Anisotropic Behavior Analyzed by Laser-Generated Lamb Waves for Fiber Composite Plates

Analyses of the anisotropic behavior of a fiber composite plate from the laser-generated ultrasonic Lamb waveforms propagating in different directions are presented by employing wavelet transform techniques. The time-frequency representation plots of the waveforms clearly exhibit the anisotropic behavior of the composite plate. The plots also indicate that the waveform mainly consists of three or four lower-order Lamb wave modes, and other higher-order modes can be neglected in extracting elastic stiffness properties by comparison of theory with experimental waveforms. The group velocity of each mode is calculated according to the group delay and the source-receiver distance.