS和TEOS的摩尔比对涂层的光学性能、硬度、附着力和耐磨性能的影响。结果表明,当MTMS和TEOS的摩尔比为2∶1时,涂层的综合性能达到最优,该涂层在经历500次耐磨试验后的雾度为12.69%,而纯PC的雾度增至42.38%。采用SEM和TEM分析了MTMS/TEOS具有优异耐磨性能的原因在于该涂层具有纳米SiO2粒子分散于有机基体的微观结构。     

The effect of rod nose shape on the internal flow fields during the ballistic penetration of sand

This paper discusses the technique of Digital Speckle Radiography (DSR) and its application to the measurement of the internal flow fields in penetration of sand by long-rod projectiles at velocities up to 200 m/s. Three different rod nose shapes were studied: flat-ended, ogive-2, and hemispherical. Impacts performed on gelatine and concrete gave significantly different displacement fields to sand. Sand, therefore, cannot either be modelled as a fluid or as a conventional solid. Simulations performed using a code written by two of the authors (Bobaru and Promratana) showed that the velocity distribution has a very different appearance to the force distribution. This suggests that processes such as reorganisation, sliding and void filling take place, allowing the grains to move in directions other than the applied force. The resulting velocity distribution bears a strong resemblance to the experimentally measured displacement fields.     

Boundary effect on the softening curve of concrete

The apparent fracture energy of concrete experimentally determined on the basis of the work of fracture in bending or wedge splitting tests becomes larger with increasing specimen dimensions. This experimental observation may be attributed to the varying local fracture energy along the crack path. When the crack tip approaches the specimen boundary, the size of the fracture process zone will be reduced and, consequently, only a portion of the fracture energy is activated; i.e., the local fracture energy is getting smaller. The influence of this boundary effect diminishes with increasing specimen size resulting in the size dependence of the apparent fracture energy determined by the work-of-fracture method as an average value in the ligament. With varying local fracture energy, the local softening curve will also show variations. The latter are subject of the present study. Wedge splitting tests with different specimen sizes as well as inverse analyses of these experiments were carried out. For the inverse analyses, the cohesive crack model was adopted and an evolutionary optimization algorithm has been used. The boundary effect on the local fracture properties was taken into account and, as a result, the variation of the softening curve along the crack path could be determined. It was found that the tail of the softening curve is shortened and lowered due to the boundary effect whereas the initial slope of this curve appears to be not affected.     

刚性卵形头弹撞击角度对编织复合材料层合板侵彻特性的影响

利用一级气炮发射卵形头弹撞击2 mm厚度的编织复合材料层合板,撞击角度分别为0°、30°和45°,通过高速相机记录弹靶撞击过程,并获得弹体速度数据。基于拟合公式处理试验数据,计算获取弹道极限,分析撞击角度对弹道极限、靶板能量吸收率及其失效模式的影响规律及机制。结果表明：弹体撞击角度为45°时,靶板弹道极限最高,其次为0°,撞击角度为30°时最小。随着冲击角度增加,层合板损伤形状从菱形逐渐转变为椭球形,损伤面积随冲击速度增加而增大,且45°冲击时层合板损伤面积最大,0°和30°冲击时损伤面积近似相等。弹体初始撞击角度对靶体失效模式存在影响,弹体撞击角度为0°时,纤维断口主要是剪切应力导致的横截面。撞击角度为30°时,纤维断口主要是剪切应力和拉伸应力导致的斜截面。45°斜撞击时,纤维断口主要是拉伸应力导致的横截面。     

XPS结合氩离子溅射剖析Si/C多层膜的化学状态

采用X射线光电子能谱结合氩离子溅射对用作锂离子电池负极的Si/C多层膜进行了表面测试及深度剖析,获得了Si/C多层膜结构中不同深度位置的成分及化学状态.分析结果表明,Si/C多层膜中各层Si、C薄膜之间存在界面元素相互扩散,扩散至相邻层薄膜中的Si、C元素主要以化合物SiC形式存在,且处于不同位置的SiC的化学键能受周...     

