Cavitation Behavior during Superplastic Deformation of AZ31 Magnesium Alloy

Superplasticity of AZ31 Mg alloy at the temperature range of 250～450℃ and stain rate range of 0.7x10-3～ 1.4x 10-1 s-1 was examined through uniaxial tensile test. Optical microscopy (OM) and scanning electron microscopy (SEM) were employed to investigate the morphology of cavities and surface relief near fracture surface, respectively.It is shown that AZ31 Mg alloy starts to exhibit superplasticity from 300℃. The maximum elongation of 362.5%was obtained at 400℃ and strain rate of 0.7×10-3 s-1. There exist many O-shaped cavities and filaments at the boundaries near fracture surface. The fracture of filaments results in intergranular cavity and the model for the formation of intergranular cavities is proposed. The growth of cavities is plasticity-controlled and the serrated boundaries of intergranular cavities agree with the results of surface relieves.     

嵌金丝凸条织物的生产实践

探讨嵌金丝凸条织物生产中的关键技术.选择纯棉纱(嵌织金丝)作经纱,纯棉纱和棉氨包芯纱作纬纱,按照一定的排花顺序设计了嵌金丝凸条织物.整经工序采用"大张力,中车速,匀卷绕"的工艺原则;浆纱工序要安装一个金丝特制筒子架,并控制好金丝退绕张力;穿综工序采用人工穿综,并要加强操作管理,严防穿错.通过采取以上措施,可保证织机效率稳定在85%以上,下机一等品率达到88.7%.     

棉与金属丝交织小提花色织物的开发

为使防电磁波纺织面料具有良好的外观效果,应用色纱及金属丝采用小提花织物组织设计方法开发了棉与金属丝交织小提花色织物,将74.8 dtex金属丝与C 14.8 tex并捻后作为纬纱间隔织入,使织物具有防电磁波功能。整经工序严格控制整经张力差异,保证花经与地经张力、排列、卷绕三均匀;浆纱工序采用高浓低粘浆液进行上浆,以改善色纱的吸浆性能;织造工序剑杆织机采用稍大的上机张力和较早的综平时间,车速为195 r/min。测试结果表明:所开发的织物强力、透气性等指标均达到色织布国家行业标准,并具有较好的防辐射功能。     

热镀锌卷尾部塔形缺陷的分析和预防措施

通过对热镀锌板卷取过程中产生卷尾塔形的分析,得出卷取张力不匹配和套筒与芯轴打滑是造成卷尾塔形缺陷的主要原因。通过改造张力卷取机的芯轴,采用恒张力控制和恒扭距控制相结合的卷取模式,优化卷取张力,有效地避免镀锌板卷尾塔形的产生。     

Robocasting of alumina hollow filament lattice structures

Robotic controlled deposition (robocasting) of an aqueous colloidal α-Al₂O₃ gel for manufacturing of cellular ceramics with periodical lattice structure was investigated. The colloidal gel was loaded with 50 vol% α-Al₂O₃ and exhibits shear-thinning behavior, a shear modulus of 288 kPa and a yield-stress of ～700 Pa. Tubular filaments of circular and rectangular cross section having an outer diameter of 1.5 mm and a capillary diameter of 0.75 mm were deposited in an oil bath to fabricate lattice truss structures with free spanning filaments. After freeze drying the robocast grids were sintered in air at 1550 °C. X-ray μ-CT revealed continuity of the tubular filaments for long distances (～650 mm). Critical conditions to avoid capillary collapse were discussed by considering bulging stress and pressure distribution within the hollow filament. At short filament length oil infiltration into the capillary driven by capillary suction supports the tubular filament whereas oil flow driven by movement of the tool nozzle causes pressure difference to increase linearly with increasing filament length.     

椭圆封头电渣焊接接时最佳焊接位置的计算机辅助设计

在分析了焊接过程的基础上,介绍了最佳焊接位置和焊接过程中溶池变化的计算方法和计算步骤,建立了相应的数学模型,并编写了简单的计算机应用程序。     

DRYING BEHAVIOR OF ACETATE FILAMENT IN DRY SPINNING

Drying behavior of acetate filament in dry spinning is investigated, including the elongational deformation of polymer solution thread in the early stage of drying. Variations of diameter, velocity, temperature, solvent concentration profile in the thread and tension distribution along the threadline in the spinning column, are calculated for spinning conditions encountered commercially by means of the equations of simultaneous momentum, heat and mass transfer between the thread and hot air flow in the spinning column. Concentration and temperature dependencies of the mutual diffusion coefficient from desorption experiment are correlated by the free volume theory. The elongational viscosity is estimated from the shear viscosity data using Krevelen theory. Residual acetone concentratio in the thread and tension at the exit of the spinning column are compared between the calculated results and the experimental data by a commercial apparatus; satisfactory agreement is found. Rapid decreases of temperature and surface concentration of the dope thread after extrusion confine the elongational deformation within several centimeters below the spinnerette. Initial elongational rate and die swell ratio are related to the winding velocity and tension at the exit of the spinning column. The tension is determined mainly by initial viscous force and air drag.     

As-deformed filament's density and transport currents of MgB2/Ti/Glidcop wire

Filamentary MgB₂/Ti/Glidcop wire has been manufactured by in situ process using hydrostatic extrusion, cold drawing and finally subjected to high pressure and standard densifications. Filament density of as-deformed wires was evaluated by micro-hardness measurements and related to applied deformation. It was found that filament's density and uniformity in as-deformed wire have a strong effect on the critical current density (J_c) of annealed samples. The highest J_c was measured for the filaments densified by cold isostatic pressing with 2 GPa and also for rotary swaged ones showing the best uniformity. Presented results showed the importance of filament density and homogeneity and also demonstrate suitability of hydrostatic extrusion for uniform long-length filamentary MgB₂ wires production.     

Analysis of multi-layered thick-walled filament-wound hydrogen storage vessels

In this paper a three-dimensional elasticity analysis on multi-layered thick-walled filament-wound hydrogen storage vessels is outlined. An exact solution to stresses of the metal liner and each anisotropic layer is presented, based on Lekhnitskii's theory and the generalized plane strain assumption. The governing equation for determining the radial displacement of the hydrogen vessel is derived and the stresses in the cylindrical coordinates are then obtained. The matrix equation that determines the integration coefficients of the governing equation is formulated by considering the boundary and interface conditions. The normal and in-plane shear stresses and the twisting rate of the vessel are calculated for various thicknesses of the aluminum liner; the results are then compared to those presented by Xia et al. It is shown that the addition of the liner significantly reduces the stress magnitude of the hydrogen vessel; this stress magnitude decreases as the liner thickness increases. The results also revealed that the twisting effect is reduced by increasing the liner thickness. The ratio of hoop-to-axial stress is no longer a constant through the vessel wall and varies within the wall thickness. In addition, various combinations of anisotropic composites and isotropic liner materials are here examined to pinpoint preferable material combinations that lead to a lower equivalent stress level of the liner and higher strength reserve of the composite laminate.     

国产PLC在64工位VFD专用自动化排气台的应用

介绍了以国产可编程逻辑控制器 (PLC)在 6 4工位真空荧光显示屏 (VFD)专用自动化排气台的应用 ,并成为系统的控制核心。全面地阐述了排气台的系统结构、工艺过程、工作原理及程序的实现 ;表明了在控制较简单的系统中 ,国产PLC有一定的实用价值。