Accurate measurement of residual stresses of 2219-T87 aluminum alloy friction stir welding joints based on properties of joints

In order to avoid the deviation caused by calculating the residual stresses of welding joints with the release coefficients of the same parent metal, a new method has been proposed based on the properties of weld joints. Since the mechanical property of 2195-F Al alloy is close to that of 2219-T87 Al alloy Friction stir welding (FSW) joint, 2195-F Al alloy is selected as the substitute material of 2219-T87 Al alloy FSW joint in the calibration test. Release coefficients of 2195-F Al alloy and proper correction coefficient are used to calculate the residual stresses of 2219-T87 Al alloy FSW joints. Compared to the results calculated with release coefficients of its parent metal, it has been proved that the proposed correction method is more precise in residual stresses measurement of weld joints. The mathematical analysis and the results of verification tests have shown that this new method is reliable, and it will provide guidance in academic research and engineering application of the spherical indentation strain-gauge method.     

Thermal oxidation of Zr-2.5Nb alloy and its biotribological properties

Zirconium alloys are potential materials for permanent implants due to their suitable mechanical strength, good biocompatibility, and superior corrosion resistance. However, Zr-2.5Nb alloys are greatly limited to the applications of artificial joints due to their poor tribological properties. Thermal oxidation is considered as a good way to improve the tribological properties of Zr-2.5Nb alloys. The effect of temperature on the properties of thermal oxidized Zr-2.5Nb alloys was investigated to understand the growth mechanism of ZrO₂ coating. In addition, the surface hardness of the thermal oxidized Zr-2.5Nb alloys was examined. Finally, the tribological properties of the thermal oxidized Zr-2.5Nb alloys were investigated to evaluate the potential application in artificial hip joints. The results showed that ZrO₂ coating was successfully synthesized on the surface of Zr-2.5Nb alloys, and the temperature has significantly effects on the thickness of the ZrO₂ coatings. It also found that thermal oxidation could significantly improve the surface hardness and wear resistance of Zr-2.5Nb alloys.     

Post-processor development for a turning and milling composite machine tool

The accomplishment of a turning and five-axis milling in only one setup is extremely useful and is possible on a turning and milling composite machine tool. In this work, we present a control algorithm and develop a post-processor for this machine, which has six linear and three rotary axes. To calculate a generalized kinematics model, coordinate systems are established by analyzing the basic kinematic chain relation of the turning and milling composite machine tool. The two vectors, which control the motions of the cutter contact workpiece, are simultaneously transformed to provide the algorithms of the rotary angles and motion coordinate. A special post-processor written in JAVA language is developed according to the proposed algorithm. To evaluate the effectiveness and accuracy of the developed post-processor, a specimen (blade) is used in the cutting simulation and real machining experiment. Experimental results showed the effectiveness and accuracy of the proposed algorithm. Furthermore, Compatibility is improved by adding new functions such as change of target machine, cutter location data change, workpiece origin offset, and cutting feed rate control.     

总变电站6kV系统备用电源自动投入装置误动作事故案例分析及整改措施

通过对总变电站6k V系统备用电源自动投入装置误动作进行分析,指出存在的缺陷,提出相应的改进措施,试验及现场运行表明这些措施是可靠有效的。     

Influence of the coupling agent on the mechanical properties of SiCf/poly(phenylene benzobisoxazole) composites

Poly(phenylene benzobisoxazole) (PBO) was first used as matrix to fabricate the two‐dimensional SiC_f/PBO composites by a lamination method. Different amounts of coupling agent were introduced to improve the bonding between silicon carbide (SiC) fibers and the PBO matrix during the fabrication of the SiC_f/PBO composites. The surface structure and composition of the as‐received PBO and PBO treated with the coupling agent were analyzed, and the morphology and flexural strength of the composites were characterized. The Fourier transform infrared analysis indicated that the hydroxyl groups from the coupling agent were successfully introduced to PBO. The flexural strength of the composites increased at first with increasing content of the coupling agent but decreased with excessive addition of the coupling agent. The flexural strength of the composites was improved from 15 to 89 MPa. The test results suggested that the interaction between the SiC fiber and the treated PBO with the coupling agent was intensified. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39805.     

β-胡萝卜素乳液的制备及其稳定性比较

以吐温80和变性淀粉为乳化剂,将β-胡萝卜素制成水溶性乳液,比较两种乳化剂制备乳液的光、热稳定性。结果发现,两种乳液在光照条件下稳定,但对热的稳定性有一定差异,吐温80制备的乳液热稳定性较差。显微照片和乳液粒径分布可知,吐温80乳液较纯胶乳液稳定。     

校企合作化学与材料专业工程创新训练平台的规划与建设

强化工程训练教学环节,是地方本科学校应用技术人才培养模式创新的核心内容。本文从指导思想、原则和目标、具体措施等方面进行阐述和探讨,论述了化学与材料专业工程创新训练平台规划与建设的内容和保证其正常运行的措施。     

发动机均质压缩燃烧单区模拟模型及其应用

介绍一种基于燃料氧化反应动力学计算的单区模型,该模型由一维空间的质量守恒方程、动量守恒方程、能量守恒方程和气体状态方程等气相化学反应动力学控制方程所组成。采用该模型并利用二甲醚氧化的详细化学反应动力学机理,对二甲醚燃料在柴油机上的均质压缩燃烧HCCI进行了模拟计算和试验研究。计算结果与试验结果比较表明,该模型对HCCI燃烧的着火始点预测很好。     

进气系统设计方法探讨

介绍功能主义设计和设计硬点的思想,提出以功能驱动的硬点结构设计方法,并通过此方法对进气系统的结构设计进行分析。着重分析空气滤清器在客车上的布置和进气系统管路的设计,得到相应的设计准则和设计硬点,为进气系统设计提供了思路方法和理论依据。     

Studies on the electrical conductivity of carbon black filled polymers

The conductivity mechanism for a carbon black (CB) filled high-density polyethylene (HDPE) compound was investigated in this work. From the experimental results obtained, it can be seen that the relation between electrical current density (J) and applied voltage across the sample (V) coincides with Simmons's equation (i.e., the electrical resistivity of the compound decreases with the applied voltage, especially at the critical voltage). The minimum electrical resistivity occurs near the glass transition temperature (T_g) of HDPE (198 K). It can be concluded that electron tunneling is an important mechanism and a dominant transport process in the HDPE/CB composite. A new model of carbon black dispersion in the matrix was established, and the resistivity was calculated by using percolation and quantum mechanical theories. © 1996 John Wiley & Sons, Inc.