用曲线大窗口平滑散斑条纹图的方法研究

提出一种计算条纹方向的简单算法,以及通过条纹方向图获得沿条纹方向的曲线窗口并对散斑条纹图进行曲线大窗口滤波的方法．实验表明此方法较好地消除了散斑条纹图的噪声,同时尽量减小了对条纹结构的损害．为从单幅散斑条纹图中应用条纹中心线法或全灰度法进一步提取相位场的后处理,奠定了良好的基础．     

基于多通道滤波技术的散斑条纹图正则化方法

在光测力学中,条纹图正则化是进一步提取条纹位相信息的重要基础。对于散斑条纹图来说,正则化的过程还需能够有效地抑制散斑噪声。本文提出一种基于多通道滤波技术的散斑条纹图正则化方法。通过使用多个Gabor滤波通道对散斑条纹图进行滤波,并且引入与条纹对比度有关的权重因子把各个滤波通道的滤波结果叠加起来,最终得到滤除了散斑噪声的正则化条纹图。数值模拟和实验结果表明,该方法在将散斑条纹图正则化的同时能够有效地滤除条纹图中的散斑噪声,为进一步提取条纹位相奠定了良好的基础。     

A new method to increase the sensitivity of photoelasticity

A method is proposed to read the isochromatic-fringe order continuously as a function of position. It utilizes the fact that the fringe order is a continuous function of the light intensity, which is converted into the density of a photographic negative and then traced out either by a microdensitometer or isodensitracer. Explicit relationship between the fringe order and the film density is obtained. Hundreds of points can be read between a half and an adjacent integral order. The method is whole field in nature and offers the possiblity of direct computer processing of photoelastic information.     

扫描云纹法中的光载波解调问题研究

本文提出一种新型的光载波技术,扫描云纹被使用为空间相位的探测器,可以用来实时地复原原始条纹.全场条纹级数可以得到快速而精确地自动识别.文中对调制度的概念及应用的充要条件进行了讨论.     

FM法锻造的模拟研究

本文利用激光云纹技术[1]模拟了砧宽比（2W/H0）为0.4、0.6、0.8时的平面FM法锻造过程，采用按云纹图修正理论滑移线场的方法[2]，提出了更接近实际的FM法滑移线场，从修正的滑移线场和云绀方图分别得到了变形区静水压应力和等效应变分布，并与普通锻造法的结果进行了比较，结果表明，两种锻造方法在锻件心部产生的最大等效应变相差不大，但EM法产生较大的静水压应力，对消除锻件内部孔洞型缺陷有利。     

基于小波分析的条纹图滤波方法

本文提出了一种新颖的干涉条纹图非线性滤波方法,可以选择性地在频域图像的不同区域选用不同的滤波方式,在滤掉图像中大部分散斑噪声的同时,能够减少信息的损失,使图像的内部边界仍然保持清晰。文中首先简介了正交小波变换的原理,然后介绍了去除散斑噪声的具体算法,最后给出了计算机模拟去噪声的结果     

Interferometrie transparenter Phasenobjekte,insbesondere bei hohen Interferenzstreifendichten,dargestellt an einem Beispiel aus der Wärmeübertragung

The assumptions of ‘ideal interferometry’ result in formulae which are easy to use for the interpretation of interferograms, but which are only valid if the interference fringe density is low. If these formulae are used at higher fringe densities, one must focus at the so-called ‘optimal focussing plane’. If the interference fringe density becomes still greater, practically any focussing position will result in deviations from ‘ideal interferometry’. With the aid of an example from heat transfer a method is presented which enables the most favourable focussing plane to be determined and which corrects the resulting deviations from ‘ideal interferometry’ by use of an iterative algorithm.     

干涉条纹图处理的等值线窗口滤波和摄像测量在国防试验的应用

对图像进行滤波或称平滑是干涉条纹图像处理中的一项重要工作。一幅未经处理的原始图像或多或少存在着不同程度的噪声干扰,特别是散斑和Insar干涉条纹图,信噪比很低,难以处理。本文针对光测力学中光学干涉方法得到的条纹图,提出了一种新的滤波方法条纹等值线窗口滤波,并对这种滤波方法进行了研究讨论,提出了几种确定等值线窗口的不同方法。这种滤波方法根据干涉条纹图不同断面上灰度分布的不同特点,选择沿条纹走向的条纹等值线窗口进行滤波,在最大消除条纹图噪声的同时,也能保证对条纹损伤最小。摄像测量技术正在迅速发展和得到广泛应用,在国防试验和航天飞行任务中发挥着不可替代的作用。本文也介绍了作者近年来在该领域所做的应用研究,包括在火箭、导弹发射试验,冲击、碰撞等过程中的动态目标运动测量;针对航天航空和力学工程领域的视频图像实时分析;飞行器三维运动测量;基于投影条纹的物体三维形貌精密测量方法研究;以及对接航天器位置和姿态的实时测量。在这些应用中都实现了高精度测量。     

