Effect of fusion welding processes on tensile properties of armor grade,high thickness,non-heat treatable aluminium alloy joints

AA5059 is one of the high strength armor grade aluminium alloy that finds its applications in the military vehicles due to the higher resistance against the armor piercing (AP) threats. This study aimed at finding the best suitable process among the fusion welding processes such as gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) by evaluating the tensile properties of AA5059 aluminium alloy joints. The fracture path was identified by mapping the low hardness distribution profile (LHDP) across the weld cross section under tensile loading. Optical and scanning electron microscopies were used to characterize the microstructural features of the welded joints at various zones. It is evident from the results that GTAW joints showed superior tensile properties compared to GMAW joints and this is primarily owing to the presence of finer grains in the weld metal zone (WMZ) and narrow heat-affected zone (HAZ). The lower heat input associated with the GTAW process effectively reduced the size of the WMZ and HAZ compared to GMAW process. Lower heat input of GTAW process results in faster cooling rate which hinders the grain growth and reduces the evaporation of magnesium in weld metal compared to GMAW joints. The fracture surface of GTAW joint consists of more dimples than GMAW joints which is an indication that the GTAW joint possess improved ductility than GMAW joint.     

电磁弹射过程中涡流引入阻力的分析

永磁直线电机能够满足电磁弹射系统短距内高加速与快制动的应用要求,但是永磁直线电机的快速运动可能引入明显的涡流效应,在电机加速度段,涡流效应引入涡流阻力,削弱了系统的弹射能力,另一方面,在电机的制动段,涡流效应引入的阻力可以帮助系统实现快速制动.针对电磁弹射系统所采用的定子开槽、集中绕组、动磁式永磁直线电机,仿真分析了动...     

焊接切割与火灾

焊割火灾事故呈上升趋势。文章分析了焊割火灾爆炸危险性,并提出了预防措施。     

Effect of energy content of the nitraminic plastic bonded explosives on their performance and sensitivity characteristics

Information about the forty nine nitraminic plastic bonded explosives (PBXs) and different nitramines were collected. Fillers of these PBXs are nitramines 1,3,5-trinitro-1,3,5-triazinane (RDX) and β-1,3,5,7-tetranitro-1,3,5-tetrazocane (β-HMX), cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (bicyclo-HMX, BCHMX) and ε-2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-HNIW, CL-20) which are bonded by polyfluoro-elastomers, polydimethyl-siloxane, poly-glycidyl azide, polyisobutylene, polystyrene-butadiene, poly-acrylonitrile-butadiene and hydroxyl-terminated polybutadiene in addition to a melt cast compositions based on 2,4,6-trinitrotoluene. For thirty two of these PBXs the relationships are specified and analyzed between heats of their combustion and relative explosive strengths; by means of these relationships it might be possible to estimate, which groupings in the macromolecule of binder could be liable to their primary fission in the PBXs initiation. Similarly, for forty two of these explosives, the relationships are described and analyzed between their enthalpies of formation and impact sensitivities; here is especially attention paid to PBXs filled by BCHMX. Specific rate constants from Vacuum Stability Test (VST) of four nitramines and twenty PBXs are introduced into relationships with their enthalpies of formation. Regarding to all the mentioned cases, increasing of energy content of the studied explosives leads to increase of the relative explosive strength or initiation reactivity, respectively. Exception with the opposite trend, the outputs of VST are for BCHMX, where in PBXs are matrices with the esteric plasticizers or the energetic poly-glycidyl azide. Admixture of RDX or HMX, respectively, into the BCHX PBXs gives ternary PBXs whose thermal stability, in the sense of applied VST, is higher comparing to the original binary explosives.     

