A role of fringe pattern catalogue in the course of interferometrically based determination of residual stresses by the hole-drilling method

A further development of the technique for residual stresses determination in thick-walled structures, which is based on a combination of the hole-drilling method and reflection hologram interferometry, is presented. A plane specimen welded from two equal parts of dimensions 130×80 mm² in plane and thickness 12 mm is the object of investigation. Weld seam is performed along the shortest side of the specimen. Residual stress field of interest is formed by a superposition of initial welding-induced field and secondary stress field caused by plastic deformation of the specimen. A set of actual fringe patterns, which corresponds to a wide variety of residual stress components both ratio and sign, are reconstructed and presented as illustrations. A series of reference fringe patterns is simulated for the most typical cases inherent in residual stress field under study. It is shown that actual interferograms obtained belong to three main groups depending on a typical form of fringes configuration. On this base the main principles of creating the general catalogue of fringe patterns are established and the first version of this catalogue, which is related to reflection hologram interferometry, is developed. A structure of the catalogue that consists of both actual interferograms and reference fringe patterns is described. Possible ways of further catalogue completing and its direct implementing in the course of quantitative determination of residual stresses are discussed. It is shown that both experimental and numerical data aggregated into the first version of the catalogue can be effectively used for a verification of various coherent optics techniques with respect to a determination of residual stress components by means of hole drilling. An analysis of capabilities of reflection hologram interferometry in the field of residual stresses determination comparing with dual-beam speckle-interferometric techniques is presented. Superimposed residual stress field is quantitatively described in detail for both specimen sides of dimensions 260×80 mm². It is shown that fine nuances inherent in residual stress distributions over different specimen faces can be reliably derived from recorded fringe patterns of any type. This study serves as an example of residual stress components determination in real structure with a type of residual stress field to be investigated is unknown before the experiment.     

Fringe interpolation by two-reference-beam holographic interferometry: Reducing sensitivity to hologram misalignment

Accurate fringe interpolation in holographic interferometry requires two-reference-beam holographic recording. Using two reference sources close together, the sensitivity to (angular) misalignement of the hologram is drastically reduced (10° instead of 0.01°). Overlapping of the cross-reconstructions can be tolerated, unless extreme precision and spatial resolution are demanded. Experimental results obtained by video processing of such holograms show an accuracy of better than $\text{1}\text{100}$ of a fringe. The optical setup becomes nearly as compact and simple as in classical holographic interferometry.     

Real-time color holographic interferometry devoted to 2D unsteady wake flows

A new optical technique based on real time holographic interferometry in true colors has been implemented around the transonic wind tunnel of the ONERA-Lille center to analyze 2D unsteady wake flows. Tests realized in color interferometry, real time and double exposure, use simultaneously three wavelengths of a continuous waves laser (argon and krypton mixed) and holograms are recorded on silver-halide single-layer panchromatic Slavich PFG03c plates. The very principle of real-time true color holographic interferometry uses three primary wavelengths (red, green and blue) to record, under no-flow conditions, the interference among the three measurement beams and the three reference beams simultaneously on a single reference hologram. After the holographic plate is developed, it is placed on the test setup again in the position it occupied during exposure and the hologram is illuminated again by the three reference beams and three measurement beams. A flat, uniform color can then be observed behind the hologram. So a horizontal, vertical, or even circular fringe pattern can be formed and the achromatic central fringe can be made out very clearly. The single color is used to determine the path difference zero on the interferograms. The flow studied was the unsteady flow downstream of a cylinder placed crosswise in the test section. A sequence of hundred interferograms was recorded on the flow around the cylinder at Mach 0.37. The vortex formation and dissipation phases can be seen very clearly, along with the fringe beat to either side of the cylinder.     

Two improved methods of surface-displacement measurements by holographic interferometry

This paper describes two new methods for measuring surface-displacements. The first method is an improvement of Ennos' scheme in that multiple object beams are used instead of multiple hologram plates. This arrangement enables the three fringe patterns required for calculating displacement components to be viewed from the same direction, i.e., normal view. Thus the necessity of laborious fringe reprojection is eliminated. The second method involves making three holograms, one situated on each of the three coordinate axes assigned to the surface. Each hologram picks up one component of displacement. Hence no separation of displacement components is required. An experimental demonstration is presented which utilizes the first technique and checks with theoretical predictions.     

