Effects of Sm addition on microstructure and mechanical properties of a Mg-10Y alloy简

To further increase the mechanical properties, 0.5wt.% Sm was introduced to a Mg-10Y alloy in this study. The effects of Sm addition on the microstructures and mechanical properties of the Mg-10Y alloy, especially the aged Mg-10Y alloy, were investigated. The microstructure observation and tensile tests were performed by using an optical microscopy, a scanning electron microscopy and a universal material testing machine, respectively. The phase analysis was performed using X-ray diffractometer. The results show that the 0.5wt.% Sm addition can not only promote the formation of fine and dispersed Mg24Y5 phases, but also improve their morphology and distribution; it also increases the thermal stability of Mg24Y5 phases. Sm addition is seen to increase the ultimate tensile strength of Mg-10Y alloy at elevated temperatures(200, 250, 300 and 350 ℃), while decrease the elongation. But the elongation is still up to 7.5% even at 350 ℃. In the range of 250 ℃ to 300℃, the ultimate tensile strength of the alloy reaches its maximum(with a range average of 235 MPa) and is not sensitive to the temperature change, which is very useful to the application of heat-resistant magnesium alloys. Even at 350 ℃, the ultimate tensile strength of Mg-10Y-0.5Sm is still up to 155 MPa. Considering both of the ultimate tensile strength and elongation, the maximum application temperature of the Mg-10Y-0.5Sm alloy can be up to 300 ℃. The strengthening mechanisms of Mg-10Y-0.5Sm alloy are mainly attributed to dispersion strengthening of Mg24Y5 phase particles with a certain solubility of Sm and grain refinement strengthening of α-Mg matrix.     

柔性机械臂振动控制研究

总结并分析了柔性机械臂动力学建模和振动控制的最新进展,建立了柔性机械臂振动控制实验系统,分别采用ＰＩＤ控制策略和线性二次型最优控制（ＬＱＲ）策略对柔性机械臂的振动控制进行了实验研究,并提出ＰＩＤ了控制与闭环反馈控制相结合的有效性。实验结果表明闭环应变反馈控制比单纯的的ＰＩＤ控制更为有效。     

大柔度机械臂动力学特性研究

建立了一套柔性机械臂振动控制实验系统,该系统主要由直流伺服电机、柔性机械臂结构和支应组成。伺服控制系统由位置反馈环、速度反馈环和电流反馈环三环组成、采用光电编码器作为检测元件。对柔性臂的动力学性能进行了测试研究。建立了计及变形约束的柔性臂动力学模型,仿真与实验结果基本吻合。     

使用变频器应注意的问题

变频器在使用时,由于对变频器的选型及使用不当,往往会引起变频器不能正常运行,甚至引发设备故障,导致生产中断。该文以富士FRNPT/G7变频器为例,讲述变频器使用时应注意的几点问题。     

In vitro hydrolytic degradation of poly(para-dioxanone)/poly(d,l-lactide) blends

A series of biodegradable polymers were prepared by solution coprecipitation of poly(para-dioxanone) (PPDO) and poly(d,l-lactide) (PDLLA) in various blend ratios. Samples were compression molded into bars using a platen vulcanizing press. The in vitro hydrolytic degradation of PPDO/PDLLA blends was studied by examining the changes in weight, water absorption, tensile strength, breaking elongation, thermal properties, and morphology of the blends in phosphate buffered saline (PBS; pH 7.44) at 37 °C for 8 weeks. During the hydrolytic degradation, the weight loss and water absorption increased significantly for all samples, whereas the hydrolysis rate varied with the blend composition. The weight loss of PPDO/PDLLA 80/20, which showed the smallest degradation rate, was lower than that of pure PPDO for almost all of the hydrolytic degradation period. The results showed that the blend composition played an important role in determining the degradation behaviors of blends.     

Novel DS／SSMA Systems with Trellis—Coded Sequence and Phase Modulation

ＮｏｖｅｌＤＳ／ＳＳＭＡＳｙｓｔｅｍｓｗｉｔｈＴｒｅｌｌｉｓ－ＣｏｄｅｄＳｅｑｕｅｎｃｅａｎｄＰｈａｓｅＭｏｄｕｌａｔｉｏｎＺｈａｎｇＱｉｎｇ；ＢｉＧｕａｎｇｇｕｏ（ＳｏｕｔｈｅａｓｔＵｎｉｖｅｒｓｉｔｙ，Ｎａｎｊｉｎｇ２１００１８）Ａｂｓｔｒａｃｔ...     

ISA－1型中、低压变电站成套微机保护的典型配置简介

介绍了ISA-1型变电站成套微机保护针对中低压变电站总结出的一整套保护典型配置方案， 包括主要电气元件的保护配置，如主变、馈线、电容器和电动机等，以及自动控制装置和辅 助保护，如备用电源自投等。本文提出的配置方案已广泛应用于工程设计。     

SEMANTIC NETWORK PRESENTATION OF MECHANICAL MOTION SCHEME AND ITS MECHANISM TYPES SELECTION METHOD

The Presentation method of the mechanical motion scheme must support the whole processof conceptual design. To meet the requirement, a semantic network method is selected to representprocess level, action level, mechanism level and relationships among them. Computer aided motioncycle chart exploration can be realized by the representation and revision of time coordinaton ofmechanism actions and their effect on the design scheme. The uncertain reasoning technology based onsemantic network is applied in the mechanism types selection of the needle driving mechanism ofindustrial sewing mechanism, and the application indicated it is correct, useful and advance.     

MODELING AND COMPENSATION TECHNIQUE FOR THE GEOMETRIC ERRORS OF FIVE－AXIS CNC MACHINE TOOLS

One of the important trends in precision machining is the development of real-time error compensation technique. The error compensation for multi-axis CNC machine tools is very difficult and attractive. The modeling for the geometric error of five-axis CNC machine tools based on multi-body systems is proposed. And the key technique of the compensation-identifying geometric error parameters-is developed. The simulation of cutting workpiece to verify the modeling based on the multi-body systems is also considered.