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。     

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。     

A fringe-compensation technique for stress analysis by reflection holographic interferometry

The use of holographic interferometry for stress analysis of nontransparent objects is limited by rigid-body displacements of the object. These displacements can alter the fringe patterns and often cause the fringes to disappear completely. A technique of compensation for this deterioration of the fringe pattern forreal-time holographic interferometry is described in this paper. It is especially designed to permit the accurate measurement of the out-of-plane component of strain near regions of stress concentration in plates that are subjected to in-plane loading. It is first shown that the fringes caused by a pure rigid-body displacement can be eliminated almost completely by translations of the hologram and rotation of the illumination wave. This procedure is first described when the displacement is known; then when it is unknown. A method to estimate the error made in the correction is presented. In actual stress-analysis problems, the object is both rigidly displaced and strained. Assuming the rigid displacement is known and corrected as previously, the analysis is developed to relate the fringe pattern to the strain-related displacement. This analysis takes into account the optical modifications of the system that are necessary to achieve the rigid-body-displacement correction. When the rigid-body displacement is unknown, the method is shown still to be workable through the use of various symmetries and boundary conditions. Two sample interferograms are presented as illustrations. Quantitative treatment of data from one of these are presented in a companion paper.     

Frequency modulation interpretation of fringes and computation of strains

Phase modulation is a traditional model for the interpretation of fringe patterns that provide displacement information, moiré, holographic interferometry, and speckle techniques. An alternative interpretation of the fringes is to consider them as frequency modulated signals. This change of interpretation has profound practical consequences if the space-frequency representation of signals is applied. The utilization of the energy representation of a signal in the coordinates-frequency space provides powerful procedures to retrieve strains distributions directly, from fringe patterns without resorting to differentiation of the displacements. This approach also simplifies the determination of displacements replacing unwrapping procedures by integration of the strains, a robust operation in the presence of noise. The Gabor transform, wavelet transforms, and quadratic representations of the energy of signals are tools that are available to carry out the practical implementation of this approach to fringe processing. This paper extends to two dimensions the methodology developed for one dimension in a previous paper. This paper was presented, in part, at a symposium honoring Dr. Christian P. Burger,Novel Applications of Experimental Methods in Mechanics, held at the 2003 SEM Annual Conference and Exposition on Experimental and Applied Mechanics June 2–4, Chartotte, NC.     

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.     

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。     

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.     

加窗傅里叶滤波和相干增强扩散在条纹去噪中的比较分析

光学干涉测量具有非接触、高精度和全场测量的优点,能对形变、折射率、位移等信息进行测量。噪声滤除是光学干涉测量产生的条纹图像处理的一个关键问题。加窗傅里叶滤波(Windowed Fourier Filtering,WFF)与自适应加窗傅里叶滤波(Adaptive Windowed Fourier Filtering,AWFF)是有效的频域去噪算法。相干增强扩散(Coherence Enhancing Diffusion,CED)则是基于偏微分方程的空域去噪算法。针对条纹去噪问题,比较了WFF、AWFF和CED在不同密度和不同噪声类型的条纹图上的表现,分析了它们的适用条纹类型。     

云纹干涉法瞬态应变分析

本文将单光束错位云纹干涉法应用于动态测量,获得了一种可独立求解全场瞬态应变分量,不受材料限制的动态测量新方法。文中应用该方法对一个受冲击载荷的带也孔方板的动态应变传播过程及对称面上的动应变分布进行了研究,得到了比较理想的结果。     

Computerized fringe analysis in photomechanics

A generalized method is presented for analyzing the fringe patterns frequently encountered in experimental mechanics. By utilizing digital-image-processing and computer-graphics techniques, a set of menu-driven software is developed for interactively implementing the fringe processing. Tests of this software on the images obtained experimentally by photoelasticity, holographic interferometry and speckle interferometry demonstrate its usefulness. Good agreement between the experimental and theoretical results is established.     

The development of orthogonal bicolored moiré fringes

This paper presents the results of an investigation to develop new techniques to enhance the moiré method of mechanical interferometry. The program demonstrated the practicality of developing the use of orthogonal bicolored moiré fringes with the unique capability to selectively display either set of fringes while obscuring the other set. An interpolation method for the determination of fractional fringe orders is also discussed.     

A neoteric interferometer for use in holographic photoelasticity

A shortcoming of the conventional holographic interferometer used in photoelasticity is that, for the double-exposure cases, the resulting fringe patterns are a complex combination of conventional isochromatic and isopachic fringes. This paper describes a holographic interferometer that may be used to obtain separate but simultaneous isochromatic- and isopachic-fringe patterns for photoelastic models in states of plane stress. The method requires a model with a partially reflecting front surface. Isopachics, which are proportional to the thickness change, are recorded using holographic interferometry from the transmitted light. The isochromatics are obtained from the transmitted light by conventional means. General equations relating the surface displacement of the specimen to the observed fringe patterns are developed, and examples of static and dynamic loadings are shown.     

Evaluation of rigid rotations in flexural loading tests by holographic interferometry

The authors develop a simple method based on holographic interferometry for determining the Poisson's ratio and the Young's modulus for a specimen subjected to four-point flexural testing that evaluates and eliminates the effects of the unwanted rigid-body rotations. In the experimental setup, they use an additional mirror to record the underside and the front surface of the specimen simultaneously. The theoretical analysis shows that it is possible to correlate the holographic fringe pattern of the underside and front surface of the sample. Each rotation angle can be evaluated by counting the fringe orders between two points chosen on the two fringe patterns.     

