Análise das métricas de dano associadas à técnica da impedância eletromecânica para o monitoramento de integridade estrutural

Abstract

The basic concept of impedance-based structure health monitoring is the measuring of the variation of the electromechanical impedance of the structure as caused by the presence of damage, by using patches of piezoelectric material bonded on the surface of the structure or embedded in the structure. The measured impedance is directly related to the mechanical impedance of the structure. Based on the variation of the impedance signal, the presence of damage can be determined. In order to quantify damage, a metric is specially defined, which allows to assign a characteristic scalar value to the fault. The objective of this work is to evaluate the various metrics suggested by the literature. Primarily, this work intends to identify small damage in simple structures, evaluating the damage metrics and trying to determine which one shows the best behavior for the purposes of identification. Afterwards, incipient damage in an aeronautical structure, such as the loss of a rivet, is attempted to be identified. Again, the metrics suggested in the literature are evaluated. For this structure, it was statistically evaluated in the perspective of determining if the metrics were actually able to identify the damage. The structure health monitoring method based on the electromechanical impedance was also applied to fatigue tests by monitoring the impedance signal for each previously defined number of cycles. At the end of these tests, a polynomial meta-model was built in order to predict the number of cycles that lead to the collapse of a test sample, based on the measurements of the electromechanical impedance. From the results obtained by this contribution it was possible to conclude that the technique is sensitive to incipient damage. Moreover, it can be observed that, for each analyzed case, one of the metrics is better adjusted than the others. For this reason it is necessary to test all the metrics to determine which one is the most suitable for each problem. Finally, it is observed that it is possible to establish relations between the applied tension cycles in a fatigue test and the measurements of the electromechanical impedance.