High performance low cost steels with ultrafine grained and multi-phased microstructure

Ultrafine grained ferrite was obtained through tempering cold rolled martensite with an average grain size of 200―400 nm in a low carbon and a microalloyed steel. Thermal and mechanical stability of the two steels was studied. Due to the pinning effect of microalloyed precipitates on the movement of dislocations and grain boundaries, the recrystallization and grain growth rate were retarded, and the thermal stability of ultrafine grained microstructure was improved. The ultrafine grained ferritic steel was ...     

Dynamic response of ultralight all-metallic sandwich panel with 3D tube cellular core to shallow-buried explosives

The underbody of a vehicle system, either military or civil, is typically made of a relatively thin metallic plate, thus vulnerable to mine blast attacks. To improve the blast resistance, a multitude of protective structures have been proposed as attachments to the thin plate. In the present study, a novel ultralight all-metallic sandwich panel with three-dimensional(3D) tube cellular cores mounted to the vehicle underbody was envisioned as such a protective system. A metallic substrate(mimicking vehicle bottom)was placed above the proposed sandwich panel to construct a sandwich-substrate combinative structure. A series of sandwich panels having 3D tube cellular cores were fabricated via argon protected welding and laser welding. Mechanical responses of the combinative structure subjected to the denotation of 6 kg TNT explosives shallow-buried in dry sand were experimentally measured. Full numerical simulations with the method of finite elements(FE) were subsequently carried out to explore the physical mechanisms underlying the observed dynamic performance and quantify the effects of key geometrical parameters and connection conditions of the protective system. The performance of the proposed sandwich panel under shallow-buried explosives was also compared with competing sandwich constructions having equal mass. Finally, a preliminary optimal design of the 3D tube cellular core was carried out.     

Winkler地基上输流管道的临界流速分析

应用Galerkin法和复模态法研究Winkler弹性地基上两端铰支输流管道的临界流速问题。将系统偏微分控制方程进行Galerkin离散后,根据系统静态失稳条件求得临界流速,并利用复模态法对偏微分控制方程直接求解加以验证。结果表明:较低阶Galerkin法只适用于弱刚性地基情况,而当地基刚性比较强时,采用较高阶Galerkin法才能得到精确的结果。研究同时发现,临界流速只与地基刚度及管道轴向预紧力有关,而管道黏弹性系数及质量比等参数不会影响临界流速。     

机械车库载车板防坠落安全机构

在机械式停车设备产品中，平面移动、巷道堆垛、垂直升降停车设备产品因其自动化程度，且通常设置在建筑的地下或高层建筑内，因而近年来引起国内许多城市的热切关注，这些类别的停车设备市场优势日益明显。该类设备通常通过载车板承载车辆，由升降机、堆垛机或搬运小车将载车板搬运到立体车库的相应停车位。     

与时俱进统筹规划--不断完善的广州市无线电监测网

0引言 无线电管理就是频谱资源的有效利用和管理,不仅涉及国家安全、民航通信、广播电视等重要领域,也涉及到“三防”、移动通信等人民群众日常生活的各个方面.随着无线电通信事业高速发展,无线电台站数量大量增加,新技术、新业务、新设备不断涌现,使有限的无线电频谱资源更为紧张.无线电干扰增多,电磁环境趋于恶化,无线电频率与台站的管理和无线电监测工作越来越复杂而繁重,对无线电管理的要求越来越高.为维护好空中电波秩序,充分利用和保护无线电频谱资源,提高科学管理水平,需要不断加强无线电管理技术设施的建设来适应形势的发展.