Fatigue damage identification by means of modal parameters

The object of the present paper is an experimental investigation about high cycles fatigue damage and corresponding variation of modal parameters (internal damping and resonant frequency) in steel specimens. On the basis of a modal approach, a mixed technique has been developed in order to relate fatigue damage and intrinsic properties of the material. In particular, the experimental procedure consists of the modal parameters assessment on C45 and C40 steel specimens, once before fatigue test beginning, and thus repeated after every 105 cycles, both with constant and increasing loading levels (below or above fatigue limit). Finally, infrared thermography has been used to emphasize the specimen thermal emission and the related damage phenomena.