Investigation of classical and nonclassical nonlinearity in metals
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Levy, Katherine Marie Scott
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Abstract
Nonlinear ultrasound (NLU) techniques such as second harmonic generation (SHG) and nonlinear resonant ultrasound spectroscopy (NRUS) have shown promise in detecting microstructural damage in materials before macroscopic failure can occur. However, before these methods can be implemented in the field, a better understanding of the relationship between the microstructural mechanisms and the nonlinear techniques needs to be established. This is done in this research by isolating multiple mechanisms and studying their relationship to the nonlinearity parameters β and α. These are the two parameters that are measured using SHG and NRUS, respectively. These parameters can then be related back to material properties through the nonlinear elastic stress-strain relationship and eventually be used as quantitative inputs for life prediction models.
This research focuses on three microstructural mechanisms: precipitate growth in and along the grain boundaries, dislocations, and precipitate pinned dislocations. These mechanisms are studied through the sensitization of 304 stainless steel, the annealing of 316L stainless steel, and the heat treatment of Fe-Cu, respectively. Additionally, the results from two previous studies (precipitate pinned dislocations – 17-4PH and a combination of mechanisms - Cr9Mo1) are considered to get a deeper overall understanding of the mechanisms and their relationship to NLU . Through the experimental measurements and analysis, the response of β and α to each microstructural mechanism is determined. It is found that both techniques are highly sensitive to changes in the microstructure but do not always have the same response to each mechanism.
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Date
2019-11-11
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Dissertation