Abstract: Due to ultrasonic guided waves propagating in composite plates are characterized with skew effect, it makes there exists a certain discrepancy between experimentally measured and theoretical group velocities. Therefore, it is needed to calibrate the amplitude and propagation direction of group velocity. Dispersion equation of ultrasonic guided waves in the composite plate is numerically solved and theoretical phase velocity dispersion curves of S0 mode at different directions are obtained. The amplitude and propagation direction of group velocities of S0 mode are calibration based on group velocity calibration principle. Calibrated and experimental group velocities are well matched. In experiments, S0 mode at 200 kHz is used to inspect the artificial defect in the carbon fiber composite plate. Experimental results show accurate localization of the defect can be achieved by using calibrated and experimental group velocities and localization results by using these two types of group velocities are consistent with each other. As a result, the abilities of defect localization and identification of ultrasonic guided waves can be effectively enhanced by using group velocity calibration principle in composite plates.

Key words: Composite plate, Defect detection, Group velocity, Skew effect, Ultrasonic guided waves