Development of Simple Strain Distribution Measurement System by Interferometry Using CCD Image Elements

Abstract

A simple measurement system for strain distribution has been developed on the basis of moire interferometry using CCD camera. A direct image of moire fringe can be obtained from the grid on surface of a plate specimen. After simply preprocessing the image, the system allows us to get the strain distribution in a few seconds. This paper describes the application of the system to large plate specimens by creep testing. The interference fringe generated by a CCD image agrees with the conventional moire fringe. Thus we can apply the system to measure the strain distribution of interrupted creep specimens. Since the system uses the simple configuration of a CCD camera and a personal computer for gridded specimens, little skill is needed to apply it. When the surface conditions are not smooth enough, a simplified smoothing treatment helps us to improve the accuracy of strain measurement. The range of measurement can be localized by the zooming function of the camera. Another feature of the new method is that it can be used in nearly real-time situation.