Book•
Digital Photoelasticity: Advanced Techniques and Applications
01 Jan 2000-
TL;DR: In this article, phase shifting, Polarization Stepping and Fourier Transform Methods are used for phase unwrapping and Optically Enhanced Tiling in digital photoelasticity.
Abstract: Transmission Photoelasticity.- Reflection Photoelasticity.- Digital Image Processing.- Fringe Multiplication.- Fringe Thinning and Fringe Clustering.- Phase Shifting, Polarization Stepping and Fourier Transform Methods.- Phase Unwrapping and Optically Enhanced Tiling in Digital Photoelasticity.- Colour Image Processing Techniques.- Evaluation of Contact Stress Parameters and Fracture Parameters.- Stress Separation Techniques.- Fusion of Digital Photoelasticity, Rapid Prototyping and Rapid Tooling Technologies.- Recent Developments and Future Trends.
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TL;DR: RGB demodulation based on a theoretically constructed LUT has been attempted to exploit the advantages of color adaptation schemes and a new color adaptation algorithm is proposed using quadratic Lagrangian interpolation polynomials, which is numerically better than the two-point linear interpolations available in the literature.
22 citations
TL;DR: In this paper, the phase values of the isoclinics are obtained from four images in the plane polarizer arrangement by rotating the polarizer and analyzer simultaneously, and a full-field description of the first principal stress orientation with respect to the horizontal axis is determined.
20 citations
TL;DR: In this paper, a comparative study of different autonomous phase unwrapping algorithm is done by solving a bench mark problem and a stress frozen slice with cut-outs, which brings out the need for domain delimiting in addition to domain masking.
Abstract: Photoelasticity is the only whole-field experimental technique which can analyse both 2-D and 3-D elasticity problems. In digital photoelasticity one gets two phase maps, one corresponding to principal stress direction (isoclinic) and the other corresponding to principal stress difference (isochromatic). The phase maps for both isoclinics and isochromatics are to be unwrapped differently for obtaining continuous phase values. Autonomous phase unwrapping is one of the challenging issues and this paper focuses on recent advances on isochromatic phase map unwrapping. A comparative study of different autonomous phase unwrapping algorithm is done by solving a bench mark problem and a stress frozen slice with cut-outs. The need for domain delimiting in addition to domain masking is brought out while using autonomous phase unwrapping algorithms.
20 citations
Cites background or methods from "Digital Photoelasticity: Advanced T..."
...The phase map is obtained using the following relations Ramesh (2000) δp = { δc for δc > 0 2π + δc for δc ≤ 0 g(x, y) = 255 2π δp, (9) where g(x, y) is the gray level of the pixel at the location (x, y)....
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...With the advent of digital computers recording of images as intensity data became easier and a separate branch of photoelasticity namely ‘digital photoelasticity’ came into existence Ramesh (2000)....
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...Use of ambiguity removal algorithms followed by unwrapping has been emphasized by Ramesh (2000) and Sai Prasad et al (2004) for effective phase unwrapping in photoelasticity....
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...Due to difficulties in not obtaining θ corresponding to either σ1 or σ2 uniformly over the complete domain Ramesh (2000), the sign of the fractional retardation is not known precisely....
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...From the intensity equations, the isoclinic and isochromatic parameter are obtained as Ramesh (2000)...
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TL;DR: In this paper, a non-invasive measurement method for inspection of naturally birefringent transparent media is presented, which is based on photoelasticity and exploits a controlled laser conoscopy technique and a scanning system to perform local measurements in the volume dimensions of the media.
Abstract: A reliable and noninvasive measurement method for the inspection of naturally birefringent transparent media is presented in this paper. It allows us to achieve a spatially resolved analysis of the stress state of birefringent materials. The developed system is based on photoelasticity and exploits a controlled laser conoscopy technique and a scanning system to perform local measurements in the volume dimensions of the media, which can be displaced over a grid of points. The configuration of the proposed laser conoscopic system is presented, and a dedicated algorithm, designed to perform digital analysis of the fringe patterns, is also described. The design and the realization of the system are discussed, as well as the advantages of the proposed system over the classic diffuse light polariscope technique. The method has been experimentally validated through laboratory tests on birefringent samples with known induced stress. The system has demonstrated its sensitivity to stress and its capability to achieve a spatial resolution on the order of 0.1 mm to resolve stress gradients (uncertainty on the stress amplitude of ± 0.1 MPa ).
19 citations
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