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(Color online) Front and top view of the sample, showing dimensions (in mm), critical zone, and crack position. The positions of the PZT transducers are labeled T1–T4.
(Color online) Time reversal experiment using a chirped source signal, pulse compression, and inverse filtering on the steering actuator bracket. (a) shows the maximum amplitude of the TRA signal around the focus in 2D. (b) is for a horizontal line through the focus centre. (c) shows a zoom of the time signal at focal time in the focus centre.
(Color online) Illustration of the dipole vibration TRA showing the 2D distribution of the measured amplitudes around the double peak focus zone (plot (a)). The amplitudes vary from −15 mm/s to 15 mm/s. The line plot (b) corresponds to the amplitudes on a horizontal line connecting the two focal points within the scanned zone (a).
(Color online) Investigation of the on-crack measured nonlinear contribution using a vibration dipole TRA experiment showing the SNR of the PI-filtered signals as a function the dipole distance.
(Color online) Nonlinear signatures (SNR after pulse inversion filtering) obtained with the vibration dipole TRA experiment for the two samples. The damaged bracket (a) shows a clear nonlinear response. The undamaged bracket (b) shows no localized nonlinearity.
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