Experimental research on acousto-ultrasonic inspection of composites by PZT patches and wavelet analysis

摘要

In smart composite structures, piezoelectric patches are usually bonded to surfaces or embedded in structures for strain measurement and active control. This paper investigates applications of these patches for acousto-ultrasonic(AU) inspection of structure without special design or additional change of their shapes and configurations. By using these multi-functional built-in transducers, the smart composite has the potential to monitor a large area on the structure with AU method. Experiments were conducted on a fiber-epoxy composite beam. A PZT transmitter pasted on the beam was stimulated by a nanosecond pulse generator, reflected stress wave caused by edges of the beam was clearly observed. Artificial slots on the beam can be well located from the arriving time of the reflected waves, their size can be estimated from the shape and peak value of the waves reflected by or propagating through slot. Wavelet analysis was used to extract features from the measured signals. Local maxima of coefficients of Mexico hat wavelet decomposition were employed as features to describe arriving time and slope of signals. Features in different damage conditions were compared, results show these features can represent both the location and extent of the simulated damages.