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.

A review of automated methods for the collection and analysis of photoelastic data

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.

Digital photoelasticity – A comprehensive review

Review of RGB photoelasticity

Digital photoelasticity: Recent developments and diverse applications

This paper considers the main developments of RGB photoelasticity with reference to the maximum measurable retardation. In this paper, a new procedure based on the standard error function evaluated on a subset of the calibration array is also proposed and experimentally tested. The experiments show that the filament lamp makes it possible to find retardations until approximately 4 fringe orders while the fluorescent lamp makes it possible to determine higher fringe orders (12 fringe orders in this paper) owing to the discrete spectrum of the source. The paper shows that, by using the incandescent lamp, the primary limiting factor is the lack of modulation of the R, G and B signals whereas, by using the fluorescent lamp, the limitation of the maximum fringe order derives mainly from the gradient of the fringes and the procedure of search of the retardation.

RGB Photoelasticity: Review and Improvements

The early application of digital image processing (DIP) technique to automate photoelastic analysis is based on black and white (B & W ) image processing systems. The various methodologies reported can be traced to rely upon one or several features ofa B &W DIP system. With the advancements in computer technology, nowadays colour image processing systems are available at affordable prices. A systematic study has been carried out on how to use the red green blue (RGB) value recorded using a colour image processing system for determining fringe orders up to 3 in a fringe field. The study has revealed that instead of directly using RGB values corresponding to a dark field image, if the difference of RGB values between bright and darkfield images is used, the number of noise points is less. Experiments have been carried out for several arbitrary lines in a circular disk under diametral compression and the results are found to be good.

Sanjeev S. Deshmukh

Papers

Three fringe photoelasticity ‐ use of colour image processing hardware to automate ordering of isochromatics