载波相移全息干涉计量

本文报道了一项称为载波相移全息干涉计量的自动相位估算的新技术。该技术的主要特点是不同相移的条纹图案可用双曝光全息重视。这样即可用来对与时间相关的问题进行自动相位估算。     

二维彩虹全息图母版的非相干光拷贝技术

描述一种用非干光制作二维彩虹模压全息图母版的新技术。该技术用紫外灯作为记录光不原,记录系统中不用任何光学元件。记录过程不需防振条件,色彩编码 狭缝像的“彩虹版”上进行条纹复制而获得。彩虹版可以无数次重复使用,所以全息图母版的记录十分简单。该技术投资少、效率高,制出的全息图质量好,对大批量模压全息图制造有很高的实用价值。     

Anisotropic partial differential equation noise-reduction algorithm based on fringe feature for ESPI

Noise reduction is one of the most exciting problems in electronic speckle pattern interferometry. We present a new anisotropic partial differential equation noise-reduction algorithm based on fringe orientation for interferometric fringe patterns. The proposed equation performs diffusion along the two directions of fringe gradient and isophote line, which are extracted accurately according to fringe feature. By restriction of diffusion in the gradient direction of fringe patterns, this method can provide optimal results in denoising but does not destroy fringe edges. The experimental results show that this technique is more capable of significantly improving the quality of the fringe patterns than the classical anisotropic diffusion equation proposed by Perona and Malik. Based on our filtered fringe patterns, the phase map obtained by phase-shifting technique can be extracted more accurately. It is an effective pre-processing method for electronic speckle pattern interferometry.     

Effect of aberrations in formation of holographic lateral shear interferograms under high measurement sensitivity

Analysis of the effect of aberrations of a system for recording and optical processing of holograms, as well as of inhomogeneities in hologram bases, on fringe distortion is performed for different methods of holographic shearing interferometry. Different dependences of the degree of fringe distortion in lateral shear interferograms on the measurement sensitivity are revealed. A method of excluding aberrations in formation of shear interferograms is proposed for the cases of single-and double-exposure holograms. Experimental results are reported.     

Classification of holographic fringe patterns inherent in through hole drilling in residual stress field

Comparative analysis of actual fringe patterns, which are induced by combined implementing the hole drilling method and reflection hologram interferometry for residual stresses determination, is presented. Involved considerations are related to plane thin-walled structural elements. A set of interferograms of perfect (ideal) form is selected proceeding from one-side measurements. A base for recognising each specific ideal configuration is a fine coincidence between actual interferograms and analogous reference fringe patterns constructed for the same stress state. Perfect (ideal) both actual and reference fringe patterns are defined as a response of pure membrane 2D stress field on through hole drilling between exposures. Main principles of creating the regular catalogue of reference fringe patterns inherent in through hole drilling in thin-walled components are formulated. Emphasis is made on a careful collecting and classifying actual interferograms with clear indications of bending stress presence in total residual stress field. Evidences needed for a reliable classification of the type of residual stresses field of interest are established and verified. A response of superimposed residual stress field, which consists of both membrane and bending components, is characterised by various deviations of each specific fringe pattern from an ideal form. More deep analysis of fringe patterns related to superimposed residual stress field is based on specially designed technique. The main essence of the approach developed is simultaneous measurements of through hole distortions in two principal strain directions on opposite sides of thin plane specimen. These sides are faces of the drill entrance and exit. Sophisticated optical set-up that is capable of obtaining high-quality fringe patterns in the course of two-side measurements is developed and implemented. Typical set of fringe patterns obtained for single probe hole on opposite specimen faces is presented.     

Measurement of properties of silver telluride thin films using holography

Holography is an interferometric method of recording the light waves diffracted by a subject illuminated with coherent light. Holographic interferometry (H.I.) is one of the most important applications of holography. It is concerned with the formation and interpretation of fringe patterns, which appears when a wave generated at some earlier time and stored in a hologram is later reconstructed by interfering with comparison wave. We report a technique, which uses double exposure holographic interferometry together with simple mathematical interpretation, which allow immediate finding of stress and thickness of thin film. We tested the same for different normalities of solutions. It was further noticed that the fringe spacing changes with solution concentration as well as time of deposition. The thin films are prepared using electrodeposition technique. It’s structural, morphological and optical study carried out by XRD, SEM, and UV-Vis-NIR spectrophotometer.     

数字全息干涉术用于微波等离子体推进器羽流场的研究

利用数字全息干涉术研究了微波等离子体推进器羽流场的分布特征,由所记录的羽流场的数字全息图,经数值再现,得到了羽流场的相位分布,进而计算出等离子体羽流场的电子数密度.通过相位倍增法增加了羽流场的干涉条纹密度,从而能够更直观地反映出羽流场的折射率分布.结果表明,数字全息干涉术是研究微波等离子体推进器羽流场的一种有效方法.     

大景深多重全息术及其应用

提出并实现服用一般Ｈｅ－Ｎｅ激光器记录的大景攀重全息术，这种技术是根据光源时间相干性的特点，在参考光上作光路补偿来扩大景深，并用旋转光楔调制两平面参考波，记录大景深物场的多重全息图，这是一种重像数可以选择的大景深多重全息术，文中给出理论分析和实验结果，理论分析与实验结果是吻合的，文中还提出了用旋转光楔实现多路多参考光编码记录的多通道大景深全息干涉计量术，这种技术可用于研究大景深物场的时间序列动态过     

Reference fringes in holographic interferometry

This paper describes the application of reference fringes in double exposure holography of transient phase objects. This includes selection of fringe patterns and fringe number densities suitable for the quantitative analysis of the hologram. Methods of realizing different reference fringe patterns are presented. As the focus of the interference fringes depends on the optical arrangement, different systems are discussed.     

