Date of Award
Maev, Roman Gr.,
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Damage mechanics is a relatively new and powerful approach to the analysis of material degradation and failure. The idea is to build a continuum model of a solid containing a distribution of microcracks. Such a model, relying on the thermodynamics and statistical mechanics of microcracks, very naturally ties into other continuum models of solids, including acoustic and elastic models. In this dissertation, the impact of material and structural damage is investigated, with an emphasis on the relation between this effect and specific second order ultrasonic effects. The investigation has two main streams. The first, more experimental stream involves damage in the bulk. In this case, we chose to look at fatigue damage in the Ni-based alloy, waspaloy, which is used particularly for high strength, high temperature applications in the aerospace industry, as well as exhibiting very intriguing physical and thermodynamic properties. The approach was to monitor the changes in two second order parameters, the so-called nonlinearity, or beta parameter, and the acousto-elastic parameter. Results of these experiments seem to indicate that the latter is a better indicator of fatigue and damage, at least in this material. The second, more theoretical stream concerns damage along an individual weak interface. In this case, a nonlinear "thin layer" model was developed for propagation of ultrasonic waves through a weak bonded interface, as well as a time-domain approach to a general solution to this problem for a multiply layered system. This was combined with a simple damage model, and used to demonstrate how poorly bonded interfaces may be interpreted as locally damaged materials. It was also demonstrated how the nonlinearity of intensive ultrasound passing through or reflecting off an interface bond may be used, along with an appropriate damage model, to estimate the ultimate strength of this bond. Source: Dissertation Abstracts International, Volume: 65-10, Section: B, page: 5188. Adviser: Roman Gr. Maev. Thesis (Ph.D.)--University of Windsor (Canada), 2004.
O'Neill, Brian E., "Second order effects of structural and material damage on ultrasonic waves." (2004). Electronic Theses and Dissertations. 3391.