We present the application of a regularization algorithm to the processing of photoelastic fringe patterns. Fringe patterns in integrated photoelasticity article in journal of the optical society of america a 267. If a photoelastic model exhibits a perfectly linear elastic behavior, the difference in the principal strain can be measured by established the fringe order n. Phase measuring algorithm for extraction of isochromatics of. Isochromatic fringe pattern article about isochromatic. The modulation of the isoclinic phase map depends on the iso. One is that isoclinic and isochromatic fringe patterns are completely mixed. Weichih wang department of mechancial engineering university. Previous discussion centered on isochromatic fringes, i. These patterns are related to the principalstress differences and to the. The isochromatic fringes surrounding a crack propagating along a bimaterial interface have been developed and characterized. The isochromatic phase map is then obtained by the sixstep.
Image capturing and digital processing techniques also allow for the separation of. An image analysis technique for constructing isostatics from. The basic instrument in photoelasticity is the socalled polariscope. This work concerns the study of stresses distribution in a photoelastic specimen by using bidimensional photoelasticimetry and optical phase evaluation methods. Characterization of isochromatic fringe patterns for a. The unambiguous isoclinic angle map is then calculated using the regularized isochromatic map. The method yields two types of fringe patterns, namely, isoclinic and isochromatic parameters. For the isochromatic computation there exist several possibilities but one of the best. Separation of isoclinics and isochromatics from photoelastic.
The method used is a modified regularized phasetracking rpt algorithm applied to phaseshifted images. Image capturing and digital processing techniques also allow for the separation of the isoclinic and isochromatic fringe patterns. Theoretical reconstruction of fringe patterns 67 25. Automated detection of singularities from orientation map of. Method 1 one of the simplest methods is by using a darkfield set up and a brightfield set up. In recent years phasemeasuring techniques have been applied to the problem of extracting information of photoelastic data. Series of a the photoelastic fringe patterns, b the isoclinics and c the isochromatics obtained by the proposed method. Phase measuring algorithm for extraction of isochromatics. Fringe patterns were examined under both plane and circular polariscope arrangements using sodium vapour light. The method uses a plan polariscope with two different filters to calculate the. Isochromatics are interpreted as phase paths or level curves of a hamiltonian system.
The isoclinic fringe pattern enables the isoclinic parameter. In photoelasticimetry technique, isochromatic fringe patterns are generated experimentally by a circular polariscope and the phase distribution is extracted from the monogenic signal. The birefringent property of an optical resinfor the study. Isochromatic fringe patterns around a steel platelet in a photoelastic twopart epoxy resin. The conoscopic interference patterns of crystals are calculated for any orientation biaxial crystal, which include information of isochromatic curve and isogyre. Photostress fringe pattern appears as a series of successive and contiguous. Complete analysis of photoelastic fringe patterns using. Determination of isoclinics in photoelasticity with a fast. In terms of the isochromatic pattern, the isochromatic fringe order, n, at a. But when the difference of the fringe orders reaches 0. A parametric investigation has also been conducted to study the influence of various fracture parameters on this isochromatic fringe pattern. In addition, holographic recording of four fringe patterns is applied for retrieval of isopachic fringes which give the sum of principal stresses.
In addition, holographic recording of four fringe patterns is applied for retrieval of isopachic fringes which. Doitpoms tlp library introduction to photoelasticity. Distorsion of isochromatic fringes in the process of stress. Stress concentrations for slotted plates in biaxial stress. May 29, 2002 complete analysis of photoelastic fringe patterns using two wavelengths chen, terry y.
The isochromatic fringes indicate the lines along which the principal stress difference is equal to a constant and are of main significance in this study. In the case of isoclinics the method can deal with problems associated with. The analyze of the scattered light gives fringes equivalent to the ones obtained in a plane polariscope isochromatic and isoclinic fringes. Isoclinic fringes can be removed by using a circular polariser. Using photoelasticity, isochromatic and isoclinic fringe patterns can be generated in a model specimen with an applied load. Isoclinic fringes can be observed by reducing the number of isochromatic fringes through either applying a smaller load or by using a material with a high material fringe constant. Colour adaptation in three fringe photoelasticity request pdf. Further applications of holography to photoelasticity. Reflection photoelastic stress analysis of dental bridge. This is accomplished by using two orthogonally polarized reference beams so arranged that the reconstructed crosstalk images do not overlap. Isochromatic and the entire family of isoclinic fringe patterns may be obtained by examining the holographic image, a posteriori. Robust isoclinic calculation for automatic analysis of photoelastic fringe patterns quiroga, j. Isochromatic fringes are lines of constant principal stress.
