Phase Stepping Shearography for Testing Commercial Aircraft Structures: An Application Review of Advanced Image Processing Techniques for Shearography

摘要

Interferometric NDT methods have a long history in the laboratories of DAIMLER BENZ AEROSPACE Airbus, even first papers about early approaches to shearography go back into the late seventies, when in the Lemwerder Labs of former VFW-Fokker the first shearography setup was assembled [1]. That time using film or thermoplast camera the method proved to be too complicated for in field applications. During the following years the acceptance of interferometric NDT methods remained poor as the typical test results were represented by complex fringe patterns. These patterns could be interpreted only by well trained specialists. It was sometimes impossible to extract the defect information from complex fringe patterns caused by the geometry of the test specimen. In the spectrum of different approaches to overcome this problem the phase stepping fringe analysis method showed great potential in conjunction with the capabilities of shearography.