| Résumé | Double pass retroreflection (D SightTM) optical systems for corrosion detection have been developed over the last three years, and commercial systems are already in the hands of customers. D Sight Aircraft Inspection Systems (DAIS) have initially been conceived as methods for rapidly locating defects in aircraft structures. While these defects were to be inspected by more traditional and slower methods, in the course of research studies initiated to support the DAIS development, it was realized that the bulging of skins between the rivets (pillowing) can be detected with DAIS at very low levels of corrosion thinning (less than 3%). Modelling of corrosion pillowing was then undertaken using closed form and finite element methods. Riveted skin surface deformations were calculated at various levels of corrosion, and a ray tracing program was used to simulate DAIS images. Several factors affecting these images were investigated: relative and absolute skin thickness in the joint, rivet patterns and spacing, as well as surface reflectivity. Using the results obtained it is now possible to estimate the level of corrosion in a joint using simulated images and simple graphs, and this could be expressed in percent corrosion or stress terms. |
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