Binarization of scanning Moiré fringe pattern

This paper describes a digital picture processing method to obtain a binary scanning moiré pattern. In this method, a bias component due to the illumination light distribution is eliminated from the scanning moiré fringe pattern to detect the zero-crossing points of the moiré profile. The binary fringe pattern is then obtained from the zero-crossing points. Experiments indicate that the method is useful for facilitating three-dimensional automatic measurement using moiré topography.     

Applications of Moiré topography measurement methods in industry

Moiré topography is able to determine the shape of an object, by pattern measuring, in a short time. Recently moiré topography has been used in various industrial fields because it has superior features that point measurement doesn't have. As it becomes popular various related techniques that fit specific needs have been developed and there is the prospect that moiré topography will become a more important measurement method and strengthen its position in the near future.

This paper explains the grid irradiation method and the grid projection method as the basis of the moiré topography measurement method and describes the existing status and prospects of utilizing moiré topography measurement in the applied fields of shape measurement, flatness measurement and detection of abnormality.     

Large-deformation analysis in microscopic area using micro-moiré methods with a focused ion beam milling grating

In this study, the focused ion beam (FIB) milling method is applied to fabricate sub-micron grating on TiNi shape memory alloy materials. With self-made FIB milling gratings, scanning electron microscope (SEM) micro-moiré and digital moiré methods are successfully used to measure large deformation of porous TiNi shape memory alloys (SMA) in uni-axial compressive tests. The principles of the SEM micro-moiré method and digital moiré method are introduced, and applied to calculate large strain. The full field deformation around shear bands can be measured precisely. During the investigation, the phenomenon of furcated moiré fringes was found, and a corresponding explanation is given in this paper. The furcated fringes are generated in the locations of combined shear bands where sudden changes of strain occur. Successful results also verify that the FIB milling gratings are suitable for micro-moiré measurement and can generate high quality moiré fringes.     

Suppression of moiré fringes due to sampling of halftone screened images

When a halftone screened image is discretely sampled by, for example, a CCD array, moiré fringes sometimes appear. These moiré fringes are caused by aliasing errors due to the improper sampling rate. To suppress these fringes, a dual sampling method is proposed. In this method, halftone screened images are sampled twice with different sampling rates, and the selection of proper frequency components less suffering from aliasing errors can effectively suppress moiré fringes.     

Fourier transform moiré tomography for high-sensitivity mapping asymmetric 3-D temperature field

Fourier transform evaluation for moiré deflectogram is proposed to automatically map the temperature field. The moiré deflectogram is generated by conventional deflectometer and is analyzed by means of Fourier transform algorithm. The convolution backprojection algorithm is used for the optical tomography. Asymmetric 3-D gas temperature distribution for a given layer is reconstructed.     

Nonparaxial method for computing the gradient field of a wavefront using moiré deflectometry

A nonparaxial method in moiré deflectometry to obtain the gradient field of a wavefront under test is proposed. This method uses only two deflectograms without any information about the phase object. As a result, director cosines of the gradient field are computed from moiré fringe deviations on both deflectograms without ambiguities. The method is proved by using a synthetic wavefront simulation.     

Moiré deflectometry—ray tracing interferometry

A method for ray deflection mapping, moiré deflectometry, which is fully compatible with interferometry, is described and demonstrated by numerous examples, including testing of optical components, visualization of flow, study of transient phenomena, and modulation transfer function analysis. Unlike interferometry, moiré deflectometry is a pure ray tracing technique and, therefore, the analysis of three- dimensional objects is greatly simplified. Although the ray tracing approach to optical systems is much older than wave theory, moiré deflectometry seems to be the first attempt to apply ray tracing methods systematically to optical metrology. Moiré deflectometry is fully quantitative, interferometry-compatible in accuracy and has the additional advantage of tunable sensitivity.     

Measurement of nonlinear refraction of dyes doped liquid crystal using moiré deflectometry

Recently the nonlinear effects of the azo-dye doped liquid crystals have attracted much interest. In this paper the nonlinear refractive indices, n₂, of two dyes (Sudan Black B, Sudan III) doped nematic liquid crystal were measured at low laser powers using moiré deflectometry technique. The results show when a nonlinear sample is placed in moiré deflectometry setup, the moiré fringe patterns will rotate around the beam center because of self-focusing effect in the sample. By measuring this rotation, the magnitude and the sign of nonlinear refractive index were calculated. The n₂ values for Sudan black B is larger than Sudan III, because of some differences in molecular structure and molecular polarization.     

On the determination of elastic residual strain fields in rail wheels using moiré interferometry

Moiré interferometry was used to determine the residual strain fields in a rail wheel. Hoop, radial, and shear displacement fields were determined in a whole field manner using a novel four-beam moiré interferometer. Diffraction gratings of 150 lines/mm were employed on the specimen surface. A system of data interpolation utilizing a simple control sample scheme was developed for field environments where sample loading occurs away from the optical device. Agreement was found between the moiré technique and physical measurements of wheel contraction during sectioning. Marginal agreement was found with strain gage measurements.     

Adaptation of video moiré techniques to undersea mapping and surface shape determination

Fixed and variable resolution video moiré techniques have been used to project structured illumination in a model undersea environment and a prototype system has been developed which generates equal depth contours of undersea objects and has applications in sizing, orientation and ranging. An advantage of this system is that the entire field is continously illuminated, and the moiré contours and images are formed at video rates. The spatial frequency of the structured illumination can be continously varied, providing optimal contours for a variety of object sizes. The data can be easily interpreted by eye or processed by computer to obtain surface shape, range and orientation of a known structure.     

