Piezoactuators
Due to increasing complexity of everyday used civil objects such as airplanes, nuclear power plants, bridges and rotor blades of wind turbines, damage detecting technologies are of a great importance. Therefore structural health monitoring (SHM) is a promising branch in worldwide science. One method in this field is to use guided waves actuated and recorded by a certain number of piezoelectric waver active sensors (PWAS). Especially for long term monitoring, sensors might be the weakest link in the SHM system. Failure of actuators might lead to significant problems and evidently the monitoring of actuators themselves is necessary. The aim of the present work is to collect knowledge about the effects of partially debonded PWAS. Therefore an experimental setup with 16 partially debonded actuators is used to investigate the excitation of an aluminum plate. Phenomena accompanying wave excitation by debonded actuators are also analyzed. Collected knowledge is analyzed in order to identify existence, location and shape of a debonded part of the actuator.
Circular piezo wafer active sensor with disk-wrapped electrode are widely used in practical applications. In order to reveal the difference in the wavefield, generated by the bonded and debonded actuators a Laser Doppler Vibrometer setup is used. Sixteen PWASs are glued with various debonding to an aluminum plate of the dimensions 500 mm by 500 mm and a thickness of 2 mm. When a transducer is excited by a Hann-windowed toneburst voltage signal of a certain central frequency a propagating wave is produced and the laser vibrometer measures the velocity of the out of plane motion on the surface of the plate. The measurements are made with various central frequencies from 30 kHz to 180 kHz. For a certain sufficiently debonded PWAS some interesting abnormalities are detected for higher frequencies. A sizable increase in the amplitude of the velocity of the motion was observed (up to 300 percent in comparison to perfectly bonded PWAS). It was revealed that the velocities of the motion and carrier frequencies depend on shape of the debonded part of the PWAS. Continuous wavelet transform is applied to the recorded signal in order to compute the carrier frequency of the generated wavefield and to identify the debonded part of the investigated PWAS. The Gabor wavelet is selected as a kernel function due to its waveform is similar to the signal used in the experiment.
