Conventional contact ultrasonic methods suffer from large variability, which
is known to originate from a number of sources such as coupling variability, and the
surface roughness at the transducer/specimen interface. The inherently small higherharmonic
signals can be significantly influenced by the changes in contact conditions,
especially in nonlinear ultrasonic measurements. For this reason, the noncontact
generation and detection techniques are very attractive. This research first focuses
on the optical generation of tone-burst surface acoustic waves in a metallic specimen.
Two methods that use laser light as an optical source are compared for generating
surface acoustics waves in the 5 MHz range. Both the shadow mask and diffraction
grating are used to convert a laser pulse to a tone-burst signal pattern on the specimen.
The generated signals are detected by a wedge transducer at a fixed location and then
the harmonic contents in the generated signals and the repeatability of the methods
are evaluated. Finally, the developed method is used to characterize the material
nonlinearity of aluminum (Al 6061) and steel (A36). The results showed repeatable
measurements for ablative signal excitation on aluminum.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/45812 |
| Date | 27 August 2012 |
| Creators | Swacek, Christian Bernhard |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Detected Language | English |
| Type | Thesis |
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