NDE of Crevice Corrosion Using Electronic Speckle Pattern Interferometry and Digital Speckle Correlation

Two optical techniques, ESPI (Electronic Speckle Pattern Interferometry) and Digital Speckle Correlation are employed to reveal the existence of crevice corrosion which is usually undetectable from outside by visual inspection. The ESPI is configured to measure out-of-plane displacement. Both thermal loading and vacuum loading are used. The anomaly of fringe patterns reveals the existence of crevice corrosion hidden between two metallic plates. Not only the location of delects, but also the approximate size can be estimated Digital Speckle Correlation technique takes advantage of laser speckle properties. The speckle decorrelation due to out-of-plane displacement in the region with crevice corrosion is bigger than without defects. This difference is calculated by a digital correlation algorithm, which reveals the crevice corrosion.