Fringe Sharpening Research Articles

Image Processing Algorithm for Fringe Analysis in Photoelasticity

Photoelastic fringe patterns recognition are carried out using a circular polariscope on a four point beam loaded by pure bending and they are processed with image processing algorithm in a personal computer. The aim of the present paper stress analysis of the photoelastic fringe in a rectangular cross section beam using digital image processing technology. An algorithm is developed to visualize the stress pattern acting in photoelastic models using fringe sharpening in conjunction with MATLAB software. Photoelasicity is a non-destructive experimental tool can be used for visual representation of stress patterns allowing for stress analysis. The present paper presents an image processing algorithm executed in a personal computer and obtained stress pattern recognition using digital image processing with histogram.

Multiple beam atom interferometer: theory and experiment

We first give a detailed account of the theory of atom interferometers based on a sequence of laser pulses pro- jecting the atomic wave packets onto a spatially separating dark superposition state. We then describe the experimen- tal realization of a multiple beam atom interferometer based on this method. In our experiment, we observe an interfer- ence signal that shows the sharply peaked Airy-function like pattern characteristic for multiple beam interference. Besides this fringe sharpening effect, we observe a further significant difference compared to the signal of a conventional two-beam atom interferometer. When the time between the beamsplit- ting pulses is varied, we observe collapse and revival of the fringe pattern, which is caused by a recoil phase shift increas- ing quadratically with the transverse atomic momentum.

Isochromatic fringe sharpening and interpolation along an isoclinic countour, with application to fracture mechanics

A method is presented for photoelastic analyses whereby fractional fringe orders are determined with enhanced accuracy. It utilizes data from the Tardy compensation method and combines the data by a robust algorithm to produce highly sharpened isochromatic fringe contours in the immediate vicinity of an isoclinic line. Their sharpness provides accurate assessment of fractional fringe orders at a point, relative to that achieved with the broad fringes of the standard Tardy method. Errors introduced by small isoclinic deviations are quantified and found to be inconsequential. The method is well suited to the application of linear elastic fracture mechanics in fracture studies of threedimensional photoelasticity models of complex structures. It is demonstrated for the determination of stress intensity factor at a crack in the solid fuel element of a rocket motor, when the solid fuel is subjected to internal pressure. Other applications are practical, too.

Accurate Measurement of Residual Stresses of Glass Rods by Photoelasticity

Risidual stress of cylindrical glass rods are measured by photoelasticity to study the variation of stresses with respect to heat treatment temperatures. In order to measure the stresses accurately, fringe sharpening and multiplication techniques are applied to the determination of photoelastic fringe orders. Filon's separationmethod is used to resolve circumferential and redial stress ocmponents from isochromatic fringes which are the same as in-plane maximum shearing stresses. According to the photoelastic measurements, residual stress is increased as the heat treatment temperature of the rods is raised from to All the circumferential stress components are changed from tensile stresses to compressive ones at approximate / = 0.6, where / is outer radius and any measured radius. This analysis shows that residual stresses of the glass rods approach zero if the rods are heat-treated near the strain point.

A Review of Fabry and Perot discoveries

It is a great pleasure for us, daily Fabry-Perot interferometer (hereafter referred to as FP) users, to pay homage to the genius inventors of the FP. Each day we are still bewildered by the power of this instrument which mainly consists of two pieces of half-silvered glass. Even if equations of physics are perfectly able to describe multiple-beam interferences (hereafter referred to as MBI), something magic remains in our mind.We will tackle this paper from a historical point of view. As any discovery, the invention of the FP did not occur just by chance from nowhere. As pointed out by Connes (1986) the invention of the multiple-beam interferometer may be understood as having proceeded from the fortunate convergence of two independent developments: (i) During 2 centuries, MBI has been observed and even computed but its specific and pregnant feature, the fringe sharpening, was not understood before Fabry’s thesis, (ii) A long production of mirrors, leading to the semi-transparent silver film.

ISOCHROMATIC FRINGE SHARPENING AND MULTIPLICATION

Since the isochromatic fringes of photoelasticity are broad, uncertainties in the locations of fringe centerlines (intensity minima and maxima) limit the accuracy of the experimental data. This paper presents an image processing scheme to combine the light field and dark field isochromatic fringes. It produces highly sharpened isochromatic fringe contours with twice as many contours as the number of fringes in the light or dark field. Although simple, the method is robust. It produces sharpened fringe contours everywhere in the field, independent of background noise. Fringe sharpening is remarkable even for the region where the difference of principal stresses vary slowly. In this paper, the mathematical and physical description of the method is presented and the method is demonstrated by a simply supported beam in flexure.

