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981.
This paper studies the friction stir spot welding of AA2024-T3/AA7075-T6 Al alloys in the ambient and underwater environments by clarifying the nugget features,microstructure,fracture and mechanical properties of the joints.The results show that the water-cooling medium exhibits a significant heat absorption capacity in the AA2024-T3/AA7075-T6 welded joint.Nugget features such as stir zone width,circular imprints,average grain sizes,and angular inter-material hooking are reduced by the water-cooling effect in the joints.Narrower whitish(intercalated structures)bands are formed in the under-water joints while Mg2Si and Al2CuMg precipitates are formed in the ambient and the underwater welded joints respectively.An increase in tool rotational speed(600-1400 rpm)and plunge depth(0.1-0.5 mm)increases the tensile-shear force of the welded AA2024-T3/AA7075-T6 joints in both the ambient and underwater environments.The maximum tensile-shear forces of 5900 N and 6700 N were obtained in the ambient and the underwater welds respectively. 相似文献
982.
This paper presents a comprehensive review of the research studies on direct energy system effect on aircraft composite structures to develop a good understanding of state-of-the-art research and devel-opment in this area. The review begins with the application of composite materials in the aircraft structures and highlights their particular areas of application and limitations. An overview of directed energy system is given. Some of the commonly used systems in this category are discussed and the working principles of laser energy systems are described. The experimental and numerical studies re-ported regarding the aircraft composite structures subject to the effect of directed energy systems, especially the laser systems are reviewed in detail. In particularly, the general effects of laser systems and the relevant damage mechanisms against the composite structures are reported. The review draws attention to the recent research and findings in this field and is expected to guide engineers/researchers in future theoretical, numerical, and experimental studies. 相似文献
983.
The simulation of the artillery interior and intermediate ballistics problem is performed to investigate the influence of a gas dynamics device, muzzle brake, on the muzzle hazard phenomena, such as flash and blast waves. The correlation of the chemical reactions with the characteristics of the muzzle flow field is analyzed by the simulation for a further understanding of the secondary combustion phenom-enon of the muzzle flow. The novel structure of muzzle flow caused by the muzzle brake is presented by the simultaneous solution of the interior ballistics model and multi-species Navier-Stokes equations in order to analyze the influence of the muzzle brake structure on the chemical reactions. The secondary combustion of the muzzle flow due to the oxygen-supplement chemical reactions is obtained by the chemical reaction kinetic model. The interaction of the blast waves released from the muzzle brake is illustrated in detail and the mechanism of the formation of muzzle flash is analyzed. This research provides a reference for the studies on the suppression of the muzzle flash. 相似文献
984.
Yue-ting Wang Xiao-ting Zhang Jian-bing Xu Yun Shen Cheng-ai Wang Fu-wei Li Ze-hua Zhang Jian Chen Ying-hua Ye Rui-qi Shen 《防务技术》2021,17(4):1307-1312
In this study, Al-CuO nanocomposites were fabricated by sol-gel method. As a contrast, the thermite was prepared by physical mixing at the equivalence ratio of 0.5, 1, 2, respectively. The intermediates and samples as prepared were characterized by SEM and XRD. The exothermic properties of the two samples prepared at different equivalence ratios were tested and the reaction products were characterized by XRD. The SEM results show that the sample prepared by the sol-gel method demonstrates a micron-sized agglomerated sphere formed by a mutual wrapping of Al NPs and CuO NPs, and the particles are evenly distributed in the agglomerate. In addition, when the content of Al powder is seriously insufficient, the heat release of the sample prepared by physical mixing is 1.6 times that of by sol-gel method. With the increase of Al powder content, the exothermic properties of Al/CuO NPs prepared by sol-gel method began to increase significantly compared with physical mixing and the difference is 1.5 times when the equivalence ratio increases to 2. It can be concluded that the reason for this result may be attributed to the different mass transfer modes of components due to the different morphologies of samples. 相似文献
985.
物联网容易遭受多类拒绝服务攻击,其中黑洞攻击是最严重的攻击之一.为此,提出基于投票法的黑洞攻击检测算法(Voting Method-based Blackhole Attack Detection,VMBAD).通过VMBAD算法检测RPL协议上的黑洞攻击.先通过过滤器构建嫌疑节点,再验证嫌疑节点的行为,各节点作出自己的决策意见,并传输到边界路由(Bor-der Router,BR).接收后,BR利用投票机制融合各节点的决策意见,进行最终的决策,进而判断节点是否为黑洞攻击节点.一旦认定为黑洞攻击,就将黑洞攻击节点与网络隔离,使其不参与RPL路由.仿真结果表明,VMBAD算法能够有效地检测黑洞攻击节点,并且通过排除攻击节点,提高了数据包传递率. 相似文献
986.
987.
988.
文中简单介绍了自由电子激光粒子模拟方法,用■维完全相对论性电磁模程序模拟了相对论电子束通过回旋磁场产生电磁辐射的过程,并作了理论解释;研究了纵向引导磁场对能量转换效率的影响。 相似文献
989.
In this article, a model for a repairable consecutive‐k‐out‐of‐n: F system with Markov dependence is studied. A binary vector is used to represent the system state. The failure rate of a component in the system depends on the state of the preceding component. The failure risk of a system state is then introduced. On the basis of the failure risk, a priority repair rule is adopted. Then the transition density matrix can be determined, and the analysis of the system reliability can be conducted accordingly. One example each of a linear and a circular system is then studied in detail to explain the model and methodology developed in this paper. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 18–39, 2000 相似文献
990.
对模糊控制进行了介绍 ,构造出一种模糊控制器 ,将其编成微机程序 ,使其完成模糊控制功能 .研究它在舰用燃气轮机控制中的应用 .进行了多次燃气轮机模拟试车 ,当对燃气轮机控制系统加入扭矩和振动等控制信号时 ,燃气轮机的稳态和加速过程都获得了良好的控制品质 ,为舰用燃气轮机的控制探索了一种新方法 相似文献