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Journal ArticleDOI

Towards RGB photoelasticity: Full-field automated photoelasticity in white light

01 Sep 1995-Experimental Mechanics (Kluwer Academic Publishers)-Vol. 35, Iss: 3, pp 193-200
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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Journal ArticleDOI
TL;DR: In this article, some considerations regarding the use of color digital imaging systems in experimental mechanics applications have been discussed and two examples in the areas of photoelastic fringe analysis and machining chip color classification were presented.
Abstract: In this paper, some considerations regarding the use of color digital imaging systems in experimental mechanics applications have been discussed. Two examples in the areas of photoelastic fringe analysis and machining chip color classification were presented. The author feels that the increasing availability of affordable color imaging systems will allow the discovery of many interesting applications in the areas of experimental mechanics and engineering.

19 citations

Journal ArticleDOI
TL;DR: In this article, a novel approach to plot photoelastic fringe contours from 3D finite element results is presented, which uses a scanning approach and the evaluation of total fringe order is achieved by combining a file structure and subsequent sorting of these data to enable integration along the light path.
Abstract: A novel approach to plot photoelastic fringe contours from three-dimensional finite element results is presented. Plotting of fringe contours from 3D FE models requires the calculation of secondary principal stresses along the light path. The definition of secondary principal stresses and the calculation of relevant photoelastic data for fringe plotting are discussed. The plotting scheme uses a scanning approach and the evaluation of total fringe order is achieved by combining a file structure and subsequent sorting of these data to enable integration along the light path. The methodology is validated for the problem of a cantilever beam with an edge load. The usefulness of the methodology to verify 3D FE modelling and for experimentalists to design their experiments is indicated. Copyright © 2006 John Wiley & Sons, Ltd.

19 citations

Journal ArticleDOI
TL;DR: Noise produced in the fringe maps due to the presence of color abberations at the starting pixels of the rows is highlighted, wherein a modified regularized algorithm and an improved LUT calibration have been employed in tandem.

19 citations

Journal ArticleDOI
TL;DR: In this paper, the carrier fringes method has been proposed in digital photoelasticity in combination with techniques such as Fourier transform and phase shifting method, without considering the influence of the isoclinics on the isochromatic patterns analysis.

18 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

Journal ArticleDOI
01 May 1991-Strain
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

Journal ArticleDOI
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....

    [...]

  • ...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)....

    [...]

  • ...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....

    [...]

Book ChapterDOI
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

Journal ArticleDOI
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