纳/微米弹流油膜厚度测量系统

介绍了1种基于多光束干涉强度的弹流油膜厚度测量系统,包括其测量原理和测量系统的设计与组成.针对光弹流接触副,给出了简单易行的干涉级次判定方法.结果表明,该测量系统具有纳米量级的分辨率,可实现由纳米膜厚到微米膜厚的连续测量,适用于超薄弹流油膜厚度和微米级弹流油膜局部微小变化的研究.测量结果与已有的理论和研究结果吻合,证明了测量系统的可靠性.     

基于双色光干涉的面接触润滑油膜在线测量

根据面接触润滑油膜红绿双色光干涉强度调制信号,构造了基于光流和动态时间弯曲技术的追踪算法,对一维调制光强曲线上与膜厚具有对应关系的特定目标区域进行实时追踪,从而实现了在线实时膜厚测量.通过与稳态离线测量结果对比,验证了该在线测量系统的准确性和可靠性.利用该系统对三角波形式变速过程中流体动压润滑瞬时膜厚进行了测量,揭示了膜厚滞后于速度变化的规律.     

微型滑块面接触润滑油膜测量系统

本文介绍了1种微型面接触润滑油膜厚度测量系统,在一定载荷下以静止的微型滑块平面和旋转的光学透明圆盘平面形成流体动压润滑油膜,利用光干涉方法对润滑油膜的最小厚度值进行测量.微型滑块工作面为高反射率研抛平面,光学透明圆盘表面镀有析光薄膜,利用1种柔-刚性结构对微型滑块进行定位,可实现滑块平面对圆盘平面倾角的任意调节和动态保持.使用该测量系统还可以获得在不同的滑块倾角、速度和载荷下的面接触润滑油膜.并且测量结果与经典润滑理论有较好的一致性.     

面接触润滑油膜测量系统滑块倾角的快速计算

在面接触润滑油膜厚度的光干涉测量中,需要确定滑块和玻璃盘所形成的微小倾角.一般通过目测干涉条纹的数量计算倾角,效率低且误差大.根据滑块表面干涉条纹等距,光强呈周期性变化的特点,对滑块面的干涉光强曲线进行傅里叶变换,综合采用Rife-Jane和重叠FFT相位差法进行频率插值,较好地消除了频谱泄漏,较准确计算干涉条纹数量,从而得到滑块与玻璃盘间的倾角.试验证明:当条纹数量大于5时该方法的测量相对误差在1%以下,具有很强的抗干扰能力.对不同倾角下的油膜厚度进行了测量,得出了润滑油膜的无量纲承载量-滑块收敛比曲线.结果表明:膜厚较高时,无量纲载荷最大值出现在收敛比为1.2左右的位置,但当膜厚较低时,无量纲载荷最大值出现在收敛比大于2的位置,偏离了经典理论.     

固液润湿性对流体动压润滑薄膜的影响

利用自行开发的微型面接触润滑油膜测量系统,研究了固液润湿性对流体动压润滑油膜厚度的影响.试验中以静止的微型滑块平面和旋转的光学透明圆盘平面形成润滑副.固液的润湿性通过接触角判定,不同材料的微滑块平面和润滑液体形成不同的界面.在保持载荷和面接触楔形角不变的条件下对油膜厚度-速度关系进行了测量.结果表明:对于固液润湿性强的界面,形成的油膜厚度与经典润滑理论有较好的一致性;当固液润湿性明显降低时,测量得到的油膜厚度减小.对于试验中观察到的界面效应,应用界面滑移理论进行了初步分析.     

不同滑滚比下润滑油膜流变特性试验观察与数值模拟

通过在原有的球-盘接触光干涉润滑油膜测量装置上增设摩擦力测量单元,实现了任意滑滚比下油膜厚度和摩擦系数的同步测量与润滑状态的直观识别. 采用FVA3参考油,分析了不同滑滚比、速度和载荷下的摩擦系数变化规律,并结合油膜干涉图明确了润滑状态与热效应机制,推断出摩擦系数曲面在较低速工况存在混合润滑区域;通过采用基于恢复时间的流变模型对FVA3油品的流变润滑进行数值模拟,并与同等工况下的试验结果进行定量对比,两者取得了良好的吻合性,验证了试验测量的准确性和流变模型的适用性.      

冲击载荷下蛋白质水溶液吸附成膜的润滑试验研究

利用球盘接触形式的光干涉膜厚测量试验机,研究了周期冲击载荷作用下蛋白质水溶液在材料表面的吸附膜生长特性.对比了溶液蛋白质组分、亲疏水对偶表面和冲击条件对球盘接触区蛋白质吸附膜厚的影响.结果显示动态冲击下蛋白质的吸附膜厚要远高于静态吸附,吸附膜不断在接触区生长,之后趋于稳定.金属钢球比陶瓷球、疏水盘表面比亲水盘面,均更有利于蛋白质吸附膜的生长.同时发现吸附膜厚与单一蛋白质的浓度关系不大,却和蛋白质种类关系很大,球蛋白比白蛋白具有更好的吸附成膜性能.     

