The use of composite materials in aircraft industry is becoming more common because of high stiffness‐to‐weight ratio. Adhesively bonded, metallic stiffeners are also widely used for increasing the transverse stiffness of thin composite components. However, small defects in the adhesive (porosity, cracks, …) may exist after the bonding is realized, and become larger during the in‐service life, thus causing severe damages to the whole structure. For obvious safety reasons, the non‐destructive testing of such critical bond‐lines is very important. More specifically, it is of importance to size disbonds that may exist between a stiffener and a composite component. Recently, a 2D, Finite‐Element‐based inverse technique has been developed for sizing defects in plates, using Lamb waves. Here, this technique is used for sizing the width of a disbond running parallel to an Aluminum stiffener adhesively attached to a Carbon‐Epoxy plate. A pure incident S0 mode is experimentally sent towards the stiffener, and the amplitudes of reflected and transmitted S0 and A0 modes are measured, and used as input data for the inversion process. The FE model and postprocessing are optimized so that fast computations can be run for numerous values of the aimed disbond width. The inversion process shows very good and fast convergence to the actual width of the hidden disbond.

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