Bondline inspection of complex structures using guided waves

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Bondline inspection of complex structures using guided waves

Hauck, Eric T. / Rose, Joseph L. / Moose, Clark A.

The use of structural adhesive joints is increasing in aerospace and naval applications. Scarf joints, used where dissimilar materials, such as metals and fiber reinforced composite materials are bonded, are difficult to inspect with traditional NDE methods. Ultrasonic guided wave transducers are developed using a hybrid semi-analytical finite element technique to assure the interrogation of the critical region of the joint. Further manipulation of the wave structure of the guided wave is performed using a transitional waveguide so that the impingement of ultrasonic energy into the joint is parallel with the joint interfaces. Modes and frequencies can be identified to activate a guided wave with maximum shear stress at both the steel/epoxy interface and the epoxy/composite interface in the scarf joint. When generating guided waves in the scarf joint using comb loading alone, wave modes can be identified that have minimal wave structure change for comb loading across the taper for a more 'global' inspection; and wave modes influenced by the changes in the structures geometry can potentially be used for defect localization. The wave guide template concept is a feasible method for impinging guide waves in a complex structure. Further fine tuning of the wave guide template with comb loading will allow for complete coverage of the scarf joint with defect localization.