Diagnostics for piezoelectric transducers under cyclic loads deployed for structural health monitoring applications

Abstract

Accurate sensor self-diagnostics are a key component of successful structural health monitoring (SHM) systems. Transducer failure can be a significant source of failure in SHM systems, and neglecting to incorporate an adequate sensor diagnostics capability can lead to false positives in damage detection. Any permanently installed SHM system will thus require the ability to accurately monitor the health of the sensors themselves, so that when deviations in baseline measurements are observed, one can clearly distinguish between structural changes and sensor malfunction. This paper presents an overview of sensor diagnostics for active-sensing SHM systems employing piezoelectric transducers, and it reviews the sensor diagnostics results from an experimental case study in which a 9 m wind turbine rotor blade was dynamically loaded in a fatigue test until reaching catastrophic failure. The fatigue test for this rotor blade was unexpectedly long, requiring more than 8 million fatigue cycles before failure. Based on previous experiments, it was expected that the rotor blade would reach failure near 2 million fatigue cycles. Several sensors failed in the course of this much longer than expected test, although 48 out of 49 installed piezoelectric transducers survived beyond the anticipated 2 million fatigue cycles. Of the transducers that did fail in the course of the test, the sensor diagnostics methods presented here were effective in identifying them for replacement and/or data cleansing. Finally, while most sensor diagnostics studies have been performed in a controlled, static environment, some data in this study were collected as the rotor blade underwent cyclic loading, resulting in nonstationary structural impedance. This loading condition motivated the implementation of a new, additional data normalization step for sensor diagnostics with piezoelectric transducers in operational environments.

Damage Sensing in Blades

“…Therefore, more robust and reliable systems (transducers and equipment) are required in order to deploy this technology in wind turbine blades. Investigations in self-diagnosis of transducers during operation have been carried out by Taylor et al (2013c), where they proposed a technique to analyse the impedance of the transducer in order to distinguish between structural damage and transducer malfunction, avoiding false positives in damage detection. Figure 3.5 depicts a signal that can be acquired through the application of Guided Wave Technology in an aluminium plate.…”

A Multi-scale Approach to Statistical and Model-based Structural Health Monitoring with Application to Embedded Sensing for Wind Energy

“…Chapter 4 focuses on diagnostics for piezoelectric sensors using impedance measurements, and in particular provides two key contributions to the SHM community in the application of piezoelectric transducers: (1) the assessment of sensor performance and failure modes over a long-duration fatigue test in a severe loading environment, and (2) the identification and normalization of nonstationary impedance measurements collected during cyclic loading of a structure [6]. This situation is significant, because many structures commonly considered candidates for embedded SHM undergo cyclic loads while in operation, including aircraft, automobiles, bridges, and wind turbine flexible members.…”

“…Advances in impedance-based methods for SHM [55,56], the development of sensor diagnostics methods for the piezoelectric transducers that implement them [6,56,57], and the availability of low-power integrated circuits (ICs) for impedance measurement, such as the AD5933 from Analog Devices, have combined to unleash a deluge of low-power, impedance-based sensor nodes on the SHM community. Some of these nodes are listed in Table 5.…”

Self-Diagnosis and Self-Reconfiguration of Piezoelectric Actuator and Sensor Network for Large Structural Health Monitoring

“…Bhalla and Soh (2004) find that the imaginary part of the electrical admittance of PZT sensor may play a meaningful role in detecting the bonding of sensor [7]. Park 2009, and 2013) employs the capacitive of PZT sensor to identify the degradation of its mechanical/electrical properties and bonding [8][9][10]. It is also utilized to distinguish response changes caused by sensor failure and structural damage.…”