These fringe patterns provide both magnitude and directions of stresses. In this method we obtained a fringe pattern like in a light plane polariscope. Complete analysis of photoelastic fringe patterns using two wavelengths complete analysis of photoelastic fringe patterns using two wavelengths chen, terry y. To accomplish step l, the isochromatic and isoclinic fringe patterns must be recorded at. The two types of fringes can be distinguished by rotating the specimen in a plane polariscope. The former corresponds to the principal stress direction whereas the latter correlates to the contours of principal stress differences. In particular, we present an algorithm for isoclinicisochromatic separation that uses only five images.
Application of principal component analysis in phase. Photoelastic fringe pattern analysis by realtime phase. Results the isochromatic and isoclinic fringe patterns in the. In the article we show the possibility of distorting the results of the experiment by photoelasticity path, in case the isochromatic fringe patterns are recorded by the camera. The plane polariscope provides a full stress field around the notch in the form of a combination of isochromatic and isoclinic fringe patterns which reveal, respectively, the principal stress magnitudes and their directions. An image analysis technique for constructing isostatics. Pdf separation of isochromatics and isoclinics from photoelastic. The two types of fringes can be distinguished by rotating the specimen in a. Photoelastic experiments also informally referred to as photoelasticity are an. A standard plane polariscope shows both isochromatic and isoclinic fringes, and this makes quantitative stress analysis difficult. Photoelasticity describes changes in the optical properties of a material under mechanical deformation. The isochromatic and isoclinic fringe patterns are used to determine stresses.
Sep 29, 2008 robust isoclinic calculation for automatic analysis of photoelastic fringe patterns quiroga, j. The tintofpassage is the purple color with wavelength 575 nm to obtain the actual magnitude of the maximum shear stress at some point in the model, first calibrate the model material to get the stressoptic coefficient c and measure the thickness t of the model determine the fractional fringe number n of the isochromatic fringe pattern at the point in question and use the equation. The isochromatic fringes are related to the difference between the two principal stresses and the isoclinics give the direction of the principal stresses of any point in the model. Possible singularities of the fringe pattern are analyzed.
Photoelasticity is a useful technique for stress analysis which requires the processing of fringe patterns. Robust isoclinic calculation for automatic analysis. Application of principal component analysis in phaseshifting. Robust and fast algorithm demonstrated on troublesome fringe pattern.
The structure of the isochromatic fringe pattern in a twodimensional photoelastic model is investigated with the phase diagram method of the theory of dynamic systems. We present a new phasemeasuring algorithm for extraction of the isochromatics of photoelastic. The stress strain relationship for 2d state of stress are given by. Complete analysis of photoelastic fringe patterns using two.
Key wordsphotoelasticityisochromaticsisoclinicsfringephase. Effect of variation of concrete properties on the accuracy. The orientation of the first principal stress is determined by expanding the isoclinic phase based on the slope of the isostatics. The method uses a plan polariscope with two different filters to calculate the photoelastic parameters, and to compensate the influence of the isochromatic fringes on the isoclinic pattern. Phase distributions of a the isoclinic parameter and b the isochromatic parameter along the y0. The method uses a plan polariscope with two different filters to calculate the photoelastic parameters, and. If the birefringence is linearly related to the stresses in the material, these fringes can be used to calculate the intensity of s 1s 2, or equivalently the maximum shear stress, at any point in the. Determination of isoclinic map for complex photoelastic. For the isochromatic computation there exist several possibilities but one of the best, from the point of view of reliability and automatization, is the phase shift technique. Distorsion of isochromatic fringes in the process of. Automatic determination of parameters in photoelasticity.