From Newtonian fits to Wellsian heat rays: the history of multiple-beam interference

The invention of the multiple-beam interferometer may be understood as having proceeded from the fortunate convergence of two independent developments. On the one hand, during two centuries of near-misses, the multiple-beam interference phenomenon was consistently observed (and even computed by Poisson and Airy) but its specific and pregnant feature, the fringe sharpening was not understood before the 1892 Thesis of Charles Fabry. Throughout, the motivation had been purely intellectual search. On the other hand, a long succession of technicians, most of them unknown, strove to produce better mirrors for wholly commercial purposes; the end result was the semi-transparent silver film, essential for multiple-beam interferometry. The corresponding fringes, first observed by Boulouch, were immediately put to good use by Fabry and Perot in 1896. Through a remarkable coincidence, essentially the same phenomena were simultaneously discovered in the Hertz laboratory with Hertzian waves. One more convergence, with Einsteinian stimulated emission, has since given us coherent light.

Fringe sharpening in lateral shear interferometry

Two methods of sharpening the interference fringes in lateral shear interferometry are described. One method exploits the non-linearity of the recording process, while the other is based on the characteristics of the multiply-recorded diffractive element. Both methods can be combined to obtain further fringe sharpening in the higher orders.

Fringe sharpening and information coupling in speckle shear interferometry

Fringe sharpening is required to obtain a higher accuracy of measurement. Nonlinear recording and consequently filtering at the higher-order halos for image formation give sharpened fringes in the image. Furthermore, if the apertures during recording are properly arranged, cross-frequency orders appear, which when used for filtering provide moire fringes of higher contrast due to intercoupling.

Effect of Complementary Gratings in Fringe Sharpening on Fringe Orders

Effect of Complementary Gratings in Fringe Sharpening on Fringe Orders

Two-color Grating Aids Moiré-fringe Sharpening

It is well known in moire analysis that beneficial fringe sharpening occurs when a pair of complementary gratings are employed in place of a single conventional grating to record successively the unloaded and loaded states of a model or a specimen. In this regard we propose that just a single, select, two-color grating in conjunction with suitable color filters can substitute the complementary pair. The idea is new and simple to apply.

Moiré fringe profile prediction method and its application to fringe sharpening

The fringe profile of the moiré pattern resulting from the interaction between a regular and a distorted binary grating is studied. The moiré fringe profile prediction method in a generalized form is deduced and summarized in a table illustrating the relationship between the profile parameters of superposed gratings and those of moiré fringes. The method is confirmed by computer simulation and experiment. The conditions for dark and bright fringe sharpening are obtained by using the derived prediction method.

Fringe sharpening and diffraction in nonlinear two-exposure holographic interferometry

Fringe sharpening occurs in the higher diffraction orders of nonlinear two-exposure holographic interferograms. The fringe functions in these various orders are modified by diffraction. At the Talbot distance the fringes replicate those near the plate, and a variety of fringe patterns can be obtained at different propagation distances.

Flow visualization by an improved double exposure method in holography

Some optical differential interferometric techniques were investigated in order to measure the density distribution in the air jet flow of a small scale flow cell while excluding the effects of the optical distortion of its glass windows. A technique using moiré fringe formation by rotating the reference wave in one exposure of the double exposure method was found to be most suitable for this purpose. High contrast and multiplication of moiré fringes can be obtained by a moiré fringe sharpening and multiplication method.

Fizeau Interferometer–Fringe Sharpening

A vector representation of the formation of fringe profiles in a Fizeau (wedge) interferometer shows that, under certain conditions, off-axis illumination may lead to fringe sharpening. The incident angle is such that the beam is first reflected toward the apex of the wedge and, following a certain controllable number of reflections, is reflected away from the apex. A typical example is shown.

Sharpening and multiplication of moiré fringes

Moire fringe sharpening is produced when the widths of clear and opaque bands in a pair of super-imposed screens are complementary. Fringe multiplication is produced when the frequency of lines in the reference screen exceeds the frequency in the specimen screen by an integral factor. The number of moire fringes then formed corresponds to the greater frequency.

The influence of grid geometry on moiré fringe properties

General equations are developed which relate the characteristics of moiré fringes to the geometry of two superposed, dissimilar grid systems. Equations are derived geometrically, assuming the rectilinear propagation of light, and the analysis is restricted to a consideration of linear, periodic, mutually inclined systems. Criteria are established for the production of first and second order fringe systems, and some particular cases of grid geometry are examined in detail. The concepts of mixed grids and hybrid grid combinations are introduced, and the principles and possible applications of fringe sharpening, fringe multiplication and dual sensitivity systems are discussed.