Quantitative evaluation of corrosion by a digital fringe projection technique

Abstract

A novel digital fringe projection (DFP) technique has been developed for the detection and quantitative evaluation of corrosion on engineering structures. DFP detects and evaluates corrosion by measuring surface topographical changes caused by corrosion. By using a novel digital projection display technology, the technique provides the capability of digitally projecting fringe patterns with extremely high brightness and contrast ratio. Fringe patterns are created by software, which allows for instant changes of intensity profile, phase, and spacing. Digitally accurate, software-based phase shifting technique is employed to significantly improve measurement resolution. Phase wrapping and unwrapping are done automatically by a specially developed software. With a high-resolution CCD camera, a total of 4 million surface contour data are generated for each specimen measured. This technique has the potential of providing rapid on-site inspection and evaluation of corrosion on large structures. Experimental results on various corrosion specimens are presented and discussed.