Abstract
For the non-destructive evaluation (NDE) of surface and near-surface defects, a portable laser-ultrasound system is described. Nd:YAG laser pulses with energies up to about 15 mJ are used to produce thermoelastic ultrasound. The pulses are delivered to the material surface via an optical fiber and focused to a line source by a cylindrical lens within a scanning head. Uniquely, this same head contains a miniaturized in-plane electromagnetic acoustic transducer (EMAT) receiver, sepd. by a fixed distance (40 mm) from the optical fiber. In combination, they are able to scan a sample surface. Signal capture and processing routines are used to generate B-scan images of the test sample. Images reveal a range of ultrasonic transients. They include surface skimming longitudinal (Ls), Rayleigh waves, bulk longitudinal (L) and bulk shear (S) waves. In the present system, transient acoustic fields generated by the interaction of the Rayleigh waves with surface-breaking artificial slots provide important information on the position and geometry of the slot. B-scan images are exploited to visualize any changes due to a defect. Typically B-scan images have been obtained by the compilation of 250 A-scan waveforms, and a no. of images are presented. They show signal amplitudes that are enhanced by at least a factor of 1.6 from Rayleigh slot interactions, as well as evidence of diffraction effects. [on SciFinder (R)]
| Original language | English |
|---|---|
| Title of host publication | Nondestructive Characterization of Materials XI, Proceedings of the International Symposium, 11th, Berlin, Germany, June 24-28, 2002 |
| Publication status | Published - 2003 |
Keywords
- Imaging (acoustic; laser-ultrasound imaging system for nondestructive evaluation of surface and near-surface defects); Sound and Ultrasound; Surface defects (laser-ultrasound imaging system for nondestructive evaluation of surface and near-surface defects); Testing of materials (nondestructive; laser-ultrasound imaging system for nondestructive evaluation of surface and near-surface defects); Laser radiation (pulsed; laser-ultrasound imaging system for nondestructive evaluation of surface and near-surface defects)