The use of photoelasticity to identify surface shear. Unwrapping of isochromatic fringe orders using fringe. A new approach for wholefield digital determination of isoclinic angle and total isochromatic fringe order is presented. The process has been demonstrated to be robust and reasonably quick for crack tip fringe patterns. Experimental analysis a three point loading beam is analyzed in a plan polariscope which allows observing two types of photoelastic fringes, the isochromatics and the isoclinics. Thus, we will present first the procedure to demodulate the isoclinic fringe pattern using the proposed pca algorithm and, afterwards, we will make use the information obtained from the isoclinics fringe pattern to demodulate the isochromatics one. A direct approach to inplane stress separation using. When the load reached 88%95% of the peak load, higher degree of the isochromatic fringe began to localize in the zone where the forthcoming fault would be located. Introduction to stress analysis by the photostress method. The farfield diffraction patterns containing information on the isochromatic, isoclinic and isopachic fringes were then recorded on a water cooled andor zyla 4. In some configurations of this instrument, a mix of fringe patterns is generated which are. There are two main steps in the analysis of photoelastic fringe patterns. The algorithm permits the extraction of the isochromatic phase with almost no influence from the isoclinics, thus avoiding the usual problems of lowmodulation. Photoelasticity has been used for a variety of stress analyses and even for routine use in design, particularly before the advent of numerical methods, such as finite elements or boundary elements.
Automated detection of singularities from orientation map. The dark field set up gives fringes representing an integral number of. Fullfield stress determination in photoelasticity with. Separation of isochromatic and isoclinic patterns of a slice optically. The use of photoelasticity to identify surface shear stresses.
We present a new phasemeasuring algorithm for extraction of the isochromatics of photoelastic fringe patterns. Osa separation of isoclinics and isochromatics from. Tlp library introduction to photoelasticity introduction doitpoms. The colour or intensity of the isochromatic fringe is indicative. Brown and sullivan i 1 took this a step further when they showed that the isoclinic angle could be determined using phasestepping techniques in such a half fringe field as well as the isophachic fringe sums of principal stresses value.
Fringe patterns in integrated photoelasticity request pdf. Three fringe photoelasticity tfp can give the total fringe order from a single colour isochromatic fringe field by suitably comparing the colour with a calibration specimen. Isochromatic definition of isochromatic by the free dictionary. When the two quarter wave lenses are removed a plane polariscope results and both isochromatic and isoclinic fringe patterns are observed. The produced optical patterns must be analyzed us ing complicated finite difference approaches. The relevant fracture parameters of interest were the cracktip velocity, the mode mixity of loading and the nonsingular. In some configurations of this instrument, a mix of fringe patterns is generated which are called isoclinic and isochromatic fringe patterns. It is a property of all dielectric media and is often used to experimentally determine the stress distribution in a material, where it gives a picture of stress distributions around discontinuities in materials. Determination of the isoclinic map for complex photoelastic. The following distinctive optical phenomena were predicted theoretically and observed in the highspeed photoelastic patterns.
In this way, an unambiguous map can be straightforwardly unwrapped and calibrated to generate an isochromatic map. Phase measuring algorithm for extraction of isochromatics of photoelastic fringe patterns j. The stress analysis of these materials has the added dimension of time. Isochromatic definition of isochromatic by medical. Isoclinic fringes related to direction of principal stresses variety of digital fringe processing rgb photoelasticity no userinput for calibration of fringe map limited to isochromatic fringe orders less than 3 fourier transforms highquality isochromatic and isoclinic data requires tens of images fringe unwrapping and usercalibration phase. Robust isoclinic calculation for automatic analysis of. Isochromatic fringes are lines of constant principal stress difference.
Fullfield stress determination in photoelasticity with phase. The recording of the color spectrum may be distorted by inappropriate selection of the recording medium, which is reflected by different types of aberrations. Isoclinic fringes depend on the orientation of crossed filter set whereas the isochromatic fringes depend on the stressoptic effect. Isoclinic fringe patterns appear as dark lines on the image and are used to determine the direction of the principal stress.
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