Real time acquisition of ESPI specklegram and automated analysis for NDE

Electronic Speckle Pattern Interferometry (ESPI) is a fast developing whole field optical technique used for the measurement of optical phase changes under object deformations and has evolved as a powerful on-line nondestructive evaluation (NDE) tool. In ESPI the speckle interferometry data of the object under different loading conditions are stored as digital images and then converted into interference fringes by digital subtraction or by addition method. These interference patterns correspond to surface displacements, which in turn relates to the strain variation in the specimen. Defects in the specimen produce a strain concentration on loading and generate a fringe anomaly in the interferogram. These anomalies in the interferogram are analyzed for the characterisation of defects in the material. This technique is used as an effective tool in Non-Destructive Evaluation (NDE). In this paper a method for on-line analysis of ESPI fringe patterns for the qualitative evaluation in the materials is presented. Continuous acquisition and simultaneous digital processing of specklegrams has been developed for generating the fringe patterns. The image acquisition and processing system used for the present study is an algorithm developed by using Imaging Graphs software. Image processing techniques are introduced for contrast enhancement, noise reduction and fringe sharpening for the on-line detection of different types of defects in the material.