二次曝光散斑图的透过率自相关函数

二次曝光散斑图测量的面内位移信息是以透过率自相关函数的形式记录在散斑图中的.本文计算了激光散斑图及白光散斑图的自相关函数;给出了其解析表达式.文中指出,激光散斑图照相系统的点扩散函数重叠面积是决定自相关函数的主要因素,而白光散斑图的自相关函数则与之无关.这一结果为进一步分析散斑干涉场条纹质量提供了依据.     

散斑全息干涉法测量面内位移和应变

测量面内位移和应变有很多方法,诸如莫尔条纹法、全息干涉法、激光散斑干涉法等属于近代光学方法。其中莫尔条纹法需要在试件表面布上极细的网格,这在工艺上较难;而全息干涉法又需沿不同方向进行全息照相,要求较高,数据处理的程序也较繁复.最近国外采用激光散斑干涉来测量面内位移和应变,发展很快。激光散斑干涉法亦有多种。成象散斑干涉是记录被相干光照明的物体经透镜成像后所形成的具有斑点图信息的物体象,照明光可用单光束或多光束:光栏也可以是单孔或多孔。我们曾采用单光束和单孔成象的散斑干涉法对游标盘的转动进行了定标试验。另一种散斑干涉法是直接将感光片和被测物表面贴近,并牢靠地固定其相对位置.再用一束准直激光直接从感光片背面射入。由于照明光与物体表面的漫反射光是从接近180°的方向射到感光层,因而感光片记录的信息中不仅有斑点图信息,而且还包含有能实现白光再现的全息图信息,我们暂且称其为散斑全息干涉法.本文主要介绍散斑全息干涉的物理原理和它的实验方法,并利用杨氏干涉法对游标盘转动后的位移量定标和对单向拉伸的矩形板中的圆孔应力集中系数进行了定标,取得了实验结果。此外,还指出了散斑干涉法的缺点和局限性。     

用于位移、应变分析的激光散斑干涉的全场分析

本文叙述用于位移、应变分析的激光散斑干涉的全场分析法,提出了三种新的散斑照相法:十字缝光阑法、矩形多孔光阑法、移动或旋转孔光阑法.对这些方法进行了理论分析和实验验证.结果表明;采用这些方法进行散斑照相,在全场分析时可以有很宽的滤波变化范围而同时有较高的观察光强,因而可以获得清晰的、位移灵敏度可变的类似于全息干涉图一样的位移场分布图,这无疑为散斑干涉的应用提供了很大的方便,使全场分析法更具有现实性.     

应用激光散斑技术研究稳定扩展过程中的裂纹张开位移

本文应用激光散斑照相放大技术和夹层散斑技术,测量了稳定扩展过程中的裂端张开位移和裂端前方纵向应变的变化,并提供了部分实验结果. 1.实验测试技术和数据处理 实验采用了散斑照相放大光路,放大10倍,并用夹层散斑法记录散斑场.试件有两种,一种是0.2毫米厚的铝箔试件(E=8500kg/mm~2,σ_(0.2)=14.2kg/mm~2,σ_b=15.4kg/mm~2),双边裂纹,尺寸见图1.两条裂纹长短不等,测量长裂纹裂端的变形.为了观察远场应变随裂纹缓慢扩展的变化,在试件上贴了一个2×3毫米的应变片,实验中用应变仪进行测量.第二种试件是0.1毫米厚的紫铜箔试件,单边裂纹,尺寸见图2.     

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。     

用直接散斑法对平面应力问题进行全场应变分布测定的实验与分析

本文通过直接散斑法和云纹法测定带小孔薄板在单向拉伸载荷作用下的应变分布,分析了激光散斑法和云纹法之间的内在关系,讨论了直接记录的散斑底片和照相记录的散斑底片各自在频率响应上所呈现出的差别,利用空间频率概念作为定量刻划散斑法和云纹法在测量应变时的灵敏度的共同标准。实验中所测应变范围较大,包括完全弹性应变、局部屈服应变以及卸载后的残余应变。得到的均是全场分布信息,实验值与计算结果符合较好。     

激光散斑复合错位干涉法

本文对利用光楔的激光散斑复合错位干涉法作了修正。分析了用等分直角错位光楔和等分60°错位光楔时,双曝光散斑图的频谱特性,提出用作图法确定频散晕的周界。建议在滤波时选用高通滤波以减小或消除散斑照相的噪声影响和增加信息。     

应用激光散斑照相放大技术和夹层散斑技术研究裂端附近应变场

本文研究了激光散斑照相放大技术和夹层散斑技术。激光散斑照相放大技术可以用来测量裂端附近一毫米范围内的应变分布。夹层散斑技术便于用来测量应变分布随加载过程的变化。应用这两种技术,我们测出了裂端附近1.7mm×1.5mm范围内的应变场及其随加载过程的变化,并提供了实验结果。此外,我们还提供了裂纹扩展过程中裂端前方不断出现小孔现象的照片。     

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。     

基于单像素成像的微小位移测量方法

激光散斑位移测量法是一种重要的现代光学位移测量方法,由于受到图像传感器元件感光性能限制,难以在强干扰光条件下获得有效散斑场信息,进而无法获取位移场数据,因此,基于单像素成像技术,本文提出一种新的激光散斑位移测量方法:对散斑信息进行图案编码调制,并使用单像素探测器采集调制后的光强信息;利用Walsh-Hadamard Transformation(WHT)成像算法对散斑场图像进行重建;最后结合自相关算法确定物体的位移场信息。分别利用商业相机和单像素成像技术对散射介质的单轴微小位移进行测量,结果表明基于单像素成像技术的激光散斑位移测量技术可以获得较好的测量结果。相比于传统测量方法,基于单像素成像技术的激光散斑位移测量方法在复杂环境中具有一定的优势,可实现强光干扰下的位移场测量。     

