STP1296: Effects of Mixed Mode I/II Loading and Grain Orientation on Crack Initiation and Stable Tearing in 2024-T3 Aluminum

    Amstutz, BE
    Graduate student, professor, and undergraduate student, University of South Carolina, Columbia, SC

    Sutton, MA
    Graduate student, professor, and undergraduate student, University of South Carolina, Columbia, SC

    Dawicke, DS
    Senior scientist, AS & M, Inc., Hampton, VA

    Boone, ML
    Graduate student, professor, and undergraduate student, University of South Carolina, Columbia, SC

    Pages: 21    Published: Jan 1997


    Abstract

    The effects of material grain orientation and Mixed Mode I/II loading on crack initiation and stable tearing in 2.3-mm-thick, unclad 2024-T3 aluminum is experimentally investigated. Mode I experiments were performed on center-cracked specimens with the crack being oriented at various angles relative to the rolling direction. Defining θ to be the angle between the normal to the initial crack plane and the loading direction, Mode I/II experiments were performed using an Arcan test fixture for 0° ≤ θ ≤ 90° [corresponding to 90° ≥ β ≥ 0°, where β = atan (KII/KI)] with the crack oriented either along the rolling direction (T-L) or perpendicular to the rolling direction (L-T).

    Results indicate that: 1. The Mode I crack tip opening displacement (CTOD) is a strong function of the orientation of the crack relative to the rolling direction; CTOD for a T-L specimen is 0.84 mm, increasing linearly with orientation angle to 1.05 mm for an L-T case. 2. The Mode I/II CTOD increases rapidly during initial increments of crack growth and then decreases towards a constant value as crack growth continues. 3. For θ < 68° (β > 29°), all cracks kinked and the Mode I/II plastic zones are similar to rotated Mode I plastic zones throughout the crack growth process. 4. JII = 0 reasonably predicts the direction of tension-dominated crack growth, but does not predict the transition to shear crack growth which occurs for θ ≥ 75°. 5. KIIKI for θ ≈ 58° (β = 45°) does not quantitatively predict the transition to shear crack growth for θ ≥ 75° (β ≤ 22°), but does provide an indication of changing conditions in the crack tip region.

    Keywords:

    Mixed Mode I/II, stable crack growth, CTOD/CTOA, experiments


    Paper ID: STP16231S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP16231S


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