Fatigue damage assessment and detection in notched components based on phenomenological models and operational modal analysis

Resumen

The calculation of accumulated fatigue damage and the remaining fatigue life of in-service-structures, as tools for the prediction of failure, being nowadays one of the main challenges in structural integrity analysis. Alternatively, Operational Modal Analysis (OMA) can be used to detect damage comparing the modal parameters (e.g., natural frequencies, mode shapes, etc.) corresponding to both damaged and undamaged states of the structural component. Both approaches are, indeed, two different techniques to predict and detect the fatigue failure of structures in service. Nevertheless, the derivation of relations between the accumulated fatigue damage and the corresponding changes in the modal parameters of the structural component is not straightforward. In this work, an experimental fatigue campaign has been performed on a S275 steel beam, with square section of 25 mm, involving different kind of stress concentrators. On the one hand, the analytical definition of the S-N curves has been derived based on a probabilistic approach. On the other hand, damage detection techniques have been applied based on changes in the natural frequencies estimated with operational modal analysis. As a result, the probabilities of fatigue failure corresponding to a reduction in the natural frequencies of 2 %, 3 % and 5 % are obtained for the first three vibration modes.