Determination of fracture toughness by photoelastic coating

The photoelastic-coating method was applied to the determination of fracture toughness in aluminum plates. The specimens were plates with a central transverse crack. Determinations were made first by the compliance method. The specimens were loaded statically to failure. The opening displacement across the crack was measured with a clip gage. In using this photoelastic-coating method, the stress-intensity factor was obtained in terms of the radius and fringe order of various isochromatic fringe loops using an extrapolation law. An apparent stress-intensity factor was obtained from several isochromatic fringe patterns away from the crack tip and then extrapolated to the crack tip to determine the true value. Results obtained by the photoelastic-coating method are higher than those obtained by the compliance method for all loads, due to the bluntness of the crack tip in the first set of specimens. Theoretical predictions fall between the compliance method and photoelastic-coating results. Paper was presented at V International Congress on Experimental Mechanics held in Montreal, Quebec, Canada on June 10–15, 1984.     

A Procedure for Accurate One-Dimensional Strain Measurement Using the Grid Method

This paper deals with the accurate calculation of strain using the grid method. The strain field is first directly deduced from the fringe pattern without calculating the displacement field. This procedure is validated with two numerical examples. Two types of experiment are then carried out: a translation and a tensile test. It is observed that some additional fictitious strains appear in both cases. They are due to two main reasons which interact with each other: the grid defects and the displacement of the grid lines during testing. A suitable procedure is proposed to cancel out these fictitious strains. This procedure is successfully applied in two cases of fringe patterns.     

Optical Metrology by Fringe Processing on Independent Windows Using a Genetic Algorithm

We present a method to retrieve the phase of a fringe pattern based on the window fringe pattern demodulation technique (WFPD). The overlapped phase similarity criterion is avoided in the proposed method, and it is substituted by a second order smoothness criterion. The fringe processing on independent windows (FPIW) method can measure physical quantities from closed and near sub-sampled fringe patterns by a simplified cost or fitness function. The fringe image is divided into a set of partially overlapping windows. In these sub-images the estimated phase is modelled as a parametric analytic-function, and its parameters are optimized using a genetic algorithm (GA). This analytic-function is used to estimate the phase in the area framed by the window. Phases from all windows are sequentially spliced to retrieve the whole phase field. A media filter is applied over the entire phase field to smooth the irregularities that appear in the junctures between windows.     

Colour Adaptation in Three Fringe Photoelasticity

Three fringe photoelasticity (TFP) can give the total fringe order from a single colour isochromatic fringe field by suitably comparing the colour with a calibration specimen. The fringe order evaluation can be erroneous when the materials for the calibration specimen and the application specimen are different. This is because of the colour variation between the two materials. This is conventionally handled by preparing individual calibration tables for each application. A new methodology to tune the calibration table obtained for a single material to accommodate the tint variation in TFP is proposed for the use of different specimen materials. Discontinuities in fringe order variation are smoothed using the refined TFP (RTFP) procedure. The elegance of the new methodology for solving a multi-material system is bought out by solving the problem of a bi-material Brazilian disc. The results obtained are compared with the phase shifting technique.     

一种通过条纹方向图提取散斑条纹中心线的方法

在光测力学中,如何从单幅散斑干涉条纹图中消除散斑噪声,高精度自动提取相位信息,是一项较困难的工作。本文提出了一种计算条纹方向的简单算法,以及通过条纹方向图提取散斑条纹中心线的方法。实验表明此方法对高噪声的散斑条纹图非常有效。     

Differential interferometry with adjustable spatial carrier fringes for turbine blade cascade flow investigations

 Digital evaluated differential interferometry using adjustable spatial carrier fringes was applied to flow measurements in a transonic turbine blade cascade. The interferograms were evaluated using a two-dimensional Fourier Analysis. This evaluation provided density gradient maps of the flow field in a digital form. A specially designed interferometer was used allowing adjustment of sensitivity and superposition of carrier-fringe system separately. This type of interferometer is also highly insensitive to vibration noise. For a turbine blade cooling film a comparison of this type of differential interferometry with holographic interferometry and a Schlieren visualisation is also given. As a result differential interferometry using adjustable spatial carrier fringes and digital fringe analysis gave density-gradient maps similar to Schlieren recordings but of quantitative nature, thus enabling compensation of wave front distortions. Integration of these density gradient maps resulted in density maps which were then compared to recordings done with pulsed holographic interferometry. Received: 27 December 1996/Accepted: 30 April 1997     

