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.
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TL;DR: An overview of the principal techniques of digital fringe processing is provided within a single theoretical framework in this paper, where experiments involving more I x 10 6 quantitative fringe order measurements are possible and practical on a routine basis using the current technology.
Abstract: The enormously enhanced power of photoelasticity resulting from adoption of digital technologies is highlighted and discussed. An overview of the principal techniques of digital fringe processing is provided within a single theoretical framework. The practical application of the new technologies using both conventional instruments and novel optical devices is discussed. Experiments involving more I x 10 6 quantitative fringe order measurements are possible and practical on a routine basis using the current technology. Products based on this research are beginning to appear on the market so that many new application areas are opening up for photoelasticity, such as dynamic events, real-time fatigue crack analysis, monitoring polarisation changes at a microscopic level in materials; detailed validation of numerical simulations, particularly of complex geometry and loading; and in-service monitoring using reflection photoelasticity of damage in both homogeneous and heterogeneous materials, such as composites.
106 citations
Cites background or methods from "Towards RGB photoelasticity: Full-f..."
...[19] have described an empirical method based on a look-up table formed from RGB images of a calibration specimen....
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...[19] is straightforward to implement, while the algorithms required for phase-stepping are more involved, particularly if unwrapping is required....
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TL;DR: A survey of recent methods of automated photoElasticity developed in the last 20 years, i.e. methods of the fringe centres, half-fringe photoelasticity, phase-stepping photoelasticsity, methods based on the Fourier transform, spectral content analysis (SCA) and RGB (red, green, blue) photoel elasticity are provided.
Abstract: Photoelasticity is one of the most widely used full-field methods for experimental stress analysis. However, the collection of photoelastic parameters can be a long and tedious process. The advent of automated photoelastic systems has allowed the experimentalists to speed up the rate of analysis and to perform more complex investigations.This paper provides a survey of recent methods of automated photoelasticity developed in the last 20 years, i.e. methods of the fringe centres, half-fringe photoelasticity, phase-stepping photoelasticity, methods based on the Fourier transform, spectral content analysis (SCA) and RGB (red, green, blue) photoelasticity.
95 citations
TL;DR: In this article, a novel instrument is described for the simultaneous observation and capture of four phase-stepped photoelastic images and a theoretical description of the optics of the instrument is presented for the first time.
Abstract: A novel instrument is described for the simultaneous observation and capture of four phase-stepped photoelastic images. A theoretical description of the optics of the instrument is presented for the first time. Three examples are given of the use of the instrument in reflection photoelasticity to generate full-field maps of isochromatic and isoclinic parameters. The results from these experiments show close correlation to results from both theoretical analyses and manual measurements. The instrument can be used in either reflection or transmission mode and it is concluded that the new instrument significantly enhances the potential for real-time studies using reflection photoelasticity.
79 citations
TL;DR: This review thematically classifies all the developments in digital photoelasticity and highlights the relative merits and drawbacks of the various techniques to allow an end-user to make an informed choice on the type of technique to be used in a particular situation.
Abstract: Digital photoelasticity has rapidly progressed in the last few years and has matured into an industry-friendly technique. This review thematically classifies all the developments in digital photoelasticity and highlights the relative merits and drawbacks of the various techniques. The overall objective is to provide enough information and guidance to allow an end-user to make an informed choice on the type of technique to be used in a particular situation.
78 citations
TL;DR: It is shown how the phase δ, and thus optical retardance, can be extracted from combining measurements of |sin δ| at different wavelengths, and the algorithm derived in this paper is valid not only for birefringence studies, but can be applied to all studies of interfering light waves.
