Application Cases

Experiment Name: Damage Localization Method Based on PZT-Arrayed Lamb Wave Directional Algorithm

Research Direction: Damage Localization

Test Objective:
Lamb waves are elastic guided waves that propagate in solid plates or layered structures with free boundaries. Due to their inherent propagation characteristics—such as low attenuation along the propagation path, minimal energy loss, and long transmission distance—they have become an important tool in the field of nondestructive testing (NDT). For aerospace structures made of carbon fiber-reinforced polymer (CFRP) composites, Lamb wave applications are particularly common. When conducting NDT on such structures, the choice of damage detection tools and methods is critical. Piezoelectric transducers (PZTs) are commonly used as detection tools. The thin and light nature of PZTs makes them widely applicable in ultrasonic NDT. When the ratio of the PZT diameter to the Lamb wavelength is sufficiently small, the PZT can be considered an ideal detection tool. The dual-sided excitation method, which involves placing PZTs on both the top and bottom surfaces of the plate, effectively suppresses the multimode characteristics of Lamb waves. Different arrangements of PZTs affect the damage localization results, and it has been demonstrated that PZTs have higher sensitivity in damage detection compared to laser vibrometers.

Testing Equipment: ATA-1372A power amplifier, arbitrary waveform generator, PZT transducer, PZT sensor, PX-Ie8840 controller, GTP-150A-2 probe.

Experimental Procedure:

Figure: Schematic Diagram of the Experimental System

This experimental system employs the conventional Lamb wave excitation and reception setup, as shown in the figure above. The system includes an arbitrary waveform generator, an ATA-1372A power amplifier, and a PZT transducer for excitation. The receiving apparatus includes a PZT sensor and a digitizer. Both the arbitrary waveform generator and the digitizer are controlled by the PX-Ie8840 controller. Connections between the waveform generator/digitizer and the PZTs are made via probes. The input signal generated by the arbitrary waveform generator is amplified by the voltage amplifier and sent to the PZT actuator. The Lamb wave signal generated by the PZT propagates through the composite material plate for a certain distance before being received by the PZT sensor. The data is then acquired by the digitizer and saved to a computer. The excitation waveform used in the experiment was a 5-cycle sine wave modulated with a Hanning window at a frequency fo (300 kHz).

Experimental Results:

Figure: Response Signals of PZT Before and After Damage

Using MATLAB software, a signal processing method based on cross-correlation theory was developed. Under the excitation frequency of 300 kHz, the experimentally measured signal data were processed. Based on the difference between the structural health response signal and the structural damage response signal, this method successfully extracted the damage-scattered signal. After reconstructing the scattered signal, the arrival times corresponding to the peaks of each wave packet of the damage-scattered signal were obtained. Using the positions of the PZT array elements in the plate and selecting PZT elements 2 and 5 as reference PZTs, the coordinates of each PZT were substituted into the damage direction calculation formula. The damage determination method, utilizing the damage direction algorithm, determined the direction of one of the Lamb waves scattered by the damage hole as received by each PZT node. The distance between the damage position determined by the intersection of these directions and the actual damage location was 8.05 mm, an error within an acceptable range.

Future research will focus on multi-damage problems. Considering the multi-directionality of multiple damages and the complexity of signal processing involved, the propagation velocity of Lamb waves in CFRP composites and the signal processing methods will be optimized to extract the arrival times of multiple damage envelopes from the multi-damage scattered signals, enabling multi-damage localization. Furthermore, the maximum spacing of the PZT array will be discussed to determine the appropriate range of PZT spacing and to improve the damage direction algorithm, thereby further refining the damage localization method.

Aigtek ATA-1372A Broadband Power Amplifier:

Figure: Specifications of the ATA-1372A Power Amplifier