Ultrasonic non-destructive testing and evaluation (NDT/E) techniques offer a viable solution for detection of various kinds of defects. However, they are often expensive and difficult to apply especially to large structures. As a result, ultrasonic automated damage detection known as structural health monitoring (SHM) has emerged in recent years and significantly advanced through improved understanding and interpretation of signals produced by piezoelectric transducers.&nbsp; The aim of ultrasonic SHM system is to improve safety and reliability while also reducing maintenance costs of engineering structures.Many researchers have employed surface-mounted d31 piezoelectric transducers made of lead zirconate titante (PZT) to identify different types of defects by sensing and actuating guided waves such as S0 and A0 modes. Another category of piezoelectric transducers characterized by d15 property has received less scientific attention in the field of ultrasonic inspection despite their excellent sensitivity and practical potential. This study investigates the use of shear deforming (d15) piezoelectric transducers to actuate and sense antisymmetric waves and address the challenge of detecting delamination in laminated structures. Internally embedded d15 piezoelectric transducers provides multiple for inspection of laminate structures such as direct coupling to adhesive joints, reducing the complexity of signal processing by suppressing symmetric modes, and offering greater actuation strength.A laminated beam consisted of internally embedded d15 piezoelectric transducers in a pitch-catch configuration was fabricated with artificial delamination created at the interface of aluminum layers. The severity of damage was also varied to evaluate the effectiveness of the approach to detect delamination and to predict its propagation path. A five-peak tone burst signal centered at 30 kHz was supplied to PZT actuators throughout the experiment to produce antisymmetric waves in the laminate specimen.It was found that the closer the delamination occurred to the d15 PZT actuator the greater the change in signal increasing the probability to be identified using antisymmetric A0 wave mode. The analysis suggests that d15 PZT actuators should be placed in regions where delamination is likely to occur in laminated structures. Also, the propagation path of delamination was successfully predicted using a set of sensor signals processed using damage index methods including Pearson correlation coefficient, normalized signal energy, and root mean square deviation. The actuation strength and wavelength of propagating waves are expected to improve the sensitivity to delamination. Evaluation of the results indicated that embedded d15 piezoelectric transducers exclusively couple to antisymmetric guided waves and can advance signal analysis for detection of delaminations with ultrasonic structural health monitoring systems.

Using d15 Piezoelectric Transducers for Ultrasonic Inspection of Delamination in Laminated Structures

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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