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101.
A large variety of porous fluorescent glasses were prepared and the concentration of different elements in these glasses was analyzed. The start porous glasses were soaked in a solution containing soluble salts and then heated at 650 ℃ for 3 h to decompose the salts in the pores into oxides. Fluorescent agents, such as UO3, Eu203, were impregnated into the porous glasses to prepare the fluorescent glasses. The results show that soaking is a feasible method to prepare the glass sphere with compositions distinguishable from each other and easy to be located in a complicated background. Six or more components can be impregnated together into one glass sample and the concentration of them can be analyzed accurately. UO3 and Eu203 can be impregnated into porous glass to make the glass strongly fluorescent. Higher concentration of Eu203 produces stronger fluorescence while higher concentration of UO3 reduces the fluorescence intensity because of the concentration quenching effect. 相似文献
102.
The finite element method (FEM) simulation of deep-drawing of steel sheet with nickel coating based on the solid element and dynamic explicit method was reported. Penalty function method was used to treat the contact algorithm. The friction between the punch and coating sheet was based on a Coulomb formulation. The combination of coating and substrate was defined as tied with failure contact. The results of the simulation illustrate that the steel sheet and the nickel coating do not delaminate at the interface. The stress field of the nickel coating is more complicated thala that of the steel substrate. Furthermore, it is found that the punch-nose radius is the most unsubstantial part for the intensity of the entire deep-drawing part and the thinnest part, it is a dangerous zone for the break. At this zone, the thickness thinning of the steel sheet and the nickel coating are up to 4.8% and 6.7%, respectively. Meanwhile, it is found that the curve of the variable blankholder force (VBHF) designed can improve the formability of sheet. 相似文献
103.
Gang Liu Zhongqin Lin Youxia Bao J. Cao 《Journal of Materials Engineering and Performance》2002,11(1):64-70
Springback is the main concern in U-shaped part forming, which would adversely affect desired part geometries. The use of
variable blankholder force in the forming process is one effective method to reduce springback. However, there has not been
a systematic way to determine the blankholder force trajectory. In this article, a methodology of obtaining this blankholder
force trajectory in forming a U-shaped part that considers the wrinkling limit and fracture limit in the forming process was
proposed. The method was validated numerically by using the Finite Element Method to simulate the benchmark of a 2-D draw
bending problem in NUMISHEET’93. With the calculated blankholder force trajectory, higher forming quality was obtained and
compared with constant blankholder force cases. Springback was kept at a minimum while avoiding cracking. 相似文献
104.
镁合金的活性电弧焊接 总被引:7,自引:2,他引:7
在不同的电流条件下,研究了9种常见氧化物、氟化物、氯化物活性剂在镁合金交流氩弧焊及变极性等离子焊弧中的行为.结果表明:活性剂TiO2、Cr2O3、AlF3、NiCl2、CdCl2、ZnCl2、MgCl2使镁合金交流氩弧焊焊缝熔深增加;MgF2、SiO2使镁合金交流氩弧焊焊缝熔深减小;TiO2、SiO2、Cr2O3、AlF3、NiCl2、CdCl2使镁合金变极性等离子弧焊焊缝熔深增加;MgF2、ZnCl2、MgCl2使镁合金变极性等离子弧焊焊缝熔深减小;活性剂对镁合金交流氩弧焊焊缝熔深增加的作用大于对镁合金变极性等离子弧焊的;电弧收缩是活性剂使得镁合金电弧焊焊缝熔深增加的原因之一;活性剂的加入使得焊缝的晶粒比未涂敷活性剂时粗大. 相似文献
105.
106.
107.
滑模变结构控制的抖振问题研究 总被引:8,自引:1,他引:8
文章在分析变结构控制(VSC)系统抖振发生机理基础上,讨论了几种消除或削弱抖振的途径。提出了一种类似于模糊推理的VSC方法,并给出了在加工过程控制中的应用实例,仿真结果表明,该方法能够有效地削弱系统抖振,而不会影响控制器的鲁棒性能。 相似文献
108.
针对非完整约束下质心偏移的移动机器人,提出了一种改进滑模变结构的轨迹跟踪控制方法,并通过此方法得到一种具有全局渐近稳定性的跟踪控制器。以三轮移动机器人的运动模型为基础,该跟踪控制器的设计分为两部分:第一部分是采用X方向和前向角方向同时具有虚拟反馈变量,通过Lyapunov方法对控制系统进行稳定性分析,设计出切换函数;第二部分是滑模控制器设计,采用指数趋近律,使用S型指数函数代替符号函数,减少了滑模变结构控制的抖动,由此设计出了线速度和角速度的控制律,用来渐近整定移动机器人跟踪误差,实现了对参考轨迹的全局渐近跟踪。实验结果表明:该控制律能够在极短时间内趋于稳定,其跟踪平面坐标误差和前向角误差也能在极短时间内收敛于0,并且移动机器人也能够有效地跟踪期望轨迹,其控制效果具有明显的改善,且具有很好的抗干扰性能。 相似文献
109.
摄像稳定平台中摩擦补偿变结构控制研究 总被引:1,自引:0,他引:1
为获取清晰稳定的视频图像,必须利用稳定平台给船载摄像机提供一个良好的空间稳定环境。该平台为一个三轴机械设备,当船体处于不同的运动姿态时,轴系间摩擦力矩会改变,因此提出一种考虑摩擦补偿的变结构控制方法。仿真和研究结果表明,与经典PID控制方法相比,变结构控制器能有效消除因摩擦引起的"爬行"和"平顶"现象。使用指数趋近律的变结构控制算法使系统快速跟踪指令信号,动态效果良好。 相似文献
110.
Variable precision intuitionistic fuzzy rough set model and applications based on conflict distance 下载免费PDF全文
Due to the complexity and uncertainty of the physical world, as well as the limitation of human ability to comprehend, it is very difficult for any single method of uncertainty to effectively deal with the decision‐making problem that exists in real life. So, it is natural for us to think about incorporating the advantages of various theories of uncertainty to develop a more powerful hybrid method of soft decision‐making. In view of this recognition, the thought and method of intuitionistic fuzzy sets and variable precision rough sets are used to construct a novel intuitionistic fuzzy rough set model. With respect to the fact that the information system is intuitionistic fuzzy, the idea of measuring intuitionistic fuzzy similarity is used to define conflict distance. After that, this concept is combined with the variable precision rough sets so that a variable precision intuitionistic fuzzy rough set model is established, and its properties are investigated. After proposing an attribute reduction algorithm based on variable precision intuitionistic fuzzy rough sets, a case study is used to verify the feasibility and effectiveness of our novel model. The results show that our model indeed improves the classification ability of earlier models and possesses some ability to tolerate faults through adjusting the parameter λ and the confidence threshold β; it realizes the correct classification and extracts the decision rules. 相似文献