Fabrication of Titanium Aluminides via Powder-Cored Wire Arc Additive Manufacturing: Microstructural and Mechanical Characterization

Herein, an innovative powder-cored wire arc additive manufacturing (PC-WAAM) process is proposed to fabricate γ-TiAl thin-walled intermetallic alloy. The metallography, phase composition, and mechanical properties at different thin-wall locations are characterized. The results show that the alternatively distributed layer-like microstructure composed of α₂ (Ti₃Al) and γ (TiAl) phases is obtained along the building direction. The content of α₂ phase exhibits the tendency of decreasing from the bottom to top region. This unique microstructure characteristic is closely related to the typical thermal cycling history during deposition. Moreover, the tensile strength and microhardness of the top region are lower than the middle and bottom region. In general, the current PC-WAAM technique shows promising capability of fabricating γ-TiAl intermetallic alloy with low cost. This work becomes a valuable reference for understanding the evolution mechanism of microstructure and paves the way for the flexible and customized additive manufacturing of γ-TiAl alloy.     

Computational Parametric Analysis of Cellular Solids with the Miura-Ori Metamaterial Geometry under Quasistatic Compressive Loads

Origami-based metamaterials have widespread application prospects in various industries including aerospace, automotive, flexible electronics, and civil engineering structures. Among the wide range of origami patterns, the fourfold tessellation known as Miura-ori is of particular attraction to engineers and designers. More specifically, researchers have proposed different 3D structures and metamaterials based on the geometric characteristics of this classic origami pattern. Herein, a computational modeling approach for the design and evaluation of 3D cellular solids with the Miura-ori metamaterial geometry which can be of zero or nonzero thicknesses is presented. To this end, first, a range of design alternatives generated based on a numerical parametric model is designed. Next, their mechanical properties and failure behavior under quasistatic axial compressive loads along three perpendicular directions are analyzed. Then, the effects of various geometric parameters on their energy absorption behavior under compression in the most appropriate direction are investigated. The findings of this study provide a basis for future experimental investigations and the potential application of such cellular solids for energy-absorbing purposes.     

Internet of Cultural Things: Current Research,Challenges and Opportunities

Driven by the visions of the Internet of Things (IoT), Artificial Intelligence (AI), and 5G communications, the Internet of Cultural Things (IoCT) realize the comprehensive interconnection among cultural products, cultural services, cultural resources, and cultural platforms, bringing individuals with richer humanistic experience, increasing economic benefits for the cultural sector, and promoting the development of cultural heritage protection and education. At present, IoCT has received widespread attention in both industry and academia. To explore new research opportunities and assist users in constructing suitable IoCT systems for specific applications, this survey provides a comprehensive overview of the IoCT components and key technologies. A comparison study of representative IoCT systems is presented according to their applicability. A general platform architecture of IoCT is proposed to link cultural objects with the internet and human. Finally, open issues for research challenges and future opportunities of IoCT are also studied in this paper.     

带DDE通讯功能的控制仪表

带DDE通讯功能的控制仪表可以在WINDOWS环境下利用商用软件进行各种数据的读取和仪表参数的修改．从而构成具有较高性能价格比的方便易用的集散控制系统．     

Sirofil纱线的强伸及耐磨性分析

选择不同捻系数的同种Ｓｉｒｏｆｉｌ纱作试样,通过强伸试验,得出了在临界捻系数时纱线具有最高拉伸强力的结果。耐磨性试验初步表明了Ｓｉｒｏｆｉｌ纱的耐磨性优于全毛股线和全毛单纱     

Modified white-light Mach-Zehnder interferometer for direct group-delay measurements

A modified white-light Mach-Zehnder interferometer based on a single beam splitter is described for direct group-delay measurements. The arms of the interferometer are folded in such a manner that a single beam splitter can be used to split the incoming beam and combine the outgoing beams. This method offers a twofold advantage: The measuring range of the interferometer is twice as large as that of the Michelson interferometer, and the systematic error that is associated with the beam splitter is minimized because of the configuration. We report the results of measurements on various optical components performed in the 555-630-nm spectral region and propose a scheme for the processing of the experimental data. We present a comparison of the data analyzed by the proposed processing scheme along with the theoretical calculations.     

Study of the diffusion of Al–Li alloys subjected to an electric field

An experimental investigation of the homogenization treatment of 2091 Al–Li alloy in the presence of an electric field, has revealed the phenomena of reduced volume fraction, small size, spherical shape and random distribution of second-phase particles, which bring about an increase in ductility. The results show that the dissolution of second-phase particles is promoted by means of the vacancy mechanism, because of the larger diffusion coefficient of solute atoms than the vacancy–solute complexes at the beginning of the homogenization treatment. By increasing the homogenization time and applying an electric field, the diffusion coefficient of vacancy-solute complexes is raised, whereas that of solute atoms is reduced, because of the decreased potential energy of the second phase at grain boundaries. Therefore, the non-equilibrium segregation of magnesium and copper elements is generated near the surface of the ingot by a complex mechanism. An experimental study of the solution treatment under an electric field, revealed that the lithium non-equilibrium segregation is induced at grain boundaries responsible for the precipitates. © 1998 Chapman & Hall     

ERWIN: an E-region wind interferometer

A field-widened Michelson interferometer designed to measure upper atmospheric winds at three altitudes near the mesopause by using airglow emissions from O(1)S, OH, and O(2) is described. A very large path difference (11 cm) is used to suppress the fringes from the hot F-region emission of O(1)S and to facilitate accurate measurements. Field widening and thermal compensation are achieved over the large spectral range (557.7-866.0 nm) by the use of three types of glass in the interferometer's arms. The instrument was installed at Resolute Bay, Canada (74.3 N, 94.5 W), in November 1992 and has been operated remotely from Toronto for four winter seasons. Some examples of data are shown to illustrate ERWIN's performance.     

Experimental study on fitness of one-piece casting osseointegrated implant frameworks with relation to fixture abutment positions

An experiment on fitness of one-piece casting osseointegrated implant frameworks was performed among three fixture abument positions where other conditions were controlled. The result revealed that there was statistically significant differences in dimensional change among the three fixture abument positions. In terms of the relation between abument position and fitness, the more backward the abument position was, the worse the osseointegrated framework fitness was. The frameworks showed deformations in "arch form" and "warp" in three dimensions.     

矿用变频器功率器件选型及其驱动保护设计

分析了煤矿井下设备对变频器功率器件IGBT的需求和在IGBT选型时需要考虑的电气参数,介绍了基于2SD315模块的IGBT驱动保护电路的设计。实际应用表明,采用文中介绍的方法选用的IGBT和设计的驱动保护电路后,变频器运行稳定,IGBT驱动有效,保护完善。