Flaw detection and characterization using shearography

Abstract

Shearography is a laser interferometric method developed originally for full field observation of surface strains of components. Since flaws usually induce strain concentrations around them, shearography can be employed to detect the flaws. Conventional shearography involves exposing high resolution films before and after the components are loaded. The exposed films are developed and then viewed via a high-pass filtering optical setup. Though the images obtained are good, this method is time-consuming. With the advent of high-speed computers, associated sophisticated imaging hardware and software, the Digital Speckle Shearing Interferometry (DSSI) method which employs a CCD (charged-coupled device) camera and computer image processing to produce the interferometric fringe patterns has been developed. In contrast with the conventional shearography, the electronic version does not require any film and is faster. The techniques are used to detect and characterise (a) flaws simulating delaminations in composites and (b) thinning in pipes.