Effectiveness of the FRF curvature technique for structural health monitoring

Having the advantage, with respect to other vibration-based approaches, of not requiring modal identification, the FRF-curvature technique may be rather effective to detect damage in civil and mechanical structures. The accuracy of this technique, however, is strongly affected by the choice of the examined frequency range. Experimental tests and numerical analyses carried out on two different steel beams, where damage is simulated through holes of different diameter and the excitation is applied through impulsive loads, show that the application of the FRF-curvature technique within frequency ranges below or across resonance frequencies often lead to poor identification and localization of damaged regions. In contrast, when high-coherence frequency ranges are considered, the technique leads to successfully identify and localize multiple damage sites, even though the relative levels of damage severity could not be assessed with confidence. The results of the investigation also highlight the significant role played by the density of the measurement grid on the accuracy of the damage detection through this technique.