条状润湿表面对面接触限量润滑油膜的影响研究

利用面接触油膜润滑测量系统,研究了条状润湿表面对有限量供油条件下入口区供油分布及润滑油膜厚度的影响. 对玻璃盘润滑轨道两侧进行疏油化处理,形成中央条状润湿区域,在有限量供油条件下测量不同速度下的油膜厚度. 结果表明在表面力驱动下,润滑油向中央条状亲油区域集中,改善了入口区供油,促进了限量供油条件下的油膜形成. 相对油膜厚度随速度的增加呈“S”型变化,同时研究了润滑油黏度及供油量等工作参数对条状润湿轨道作用的影响.      

固体表面FAS膜转移对面接触油膜润滑影响的试验研究

利用滑块-盘面接触润滑油膜测量系统,在限量供油条件下,研究了滑块表面涂镀的疏油FAS(C₁₃H₁₃F₁₇O₃Si)膜对油膜润滑的影响. 结果表明:部分FAS膜可以透过油膜自发地转移到玻璃盘上;由于FAS转移膜的反润湿作用,玻璃盘面上接触区出口的润滑油膜回流增强;润滑油在玻璃盘润滑轨道上由原来的双侧脊分布转变为离散液滴分布,并向润滑轨道中心区域聚集,增强了入口区供油,油膜厚度增加.      

定量供油下球-环/球-盘接触形式润滑特性对比

采用球-环接触和球-盘接触形式的光干涉润滑油膜测量仪,在定量供油条件下观察两种接触形式下的不同润滑特性,分析了润滑差异性的内在机制. 结果显示:在低速条件下球-盘接触膜厚始终高于球-环接触膜厚,由接触几何特性差异导致的不同动压效应、侧泄效应和润滑剂流动是其主要原因;在高速条件下球-盘接触形式易出现入口乏油,而球-环接触在整个测试速度范围内未出现乏油,不同的离心力作用方向是导致这种差异的诱因. 试验还观察与分析了黏度对两种接触方式下润滑特性的影响:低速条件下,高黏度润滑剂易导致球-环接触出现乏油;高速条件下,高黏度润滑剂能够推迟球-盘接触时乏油状态的出现.      

双参考光全息—散斑干涉术的原理和实验

本文用统计光学方法对双参考光全息——散斑干涉术进行了详尽的理论分析,给出了全息和散斑干涉场区域平均光强分布与光学系统主要参数及三维变形场各分量之间关系的解析表达式,进而讨论了离面位移和面内位移测量的上、下限,最后还给出了有关的实验结果。     

利用光学干涉条纹图相位分析测量纳米位移

Optical methods such as Twyman-Green interferometry, moiré interferometry, holographic interferometry and speckle interferometry are useful to measure displacement and strain in the full-field of structures. Recently phase analysis method of fringe patterns obtained by these optical methods becomes popular, and it provides accurate quantitative results in the full-field. In this paper, in order to measure displacement and strain, real-time or high-speed nano-meter displacement measurement methods developed by the authors are introduced. That is, (1) out-of-plane displacement analysis by Twyman-Green interferometry using integrated phase-shifting method using Fourier transform phase-shifting method, (2) simultaneous two-dimensional in-plane displacement analysis by moiré interferometry and (3) out-of-plane displacement analysis by phase-shifting digital holographic interferometry. The theories and applications are shown.     

Three-dimensional thermal deformations observed in SMT assembly during power cycling

The three-dimensional displacement fields of thermal-force coupling fatigue in a surface mounted plastic-quad-flat-pack (PQFP) assembly during power cycling by using the combination of holographic interferometry and high sensitivity moire interferometry is presented in this paper. Detailed in-plane and out-of-plane whole-field displacement data of the top and bottom ends of gull wing leads and their distributions along the edge of PQFP are provided. It was found that the maximum deformations of gull wing leads occur at the four corners of PQFP. The result presented herein should be useful in the evaluation of thermal fatigue damage mechanism of surface mount assemblies.     

Phase-stepped ESPI and moiré interferometry for measuring stress-intensity factor andJ integral

Electronic-speckle-pattern interferometry and moiré interferometry have been used to calculateK ₁ andJ for compact tension specimens. Automated-fringe-pattern analysis enables the full-field of data to be used with the minimum of operator intervention. Measurements are shown to be accurate to within 10 percent. TheJ-measurement procedure employed could form the basis of an automatic-fault detection system.     

