Model-based detection of sensor faults under changing temperature conditions

Abstract

Nowadays, a variety of civil, aeronautic or mechanical engineering structures need regular inspections. While nondestructive testing has become state of the art, there is a trend towards online testing on demand using built-in sensors. A vast amount of in-service monitoring, as part of structural health monitoring, uses piezoelectric elements. Their deployment requires a control of the sensor performance in order to prevent false alarm. Several kinds of damage can influence the sensor performance, for example, degradation of piezoceramic or adhesive, debonding or breakage of the element. Therefore, this paper aims to detect damage of circular piezoelectric elements and their bonding layers during in-service monitoring. For this purpose, a local method, using the coupled electro-mechanical admittance, is proposed. However, changing environmental and operational conditions such as temperature have an effect on the measured quantities, masking the damage. To cope with this, the dynamic behaviour of an attached piezoelectric element including temperature trends is modelled to enable physics-based temperature compensation. This novel combination of an improved analytical model, updated according to impedance measurements, realizes a method less dependent on experimental baseline data, than the sole comparison of experimental data, established in many monitoring systems. By comparison with experimentally obtained electro-mechanical susceptance the physical model of circular piezoelectric elements is validated. The feasibility of the proposed method is presented employing experimental data of piezoelectric elements mounted on aluminium coupons, partly damaged with degradation and sensor breakage. The application produces promising results, detecting the created defects.

Failure Assessment of Piezoelectric Actuators and Sensors for Increased Reliability of SHM Systems

“…Using more information like the resonance behavior included in the EMI-spectrum enables the detection of minor PWAS faults and is especially valuable for the inspection of embedded transducers [40][41][42]. This is possible with the use of a physical model [4] or by utilizing purely datadriven approaches [43]. A simplified measurement of the EMI spectrum suggested in [44] and implemented, e.g., in [45] enables a quick measurement of the EMI spectrum with the same equipment as used for AU-based SHM systems.…”

“…Using principal component analysis (PCA), they can be aggregated to a damage index DI model . For details, the reader is referred to [4,42].…”

“…Moreover, a shear layer coupling between PWAS and structure, achieved by the adhesive layer, needs to be considered. Based on [21,23], in [4], a model was developed, which includes these effects and focuses on the PWAS signature, including resonances and antiresonances of the EMI spectrum Z ω ðÞ .…”

“…This is not the case for all applications. Therefore, in [4,5], a physics-based compensation of the influences of temperature changes is used for EMI and acousto-ultrasonics (AU)-based methods. The effort for this method is large, as the temperature dependence of all significant parameters has to be included within the model.…”

Simultaneous Influence of Static Load and Temperature on the Electromechanical Signature of Piezoelectric Elements Bonded to Composite Aeronautic Structures

“…In an aeronautic context, temperature variations as well as static loads induced on the structure during a flight can both be very important. Experiments have been carried out that focused on temperature [5][6][7][8][9][10][11][12][13][14][15][16][17] or static loads [18][19][20][21][22], but rarely simultaneously [23][24][25][26]. Regarding temperature effects, it has been observed that the effect of temperature changes consists of a shift of the piezoelectric resonance frequencies.…”