Digital photoelasticity – A comprehensive review

Review of RGB photoelasticity

Abstract: Automatic methods of photoelasticity have had a significant progress with the development of automatic acquisition and image processing methods. This article concerns RGB photoelasticity, which allows the determination of the photoelastic retardation using, usually, a single acquisition of the isochromatic fringes in white light by a colour camera. In particular, the article presents an overview of the main characteristics of RGB photoelasticity that is influence of the quarter-wave plate error, number of acquisitions, type of light source, determination of low and high fringe orders, methods for searching the retardation, scanning procedures, calibration on a material different from that under test, combined use of the RGB and phase shifting methods. A short section on the applications of RGB photoelasticity completes the article.

Visualization of the three-dimensional structure and stress field of aggregated concrete materials through 3D printing and frozen-stress techniques

Abstract: Characterization of the three-dimensional stress field of concrete materials is crucial to understanding their mechanical properties and failure mechanisms, but their hidden and complex meso-scale structure makes physically extracting and visualizing this information intractable. This paper therefore presents a new approach that uses 3D printed models based on X-ray microfocus computed tomography (CT) imaging of a concrete sample to replicate its complex aggregate structure in a transparent matrix. The associated three-dimensional stress field is visually characterized at mesoscale through uniaxial compression tests and photoelastic techniques that incorporate a three-dimensional frozen-stress test to analyse the effects of randomly distributed aggregates. These results are used to validate the accuracy of simulated data created using the finite element method, which allows a comparison to be made between two-dimensional and three-dimensional heterogeneous aggregated models. The study indicates that meso-heterogeneity has more influence on the stress state of localized areas than the entire field. Compared to 2D structures, 3D structures possess a lower stress concentration due to the lateral inertial confinement effect. The difference in stress field between the two structure types is therefore attributable to a combination of structural heterogeneity and lateral inertial confinement.

Optical measurement techniques – A push for digitization

Abstract: Keywords: Speckle interferometry ; Digital holographic interferometry ; Digital image correlation ; Fringe projection profilometry ; Digital photoelasticity Reference EPFL-ARTICLE-222716doi:10.1016/j.optlaseng.2016.05.002View record in Web of Science Record created on 2016-10-26, modified on 2017-03-09

Experimental investigation of the systematic error on photomechanic methods induced by camera self-heating

Abstract: The systematic error for photomechanic methods caused by self-heating induced image expansion when using a digital camera was systematically studied, and a new physical model to explain the mechanism has been proposed and verified. The experimental results showed that the thermal expansion of the camera outer case and lens mount, instead of mechanical components within the camera, were the main reason for image expansion. The corresponding systematic error for both image analysis and fringe analysis based photomechanic methods were analyzed and measured, then error compensation techniques were proposed and verified.

Digital photoelasticity of glass: A comprehensive review

Abstract: The recent advances in digital photoelasticity have made it possible to use it conveniently for the stress analysis of articles and components made of glass. Depending on the application, the retardation levels to be measured range from a few nanometres to several thousand nanometres, which necessitates different techniques and associated equipments. This paper reviews the recent advances in the photoelasticity of glass with a focus on the techniques/methods developed in the last decade. A brief introduction to the residual stress in glass is provided initially to bring out its tensorial nature. The subsequent sections are organised thematically rather than chronologically, for better readability and easy access of information.

Springer Handbook of Experimental Solid Mechanics

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Fourier fringe analysis: the two-dimensional phase unwrapping problem.

Abstract: A new phase unwrapping algorithm is described that uses local phase information to mask out those parts of the field that cause inconsistencies in the unwrapping. Unlike earlier techniques, which produce only a consistent unwrapping of the phase in the presence of discontinuities, this technique can produce an approximately correct unwrapping. The technique is tolerant of discontinuities and noise in the phase and is fast, efficient, and simple to implement. In the absence of discontinuities an rms signal-to-noise ratio in the wrapped phase of <2:1 can be tolerated.

Towards full field automated photoelastic analysis of complex components

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.

Demodulation of a single interferogram by use of a two-dimensional regularized phase-tracking technique

Abstract: We present a two-dimensional regularized phase-tracking technique that is capable of demodulating a single fringe pattern with either open or closed fringes. The proposed regularized phase-tracking system gives the detected phase continuously so that no further unwrapping is needed over the detected phase.

Digital Photoelasticity: Advanced Techniques and Applications

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.