Effects of jute fibre content on the mechanical and dynamic mechanical properties of the composites in structural applications

Due to notable characteristics, sustainability concept and environmental issues, hybridisation natural with synthetic fibres to fabricate composites have been rapidly gaining market share in different applications (structural, military, aerospace and automotive vehicles). Compression, tension and fatigue tests of various stacking sequences of plain jute/carbon reinforced (PVB) polyvinyl butyral by hot hydraulic press technique were experimentally conducted. Six types of fabricated composites with various constituents (jute, carbon and their hybrids) were fabricated and tested. Notably, fatigue lifetime of hybrids increases with increasing the carbon content relative to the jute fibre content. On the other hand, Jute composites possess high strain compared to pure carbon composite, which gives an overall improvement in mechanical behaviours. Interestingly, H1 hybrid with Carbon/Jute/Carbon sequences offers similar fatigue stiffness behaviour of H3 hybrid with Carbon/Jute/Carbon/Jute sequences when subjected to cyclic loading. Carbon composite (C) exhibited the highest fatigue resistance, whiles jute composite (J) possessed the highest strain and semi brittle trends in both mechanical and fatigue performance. Results concluded that plain jute fibres could partially replace high-cost synthetic carbon fibres to produce more eco-friendly hybrids to be utilised in different composites industries.     

基于灰色理论的鱼雷装载可靠性分析

为解决在鱼雷装载可靠度试验数据较少的情况下进行装载可靠性分析困难的问题,利用灰色系统理论及 GM(1,2)建模的思想,研究了鱼雷装载可靠度和工作可靠度之间的灰色关系,基于灰色系统理论建立了两者之间关系的数学模型.计算实例表明,该方法简单实用,可在鱼雷装载可靠度数据样本量较少的情况下对鱼雷装戢可靠度进行有效预测,为鱼雷装载可靠度的评定提供了理论参考.     

辐射叶加载的短波宽带鞭状天线优化设计

提出一款具有多层辐射叶结构的新型鞭状天线,在10 m鞭状天线体上设置不同的辐射叶层数、半径、长度、分支数、仰角及其分布情况,研究其对天线辐射性能的影响,综合考虑选择一套最合适的辐射叶结构,并为天线进行双加载和宽带匹配网络的算法优化。仿真结果表明,与现有的普通宽带鞭状天线相比,增益和效率得到了普遍提高,在低频段增益最高提高了3 dB,效率最高提高了5%;在高频段增益最高提高了5 dB,效率最高提高了35%,方向图上翘也得到了一定的抑制,为改善现有的宽带鞭状天线提供一种新的结构设计方法。     

Fragment spatial distribution of prismatic casing under internal explosive loading

Non-cylindrical casings filled with explosives have undergone rapid development in warhead design and explosion control. The fragment spatial distribution of prismatic casings is more complex than that of traditional cylindrical casings. In this study, numerical and experimental investigations into the fragment spatial distribution of a prismatic casing were conducted. A new numerical method, which adds the Lagrangian marker points to the Eulerian grid, was proposed to track the multi-material interfaces and material dynamic fractures. Physical quantity mappings between the Lagrangian marker points and Eulerian grid were achieved by their topological relationship. Thereafter, the fragment spatial distributions of the prismatic casing with different fragment sizes, fragment shapes, and casing geometries were obtained using the numerical method. Moreover, fragment spatial distribution experiments were conducted on the prismatic casing with different fragment sizes and shapes, and the experimental data were compared with the numerical results. The effects of the fragment and casing geometry on the fragment spatial distributions were determined by analyzing the numerical results and experimental data. Finally, a formula including the casing geometry parameters was fitted to predict the fragment spatial distribution of the prismatic casing under internal explosive loading.