Abstract: Modulation techniques for measuring changes in optical birefringence, such as the rotating-polariser method (Wood & Glazer, 1980, J. Appl. Crystallogr. 13, 217), allow one to determine |sin δ|, δ = 2πLΔn/λ, Δn= double refraction, L = light path and λ = wavelength. However, they generally suffer from not providing absolute values of the optical retardance or are limited to relatively low retardance values. In addition, knowledge of the absolute phase is required when establishing the correct values of optical orientation information. In this paper, it is shown how the phase δ, and thus optical retardance, can be extracted from combining measurements of |sin δ| at different wavelengths. The new approach works on each single point of a 2-D picture without the need to correlate with neighbouring points. There is virtually no limit to the retardance, and the computational efforts are small compared with other methods (e.g. Ajovalasit et al. 1998, J. Strain Analysis 33, 75). When used with imaging techniques, such as the rotating polariser method of Glazer, Lewis & Kaminsky 1996 (Proc. R. Soc. London SeriesA452, 2751) this process has the potential to identify automatically optically anisotropic substances under the microscope. The algorithm derived in this paper is valid not only for birefringence studies, but can be applied to all studies of interfering light waves.
76 citations
Cites methods from "Towards RGB photoelasticity: Full-f..."
...This approach is called the RGB-method, as it involves the red, green and blue values of a video camera with which the experiment is made (Ajovalasit et al., 1995)....
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References
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TL;DR: In this paper, a minicomputer connected to a video-frame store has direct access to any picture point in the store, and it is possible to evaluate the photo-elastic-fringe pattern in the computer by special developed software.
Abstract: TV technology combined with a modern video-frame store is used to store the complete fringe pattern in digitized form in real time. A minicomputer connected to the store has direct access to any picture point in the store. In this manner, it is possible to evaluate the photoelastic-fringe pattern in the computer by special developed software.
66 citations
TL;DR: In this paper, a carrier fringe technique for photoelasticity stress analysis is described and verified experimentally, where linear carrier fringes generated by using a quartz wedge are superimposed on fringes formed by the stressed model and the resultant fringe pattern is captured using a charge coupled device camera and stored in a digital frame buffer.
60 citations
TL;DR: In this article, the spectral contents of the light beam were used to extract the value of retardation from the spectral content of a light beam and three different techniques to evaluate the retardation values in real time.
Abstract: Traditional photoelasticity has started to lose its appeal since it requires a well-trained specialist to acquire and interpret results. A spectral-contents-analysis approach may help to revive this old, but still useful technique. Light intensity of the beam passed through the stressed specimen contains all the information necessary to automatically extract the value of retardation. This is done by using a photodiode array to investigate the spectral contents of the light beam. Three different techniques to extract the value of retardation from the spectral contents of the light are discussed and evaluated. An experimental system was built which demonstrates the ability to evaluate retardation values in real time.
53 citations
TL;DR: In this article, a real-time computer-aided FRinge-pattern AN-alyzer (CAFRAN) system for the analysis of photoelastic fringe is developed, which utilizes image analysis or pattern recognition technique and discretized-computation process in terms of finite-element method.
Abstract: A real-time “Computer-Aided FRinge-pattern AN-alyzer” (CAFRAN) system for the analysis of photoelastic fringe is developed. The pattern-analyzing process which utilizes image analysis or pattern-recognition technique and discretized-computation process in terms of finite-element method play an important role in this system. The former makes it possible to readout the fringe position and the fringe order of both isochromatic and isoclinic informations, and the latter analyzes the sum of the principal stresses which constitutes the Laplace field. Both results are combined to give the distributions of stress components over the domain under consideration.
51 citations
TL;DR: The computer-aided holophotoelastic method (CAHPM) is presented and validated and with it complete experimental stress analyses of transparent structures subjected to two-dimensional states of stress can be conducted based solely on experimental data without resort to either a hybrid, iterative, or other numerical procedure.
Abstract: The computer-aided holophotoelastic method (CAHPM) is presented and validated. With it complete experimental stress analyses of transparent structures subjected to two-dimensional states of stress can be conducted based solely on experimental data without resort to either a hybrid, iterative, or other numerical procedure. The stress analysis is determined from photoelastic and holographic data, i.e., isochromatic, isoclinic, and absolute retardation results. The experimental setup and procedures are discussed and the algorithms used for the data reduction are also presented. The method is validated using a disk in diametral loading.
46 citations
"Towards RGB photoelasticity: Full-f..." refers methods in this paper
...for each index i of the calibration table; (2) searching the value of the index i that minimizes the error function ( 12 ); (3) evaluating 8~ by means of eq (11)....
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