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. (Some figures may appear in colour only in the online journal)