Implementation of the ultrasonic second harmonic generation has typically been
restricted to simple setups such as through-transmission or Rayleigh surface waves. Recent
research has evaluated the second harmonic generation in P- and SV- waves reflected from
a stress-free surface to enable the single-sided interrogation of a specimen. This research
considers the second harmonic generation in an aluminum specimen, which is analytically
evaluated using an approach based on the perturbation method. Here, the model is chosen
to mimic an experimental setup where a longitudinal wave is generated at an oblique angle
and the reflected wave is detected using a set of wedge transducers. Due to mode conversion
at the interface of the wedge and the specimen, it is necessary to evaluate longitudinal and
shear waves, determining all second harmonic waves generated in the bulk and at the stressfree
boundary. The theoretically developed model is then implemented in a commercial
finite element code, COMSOL, using increasing fundamental wave amplitudes for different
values of third order elastic constants. The results of this computational model verify the
analytical approach and the proposed measurement setup, taking into account assumptions
and approximations of the solution procedure. Furthermore, the computational model is
used to draw important conclusions relevant to the experimental setup, including the need
to avoid evolving surface waves and interactions with diffracted waves. These numerical
results are used to develop a recommendation for the measurement position and incident
angle. Finally, the nonlinearity of two different aluminum specimens is measured with
the suggested measurement setup and the results confirm the feasibility of the single-sided
determination of the acoustic nonlinearity using reflected bulk waves.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/53026 |
| Date | 12 January 2015 |
| Creators | Romer, Anne |
| Contributors | Jacobs, Laurence J. |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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