Systematic error elimination by correction of variable interferometer aberrations

The possibility of reducing the variable systematic error in interferometry measurements via a higher degree of compensation of residual aberrations of the interferometer is shown theoretically and verified experimentally. It is proven that, in the case when interferometer aberrations are variable, one reference hologram is insufficient to correct aberrations. However, using several reference holograms on which the aberrations are recorded, it is possible to reconstruct interference patterns in which the influence of residual aberrations on the behavior of bands is reduced to a definite minimal level.     

Sequential hologram interferometry with diffusely illuminated objects

Two simple holographic multiplexing techniques for sequential hologram interferometry of a diffusely illuminated object are described. These techniques enable one to use the frozen-fringe hologram interferometry to study a quasi-continuous change in the object and so regain some of the advantages of real-time hologram interferometry. In the first method of multiplexing with a single reference beam, a small angle prism is used for varying the direction of the reference beam between successive exposures and a double-exposure hologram is recorded at each position of the prism. In the second method of multiplexing with multiple reference beams, a separate reference beam is used for recording each state of the object independently and the interference pattern between any two states is obtained by simultaneous reconstruction of two light fields. The advantage of this method over the previous one is that it is also suitable for dynamic studies. Some reconstructed interferograms of a diffusely illuminated transparent object under different stresses are presented as illustrations.     

Combined implementing the hole-drilling method and reflection hologram interferometry for residual stresses determination in cylindrical shells and tubes

Main features inherent in simplified approach to residual stresses determination in cylindrical shells and tubes, external diameter of which is not less than 60 mm, by combing the hole-drilling method and reflection hologram interferometry are discussed in detail. Initial experimental information in a form of hole diameter increments in principal stress directions is derived from high-quality reflection holograms recorded near cylindrical objects of intermediate curvature value. Converting measured parameters into required stress values is based on the transition model that corresponds to plane stress conditions of pure membrane type. The technique developed is capable of determining residual stress component values within 5% accuracy in an absence of stress gradients over the probe hole diameter when a type of residual stress field corresponds to the transition model adopted. The accuracy analysis involved is based on matrix formulation of conventionally direct problem and an assumption on a pure membrane character of residual stress field under study for thin-walled shell. Required error estimations in a case of inspecting thick-walled cylindrical tube are obtained by combining the above-mentioned approach and an analogy of reconstructed fringe patterns with actual and artificial interferograms, which follow from drilling blind hole of the same geometrical parameters in thick-walled plates. Experimental verification of the developed approach is founded upon a determination of actual stresses in thin-walled cylindrical shell and obtaining residual stress distributions at the proximity of welded joint in thick-walled cylindrical tube.     

Studies on surface deformation of copper sulphide thin films by holographic interferometry technique

Holographic interferometry technique used to study the surface deformation of electrodeposited copper sulphide thin films on stainless steel substrate is here presented. It is concerned with the formation and interpretation of fringe patterns, which appears when a wave generated at some earlier time and stored in a hologram is later reconstructed by interfering with comparison wave. The proposed technique uses double exposure holographic interferometry (DEHI) together with simple mathematical relation, which allows immediate finding of stress, mass deposited and thickness of thin film. It must be further noted that, fringe spacing changes with time of deposition as well as solution concentration. The structural study (XRD) is carried out for the confirmation.     

Quantitative three-dimensional holographic interferometry for flow field analysis

Holographic interferometry offers the potential for quantitative, wholefield analysis of three-dimensional compressible flows. The technique is non-intrusive, does not require the introduction of seeding particles, and records the entire flow information within the pulse duration of a Q-switched ruby laser (˜30ns). At present, however, holographic interferometry is mainly used qualitatively due to the practical restrictions of data recording, acquisition and processing.To address the potential of holographic flow analysis a prototype multi-channel interferometer has been designed and preliminary wind tunnel results have been obtained. The proposed configuration uses specular illumination which, unlike comparable diffuse systems, does not suffer from fringe localisation and speckle noise. Beam collimation and steering through the flow field is achieved in a single operation by the use of holographic optical elements (HOEs). The resulting design is compact, light efficient, has aberration compensation, and the recorded data are conducive to both tomographic analysis and direct comparison to computational fluid dynamics (CFD) predictions.Holograms have been recorded of simple two-dimensional and axisymmetric compressible flows, to compare the accuracy of holographic density measurements with data from conventional pressure sensors and CFD codes. Data extraction from the holograms, and the elimination of rigid body motion, was achieved using digital Fourier transform fringe analysis. The introduction of phase errors by image processing has been investigated by analysing simulated fringe patterns generated from a combination of experimental amplitude information and computer generated phase data.     

Real-time and two-reference-beam hologram interferometry: effects of emulsion shrinkage

When transmission holograms are recorded on photographic materials, any change in the thickness of the photographic emulsion due to processing can produce a change in the spacing of the carrier fringes. We show that the resulting change in the angle at which the image is reconstructed when the hologram is illuminated with the original reference beam can give rise to significant errors in real-time and two-reference-beam hologram interferometry.