Electron moiré method and its application to micro-deformation measurement

In this paper, the single and two deposited metal layers method were proposed to produce the model grating for electron moiré method. The measurement principle of electron moiré method and the techniques for manufacturing model grid are expounded in detail. The accuracy of measuring strain using this method is discussed. The gratings with single deposited layer and two deposited layers with high frequency up to 5000 lines/mm were produced on different substrates. From the experimental results, both single deposited metal layer and two deposited metal layers gratings showed their heat resistance ability. Using the gratings produced and a replicated model grid, the electron moiré method was applied to measure the deformation of the strain around holes in a polyimide resin substrate, thermal strain of electronic packaging component and tensile creep around grain boundary in a pure copper specimen.     

Phase shifting SEM moiré method

A new phase shifting scanning electron microscope (SEM) moiré method is proposed in this paper. The phase shifting technique is realized in four steps from 0 to 2π by shifting electron beam in the y-axis direction controlled by the SEM system. It is successfully applied to determine the residual strain of a deformed holographic grating with a frequency of 1200 lines/mm in an electronic package. As a further application, it is used to measure the virtual strain of a MEMS structure with a 5000-line/mm grating and to determine the phase distribution of a SEM moiré formed with a 6000-line/mm grating fabricated by electron beam lithography. The experiments show the feasibility of this method. It provides a new way for disposal of fringes pattern in sub-micro moiré method.     

Application of moiré method to the study of plastic deformation processes

The moiré method can be broadly applied in metal forming processes. Many moiré fringe patterns of plastic working processes have been obtained. Based on this information, the principle of flowing metal and the distribution of strain and stress have also been obtained. These results should help us to improve the metal forming processes.     

The phase shift method applied to cross grating moiré measurements

The automatic evaluation of the grating deformation in a moiré image is greatly enhanced by the phase shift method. Based on three or more local grey values of a related number of phase shifted moiré patterns, the local displacement of a deformed grating against a reference grating, and hence the total displacement in one direction, is calculated. In this paper an extension to cross gratings is presented yielding a two- dimensional displacement field.     

Formation of unsymmetric moiré fringes and their use in moiré topography

An analytical method of predicting the intensity profile of the moiré fringes formed by a three-dimensional grating is proposed. The proposed method is proved to be effective in determining the appropriate structure of the grating and the experimental conditions for directional moiré topography.     

A moiré method of visualizing electromagnetic force lines

We propose a simple moiré method of visualizing electromagnetic force lines. The indicial equation is first derived for the tangent (or normal) curve to the electric field (or magnetic induction) around two parallel-line charges (or currents). The derived equation is then shown to have a one-to-one correspondence with that of the moiré fringe formed by two overlapped radial gratings. Since the tangent (or normal) curve to the electric field (or the magnetic induction) corresponds to the direction of the electric (or magnetic) force on a test charge (or current), the radial grating moirés can be used for the visualization of electric (or magnetic) force lines.     

Experimental tire mechanics by moiré

Tires and their component parts are made from various low modulus rubbers and cord/rubber laminates. In service they typically undergo large deformations of about 1–30%. The accurate measurement of these deformations by either pointwise (strain gage) or full-field (optical) techniques is rendered difficult in these circumstances. Ordinary strain gages reinforce these soft structures and inhibit their deformation, whereas most optical methods are too sensitive to measure large motions. These difficulties can be overcome by the judicious use of various moiré methods: moiré interferometry, geometric moiré and shadow moiré.Several applications of moiré methods to tire mechanics problems are presented. The emphasis is on the range of problems that has been successfully approached and on the results obtained. Examples are drawn from work on belt-edge strains, tread groove strains, sidewall strains, dynamic sidewall deformations and material properties determination. Proprietary details of technique are not included.     

A moiré fringe alignment aid

The task of accurately superimposing two photographic transparencies is frequently encountered in some areas of optical metrology. By recording a suitable line structure, along with the image, on each photograph, moiré fringes formed when two of the structures are superimposed can be used to give an accurate indication of the alignment of the transparencies.     

