Abstract
Initial cracks in metallic structures incline to be closed at rest. Such incipient damage generally fails to be detected and located with traditional linear ultrasonic techniques because ultrasonic waves penetrate the contact area of the closed crack. In this paper, an imaging algorithm based on nonlinear ultrasonic time reversal method is proposed to detect closed cracks in aluminum plates. Two surface-bonded piezoelectric transducer arrays are used to generate, receive, and reemit ultrasonic wave signals. The closed crack is simulated by tightening a bolt on the aluminum plate. By applying large amplitude excitation voltage on the PZT transducers, the closed crack could be opened and closed. The transmitted waves recorded by PZT array contain nonlinear components, the signals are time reversed and emitted back, and the tone burst reconstructions are achieved. The linear reciprocity and the time reversibility break down due to the presence of the nonlinear components. The correlation coefficient between the original excitation signal and the reconstructed signal is calculated to define the damage index for individual sensing path and is used to develop an imaging algorithm to locate the closed crack on the plate. The experimental results demonstrate that incident wave signals and their reconstructed signals can be used to accurately detect and locate closed cracks.
Highlights
In mechanical, aerospace, and civil infrastructures, metallic components made of aluminum are ubiquitous
The principle of the time reversal process in a twodimensional plate is illustrated in Figure 1, where a tone burst is applied to transducer A functioning as a transmitter, activating a wave signal that is captured by transducer
It indicates that this path is not influenced by the closed crack and linear scatterer and it can be treated as intact path
Summary
Aerospace, and civil infrastructures, metallic components made of aluminum are ubiquitous. More and more attentions had been drawn to the damage detection with application of time reversal wave signals. This technique uses the reconstruction property of the time reversal procedure; that is, an original wave can be reconstructed at its source point if its forward wave recorded at another point is time reversed and emitted back to the source point. Park et al investigate the time reversal process of Lamb wave signals which are transmitted and received by piezoelectric transducers bonded on plate-like structures [4]. The time reversal reconstructed wave differs from the original wave This block damage is a linear scatterer; the reconstructed signal should be close in shape to the original wave.
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