Application of macroscopic elasticity models to predict microstructurally small crack growth

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University of Alabama Libraries

The need for a more lightweight and structurally stable alloy is evident in industry. Before a specific alloy is put into industrial use, the alloy must be properly tested such that structural integrity is insured. In this study, the microstructurally small crack growth behavior in aluminum and magnesium alloys and its relationship with material microstructure is investigated under fatigue loading. Surfaces of the alloys tested were replicated using a two-part silicon epoxy where the microstructurally small surface cracks were analyzed and measured. The microstructure of the alloys tested was also investigated to see if a correlation between crack growth and microstructure could be found. Fractography and Electron Back Scatter Diffraction (EBSD) were conducted on all three alloys. In addition to the experimental aspects of this study, two linear elastic fracture mechanics models were implemented to see if the trends in crack growth rate could be predicted. The first model, a modified strip-yield model that allowed for plasticity ahead of the crack tip, adequately predicted microstructurally small crack growth for a rolled AZ31 magnesium alloy. The second model, a dislocation distribution theory model (DDM) that allowed for stress intensity factor prediction of a multiply kinked crack in a field of cracks, less than adequately predicted the small crack growth of a rolled AA2XXX and AA7XXX alloy.

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Mechanical engineering