Large deflections of fatigue cracks, high levels of macroscopically-measured crack closure and extremely low crack propagation rates occur in samples of Al-Li 2090 T8E41. Three-dimensional quantification of the changing pattern of crack face contact and of the spatial distribution of grain orientations is essential if understanding of the interplay between grain structure, crack deflection and crack closure is to be advanced. Two x-ray methods, high resolution computed tomography (i.e., microtomography) and microbeam diffraction, have been employed to investigate crack closure processes and the role of grain orientation on choice of crack path, respectively, and the results presented below summarize what has been learned thus far. Microtomography reveals that large sections of fatigue cracks close above the nominal closure load and that mixed mode surfaces are an important part of a complex three-dimensional pattern of crack face. Microbeam diffraction shows that groups of five or more adjacent grains possess nearly identical orientations (i.e., grains with spatial and orientational correlation), that this near-single-crystal mesotexture occupies fully forty percent of the sample volume and that specific orientations of these grain groups produce sharp changes in crack path.
|Original language||English (US)|
|Number of pages||8|
|Journal||Proceedings of the TMS Fall Meeting|
|State||Published - Dec 1 1999|
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