Time-Frequency Analysis of Dispersive Stress Waves by Means of Wavelet Transform : Identification of Group Velocity and Application to Ultrasonic Materials Evaluation

Abstract

The wavelet transform is applied to time-frequency analysis of dispersive stress waves. The Gabor function is adopted as the analyzing wavelet. The magnitude of the wavelet transform of wave data takes its maximum value at the time when the stress wave reaches the observation point with its group velocity at each frequency. An experiment on the flexural wave in a beam shows that the dispersion relation for the group velocity can be accurately identified by the wavelet transform of measured data. In addition, the application of the wavelet transform to ultrasonic testing of a polymer alloy shows that changes in velocity and attenuation coefficient due to mechanical damaging can be evaluated at each frequency. These results suggests that the wavelet transform has potential ability to present more detailed evaluation of material damages.