Detection of internal defects using phase shifting holographic interferometry

Abstract

Phase shifting holographic interferometry is shown to be a useful tool for detection of internal defects in materials by observing strain anomalies in a stressed object. The pos-t recording signal processing includes smoothing of the measured deformation by means of data polynomial fitting, a derivation process taken from computer vision edge detection algorithms, which makes use of a Gaussian derivative and a cubic spline interpolation, a second smoothing, a regular numeric derivative and final smoothing. Defects, ie weak areas of the sample, are detected in the second derivative of the sample deformation, which is proportional to the stress map of the sample surface. The second derivative provides information about the defect dimensions and its severity and location. A theoretical model forthe loading of a sample containing a defect is presented as well as results based on it. Good correlation between experiment and theory was found.