A new holographic interferometer for stress analysis

In holographic interferometry with a photoelastic model, two families of fringes are generated simultaneously when the model is stressed. One family represents the isochromatic-fringe pattern normally associated with photoelasticity which yields the difference between the principal stresses. The other family represents the isopachic-fringe pattern associated with interferometry which yields the sum of the principal stresses. From these complementary patterns, the magnitudes of the principal stresses can readily be determined throughout the field of observation. Unfortunately, these fringe patterns are not completely independent but interact in such a way as to make interpretation difficult in critical regions of the model. A new system has been developed which readily permits simultaneous acquisition of these fringe patterns without their undesirable mutual interaction, as well as providing increased sensitivity. This new interferometer uses a double-pass object beam and an optical rotator to eliminate the isochromatic-fringe pattern and its effect from the isopachic interferogram. Such a system has considerable value in experimental mechanics for applications to both static and dynamic model studies and to materials investigation.     

Experimental full field investigations of resonant vibrations for piezoceramic plates by an optical interferometry method

The experimental measurement of resonant frequencies for piezoelectric material is generally performed by impedance analysis. In this paper we employ an optical interferometry method, called amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI), to investigate the vibration characteristics of piezoceramic plates. This method demonstrates its advantages of combining noise reduction, like the subtraction method, and high fringe sensitivity, like the time-averaged method. As compared with the film recording and optical reconstruction procedures used for holographic interferometry, the interferometric fringes of AF-ESPI are produced instantly by a video recording system. Based on the fact that clear fringe patterns measured by the AF-ESPI method will be shown only at resonant frequencies, both the resonant frequencies and corresponding mode shapes are obtained experimentally at the same time. Excellent quality for the interferometric fringe patterns of the mode shapes is demonstrated. We find from experimental results that the out-of-plane vibration modes (type A) with lower resonant frequencies cannot be measured by impedance analysis and only the in-plane vibration modes (type B) will be shown. However, both the out-of-plane (bending) and in-plane (extension) vibration modes of piezoceramic plates are obtained by the AF-ESPI method. Finally, numberical finite element calculations are also performed, and the results are compared with the experimental measurements. Excellent agreement for the resonant frequencies and mode shapes are obtained from both results.     

Nano-meter Displacement Measurement by Phase Analysis of Fringe Patterns Obtained by Optical Methods

0Introduction Inordertomonitorthehealthofstructures,straingagesanddisplacementtransducersare usuallyused.Thereasonisthatmanyrulesorcodesforinspectionofstructuresrequiretousestrain gagesanddisplacementtransducers,anditiseasytousethem.However,thesemethodsarebasically one pointmeasurementmethods.Theyareexpensiveandtime consumingfordistributionanalysis.Opticalmethodssuchasgrating projection,geometricmoir啨,moir啨interferometry,holographic interferometryandspeckleinterferometryareusefultomeasuredi…     

Experimental observation of stress waves propagating in laminated composites

The theoretical research on stress waves propagating in laminated composites has been reported by many authors. However, there has been little work on experimental studies of stress waves in those materials. This paper presents an experimental investigation on stress waves propagating parallel to the layers of a laminated composite. A sandwich laminated composite consisting of two aluminum facings and an epoxy core is used as a specimen. The stress wave in the specimen is observed by use of high-speed holographic interferometry with a pulsed laser. In order to obtain the relative fringe orders, the interference fringe pattern in the reconstructed image is treated as an image-processing system with a personal computer. For the calculation of the in-plane displacement, an approximate relative-fringe-order method is used. The in-plane displacements obtained at some sampling points on the surface are smoothed by using a spline function. Distributions of the in-plane displacement and the shear stress are then obtained quantitatively over the whole analyzed field.     

The magic of carrier fringes in moiré interferometry

Practical applications in which carrier fringes are used with moiré interferometry for strain measurements are presented. Examples illustrate how moiré carrier fringes are applied to obtain the desired data in complex laminated composite specimens. In many cases, carrier fringes permit extraction of much more detailed information, with procedures that are easier and more accurate than those using loadinduced fringes alone. The fringe vector for carrier fringes is introduced and its application to the interpretation of fringe patterns is explained. In moiré interferometry, the carrier fringes are produced easily by adjustments of optical elements that control the virtual reference grating.     

Transportphenomena in subcooled flow boiling

Subcooled boiling has been subject of extensive research studies in the literature. So far, the approach of studying the phenomena of subcooled boiling has rather been an integral method by measuring the heat transport from the wall to the liquid and by following the growth and collapse of the bubbles. However, little is known about the heat transport at the phase interface between the surface of the bubbles and the subcooled liquid. Experimental attempts to study the transport phenomena around the bubble surface quantitatively have been performed by using the holographic interferometry, an optical method, which works in an inertialess and non-invasive way. The conventional holographic interferometry has somewhat been modified by applying the finite fringe method. With this technique interesting insights could be gained and precise quantitative data could be evaluated.     

Single-beam shearing Moiré interferometry for measuring slope and curvature of bent plates

The single-beam shearing interferometry with high-frequency phase-type blazed grating for measuring the slope and curvature contour fringes of bending plates is presented. As it is characterized by excellent fringe contrast, high sensitivity and extensive range, this method is effective for plate bending problems. Two examples of application to the clamped circular bent plate and the rectangular bent plate with edge notch are given.