In digital photoelasticity, one gets whole field information of isoclinic and isochromatic parameters based on intensity processing. Isoclinic values are undefined at isochromatic fringe contours and this appears as noise in the isoclinic phasemap which affects stress separation adversely. A new adaptive smoothing algorithm to remove the noise due to isochromatic-isoclinic interaction that automatically takes care of the isotropic points and π jumps present in the isoclinic phasemap is proposed. It is validated for the benchmark problem of a ring under diametral compression and verified for an angled bracket. © 2009 Blackwell Publishing Ltd.

Krishnamurthi Ramesh

Department of Applied Mechanics

T. Kasimayan

DIGITAL PHOTOELASTICITY

ISOCHROMATICS

ISOCLINICS

ISOTROPIC POINTS

smoothing

Adaptive algorithms

Photoelasticity

Physical optics

Stress analysis

ELASTICITY

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It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Strain

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 enduser to make an informed choice on the type of technique to be used in a particular situation.

Journal of Strain Analysis for Engineering Design

Digital photoelasticity - A comprehensive review

Digital photoelasticity is a whole field experimental technique which can analyze both 2-D and 3-D models. In this paper, stress frozen 3-D models are sliced mechanically and the whole field principal stress differences (Isochromatics) and principal stress directions (Isoclinics) are evaluated by capturing only five images using the standard optical arrangements of a conventional polariscope. The wrapped isoclinic values obtained by processing the first four colour polarization stepped images in the range -π/4 to +π/4 are unwrapped using adaptive quality guided phase unwrapping algorithm to get isoclinics in the range of -π/2 to +π/2. The total fringe order is evaluated by three fringe photoelasticity or RGB photoelasticity with its latest developments like colour adaptation combined with refined three fringe photoelasticity. The methodology is validated for two slices cut from aero-structural components. © 2010 SPIE.

Proceedings of SPIE - The International Society for Optical Engineering

Photoelastic analysis of stress frozen slices using five-step method

A methodology has been developed that will plot the whole field isoclinic and isochromatic phasemaps from 2D finite element (FE) results where the problem with a circular disc under diametral compression were used so as to explain the phasemaps. This method is useful for quite many problems such as that have one or more isotropic points, multiple connected bodies, and a cantilever beam with a central cavity under bending. In addition, the method can also serve as a handy tool that can identify the inconsistent zones in isoclinic phasemap and ambiguous zones in isoclinic phasemap in digital photoelasticity which has helped ease the solution with complex problems.

Experimental Techniques

Finite element simulation of isoclinic and isochromatic phasemaps for use in digital photoelasticity

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. © 2007 Elsevier Ltd. All rights reserved.

Optics and Lasers in Engineering

Whole field evaluation of stress components in digital photoelasticity-Issues, implementation and application

With the advent of PC-based digital image processing systems, automation of parameter estimation based on intensity processing from the entire field has now become simpler. Various methods for obtaining the isoclinic parameter using plane, circular, and mixed polariscopes have been reported in the literature. A comparative study has been conducted on the performance of these methods both qualitatively and quantitatively. The focus of the study is on how these algorithms provide the basic isoclinic data. To illustrate the performance, theoretically simulated and experimentally recorded images for a ring under diametral compression is used. The role of background light intensity and quarter-wave plate mismatch on the experimental evaluation of isoclinic data is brought out. © IMechE 2006.

Fulltext

Comparative study of evaluation of primary isoclinic data by various spatial domain methods in digital photoelasticity

An Arctangent Unwrapping Technique of Photoelasticity Using Linearly Polarized Light at Three Wavelengths

Digital Photoelasticity

Reflection Photoelasticity

Adaptive smoothing for isoclinic parameter evaluation in digital photoelasticity

Journal	Strain
ISSN	00392103
Open Access	No