Studies on Digital Shearography for Testing of Aircraft Composite Structures and Honeycomb-Based Specimen
This paper reviews shearography and its applications for testing of aircraft composite structures and honeycomb-based specimen. Shearography is a laser-based interferometry in conjunction with the digital imaging processing technique for full-field measurement of surface deformation. It reveals defects in an object by looking for defect-induced deformation anomalies. It does not require special vibration isolation, and with the development of a small and mobile measuring device (portable inspection system), it can be employed easily in field/factory environments.
Localization of damage with speckle shearography and higher order spatial derivatives
Abstract Two speckle shearography systems are described in this paper. The first is based on stroboscopic laser illumination and temporal phase modulation, whereas the second system relies on double pulse laser illumination and spatial phase modulation. These systems are applied to measure the phase maps of modal rotation fields of a damaged laminated composite plate. In order to decrease the propagation of noise, a new differentiation methodology is presented. It relies on the differentiation of the measured phase maps before they are post-processed. This leads to an improvement in the localization of damage. It was found that the fourth order spatial derivative of mode shapes also presents better damage localizations, in particular with the phase maps measured by the first shearography system.
Formation and Localization of Holographically Produced Interference Fringes
Theoretical and experimental studies are described on the formation and localization of holographically produced interference fringes. The fringes were shown to be localized where the correlation between the wave fields produced by the two objects identical in shape but different in the relative position attains the maximum value. A grating model of a diffusely reflecting surface was proposed, in exact agreement with the theory. Experiments were carried out to verify the discussions.