Abstract
A damage estimation method based on continuous wavelet transformation (CWT) of the normalized Lamb wave signals is proposed here. Lamb waves are actuated and sensed using piezoelectric (lead zirconate titanate, PZT) transducers arranged in the form of square detection cells on a plate-like structure. Excitation sequences based on pitch–catch and pulse–echo configurations are tested for the same arrangement of the transducers. The possibilities of the existence of damage for each actuator–senor pair are formed by using the normalized coefficient of CWT. The size of the possible damage region is directly controlled through envelopes defined by the coefficients of CWT, and no additional parameter is required to define its size. The aggregate damage image is constructed by the fusion of damage possibilities from all actuator–sensor pairs using damage indices based on conjunctive and compromised fusion schemes. The results indicate that the proposed method can estimate the location and severity of multiple damage with signals directly from the damaged plate, without the need of baseline signals from the undamaged plate, and the time-compensated signals provide better damage imaging than the raw signals. The most accurate and computationally inexpensive combination is the pulse–echo configuration with damage index based on conjunctive image fusion scheme. The method is computationally inexpensive and can be applied for multiple damage estimations in large structures to reduce the evaluation cost and inspection time during on-line structural health monitoring.
Highlights
The traditional nondestructive testing (NDT) methods are useful, but they are time consuming and expensive as they require the structures to be off-service and disassembled in components
The pulse–echo configuration with damage index based on conjunctive fusion scheme DIm (xi, yi ) is proposed in this method, and this combination was chosen for the remaining analyses in this paper
A damage estimation method based on coefficient of continuous wavelet transformation (CWT) of the normalized damage-scattered signals is proposed in this research
Summary
The traditional nondestructive testing (NDT) methods are useful, but they are time consuming and expensive as they require the structures to be off-service and disassembled in components. Sophisticated signal processing techniques such as fast Fourier transform [5], short-time Fourier transform [6], Hilbert transform [7], warped frequency transform [8], and signal-difference-based correlation coefficient [9,10] have been used to accurately analyze the dynamic response signals scattered by damage Among these methods, the continuous wavelet transformation (CWT) [11,12] has recently gained attention and popularity due to its powerful time–frequency feature extraction from complicated signals, its ability to detect the signal singularity for physical damage inspection, and to depress the dispersive characteristics of the Lamb waves [13,14].
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