Simultaneous Monitoring of Ageing and Damage in Large Plate-Like Composite Structures Using Integrated Peizoelectric Sensors

摘要

The health of a structure is closely linked to both the homogeneously distributed degradation of its mechanical properties during its life cycle (ageing) and to the presence of localised defects such as cracks or delaminations. In previous papers 1-3, we described an ultrasonic health monitoring method enabling the recovery of both kinds of information. The system is based upon an integrated piezoelectric element into the plate-like composite structure which avoids coupling reproducibility problems. The element dimensions can be determined in order to uncouple the frequency ranges of the thickness and radial vibration modes (Fig. 1). The thickness mode is then exploited to monitor the homogeneous ageing of the structure through electrical impedance measurement. Whereas the radial vibrations, are used to launch and detect Lamb waves, which are known to propagate over long distances. The guided waves also have the advantage to be multimodal. And the various propagating modes offer a specific sensitivity to the different kind of defect that a structure can host. The previous papers dealt respectively to each of the two possible monitoring modes of the system. In this paper, the influence of the material properties upon the limitations of the second kind of monitoring will be discussed in relation with the characteristics of the waves that the structure can propagate.