Sensitivity analysis of Johnson-Cook material parameters on adiabatic shear in different directions

ABSTRACT

This study investigates the effects of strain, strain rates, and forming directions (RD-rolling direction, TD-transverse direction, and ND-normal direction) on adiabatic shear, via dynamic impact compression tests using the Split Hopkinson Pressure Bar (SHPB) apparatus. A modified Johnson-Cook (J-C) constitutive model is proposed, which used to analyse the influence of the constitutive parameters on the sensitivity of adiabatic shear, employing a finite element software. The different sensitivities of adiabatic shear under different directions are explained by combining microscopic analysis and results from mechanical responses. The results show that the sensitivity of adiabatic shear can be related to the time of stress collapse in the following trend: ND?>?TD?>?RD; the sensitivities of these constitutive parameters on adiabatic shear are calculated and compared.     

含钒废弃物中钒的回收研究现状及展望

金属钒具备一系列优越性质,在许多领域有着广泛的应用。综述了从含钒钢渣、提钒尾渣、失活催化剂以及钒电池失效电解液等含钒废弃物中回收钒的方法,主要阐述了各种方法的原理、优缺点及发展趋势,介绍了回收钒的新工艺并指出提钒工艺的未来发展方向。     

安徽省凤阳县焦台陈含金石墨矿物质组份研究

本文通过详细的镜下光、薄片鉴定、电子探针分析、单矿物分析、物相分析等手段查明了安徽省凤阳县焦台陈含金石墨矿中矿石的化学组成、矿石中的主要矿物,对其特征做了详尽的描述,并对主要矿物石墨的粒级分布及其镶嵌特征做了认真分析,阐明了影响石墨回收的矿物学因素。     

不同改良措施对排土场土壤微形态影响的试验研究

以铁矿排土场废石土为研究对象,自制模型试验装置,设计4种基质改良方法,开展SEM检测实验,并应用IPP软件对SEM照片进行定量化分析,研究在不同改良措施下对铁矿排土场土壤微结构的影响。结果表明：单施3%有机肥土壤孔隙度为16%,与对照组排土场原矿土相比增加了60%。复合施用3%有机肥、掺拌30%的黄土的处理孔隙度达到最大33%。单施3%有机肥、5%有机肥对土壤大团聚体含量皆有显著的促进作用,复合施有机肥、掺拌黄土的处理与单施有机肥的处理对比,土壤大团聚体含量增加并不显著。各改良措施的MWD与FMD均随着土壤中大团聚体的含量增加而增加。     

双层毛细芯对环路热管传热性能的实验分析

环路热管作为一种高效的相变传热装置,其性能与位于蒸发器和储液槽之间的毛细芯结构密切相关。为了更深入研究双层毛细芯对环路热管传热性能的影响,利用不同颗粒直径铜粉制备双层毛细芯,在毛细芯总厚度为5 mm的条件下,通过调整大粒径和小粒径层的相对厚度来改变毛细芯厚度比,对平板型蒸发器环路热管启动和变工况运行进行实验测试。实验结果表明:在同一工况下,不同厚度比的双层毛细芯启动特性存在显著差异,启动过程中出现小粒径层蒸发效率低引起的温度过冲和环路热管中气液两相流变化导致的温度振荡;同时存在一个较优的双铜层毛细芯厚度比,大粒径(180～280μm)铜层厚度为3 mm可提高蒸发效率,小粒径(56～71μm)铜层厚度为2 mm可提供足够毛细抽吸力保证环路热管稳定运行。搭载该厚度毛细芯的环路热管不仅启动速度快(125 s),而且总热阻和蒸发器壁面温度均最低,最大加热功率达到120 W(21.10 W/cm~2),对应热阻为0.17 K/W。     

Single nanowire assembled by liquid dielectrophoresis for on-chip technologies

ABSTRACT

Study on dynamic tensile properties and atomic chain fabrication of single nanowire, for understanding its dynamic tensile properties and unique physical properties of atomic chain to fabricate atom scale devices, is one of frontier research issues in nano-scale science. However, how to assemble single nanowire on a tensible micro-structure becomes one of the most difficult problems, which severely restricts the development of this research field. In this paper, after the ultrahigh tensible microelectrode chip is fabricated by micro-electromechanical systems technology, hexamethyldisilazane is utilized to improve hydrophobicity of the chip, and then a micro-droplet dielectrophoresis experimental platform and technology is developed to assemble single nanowire on the sensible microelectrode. Experimental results show that accurate and efficient assembly of single Cu nanowire is realized, which contributes greatly to the further research of dynamic tensile properties and atomic chain fabrication. And for guiding the assembly experiments, finite element technology is also utilized to analyze the local micro electro-field around the microelctrodes during dieletrophoresis experiments.