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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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Book ChapterDOI
01 Jan 2000
TL;DR: With rapid advancements in computer technology, colour image processing systems are now available at affordable prices and an understanding of the various models for colour representation is required.
Abstract: With rapid advancements in computer technology, colour image processing systems are now available at affordable prices. A proper understanding of the colour image processing techniques requires an understanding of the various models for colour representation. Apart from this, one needs to know the spectral response of the colour camera and the light source. The type of colour image processing hardware used for transmission or reflection photoelastic analysis has an influence on the quality of data acquisition. Data interpretation and analysis requires the understanding of the intensity of light transmitted, for various polariscope arrangements, in white light
01 Jan 2003
TL;DR: This work addresses the problem of providing input to a novel method of interpreting photoelastic data for performing experimental stress analysis of models of engineering components by describing methods of obtaining unwrapped isoclinic and isochromatic phase maps from sequences of images captured within a computer-controlled polariscope.
Abstract: We address the problem of providing input to a novel method of interpreting photoelastic data for performing experimental stress analysis of models of engineering components. This method employs conventional photoelastic data relating to the directions of the principal stresses in the specimen (isoclinic data), along with the difference in principal stresses (isochromatic data). Both are used within an inverse boundary element model to reconstruct the load conditions at the model boundary and hence to recover the principal stresses in the specimen without recourse to numerical integration of shear stress gradient. We describe methods of obtaining unwrapped isoclinic and isochromatic phase maps from sequences of images captured within a computer-controlled polariscope. A boundary element model of the specimen, congruent with the isoclinic and isochromatic phase maps, is obtained from an image captured within the polariscope under either traditional lighting conditions or by configuring the polariscope to provide a light field background. Image segmentation reveals the boundary of the specimen, which is then described in terms of simple geometric primitives. Boundary points and geometric descriptions are both used to produce the final boundary element model. The techniques described have been applied to a number of contact specimens; results are presented and discussed.
Journal ArticleDOI
TL;DR: In this article , an exhaustive parametric study of the refining parameters is carried out by selecting a variety of fringe fields, and a framework to select refining parameters and troubleshoot refining issues is formulated based on the parametric analysis.
Journal ArticleDOI
TL;DR: In this article , the spannungsoptische Konstante von PVB und SG was ermittelt und in Gangunterschiedsmessungen die Auswirkung des Verbundprozesses analysiert.
Abstract: Die im thermischen Vorspannprozess induzierten Eigenspannungen verursachen unter polarisiertem Licht Anisotropie‐Effekte im Glas. Derzeit beschränkt sich die Kontrolle dieser Anisotropien, welche als optische Gangunterschiede quantifiziert werden, auf Einzelgläser. In dieser Studie werden erstmals spannungsoptische Untersuchungen an Verbundgläsern durchgeführt. Im Zugversuch wird die spannungsoptische Konstante von PVB und SG ermittelt und in Gangunterschiedsmessungen die Auswirkung des Verbundprozesses analysiert. Die Ergebnisse zeigen, dass ein Unterschied zwischen den Polymeren hinsichtlich ihrer spannungsoptischen Eigenschaften besteht und dass durch die Folie eine Erhöhung der Gangunterschiedswerte im Verbundglas feststellbar ist.
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