Multiplication and Extraction of Isochromatics in RGB Photoelasticity Using Image Processing.

Abstract

A method is proposed for multiplying and extracting isochromatics in RGB photoelasticity and assigning fringe orders to them. The method uses R, G and B isochromatics, which are taken using a color CCD camera in dark-and light-field circular polariscopes with a white light. Light intensities in the dark field image are subtracted from those in the light field image, and the points with zero values are extracted. The fringe orders are assigned to the multiplied and extracted fringes using calibration curves, which show the relationships between the fringe orders obtained using a single wavelength and those using R, G and B filters in the CCD camera. In order to investigate the accuracy of the method, a computer simulation is used for the theoretical isochromatics in a circular disk subjected to a concentrated load. The result shows that error of the assignment of fringe orders to multiplied and extracted isochromatics is about 1.5%. This method is applied to an epoxy resin plate with a crack at one side under 3-point bending and the stress intensity factor is determined. The result shows that the stress intensity factor is accurately determined.