Reflective fringe pattern technique for subsurface crack detection

This paper presents a novel optical technique, reflective fringe pattern (RFP), for non-destructive testing (NDT) of objects having specularly or semi-specularly reflective surfaces. The principles are based on measuring the surface deformation of a test object and identifying deformation anomalies caused by subsurface flaws. RFP is not based on optical interference and therefore, it is not subjected to the severe limitations of interferometry. Compared with the conventional methods of NDT techniques, RFP measures the response of a flaw to applied stresses, and hence it provides more direct information about the flaw criticality. In this paper, experimental demonstrations of the present technique to subsurface crack detection are presented. Two software-based methods are also adopted to enhance the flaw visibility on the output of RFP.