提高拉深模具使用寿命和零件合格率的一种有效方法--干膜润滑拉深

本文通过采用几种润滑剂分别进行不同的冷冲压拉深试验,测定了极限拉深系数等参数。实践及研究表明垫聚乙烯干膜润滑拉深对各种板材及不同的拉深成形方法都起到了提高其拉深性能的作用,对此还作了一些分析探讨,提出了相应的建议。     

组合机床动力滑台液压传动系统的理实教学

文章分析了组合机床动力滑台的工作要求,使机床液压传动系统满足工件加工时的快进、工进1、工进2、快退、停的工作任务。通过对比分析及借助拆装式液压系统教学实验平台的模拟工况分析并确定了最佳改造方案,改造后的液压系统提高了动力滑台的运动平稳性,减少了油路的元件数量,简化了系统结构,极大地提高了生产效率。分析液压油的过滤方案延长了液压油的更换周期,可以节约成本。     

关于具有摩擦力的园周运动的讨论

本文简单清楚地对具有摩擦力的园周运动的一个特例进行了讨论,并介绍两种应用数字技巧求解速度和克服摩擦力作功的方法,有助于学生们对此概念的理解和掌握。     

有限时间跟踪控制在永磁同步电动机中的应用

考虑了一类永磁同步电动机的有限时间跟踪控制问题．在控制器设计中利用中继切换控制使系统在给定的当前控制律的作用下运行到某一特定状态（或某一特定区域）后,控制律被切换到有限时间收敛的终端滑模控制器,使得系统在有限时间内达到平衡状态．有限时间跟踪控制器的设计保证了闭环系统所有信号的有界性和平衡点的全局稳定性,以及系统在有限时间内精确地跟踪给定的参考信号．最后通过一个数值仿真验证了所提算法的正确有效性．     

PTFE及POB填充PTFE复合材料的摩擦磨损性能研究

利用往复式摩擦磨损实验机,对PTFE及POB填充PTFE复合材料在不同载荷、不同频率条件下的摩擦磨损性能进行了研究.结果表明,添加POB降低了PTFE的摩擦系数,提高了PTFE的耐磨性.     

Mentoring in Contexts of Cultural and Political Friction: Moral Dilemmas of Mentors and Their Management in Practice

This paper examines the nature of moral dilemmas mentors from three different national groups (Jewish, Druze, and Arab) encounter in their work in Israeli Arab schools, how they manage these dilemmas in practice, and how the nature of particular dilemmas might connect to their management strategies. Given the multicultural and politically conflictive context of the Israeli society, a cultural and political reading of in-service mentors’ moral dilemmas reveals that mentors’ encounter and management of recurrent moral dilemmas is embedded in cultural and political issues in a way that seem to hinder their mentoring practice. Preparation programs for mentors need to highlight awareness of mentors’ own culture and that of their mentees in order to implement a culturally and politically responsive practice.     

铸铁材料受轴向压缩失效截面位置及原因分析

本文通过对铸铁受轴向压缩斜截面上剪应力和斜截面滑移错动引起摩擦力作用的考虑;以及铸铁拉、压时的应力圆进行了解析和几何分析,对铸铁压缩失效做了实际测量,获得了较为准确、可靠的铸铁压缩失效截面的位置和失效原因。     

Investigation on the factors influencing the thickness distribution of superplastic-formed components

In the superplastic sheet forming process, the uniformity of the sheet's final thickness distribution is vital for ensuring the good mechanical quality of the formed components. The influences of the component shape and the contact friction on the final thickness distribution were investigated in this work by using finite element method on a series of axisymmetric models. It was concluded that shape optimization and friction elimination are required to get uniform thickness distribution, and eventually to improve the mechanical quality of the formed components. The constitutive equation of the Ti-6Al-4V superplastic material was also determined on the basis of experimental data.     

利用函数图象对验证牛顿第二定律实验的误差分析

在验证牛顿第二定律实验中,误差存在的原因有二：一是沙桶的质量和小车质量相当;二是实验前没有平衡摩擦力或平衡摩擦力过度。两者造成小车的加速度与小车的质量倒数及绳子的拉力不成正比,可用函数图像直观地描述加速度与各变量之间的关系。