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    STP1359

    Microtexture, Asperities, and Crack Deflection in Al-Li 2090 T8E41

    Published: 01 January 1999


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    Abstract

    Roughness-induced closure is held to be responsible for very low fatigue crack growth rates observed in certain plate orientations of Al-Li 2090 T8E41, and the geometry of asperities producing this closure correlates with macrotexture. Little work, however, has focused on the role of individual grain orientations (microtexture) or of average orientation within small groups of adjacent grains (mesotexture) on the crack's path through a sample, i.e., on whether the variation in grains' orientations determines where the crack will deflect. This paper reports synchrotron X-ray microbeam diffraction mapping of the three-dimensional microtexture in samples of Al-Li 2090. Groups of adjacent pancake-shaped grains are found to have very similar orientations, producing nearly single-crystal regions approaching thicknesses of 0.3 mm along the sample's S (short-transverse) direction. These near-single-crystal volumes produce large asperities with surfaces having substantial Mode III character, asperities which appear over the range of stress intensity ranges observed (∼5 to ∼25 MPa√m). Results of these experiments suggest not only that this type of mesotexture plays an important role in determining fatigue crack path in compact tension samples of Al-Li 2090 but also that specific orientations of the groups of grains lead to large crack deflections.

    Keywords:

    crack closure (roughness-induced), fatigue, synchrotron radiation, aluminum, texture (micro-), (meso-), (macro-), X-ray diffraction (microbeam), Laue patterns, mixed-mode crack surfaces


    Author Information:

    Haase, JD
    School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

    Guvenilir, A
    School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

    M/D K-10 Yield Enhancement Technology Transfer, Motorola, Austin, TX

    Witt, JR
    School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

    Langøy, MA
    School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

    Kvaerner Oil and Gas, Stavanger,

    Stock, SR
    School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA


    Committee/Subcommittee: E08.01

    DOI: 10.1520/STP14249S