Application of laser Doppler vibrometry for ultrasonic velocity assessment in a composite panel with defect

The measurement and analysis of the velocity and other properties of guided waves are commonly carried out using a variety of techniques. Depending on devices employed in the experiments, the instrumentation limitations must be taken into account in order to ensure the accuracy of the measurements. In this paper, the characteristics of guided waves propagating in a quasi-isotropic composite with an embedded Teflon film, that can simulate the presence of a delamination, are studied. The guided waves are created by means of a piezoelectric transducer bonded to the surface of the laminate and the signals are acquired by a high precision laser Doppler vibrometer. A signal analysis methodology is adopted to estimate the group velocity of the propagating wave packet, first in the undamaged region of laminate and then in the region containing the simulated delamination. The measurement error is discussed and appropriate formulas are presented for uncertainty quantification in the velocity calculation.