Optical modulation and digital demodulation of an in-plane moiré carrier

A rotational mismatch of gratings is used to generate a fringe carrier of an in-plane moiré pattern so that specimen deformation shows itself in the form of modulation of the carrier frequency. As both the unmodulated and modulated carriers are the patterns without fringe-loop or fringe-connection, they are automatically numbered with monotonical increasing orders by a digital image processing system without any ambiguity. The orders at every pixel of the image are determined by interpolation of the orders of the tracked fringes to establish two grey image files, from the difference of which, the orders of the in-plane displacement moiré are displayed with grey-level variation.     

Development of the moiré method with special reference to its application to biostereometrics

This paper reviews the development of the moiré method in its technical means and practical application to anthropological and medical studies. Emphasis is placed on references in various fields of human biology.     

An automatic quantitative approach to additive/subtractive moiré

An automatic fringe-analysis procedure is described for additive and subtractive types of moiré. The procedure is based on the simultaneous introduction of differential phase shifts to the two superposed gratings or fringes.     

Micromechanical thermal deformation analysis of unidirectional boron/aluminum metal-matrix composite

An experiment was conducted to document thermal deformation of a unidirectionally reinforced boron/aluminum metal-matrix composite. The specimen was subject to an isothermal loading of ΔT = − 100 °C and the deformation on a free surface perpendicular to the fibers was measured by microscopic moiré interferometry. The high sensitivity and spatial resolution made it possible to elucidate the micromechanical behavior of the specimen at the fiber level. Multiplied moiré fringe patterns with a contour interval of 35 nm/fringe contour were obtained for a hexagonal array of fibers and a square array of fibers. The stress-induced strains were determined from the fringe patterns by subtracting the free thermal contraction strains. The results revealed a free surface effect and showed asymmetrical and irregular strain distributions inherent in real (non-idealized) composite materials.     

Rotation measurement using a circular moiré grating

In this study a non-contact tracker for calculating the angle of rotation of a HMD (head-mounted display) is proposed. The merit of our proposed method is that the computer will change the spatial view to match the user's head posture and keep the ‘immersion' sensation at high accuracy and precision. Our results are validated using moiré fringes as an excellent HMD tracker.     

Delamination and damage studies of composite materials using phase-shifting interferometry

Composite materials offer a unique advantage over conventional engineering materials in that structural properties can be tailored to suit specific applications. However, the inherent anisotropy and the discrete layer-by-layer fabrication method of composite materials lead to mechanical behavior and failure characteristics that are quite different from those of homogeneous materials. Consequently, failure modes such as delamination in polymer matrix composites and matrix cracking and damage in ceramic matrix materials prohibit these materials from being used in conventional engineering structures, as well as making their characterization in the laboratory difficult. In this paper, an experimental photomechanics technique called phase-shifting moiré interferometry is described. This technique is capable of providing analysts and designers (both material and structural) with detailed displacement and strain fields near discontinuities in these materials. The technique allows high resolution measurements of in-plane surface displacements to be made without introducing global smoothing errors, thus preserving the integrity of data near cracks, discontinuities and material interfaces. In this paper, the advantages of phase-shifting moiré interferometry will be illustrated through several problems involving composite materials.     

Moiré methods in interferometry

The applications of moiré methods to optical interferometry are reviewed. They are used for instrumental error subtraction, reduction of spatial frequency of interferogram fringes, increase of sensitivity and the range of applications of interferometric methods, and various information processing operations. The cases of the reference beam and shear type interferometry are treated separately.     

Assessment of the quality of reedbeds using holomicroscopic moiré

Holographic interferometry is proposed to detect the change in the mechanical responses of reed stems growing in eutrophic, as compared with those in healthy, water bodies. The detection of the difference in behaviour could be a sensitive way to index the degree of eutrophication. An interferometric method based on holomicroscopic moiré is developed and preliminary results obtained are presented.     

Fracture detection by grating moiré and in-plane ESPI techniques

Optical interferometry techniques have been used for high-precision displacement measuring. Commonly, in-plane sensitive arrangements use two symmetrical collimated wavefronts for object surface illumination. However, this is a limitation when large object surface, has to be analyzed. In this case spherical illumination is needed. As a consequence of using non-collimated symmetrical dual-beams the sensitivity vector varies with the local position on the surface target. Then, this kind of illumination is also capable of detecting a lightly and systematic out-of-plane component of deformation. In this paper a theoretical analysis of the sensitivity vector components behavior is made. Each component of the sensitivity vector to minimize the required displacement component uncertainty is calculated. This study is important in the stage of planning any interferometric measurement experiment, particularly, for moiré grating interferometric technique, which has been used only in collimated illumination. By using a spherical dual-beam optical setup, the present work shows results of fracture measuring by using moiré and speckle interferometric methods. As a result, advantages and disadvantages of both techniques are discussed and an accuracy study is reported.     

Optical strain analysis of composite and monolithic materials

Optical techniques of moiré, holography, speckle and thermographic stress analysis† are very effective for analysing engineering problems involving materials such as man-made (fibre reinforced) and natural (wood, paperboard) composites, metals and rubber. The photo-mechanical techniques are combined herein with computer-vision (digital-imaging) concepts. Attention is also devoted to hybrid methods for processing and differentiating recorded optical data. Applications include those to fracture, stress waves, paper physics, material behavior, wood engineering, energy storage, and hostile environments.