Evaluation of bonded piezoelectric AE sensor for structural health monitoring

The development of high sensitivity sensors capable of accurately reproducing propagating Lamb waves is crucial for the success of AE based structural health monitoring applications. Plate like members are the most common elements encountered in structural health monitoring. The stress waves propagate as guided waves or Lamb waves in these members. While the traditional acoustic emission sensors are sensitive to displacements normal to the surface of the structural member, the bonded sensors are sensitive to the surface strains. A calibration procedure specifically for the Lamb wave modes is devised using a Laser Vibrometer. The calibration was performed by observing the stress waves propagating in aluminum plates. Based on this calibration, it is established that the bonded PZT sensors reproduce the stress waveforms in these structures reasonably well. This ability was probably responsible for the success of these sensors in distinguishing different source mechanisms and correlation with crack growth rates seen in past studies. In addition to this calibration, the two simulated AE sources were also modeled using finite element technique. The results of the numerical simulation were found to correlate well with the experimental results.