Baseline-free delamination inspection in composite plates by synthesizing non-contact air-coupled Lamb wave scan method and virtual time reversal algorithm

Abstract

In the paper, we combined air-coupled Lamb wave scan method and virtual time reversal (VTR) algorithm and proposed a composite baseline-free delamination inspection technique of composite plates. According to VTR algorithm, time reversal process is virtually performed through signal operations and the hardware manipulation for time reversal is not required. Baseline-free damage inspection can be achieved by comparing the first input actuation signal with the reconstructed final signal obtained by VTR algorithm. An air-coupled Lamb wave scan method combined with VTR-based probabilistic imaging algorithm is developed for delamination inspection of composite plates. Carbon fiber-reinforced composite plates with the delaminations of different shapes and sizes were experimentally tested. The testing results are well in accordance with the actual delamination locations and sizes as well as the results obtained with the commercial point-to-point immersion C-scan system.

A Survey of Scrutinizing Delaminated Composites via Various Categories of Sensing Apparatus

“…According to Figure 7, air-coupled transducers and ultrasonic C-scan testing may be included in ultrasonic testing [121][122][123][124][125][126][127][128][129][130][131][132][133]. Air-coupled transducers (ACTs), when coupling media, cannot be applied is an attractive alternative to excite ultrasonic waves and receive those leaked into the air.…”

“…In the immersion testing process, a liquid couplant is employed to establish direct contact between a transducer and the composite specimen. Most of the research effort in the technical literature searched regarding the ultrasonic C-scan testing has been focused on either verification of other NDE techniques with ultrasonic C-scan as a reference standard [35,47,89,91,109,112,126] or yielding supplementary information [26,38,105,117,127].…”

“…Upon employment of signal processing techniques, ACT as well as LDV measurements analyzed within the frequency-wavenumber domain to separate wavefield images, in terms of propagation direction (forward and backward waves) and various modes (A 0 and S 0 modes) as well as remove incident waves to highlight waves scattered from delamination, have been utilized for delamination identification [125]. Exciting A 0 Lamb mode within CFRP laminates containing variously shaped and sized delamination, reconstructed C-scan images obtained by directional ACT measurement incorporating virtual time reversal have been inspected for delamination localization compared to immersion C-scan testing system [126].…”

“…Air-coupled Lamb wave images postprocessed by (a) full summation and (b) full multiplication in different scan directions for trapezoidal and circular delamination. Reproduced with permission from[126].…”

An Efficient Time Reversal Method for Lamb Wave-Based Baseline-Free Damage Detection in Composite Laminates

“…That is, the initial input signal and the secondary excitation signal are actuated by the same actuator. Liu et al [17] presented a virtual time reversal algorithm which only needs one actuating-receiving step to obtain the reconstructed signal. Agrahari et al [18] investigated the influences of adhesive layer between the transducer and the host plate, the excitation parameters, the transducer size and the plate thickness on the performance of the TRP to develop an effective damage detection strategy.…”