Abstract
Structural Health Monitoring (SHM) gives a diagnosis of a structure assessing the structural integrity and predicting the residual life through appropriate data processing and interpretation. A structure must remain in the design domain, although it can be subjected to normal aging due to usage, action of the environment, and accidental events. SHM involves the integration of electronic devices in the inspected structure that sometimes are Piezoelectric Transducers (PZT). These are lightweight and small and can be produced in different geometries. They are used both in guided wave-based and electromechanical impedance-based methods. The PZT bonding requires essential steps such as preparation of the surfaces, application of the adhesive, and assembly that make the bonding process not so easy to be realised. Furthermore, adhesives are susceptible to environmental degradation. Transducer debonding or non-uniform distributed glue underneath the sensor causes the reduction of the performance and can affect the reliability of the SHM system. In this paper, a sensor diagnostic method for the monitoring of the PZT operational status is proposed in order to detect bonding defect/damage between a PZT patch and a host structure. The authors propose a method based on the nonlinear behaviour of the contact PZT/structure that allows the identification of the damaged PZT and the geometrical characterization of the debonding. The feasibility of the diagnostic procedure is demonstrated by numerical studies and experiments, where disbonds were created by inhibiting the adhesive action on a part of the interface through Teflon film. The proposed method can be used to evaluate the sensor functionality after an extreme loading event or over a long period of service time.
Highlights
Maintenance (SM) to Condition Based Maintenance (CBM) in civil and military fields
Structural Health Monitoring (SHM) is concerned with directly assessing the state of a structure depending on the presence and extent of damage by electronic devices (e.g., Piezoelectric Transducers (PZT) sensors) permanently installed on it from [2,3,4,5,6,7]
Signals with normalised amplitude and relative Short Time Fourier Transform (STFT) at 200 kHz are plotted in Figure 6
Summary
SHM is concerned with directly assessing the state of a structure depending on the presence and extent of damage by electronic devices (e.g., Piezoelectric Transducers (PZT) sensors) permanently installed on it from [2,3,4,5,6,7]. Structural inspections with PZTs can be performed using several methods such as wave propagation, frequency response transfer function or electromechanical (E/M) impedance from [8,9,10,11]. These methodologies apply techniques which rely on PZT sensors functionality and on the state of the mechanical coupling provided by the adhesive layer. It is generally assumed that the Electronics 2018, 7, 303; doi:10.3390/electronics7110303 www.mdpi.com/journal/electronics
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