Towards RGB photoelasticity: Full-field automated photoelasticity in white light
TL;DR: A new full-field method for the automatic analysis of isochromatic fringes in white light, named RGB photoelasticity, which makes it possible to determine retardations uniquely in the range of 0–3 fringe orders.
Abstract: In this paper a new full-field method for the automatic analysis of isochromatic fringes in white light is presented. The method, named RGB photoelasticity, eliminates the typical drawbacks of the classical approach to photoelasticity in white light which requires a subjective analysis of colors and an experienced analyst to acquire and interpret the results.
Citations
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TL;DR: The use of single-colour image for determining the fringe orders in digital photoelasticity has gained importance in recent years, and in this, the fringe order are obtained by comparing the colou
Abstract: The use of single-colour image for determining the fringe orders in digital photoelasticity has gained importance in recent years, and in this, the fringe orders are obtained by comparing the colou
18 citations
Cites background or methods from "Towards RGB photoelasticity: Full-f..."
...Ajovalasit et al.4 improved the work of Quiroga et al.11 and arrived at a criterion for selecting the size of the window in the window search method and experimentally demonstrated it for a C-specimen up to 12 fringe orders....
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...Usually used calibration specimens are four-point-bent specimen,(9) eccentrically loaded tensile specimen(2,27) and eccentrically loaded channelshaped specimen.(2,8) Among these, the four-point-bent specimen is the simplest model for generating calibration table up to fringe order of 3....
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...Ajovalasit et al.4 also compared the performance of the algorithms proposed by Quiroga et al.11 and that of Madhu and Ramesh12 (RTFP) for the same C-specimen....
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...Ajovalasit et al.(8) proposed a method to reduce the noise by identifying two minima and selecting the one which had a fringe order closer to the neighbouring pixel....
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...This limitation is essentially due to the lack of spatial resolution, and the method has worked well up to a fringe resolution of 10 pixels per fringe order which tallies with the observation made by Ajovalasit et al.2...
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TL;DR: In this paper, a simple median filtering method has been proposed using a simple example of disc under diametral compression, which can be easily undertaken using any standard image processing software.
18 citations
TL;DR: The existing scanning schemes are critically evaluated for their ability to scan the entire model domain, influence of seed point selection and noise propagate, which makes them suitable especially for problems where recording multiple images is difficult.
17 citations
TL;DR: In this article, the application of the Fourier transform to photoelasticity was used in the evaluation of the retardation using a carrier system of fringes, where the error is small if the angle between the principal stresses in the model and in the carrier is less than 25 deg.
Abstract: The application of the Fourier transform to photoelasticity was used in the evaluation of the retardation using a carrier system of fringes. In photoelasticity, the light intensity from the analyzer in a circular polariscope depends on both the retardation (isochromatics) and the isoclinic parameter. The theoretical analysis shows that the angle between the principal stresses in the model and in the carrier system of fringes influences the evaluation of the retardation (isochromatics), as occurs when misaligned compensators (namely, Babinet) are used. As a consequence, this method may not be applied as a full-field technique, although the error is small if the angle between the principal stresses in the model and in the carrier is less than 25 deg. Numerical simulations and experimental tests were conducted to corroborate this prediction.
17 citations
TL;DR: A robust fringe demodulation technique applied to the analysis of tricolour isochromatic fringe patterns produced in photoelasticity using a regularized phase tracking algorithm.
Abstract: In this work we propose a robust fringe demodulation technique applied to the analysis of tricolour isochromatic fringe patterns produced in photoelasticity. The method used is a regularized phase tracking (RPT) algorithm, which takes into account the different information contained in the three bands of the colour image obtained with an RGB-CCD camera. Automatic determination of the zero-order isochromatic and the area of interest, the use of a discrete fluorescent illumination and the use of the RPT configures a robust method for automatic demodulation of isochromatic fringe patterns. The performance of the method is discussed and experimental results are presented.
17 citations
References
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Book•
01 Jan 1987
TL;DR: The "Handbook on Experimental Mechanics" as mentioned in this paper is a comprehensive reference in the field of experimental mechanics and has been used extensively in the past 50 years for a wide range of applications.
