STP1244

    Variations of a Global Constraint Factor in Cracked Bodies Under Tension and Bending Loads

    Published: Jan 1995


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    Abstract

    Elastic-plastic finite-element analyses were used to calculate stresses and displacements around a crack in finite-thickness plates for an elastic-perfectly plastic material. Middle- and edge-crack specimens were analyzed under tension and bending loads. Specimens were 1.25 to 20 mm thick with various widths and crack lengths. A global constraint factor αg, an averaged-normal-stress-to-flow-stress ratio over the plastic region, was defined to simulate three-dimensional (3D) effects in two-dimensional (2D) models. For crack lengths and uncracked ligament lengths greater than four times the thickness, the global constraint factor was found to be nearly a unique function of a normalized stress-intensity factor (related to plastic-zone-size-to-thickness ratio) from small-to large-scale yielding conditions for various specimen types and thickness. For crack-length-to-thickness ratios less than four, the global constraint factor was specimen type, crack length and thickness dependent. Using a 2D strip-yield model and the global constraint factors, plastic-zone sizes and crack-tip displacements agreed reasonably well with the 3D analyses. For a thin sheet aluminum alloy, the critical crack-tip-opening angle during stable tearing was found to be independent of specimen type and crack length for crack-length-to-thickness ratios greater than 4.

    Keywords:

    Finite elements, cracks, plasticity, fracture, constraint


    Author Information:

    Newman, JC
    Senior Scientists, Mechanics of Materials Branch, NASA Langley Research Center, Hampton, VA

    Crews, JH
    Senior Scientists, Mechanics of Materials Branch, NASA Langley Research Center, Hampton, VA

    Bigelow, CA
    Senior Scientists, Mechanics of Materials Branch, NASA Langley Research Center, Hampton, VA

    Dawicke, DS
    Senior Scientist, Analytical Services and Materials, Inc., Hampton, VA


    Paper ID: STP14629S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP14629S


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