Lamb wave excitation by Hertzian contacts with applications in NDE

摘要

Excitation of Lamb waves in solid plates by point-like Hertzianncontacts for material characterization and nondestructive testing isninvestigated. A 2 dimensional model using normal mode theory is used tonpredict the relative excitation efficiency of the lowest order Lambnwaves in anisotropic solid plates. Hertzian contact transducers withnPZT-5H piezoelectric material and quartz buffer rods are realized tonoperate in the 200 to 500 kHz range for experimental verification.nSingle mode operation with the lowest order antisymmetric Lamb wave (An0) mode is achieved in various plates at in agreement withntheoretical predictions. The technique is applied for materialncharacterization on single crystal silicon samples and defect detectionnin composite plates. The phase velocity anisotropy of the A0nmode is measured with signal-to-noise levels exceeding 65 dB. In (111)ncut silicon plates the absolute phase velocity is measured withn±0.05% accuracy. The phase velocity anisotropy and effects ofndelamination in layered composite plates are calculated using thensurface impedance approach. The experiments on graphite/epoxy compositenplates agree with these calculations and show the potential of thenmethod for defect detection with high resolution