某差速器齿轮的动态接触仿真与疲劳分析

为分析差速器齿轮的疲劳寿命,运用动态有限元与试验相结合的方法,研究了锥齿轮在啮合过程中的应力分布以及疲劳强度。首先基于CATIA软件对差速器的半轴齿轮、行星齿轮进行了参数化建模,并采用动态有限元法模拟了齿轮副在最大扭矩工况下的动态接触;再根据有限元强度分析结果,将最大接触应力作为静载输入,运用疲劳分析软件对齿轮副的接触疲劳性能进行计算;最后进行了差速器齿轮副的台架试验,并将仿真结果与台架试验进行了对比。结果表明:齿面最大接触应力产生于节圆附近,齿轮间的最大接触应力为1309MPa;半轴齿轮在90%存活率下的疲劳寿命为3.394×106;仿真结果与台架试验具有较好的一致性,齿轮满足疲劳寿命要求。将动态有限元和疲劳寿命分析方法相结合可以有效预测差速器齿轮疲劳寿命。     

氧在银／二氧化硅催化剂上的超高真空程序升温脱附

 研究了氧在Ag／SiO2催化剂上的超高真空程序升温脱附．结果表明，脱附谱中出现了对应于表面分子氧（Tp＝340K）、体相氧（Tp＝570K）和次表层氧（Tp＝700～800K）的脱附峰．由于催化剂在制备过程中经过高温焙烧，因而其表面原子氧浓度低，脱附谱中未出现原子氧的脱附峰．高温焙烧还可使表面缺陷浓度增大，有利于原子氧向体相扩散，形成体相溶解氧，也有利于体相氧向表面扩散，所以对应于体相氧的570K脱附峰较强．体相氧和次表层氧向表面的扩散遵循不同的扩散机理．     

Ag复合对La2/3(Ca0.45Sr0.55)1/3MnO3/xAg体系电输运和室温磁电阻效应影响

文中采用甘氨酸-硝酸盐法分别制备了La2/3(Ca0.45Sr0.55)1/3MnO3/xAg纳米复合材料(x=0;0.1;0.2;0.3).通过X射线衍射、扫描电子显微镜和磁电阻效应测试,对合成产物的结构及性能进行表征.结果表明,随Ag复合量增加,样品均为正交钙钛矿结构,低场室温磁电阻效应增强,电阻率减小.     

Evolution of surfaces and mechanisms of contact electrification between metals and polymers

Contact electrification (CE) is a pretty common phenomenon, but still is poorly understood. The long-standing controversy over the mechanisms of CE related to polymers is particularly intense due to their complexity. In this paper, the CE between metals and polymers is systematically studied, which shows the evolution of surfaces is accompanied by variations of CE outputs. The variations of CE charge quantity are closely related to the creep and deformation of the polymer and metal surfaces. Then the relationship between CE and polymer structures is put forward, which is essentially determined by the electronegativity of elements and the functional groups in the polymers. The effects of load and contact frequency on the CE process and outputs are also investigated, indicating the increase of CE charge quantity with load and frequency. Material transfer from polymer to metal is observed during CE while electrons transfer from metal to polymer, both of which are believed to have an influence on each other. The findings advance our understanding of the mechanism of CE between metal and polymers, and provides insights into the performance of CE-based application in various conditions, which sheds light on the design and optimization of CE-based energy harvest and self-powered sensing devices.