Ultrasonic attenuation is a useful tool in characterizing the
damage state of different materials. The attenuation coefficients
for the incident longitudinal and transverse waves are both
derived from the scattering cross section of the material.
Scattering cross section is defined as the ratio of the scattered
energy to the incident energy. The incident wave field can be
scattered at inclusions, voids and material defects; there is also
grain boundary scattering in polycrystalline materials. For
accurate material characterization, it is important to distinguish
between the different types of scattering and to relate the
attenuation to its appropriate source. This study first solves the
single scatterer problem using either the Born approximation (for
difficult scatterer shapes and for anisotropic scatterers), or the
exact solution (in cases where it is necessary to provide an
accurate description of the viscoelastic behavior of the
surrounding effective medium). Multiple scattering effects are
investigated by a differential self-consistent scheme and a
self-consistent scheme. Both multiple scattering approaches are
applicable for each single scatterer solution. The differential
self-consistent scheme describes the scattering cross section
dependent on the volume fraction of the scatterers, and is
restricted to low volume fractions and materials, where the
surrounding material is clearly distinguished from the inclusions.
The self-consistent scheme is applicable to high volume fractions
of inclusions as well as to polycrystalline materials, where the
distinction between surrounding material and inclusions is not
possible.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/4828 |
| Date | 18 November 2004 |
| Creators | Maess, Johannes Thomas |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Language | en_US |
| Detected Language | English |
| Type | Thesis |
| Format | 1666201 bytes, application/pdf |
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