A Vibration-Based Method for assessing the integrity of welded structures

A Vibration-Based Method for assessing the integrity of welded structures is presented. The proposed technique relies on fitting theoretical predictions of a lumped mass-based model of the welding with experimental measurements obtained from modal analysis. Experiments are performed in various test platens that are soldered at one or two locations and exhibit distinct welding qualities, achieved by using different control parameters in the welding process. The inertia added during the soldering execution is modelled by a lumped mass that connects to the structural element via linear springs. The associated rigidities play the role of fitting parameters and are adjusted to reproduce the (three) measured natural frequencies by means of optimisation algorithms. This method is successful in characterising the platens tested and provides an accurate and consistent (with the expected welding quality) quantification of their effective mechanical properties at the bond. We note that this is beyond the qualitative evaluation achieved with other extended Non-Destructive Testing techniques. Such characterisation is possible even without particular knowledge of modal shapes, whose experimental determination is difficult in any real structure, although different resonant frequencies must be considered to achieve reliable estimates. Based on the present results, we suggest that this technique can be used for assessing the overall integrity of welded structures in a quantitative and a reliable manner.