基于SPH方法对不同药型罩线性聚能射流形成及后效侵彻过程的模拟

为了解决传统基于网格的数值方法在模拟线性聚能射流问题时因大变形而导致网格畸变使计算难以进行的问题,本文通过自编程实现的光滑粒子法（SPH）对不同药型罩线性聚能装药射流形成及其侵彻金属靶板的过程开展了数值模拟研究,所实现的算法可以为线性聚能射流数值模拟研究提供新途径。本文所开展的研究首先基于已有的线性聚能射流试验模型进行模拟分析,采用SPH方法有效实现了线性聚能射流的形成过程,数值模拟获得的射流头部速度与试验比对误差在10%以内。然后建立了装药质量、药型罩质量和装药横截面宽度相同的前提下不同药型罩线性聚能射流模型,数值模拟获得不同药型罩形成的射流特征以及侵彻金属靶板的开口宽度和侵彻深度随时间的变化规律。研究得到的不同药型罩线性聚能射流形成及后效侵彻规律可为线性聚能射流的设计提供参考。     

The effect of thin deployable construction elements of the international space station on the probability of its hull penetration by meteoroids and orbital debris

When calculating the probability of hull penetration by meteoroid and orbital debris (M/OD) for some of the International Space Station (ISS) modules (e.g. FGB, Service module, cargo vehicle “Progress”), one has to take into account their additional shielding produced by ISS deployable construction elements (such as solar panels, radiators), which decrease M/OD penetrating probabilities. The lack of developed calculation methods of accounting for this effect has arisen the necessity to investigate the law— governed nature of particle fragmentation process accompanying high velocity penetration of thin barriers, as well as to elaborate techniques for correct calculation of the probability of no penetration (PNP) of module pressure wall. The results of thorough analysis of the theoretical and experime ntal published data as well as of data obtained in joint NASA and RSA experimental program on particle fragmentation are presented in this report in the form of normalized analytical correlation between the fragment maximum size and impact parameters. On the basis of above mentioned particle fragmentation law, the method of module hull ballistic limit curves (BLC's) recalculation is determined, which include the effect of thin barriers greatly distanced from the module hull. This BLC's are used for module PNP calculations with the help of modified version of NASA BUMPER code. The special subroutines accounting for PNP changes due to the particle collisions with ISS deployable construction elements are introduced in the BUMPER algorithm. The results of the Service module PNP calculations with account for its “shadowing” by solar panels and radiators are presented.     

Mathematical analysis for the efficiency of a semi-spherical fin with simultaneous heat and mass transfer

In this paper an analytical solution for the efficiency of a semi-spherical fin when subjected to simultaneous heat and mass transfer mechanisms is studied. For the mathematical analysis of a wet fin equation, a relationship between humidity ratio and temperature of the saturation air is needed. The driving forces for the heat and mass transfer are the temperature and humidity ratio differences, respectively. Analytical solutions are obtained for the temperature distribution over the fin surface when the fin is fully wet. It is observed that in humid conditions the fin has high efficiency to be used in industry. The variation effects of these parameters have been considered. Finally linear relation has been proposed for humidity and temperature on the fin surface.     

A DRBEM model for harbor oscillation with the effect of energy dissipation

Abstract

In this study, the numerical scheme of dual reciprocity boundary element method (DRBEM) is adopted to investigate the resonant problem in a harbor while considering the effect of energy dissipation. The numerical model employed the mild slope equation as a basic equation. To avoid complicated procedures for solving the equation, DRBEM is used to improve numerical efficiency. Computation results are compared with the existing experimental data and other theoretical results. It shows that the present model is valid and effective to solve the harbor oscillation problem.     

Surface tension of aqueous lithium bromide with heat/mass transfer enhancement additives: the effect of additive vapor transport

Heat/mass transfer enhancement additives used in aqueous lithium bromide absorption chillers are surfactants that lower the surface tension of the working fluid. It has long been speculated that the surface tension characteristics are a key to the enhancement but the point is controversial because some surfactants do not provide enhancement. In the present study, the surface tension of aqueous lithium bromide was measured, with and without various surfactant additives, using a drop weight method. Measurements were also made on water, with and without an additive. The results provide new information that clarifies several confusing aspects of the literature data. The major result is the realization that the surface tension of aqueous lithium bromide is strongly affected by the presence of surfactant vapor around the liquid interface. This apparently explains the large differences in surface tension data found in the literature since no previous studies mentioned the importance of the vapor conditions.     