功能化离子液体的合成表征及其作为润滑剂的性质

通过两步法合成了含酯基官能团的咪唑类离子液体1-乙酸乙酯基-3-甲基咪唑四氟硼酸盐，用核磁共振、红外光谱、元素分析对其进行了结构表征，证明了该合成方法的可靠性；对功能化离子液体的基本物化性质、熔点、热稳定性及其作为润滑剂的粘温性、蒸发损失、金属腐蚀性等进行了全面研究，并选择了含有相同烷基的1-丁基-3-甲基咪唑四氟硼酸盐传统离子液体进行对比，发现官能团的引入，使传统烷基咪唑类离子液体展现出不同的特性，同时发现两种离子液体均对金属表面有较强的腐蚀作用，为进一步开展功能化离子液体的摩擦学研究打下了基础。     

适用于金属物体识别的L形无芯RFID标签设计

设计了一种L形无芯射频识别标签,该标签包含6个不同尺寸的L形散射单元,利用其交叉极化方向上的反向散射场进行识别。标签基于频域特征进行编码,每个标签可携带6 bit信息。使用CST仿真软件对所设计L形无芯RFID标签进行仿真,分析了L形散射单元的尺寸变化时对标签谐振特性的影响。此外,还仿真了标签的接地板尺寸增加后的情况,证明该标签可适用于金属物体的识别或金属背景下的物体识别。     

Effect of welding processes and consumables on fatigue crack growth behaviour of armour grade quenched and tempered steel joints

Quenched and Tempered (Q&T) steels are widely used in the construction of military vehicles due to its high strength to weight ratio and high hardness. These steels are prone to hydrogen induced cracking (HIC) in the heat affected zone (HAZ) after welding. The use of austenitic stainless steel (ASS) consumables to weld the above steel was the only available remedy because of higher solubility for hydrogen in austenitic phase. The use of stainless steel consumables for a non-stainless steel base metal is not economical. Hence, alternate consumables for welding Q&T steels and their vulnerability to HIC need to be explored. Recent studies proved that low hydrogen ferritic steel (LHF) consumables can be used to weld Q&T steels, which can give very low hydrogen levels in the weld deposits. The use of ASS and LHF consumables will lead to distinct microstructures in their respective welds. This microstructural heterogeneity will have a drastic influence in the fatigue crack growth resistance of armour grade Q&T steel welds. Hence, in this investigation an attempt has been made to study the influence of welding consumables and welding processes on fatigue crack growth behaviour of armour grade Q&T Steel joints. Shielded metal arc welding (SMAW) and Flux cored arc welding (FCAW) were used for fabrication of joints using ASS and LHF consumables. The joints fabricated by SMAW process using LHF consumable exhibited superior fatigue crack growth resistance than all other joints.     

A numerical study on the disturbance of explosive reactive armors to jet penetration

The disturbance of flat and V-shaped sandwich reactive armor configurations to shaped-charge jet is studied by a numerical approach. The disturbing and cutting effects of the two reactive armor configurations to the jet are successfully captured. The predicted disturbance characteristics and patterns are in fairly good agreement with the X-ray photographic observations. The residual depth of penetration into a semi-infinitive homogeneous steel target behind the reactive armor is computed for a series of jet/armor parameters. For the flat configuration, it is demonstrated that the residual penetration depth is not significantly reduced for a normal impact while it is reduced up to 75% for an oblique impact. In comparison, the V-shaped configuration reduces the penetration depth of the jet to 90%, and it is observed that the penetration depth is not sensitive to the V-shaped angle.     

NICALON SiC/Al 预制丝热膨胀特性研究

本文研究了NICALON SiC束丝纤维增强铝预制丝在15～400℃温度区间内的热膨胀特性。研究表明预制丝两次热循环后得到的膨胀曲线不一致,该曲线在15～400℃范围的平均热膨胀系数分别为3.2×10~(-6)℃~(-1)、4.1×10~(-6)℃~(-1)。本文对预制丝的热膨胀行为进行了理论分析和探讨,计算值和实验值较为符合。     

飞行器曲线显示中的数据处理方法及实现

主要内容分为两个部分:处理方法和方法的应用。处理方法着重介绍了远程火箭弹道学和地图学的基本知识,内容包括:各种坐标之间的转换、被动段飞行轨迹的计算、常微分方程的数值解法。方法的应用以上述算法为核心,用实例说明了其使用情况,内容包括:v-t、x-y曲线中的坐标转换、v-t曲线中被动段弹道的平滑处理、箭下点曲线中的坐标转换和外推估算。