The use of automated projection interferometry in monitoring aerofoil buckling

Projection moiré is frequently used to examine the out-of-plane displacement of thin-walled shells during buckling. One way of implementing this technique is to use double exposure photography to superimpose the initial and deformed images of a grating projected onto the surface of the specimen. This generates a pattern of fringes representative of points of equal displacement, thus presenting a snapshot of the full-field buckling behavior. This paper outlines a technique to extend this method to provide a computer generated real-time fringe pattern throughout the whole buckling and post-buckling process. This is achieved by using a CCD camera and specially developed processing software to continuously superimpose the initial image of the grating (i.e., the first frame of the captured video) onto subsequent frames in which this grating is deformed due to the displacement. This method produces series of fringes in digital format, which are ideal for further processing.     

Measurement of energy release rates for delaminations in composite materials

Conventional measurements of energy release rates,G _I andG _II, for delaminations in composite materials, generally utilize loads, crack lengths and simple standard specimen geometries. In this work, a more widely applicable measurement method, using phase shifting moiré and the J integral, is presented. The experimental technique described requires only fringe-pattern information and the elastic constants for the measurements—thus it can be used when the standard methods are inapplicable. Using conventional double-cantilever beam and end-notched flexure specimens, the energy release rate has been measured simultaneously by the moiré method and the standard methods, with good agreement found between the two. This development will for the first time permit the experimental validation of new finite-element routines as they are developed.Paper was presented at the 1993 SEM Spring Conference on Experimental Mechanics held in Dearborn, MI on June 7–9.     

Additive-subtractive phase-modulated shearography with synchronized acoustic stressing

A robust electronic shearography technique is described that is immune to ambinet noise. In this technique, additive speckle-interference images containing information about the same two states of deformation of a test object undergoing acoustic stressing are acquired in each video frame. When a spatially nonuniform phase modulation is introduced in every other frame during the video sequence (using a tilting mirror) and the additive interference images are subtracted sequentially using a real-time image processor, the self-interference component of sheared-speckle interference pattern is removed. The susceptibility of this method to environmental noise caused by induced thermal noise and low frequency vibration is demonstrated to be lower than that of conventional substractive shearography methods; fringe visibility and contrast are significantly improved as well. The ability of this technique to work in a turbulent environment is demonstrated, and application to detection of structural defects in adhesively bonded structures, a problem of interest in nondestructive evaluation of structures, is shown.     

Study of thermal deformation of microelectronics packaging product by interferometric technique

In this paper, the out-of-plane deformation of silicon surface of Direct Chip Attachment (DCA) assembly, under thermal loading, was measured in real-time by Twyman/Green interferometry. The contour maps of the out-of-plane displacement fields of silicon surface under thermal loading and cycling of various temperature were obtained. Experimental results show that the relation between the out-of-plane displacement and temperature is nonlinear and varies with temperature cycling, due to nonlinear mechanical behavior of the materials used in electronic packaging. A comparison of the out-of-plane displacement fields of silicon surface measured by T/G interferometry in real-time and replicating technique of high temperature specimen grating of moire interferometry was made.     

Measurement of heat transfer at the phase interface of condensing bubbles

Using holographic interferometry and high-speed cinematography the heat transfer at the phase interface of vapor bubbles condensing in a subcooled liquid of the same substance was measured with ethanol, propanol, refrigerant R113 and water. To evaluate the axisymmetric temperature field around the bubble from the interference fringe field, the Abel integral method is not sufficient. A correction procedure considering the light deflection caused by the local temperature gradient has been developed and applied to calculate the heat transfer coefficient. The measurements were performed in the range 2 < Pr < 15 and I < Ja < 120. Measured data could be well-correlated as functions of the Prandtl and Reynolds numbers for the heat transfer coefficient and as functions of the Reynolds, Prandtl and Jacob numbers for the bubble collapse time.     

Holographic interferometric investigation of shock wave interaction with a ramp

The internal flowfield including shock reflections structure inside a 2-D half inlet model was examined by a double exposure holographic interferometry using a Q-switched pulse laser. The interferograms give detailed flow visualization pictures. The structures of regular reflection, lambda reflection and Mach reflection in the inlet channel were observed. From the analysis of fringe patterns, the quantitative distributions of flow density, pressure and Mach number of the internal flowfield have been reconstructed. The boundary layer thickening and separation in the case of lambda reflection and the Mach stem in the case of Mach reflection were clearly demonstrated in the holographic fringe patterns. The results show that the shock interacitons with the ramp and the wall introduce a complicated flow structure which could strongly affect the efficiency of the inlet.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.