Holographic implementation of holographic moiré inspection

Implementation of holographic moiré inspection is demonstrated using one hologram to project the reference grating and a further hologram to produce moiré patterns. Well contrasted moiré fringes are obtained. Results of calibration tests are reported and an example of object contouring is presented.     

Localisation of fringes in moiré topography

The moiré pattern produced by two separate gratings is characterised by a fringe localisation phenomenon. A theory based on the geometric shadow of light can account for the spatial location of moiré fringes in topographical applications. The fringe location depends on the optical arrangement of the system and also on the surface slope of the specimen. Experimental results are introduced into practical usage.     

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.     

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.     

Talbot and fourier moiré deflectometry and its applications in engineering evaluation

With the aim of providing a metrical and detection method used in plate-shell mechanics and NDE, moiré interferometry (shearing interferometry) based on the Talbot effect and Fourier principle is proposed in this paper. This method does not require the use of an imaging lens, it is simple to use, and gives accurate results. The feature of this system is entirely based on the ability of an ordinary grating as the object and reference gratings, the optical differential and multiplicative element simultaneously. This will be a further step toward the realization of the aim mentioned above.     

In-plane deformation measurement using holographic moiré

The present paper analyses the factors affecting the quality of the moiré fringes for an arbitrary displacement and deformation of the object surface. Methods for the generation of auxiliary fringes are considered and their localisation is investigated. The physical significance of speckle displacement, both in the image plane and in the pupil plane, is pointed out.     

Frequency marker based on moiré deflectometry

We propose a new method for frequency marking based on measuring the diffraction angle by moiré deflectometry. The method is demonstrated experimentally.     

Automatic fringe analysis for moiré topography

Two digital systems are developed for the automatic measurement of 3-D shapes using moiré techniques—an automatic 3-D shape measuring system using the scanning moiré method and an interactive fringe analysing system for moiré fringe photographs. In the automatic 3-D shape measuring system, a deformed grating is scanned and sampled with an electronic image scanning device so that moiré fringes are generated in a computer. This technique of electronic fringe generation eliminates ambiguity with regard to the sign of the moiré fringes. The interactive fringe analyser provides a flexible and versatile tool for moiré fringe analysis. Medical applications of these analysing systems are discussed.     

Large amplitude point-vibration measurement with optical-fiber moiré-based technique

We describe a technique that is used for the real-time measurement of the vibration of an object point. The technique can be used when the vibration is characterized by a large amplitude, i.e. several millimeters. The technique has additional advantages that it requires no special surface treatment and is insensitive to object in-plane displacements that are small. In this technique an object point is illuminated by a small diameter beam (at an angle) that is structured with straight parallel fringes. The illuminated object point is then imaged onto a Ronchi ruling. The total light transmitted through the Ronchi ruling is then used to recover the vibration of the object point, in real time, by using well-known servo techniques.     

A new real-time method of moiré interferometry for displacement derivative fringe patterns

A new method of moiré interferometry is proposed in this paper to obtain the strain fringe pattern in real time. The specimen grating is illuminated by dual beams whose optical path-difference is larger than the coherence length of the laser. The diffractions of the grating are sheared by a glass wedge to fulfil the optical differentiation. The principles based on wavefront analysis are shown and an experimental verification is reported.     

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.     

Plate bending investigations by comparative holographic moiré interferometry. Evaluation by the finite-element method

Bending of clamped defect-containing and defect-free circular plates, subjected to equal uniformly distributed loading is investigated. Using the finite-element method (FEM), a numerical model is produced and the results from the numerical computations are compared with those from a holographic experiment, based on comparative holographic moiré interferometry (CHMI). The theoretical and experimental approach to solving the problem is discussed and the measurement accuracy is analyzed. Good agreement between the numerical and experimental results is observed. The possibility of applying the techniques developed to a wide scope of mechanical problems in non-destructive testing (detection of hidden defects, cracks and debonds, as well as investigations on material fatigue and plastic deformations) is pointed out.