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Digital Photoelasticity: Advanced Techniques and Applications

01 Jan 2000-

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TL;DR: In this article, a review of the durability of Fresnel lenses used in the concentrating photovoltaic (CPV) application is reviewed from the literature, which primarily concerns monolithic lenses constructed of poly(methyl methacrylate) (PMMA), with supplemental examination of silicone-on-glass (SOG) composite lenses.
Abstract: The durability of Fresnel lenses used in the concentrating photovoltaic (CPV) application is reviewed from the literature. The examination here primarily concerns monolithic lenses constructed of poly(methyl methacrylate) (PMMA), with supplemental examination of silicone-on-glass (SOG) composite lenses. For PMMA, the review includes the topics of: optical durability (loss of transmittance with age); discoloration (the wavelength-specific loss of transmittance); microcrazing and hazing; fracture and mechanical fatigue; physical aging, creep, shape change, buckling, and warping; and solid erosion. Soiling, or the accumulation of particulate matter, is examined in the following contexts: its magnitude of reduction in transmittance; variation with time, module tilt, and wavelength; the processes of adhesion and accumulation; particle size, distribution, composition, and morphology; and its prevention. Photodegradation and thermal decomposition, mechanisms enabling aging, are examined relative to the CPV-specific environment. Aspects specific to SOG lenses include: solarization of the glass superstrate; corrosion of glass; delamination of the silicone/glass interface; change in focus due to thermal misfit between the laminate layers; and the chemical stability of poly(dimethylsiloxane) (PDMS). Recommendations for future research are provided, based on the most important and the least explored topics.

143 citations

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01 Feb 2002-Strain
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.

101 citations


Cites background from "Digital Photoelasticity: Advanced T..."

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TL;DR: In this paper, the authors employed 3D frozen stress and photoelastic technologies to characterize and visualize the stress distribution within the fractured coal under uniaxial compression and 3D printed model presented the fracture structures identical to those of the natural coal.
Abstract: Accurate characterization and visualization of the complex inner structure and stress distribution of rocks are of vital significance to solve a variety of underground engineering problems. In this paper, we incorporate several advanced technologies, such as CT scan, three-dimensional (3D) reconstruction, and 3D printing, to produce a physical model representing the natural coal rock that inherently contains complex fractures or joints. We employ 3D frozen stress and photoelastic technologies to characterize and visualize the stress distribution within the fractured rock under uniaxial compression. The 3D printed model presents the fracture structures identical to those of the natural prototype. The mechanical properties of the printed model, including uniaxial compression strength, elastic modulus, and Poissons ratio, are testified to be similar to those of the prototype coal rock. The frozen stress and photoelastic tests show that the location of stress concentration and the stress gradient around the discontinuous fractures are in good agreement with the numerical predictions of the real coal sample. The proposed method appears to be capable of visually quantifying the influences of discontinuous, irregular fractures on the strength, deformation, and stress concentration of coal rock. The method of incorporating 3D printing and frozen stress technologies shows a promising way to quantify and visualize the complex fracture structures and their influences on 3D stress distribution of underground rocks, which can also be used to verify numerical simulations.

98 citations

Journal ArticleDOI

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TL;DR: In this paper, a quality guided approach for isoclinic unwrapping is developed, which uses a ten-step phase shifting approach to obtain a smooth variation of the digital photoelastic parameters over the domain.
Abstract: In photoelasticity, the method of obtaining the individual values of principal stresses/normal stresses separately is referred to as stress separation. Shear difference is one of the widely used techniques for stress separation in photoelasticity and one needs the value of fringe order and the isoclinic angle free of noise at every pixel over the domain. For accurate parameter determination, a ten-step phase shifting approach which uses a plane polariscope for isoclinic determination and a circular polariscope for isochromatic determination is proposed. A new quality guided approach for isoclinic unwrapping is developed. Isochromatic phasemap free of ambiguous zones is obtained by a new methodology and is unwrapped by a quality-guided approach. Whole field evaluation of stress components and its representation is then presented. The models used in this study are intentionally subjected to moderate loads showing a high level of isochromatic–isoclinic interaction. In view of this, the isoclinic data has several kinks which is found to cause streak formation in the whole field representation of separated stress components. An outlier smoothing algorithm is proposed for getting a smooth variation of the digital photoelastic parameters over the domain. Use of such smoothed data for stress separation has removed the streaks and has also greatly improved the accuracy of the separated stress components.

75 citations

Journal ArticleDOI

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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.

66 citations