Critical needs of fringe-order accuracies in two-color holographic interferometry

Two-color holographic interferometry is a promising technique for separating simultaneous concentration and temperature variations in solution for crystal-growth experiments on earth and in microgravity conditions in space. The ultimate success depends on two linearly independent fringe patterns due to the different wavelengths. With available practical lasers and typical crystal-growth experimental conditions the two interference fringe patterns (other than scale effects) may not be too different. The slight error in the measured fringe order can then yield large uncertainty in temperature and concentration determination. This aspect is analytically considered for the first time in this article. A simple cell (rectangular parallelpiped) is considered containing the fluid. For simplicyt, we assume a constant field along the object-wave-propagation direction in the cell. The two reconstructed fringe patterns are then represented in terms of temperature and concentration variations. Solving two equations theoretically yields the desired temperature and concentration. However, once the fringe-postition measurement error is introduced, error in the temperature and concentration results. These errors are analytically determined. A particular case of TGS (triglycine sulfate) aqueous solution with HeNe (λ=632.8 nm) and HeCd (λ=441.6 nm) lasers for holography is critically discussed. It is found that a high degree of accuracy in the fringe order is required in this particular case. To improve fringe-position measurements, special techniques such as electronic phase measurement or heterodyne detection may be necessary. The study provides the analytical guidelines for designing the experiments and critical needs of desired physical parameters. Paper was presented at the 1990 SEM Fall Conference on Experimental Mechanics held in Baltimore, MD on November 5–8.     

载波条纹图的处理及应用

本文提出一种载波条纹的处理方法，将变形前、后的载波条纹图分别经过条纹细化、抽取中心、级数编码、全场拟合等处理，首先求出全场每个像素点上的条纹级数，然后再对应相减，以得到仅仅由于变形引起的干涉条纹的全场分布，文中应用该方法分析处理了差分干涉条纹图，测量了水平热管周围的温度场、温度梯度场及壁面换热系数。     

区域密度滤波及其在数字散斑条纹处理中的应用

利用统计学原理对数字错位散斑条纹的形成进行了系统分析，并针对散斑条纹图所特有颗粒性强的特点，提出一种新的空域滤波方法－区域密度滤波。该方法能更有效地抑制散斑图中的高频噪声，也使条纹图更平滑，并且细节得到了最大程度的保存，避免了有些空域滤波法因误差积累而导致条纹移动的问题，进一步保证了相移技术和神经网络系统的计算精度。     

Fracture investigation at V-notch tip using coherent gradient sensing (CGS)

Local deformation field and fracture characterization of mode I V-notch tip are studied using coherent gradient sensing (CGS). First, the governing equations that relate to the CGS measurements and the elastic solution at mode I V-notch tip are derived in terms of the stress intensity factor, material constant, notch angle and fringe order. Then, a series of CGS fringe patterns of mode I V-notch are simulated, and the effects of the notch angle on the shape and size of CGS fringe pattern are analyzed. Finally, the local deformation field and fracture characterization of mode I V-notch tip with different V-notch angles are experimentally investigated using three-point-bending specimen via CGS method. The CGS interference fringe patterns obtained from experiments and simulations show a good agreement. The stress intensity factor obtained from CGS measurements shows a good agreement with finite element results under K-dominant assumption.     

数字散斑剪切干涉及偏转平台法相移系统研究

在传统的剪切电子散斑干涉中 ,直接观测到的是干涉条纹图样。因此 ,如何将位移导数场的定量信息从剪切电子散斑干涉条纹图案中提取出来 ,一直是人们关心的问题。本文运用传播光矢量对数字散斑剪切干涉的条纹形成作了理论解释 ,使其物理意义更加清晰。理论分析表明 ,物体的微小偏转可引入线性附加位相。因此 ,通过连续偏转物体可实现剪切电子散斑干涉的相移。本研究通过计算机控制载物平台的精细旋转实现相移 ,结合传统的数字散斑剪切干涉技术以及四步相移算法 ,实现了数字剪切散斑干涉相移系统。利用该系统进行了中心加载、周边固定的圆盘的典型实验 ,实验结果表明该系统可以方便有效地提取出位移导数场的定量信息。