2D-C/SiC拉伸损伤的声发射信号聚类分析

对2D-C/SiC复合材料进行常温拉伸试验,利用声发射(AE)仪在线监测其损伤过程.应用K-均值聚类算法对AE信号进行模式识别,结合扫描电镜观察,发现2IC/SiC复合材料拉伸过程的损伤模式包括基体开裂、界面层脱粘、层间剥离、纤维断裂以及纤维束断裂等,并得到了各种损伤模式AE信号参数的中心值.通过对不同损伤模式AE累积事件数和累积能量随时间变化的统计分析,描述了2DC/SiC复合材料拉伸损伤演化过程.     

球链中冲击扰动的传播

采用Hertz 接触理论处理牛顿摆中球与球之间的相互接触,建立球链碰撞模型,观察到碰撞过程中类似孤立波的传播现象。为了便于处理“n 对m”碰撞的计算,编写了带有GUI (graphic user interface) 界面的计算程序,可以研究不同撞击球个数对撞击过程的影响,包括球心位置、球心速度以及相邻小球间的变形量与相互作用力随时间的变化规律。进一步比较了一维球链模型和三维有限元模型的结果,并实验观察了碰撞过程的细节,得到一致性结论。     

双"单电桥"法测量低电阻中的实用技巧例举

主要介绍了双"单电桥"法测量低电阻的基本原理与双"单电桥"法测量低电阻的几种实用技巧.     

Application of Two Novel Acoustic Emission Parameters on Identifying the Instability of Granite

The issue of monitoring and early warning of rock instability has received increasing critical attention in the study of rock engineering. To investigate the damage evolution process of granite under triaxial compression tests, acoustic emission (AE) tests were performed simultaneously. This study firstly introduced two novel parameters, i.e., the coefficient of variation (CoV) of the information entropy and correlation dimension of the amplitude data from the AE tests, to identify the precursor of the failure of granite. Then the relationship between the changes in these parameters and the stress-time curve was compared and analyzed. The results of this study show that: (1) There is a strong correlation between the CoV of the information entropy and the failure process of granite. The granite failed when the CoV curve raised to a plateau, which could be used as an indicator of rock instability. (2) The fluctuation of the correlation dimension indicates the different stages during the loading process, i.e., the initial compaction stage, the linear elastic stage, the yield stage, and the failure stage. Each stage contains a descending and a rising process in the correlation dimension curve, and the exhibited starting point or the bottom point at the correlation dimension curve could be selected as the indicator point for the rock instability. (3) The combined analysis of the Information entropy and Correlation dimension can improve the accuracy of rock instability prediction. This study provides new insights into the prediction of rock instability, which has theoretical implications for the stability of subsurface engineering rock masses.     

陶瓷材料疏水性能的研究进展

本文简述了疏水性表面的基本原理,分别从低表面能物质修饰和表面微细粗糙结构的构建两个方面,对疏水性陶瓷材料的制备技术和最新的成果进行了总结,介绍了其潜在的应用并对未来的研究方向作了展望.     

结构光测量中的高精度相位误差补偿算法

在模拟分析投影仪伽马非线性对相位误差影响的基础上,提出一种直接分析投影光栅特征并建立相位误差查找表的算法.对相位误差进行补偿.该算法通过分析一组投射到标准白色平板上的光栅图像,确定光栅相位值与相位误差的对应关系,并量化存储在一个查找表中,测量过程中使用查找表对相位误差进行补偿.实验结果表明.该方法可大大降低由投影仪伽马非线性引起的相位误差,系统测量精度达到0.043 mm,比误差补偿前提高了5.6倍.     

CHAOTIC MOTIONS AND LIMIT CYCLE FLUTTER OF TWO-DIMENSIONAL WING IN SUPERSONIC FLOW

Based on the piston theory of supersonic flow and the energy method, the flutter motion equations of a two-dimensional wing with cubic stiffness in the pitching direction are established. The aeroelastic system contains both structural and aerodynamic nonlinearities. Hopf bifurcation theory is used to analyze the flutter speed of the system. The effects of system parameters on the flutter speed are studied. The 4th order Runge-Kutta method is used to calculate the stable limit cycle responses and chaotic motions of the aeroelastic system. Results show that the number and the stability of equilibrium points of the system vary with the increase of flow speed. Besides the simple limit cycle response of period 1, there are also period-doubling responses and chaotic motions in the flutter system. The route leading to chaos in the aeroelastic model used here is the period-doubling bifurcation. The chaotic motions in the system occur only when the flow speed is higher than the linear divergent speed and the initial condition is very small. Moreover, the flow speed regions in which the system behaves chaos axe very narrow.     

五阶非线性下零色散附近的调制不稳定性

在同时考虑光纤损耗、高阶色散以及高阶非线性情况下,从广义非线性薛定谔方程出发,研究了零色散附近的调制不稳定性,分析了四阶色散和五阶非线性对增益谱的影响.结果表明：当光脉冲工作在零色散附近时,四阶色散对调制不稳定性起决定作用,它使反常色散区的增益谱变宽.在光纤正常色散区,正（负）五阶非线性使增益谱的谱宽和峰值增大（减小）;但在反常色散区,五阶非线性仅改变增益谱的峰值,几乎不影响谱宽.     

电磁轨道发射器连续发射的滑动电接触

从滑动电接触电阻大小的角度,详细分析了在时序放电条件下,两颗重约为5 g的电枢,以速度为1 000 m/s,166 Hz连续发射试验。通过近似计算电流所流经轨道电阻及电枢体电阻所产生的温升,对滑动电接触电阻的影响。结果表明:连续发射运行模式下,受轨道表面温度上升的影响,第二发电枢的滑动接触电阻略高于第一发电枢的滑动接触电阻,表面滑动电接触性能受到温升的影响,在两连发的发射情况下,其影响虽不是很大,但多发高频连续发射就必须考虑热管理问题。      

高速电枢的尾翼结构设计及实验研究

设计了T2LXD1系列电枢,分析了6061-T6铝合金材料的弹塑性特点,利用线性强化理论和接触理论并结合ANSYS软件,建立了T2LXD1系列电枢弹塑性接触模型,研究了电枢尾翼结构对电枢/导轨滑动界面接触状态的影响规律,得到了界面接触力、接触面积和接触压力分布等状态参数的数值模拟结果。利用短导轨电磁驱动系统,进行了T2LXD1系列电枢滑行实验,分析了电枢/导轨界面滑磨状态,比较了滑行性能曲线。实验结果表明:长尾翼电枢并不能带来实际接触面积的增