7D-4 Non Destructive Evaluation of Carbon Fiber Reinforced Plates Using Lamb Waves: A Comparison Between Pitch-Catch Air Coupled Techniques and Sector Images Obtained with Embedded Piezoelectric Linear Arrays

In this work, a carbon fiber composite plate with uniform thickness has been implemented with a flexible piezoelectric linear array bonded on it. A four cycles tone burst of 48 kHz has been used to excite an antisymmetric Lamb mode. Then, a 2D sector image of the plate with a delamination has been obtained using a synthetic aperture algorithm. Next, the same process has been repeated for a carbon fiber reinforced plate (CFRP) with attached stiffeners and varying thickness, with no evidence of delamination. Therefore, a conventional ultrasonic inspection, with two air coupled transducers in a pitch-catch configuration, has been performed in the same plate and compared with the sector array image. The same Lamb mode has been excited. An optical vibrometer has been used to measure the out-of-plane displacement of the propagating Lamb wave modes to calculate the propagation velocity and to help understanding the artifacts produced by the stiffeners. An optical interferometric image of the propagating wave-front showing the artifacts and signal shadows produced by a longitudinal stiffener is shown.