Acoustoelasticity in 7075-T651 Aluminum and Dependence of Third Order Elastic Constants on Fatigue Damage.
Stobbe, David M.
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Interrogating metals with ultrasonic waves can be used to evaluate their microstructural and mechanical properties. These techniques analyze ultrasonic wave features in order to make inferences on the medium of interest. Current research is being conducted to determine higher order elastic properties and characterize material degradation of 7075-T651 aluminum with ultrasonics. This thesis topic will use acoustoelasticity, the stress dependency of acoustic velocity, to accomplish these goals. Acoustoelasticity is a manifestation of the inherent nonlinearity in the interatomic binding energy, which appears mathematically as higher order elastic terms in the stress strain constitutive relation. The acoustoelasticity will be determined for longitudinal and shear waves propagating through a sample under uni-axial stress. Experimentally, specific techniques and tooling will be designed to insure accurate measurements of acoustic wave velocity as a function of stress. Using acoustoelasticity the third order elastic constants of 7075-T651 aluminum will be determined. Further, Al samples will be fatigue damaged and acoustoelasticity and third order elastic constants will be mapped versus damage. Literature will be used to verify measured values of acoustoelasticity as well as provide theoretical models for acoustoelastic dependence on damage.