Abstract: The "Handbook on Experimental Mechanics" is a comprehensive reference in the field. Since 1950, new experimental techniques, such as holography, laser speckle interferometry, optical heterodyning and modal analysis, have emerged as practical tools in the broader field of experimental mechanics. The emergence of new materials and new disciplines, such as composite materials and fracture mechanics, resulted in the evolution of traditional experimental techniques to new fields such as orthotropic photoelasticity and experimental fracture techniques. The new revised edition of the handbook includes, among other things, one new chapter on digital image processing; key sections of the handbook have been entirely rewritted or updated. The handbook should be useful to any mechanical engineer or anyone interested in stress analysis of materials.
504 citations
TL;DR: The design of a automated system for photoelastic analysis of complex components and the potential of the system for providing detailed data over the full field of view is demonstrated by the analysis of a slice from a model of a bolt.
Abstract: The design of a automated system for photoelastic analysis of complex components is described, and an outline of the theory used in its operation is given. The potential of the system for providing detailed data over the full field of view is demonstrated by the analysis of a slice from a model of a bolt.
221 citations
TL;DR: In this paper, the half-fringe photoelasticity (HFP) method is proposed for whole-field stress analysis based on a symbiosis of two techniques, namely classical photo elasticity and modern digital image analysis.
Abstract: This paper presents a new method for whole-field stress analysis based on a symbiosis of two techniques—classical photoelasticity and modern digital image analysis. The resulting method is called ‘half-fringe photoelasticity (HFP)’. Classical photoelasticity demands materials with high birefringence, which leads to extensive use of plastics as model materials. Since the behavior of these materials is often different from that of the prototype materials, their use distorts the similitude relationships. In many contemporary problems this distortion is untenable. HFP offers a way out of this dilemma. It permits materials and loads to be chosen so that no more than one half of a fringe order appears in the area of interest. Thus, for example, glass, which behaves linearly up to high stress levels and over a wide range of temperatures, could be used as model material. Alternatively, models from polymeric materials could be used under very low load in order to stay within the linear part of the stress-strain diagram and to prevent large deformations. The half-fringe-photoelasticity system, which is described here, utilizes the resulting low levels of birefringence for effective stress analysis. This paper describes the system. It outlines a calibration routine and illustrates its application to two simple problems using glass models.
126 citations
"Towards RGB photoelasticity: Full-f..." refers background or methods in this paper
...The intensity eqs ( 9 ) and (10) can be used to evaluate A only if the Fi functions, the transfer function of the digital board (relationship between the RGB values and intensity values L Ig and Ib), the dispersion of birefringence and the isoclinic angle ~ are known....
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...The equations of polariscope ( 9 ) and (10) show that the influence of errors e of optical retarders depends on the isoclinic angle cx; there is maximum error where c~ = 0 deg (principal stresses parallel to polarizers), whereas no error occurs where a -- 45 deg (principal stresses parallel to retarders)....
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...For lower orders, using eqs ( 9 ) and (10) allows us to evaluate the unknown retardation A (or 8) by processing of the acquired RGB levels....
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01 Jan 1986
TL;DR: In the following a method is proposed, which enables the complete extraction of photoelastic information at local picture elements (pixel) from series of related images of the same stress state, and was modified to meet the special requirements ofphotoelastic patterns.
Abstract: Computer-aided methods for evaluation of photoelastic patterns use video technique and digital image processing. They are based on localization of fringe centers [ 1, 2, 3, 4]. Neighbourhood operations are needed to reduce the influence of nonuniform illumination, inhomogeneous optical components and models, etc. Fractional orders of the relative retardation and of the isoclinic parameter at points between the fringes are computed by spline- functions, if the components of the plane stress state have to be derived from photoelastic data. In the following a method is proposed, which enables the complete extraction of photoelastic information at local picture elements (pixel) from series of related images of the same stress state. For this purpose the well-established phase-shifting technique (see e. g. [ 5,6]) was modified to meet the special requirements of photoelastic patterns.
78 citations
TL;DR: In this paper, a new method of photoelastic measurement has been developed, where the light emerging from a polariscope is spectrally separated and projected on a photodiode array.
Abstract: A new method of photoelastic measurement has been developed. The light emerging from a polariscope is spectrally separated and projected on a photodiode array. It is shown that the relative retardation can be retrieved from light intensity measured at several wavelengths. Key parameters affecting the precision of this approach are discussed and evaluated.
76 citations