流动显示技术及其现代发展概况

本文回顾了流动显示发展的历史,以及它在流体力学研究中所起的作用。根据获取流动信息的方式不同,流动显示技术可分为两大类型。作为近代技术发展的例子,三维非对称流干涉图的定量计算、片光技术、散斑照相术、激光诱导萤光法、多普勒干涉图象显示速度场、光电信号转换激光干涉仪、以及图象处理和计算机产生数字流谱技术均作了简要的介绍。     

刀具变形的在线散斑检测

散斑照相，防震要求低，光路简单，所需曝光时间短，符合连续激光对动态测量的要求。本文利用散斑照相法，测量了机床刀具的动态切削过程，并利用逐点分析和全场分析方法，分析了所拍摄的散斑图，得到了不同车速和不同切削用量条件下的位移场、应力场     

Speckle photographic measurement of turbulence in an air stream with fluctuating temperature

The deflection of laser light passing through the mildy heated, turbulent air stream in a lowspeed wind tunnel is measured by means of speckle photography. This optical wholefield method provides a dense distribution of data values of the deflection angle in the field of view. When isotropic turbulence is assumed, it becomes possible to calculate the correlation function of the three-dimensional, turbulent temperature (or density) field from the correlation function of the plane distribution of measured deflection angles. Spectra and characteristic length scales are determined and compared with cold-wire data reported in the literature.A version of this paper was presented at the 10th Symposium on Turbulence, University of Missouri-Rolla, Sept. 22–24, 1986To Professor R. J. Emrich on the occasion of his 70th birthday     

汽油机燃烧室内温度场测量的激光剪切干涉法

采用激光剪切干涉法测量了汽油机燃烧室内的温度场,并分析了剪切干涉法测温的基本原理,推导出利用干涉条纹图求解温度分布的关系式。在一台二冲程火花点火发动机上设置石英窗和信号同步系统,建立了适合高速摄影的激光剪切干涉测量装置。通过改变剪切干涉量,测取发动机燃烧室内干涉条纹图,从而获得缸内燃烧的二维温度场。结果表明,激光剪切干涉法抗振性强,光路简单可靠,可以进行高速摄像,是研究内燃机燃烧过程的有效方法。从温度场可以看出,燃烧过程中缸内大致可分为三个区,即已燃区、未燃区和燃烧区,具有不同的温度分布和温度梯度。燃烧区温度最高,温度梯度大;已燃区温度次之,梯度较小;未燃区温度最低,但梯度较大。     

An extended algebraic reconstruction technique (ART) for density-gradient projections: laser speckle photographic tomography

An extended algebraic reconstruction technique (ART) is presented for tomographic image reconstruction from the density-gradient projections, such as laser speckle photography. The essence of the extended ART is that the density-gradient projection data of speckle photography (Eq. (1)) are first numerically integrated to the algebraic representation of interferometric fringe number data (Eq. (12)), which ART can readily reconstruct into the cross-sectional field. The extended ART is numerically examined by using two computer synthesized phantom fields, and experimentally by using asymmetric single and double helium jets in air. The experimentally reconstructed images were also compared with the direct measurements of helium concentration using an oxygen analyzing probe. The extended ART method shows an improved accuracy and is proposed to use to tomographically reconstruct the density-gradient projections over the previous Fourier convolution (FC) method (Liu et al. 1989). Received: 26 June 1998/Accepted: 18 March 1999     

Analysis of Speckle Photographs by Subtracting Phase Functions of Digital Fourier Transforms

This paper presents a method for measuring displacements and strain in digital speckle photography that is an alternative to currently used correlation techniques. The method is analogous to heterodyne speckle photogrammetry wherein optical Fourier transforms were taken of individually recorded specklegrams and combined in a heterodyne interferometer where an electronic phase meter measured the phase differences between the two transforms. Here, digital photographs are recorded and Fourier transformed so that their phase functions can be subtracted and fitted to a linear function of the transform coordinates. The effect of different recording and processing parameters is investigated. It is found that incoherent speckles give better results than those formed by coherent laser light. In addition, image correlation is used to process an identical data set so that comparison of the two methods can be made.     

撞击载荷下数字散斑干涉法中位相的自动计量

在撞击载荷下的数字散斑干涉法（DSPI）中，本文联合应用加法和减法两种模式提出了位相测试技术，以矩形板对称轴承受撞击集中载荷为例，测量了位移场的位相分布，为了采集红宝石脉冲激光形成的数字散斑场，提出瞬态数字图像采集技术。     

Evaluation of finite-element calculations in a part-circular crack by coherent optics techniques

Two techniques, speckle photography and holographic interferometry, were used to test three-dimensional finite-element calculations in an internally pressurized cylinder with an external part-circular crack. Opening displacements along the crack line were measured by speckle photography. Radial displacements were obtained from holographic fringe patterns. Good agreement between experimental and numerical data is obtained. Stress-intensity factor variations along the crack front are calculated from numerical results.     

Speckle optical measurement of a turbulent scalar field with high fluctuation amplitudes

A turbulent temperature field is produced in the gas flow downstream of a turbulence grid by passing the flow through a plane combustion front at the grid that serves as a flame holder. RMS values of the temperature fluctuations of up to 33 K are generated thereby. Properties of the turbulent scalar are measured with an optical speckle technique. The experimental results are compared with theoretical models described by Rotta (1972) and Driscoll and Kennedy (1985). From this comparison it is evident that, even at these high fluctuation amplitudes, the turbulent temperature field still behaves as a passive scalar.