Effect of severe corrosion upon natural frequencies of beam-like structures

Corrosion, as the spontaneous process of material degradation produced by the environment, affects the reliability and safety of structures, both by reducing the section of the components, due to material loss and by diminution of the materials mechanical strength. The authors have found a mathematical relation between discontinuities in beams and changes of its natural frequencies and developed a method to identify these discontinuities. The present paper considers the more complex case of damage determined by corrosion, where beam thinning is accompanied by mass decrease. These impose considering natural frequency changes in both directions: decrease due damage and increase because of mass loss. FEM simulations and analytical investigations were carried out, in order to find the relation between mass change in different positions along the beam and the frequency increase. The results were correlated with the “classical” relation describing frequency decrease because of discontinuities. Finally, the authors developed a new relation, proper to be used for damage produced by severe corrosion, which was validated by laboratory experiments.