Use of equivalent mass method for free vibration analyses of a beam carrying multiple two‐dof spring–mass systems with inertia effect of the helical springs considered

This paper investigates the free vibration characteristics of a beam carrying multiple two‐degree‐of‐freedom (two‐dof) spring–mass systems (i.e. the loaded beam). Unlike the existing literature to neglect the inertia effect of the helical springs of each spring–mass system, this paper takes the last inertia effect into consideration. To this end, a technique to replace each two‐dof spring–mass system by a set of rigidly attached equivalent masses is presented, so that the free vibration characteristics of a loaded beam can be predicted from those of the same beam carrying multiple rigidly attached equivalent masses. In which, the equation of motion of the loaded beam is derived analytically by means of the expansion theorem (or the mode superposition method) incorporated with the natural frequencies and the mode shapes of the bare beam (i.e. the beam carrying nothing). In addition, the mass and stiffness matrices including the inertia effect of the helical springs of a two‐dof spring–mass system, required by the conventional finite element method (FEM), are also derived. All the numerical results obtained from the presented equivalent mass method (EMM) are compared with those obtained from FEM and satisfactory agreement is achieved. Because the equivalent masses of each two‐dof spring–mass system are dependent on the magnitudes of its lumped mass, spring constant and spring mass, the presented EMM provides an effective technique for evaluating the overall inertia effect of the two‐dof spring–mass systems attached to the beam. Furthermore, if the total number of two‐dof spring–mass systems attached to the beam is large, then the order of the overall property matrices for the equation of motion of the loaded beam in EMM is much less than that in FEM and the computer storage memory required by the former is also much less than that required by the latter. Copyright © 2005 John Wiley & Sons, Ltd.     

磁场辅助下ZrO2纳米颗粒质量浓度对镀层耐磨性能的影响研究

为了进一步延长45钢工件的耐磨性能,减少企业维修和更换45钢类零件的成本,在传统材料45钢表面,开展了稳恒磁场辅助的电喷镀试验研究,通过配制不同ZrO₂纳米颗粒质量浓度的镀液,制备了Ni-P-ZrO₂镀层,利用扫描电子显微镜(SEM)、能谱分析仪(EDS)、显微硬度检测仪和共聚焦显微镜等仪器对镀层表面形貌、Zr元素含量、显微硬度以及耐磨性能进行了分析。研究发现:ZrO₂纳米颗粒和稳恒磁场的加入改善了镀层表面形貌,提高了显微硬度和耐磨性能;当ZrO₂纳米颗粒质量浓度达到15 g/L时,ZrO₂纳米颗粒易出现团聚现象,不利于镀层表面性能的进一步提升。磁场辅助下,镀液中ZrO₂纳米颗粒质量浓度为10 g/L时,得到的镀层表面更加平整、显微硬度最高达到了739.30HV,且磨痕宽度、深度以及截面面积达到最小值,分别为367.617、5.673 μm和1 288.155 μm²,镀层耐磨性能最佳。     

Controllable synthesis of Co3O4 from nanosize to microsize with large-scale exposure of active crystal planes and their excellent rate capability in supercapacitors based on the crystal plane effect

Co₃O₄ nanorods, nanobelts, nanosheets and cubic/octahedral nanoparticles have been successfully synthesized with tunable size from the nanoscale to the microscale, accompanied by a variation in the nature of the exposed crystal planes. The products are formed by thermal treatment of Co(CO₃)_0.5(OH)·_0.11H₂O nanorod, nanobelt, nanosheet and nanocubic/nanooctahedral precursors at 250 °C. Detailed characterization, including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photo-electron spectroscopy (XPS), and nitrogen adsorption and desorption isotherms, revealed that the as-prepared nanorods, nanobelts, and nanosheet Co₃O₄ samples are single crystalline and mesoporous in nature with a predominance of exposed high-energy (110) crystal planes. They exhibited excellent electrochemical properties in supercapacitors, showing higher capacitance and better rate capability than conventional cubic/octahedral Co₃O₄ nanoparticles having exposed low-energy (100) and (111) planes. No decay in capacitance was observed when the scan rate was increased from 5 mV/s to 100 mV/s, or from 1 A/g to 10 A/g. The maximum value of the specific capacitance was calculated to be 162.8 F/g and the capacitance retention reached as high as 90%. Their excellent performance in supercapacitors is believed to result from the large-area exposure of active (110) crystal planes. The Co₃O₄ nanosheets showed the best performance due to their larger surface area and ability to provide a better pathway for charge transfer, and are promising electrode materials for application in practical supercapacitors.