STP1207

    An Approximate Technique for Predicting Size Effects on Cleavage Fracture Toughness (Jc) Using the Elastic T Stress

    Published: Jan 1994


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    Abstract

    This investigation examines the ability of an elastic T-stress analysis coupled with a modified boundary layer (MBL) solution to predict stresses ahead of a crack tip in a variety of planar geometries. The approximate stresses are used as input to estimate the effective driving force for cleavage fracture (J0) using the micromechanically based approach introduced by Dodds and Anderson. Finite-element analyses for a wide variety of planar-cracked geometries are conducted that have elastic biaxiality parameters (β) ranging from -0.99 (very low constraint) to +2.96 (very high constraint). The magnitude and sign of β indicate the rate at which crack-tip constraint changes with increasing applied load. All results pertain to a moderately strain-hardening material (strain-hardening exponent (n) of 10). These analyses suggest that β is an effective indicator of both the accuracy of T-MBL estimates of J0 and of applicability limits on evolving fracture analysis methods (that is, T-MBL, J-Q, and J/J0). Specifically, when ∣β∣ >0.4 these analyses show that the T-MBL approximation of J0 is accurate to within 25% of a detailed finite-element analysis. As “structural-type” configurations, that is, shallow cracks in tension, generally have ∣β∣ >0.4, it appears that only an elastic analysis may be needed to determine reasonably accurate J0 values for structural conditions.

    Keywords:

    elastic-plastic fracture mechanics, size effects, finite-element analysis, modified boundary layer, T, stress, J, SSY, J, 0, Q, structural integrity assessment


    Author Information:

    Kirk, MT
    Manager, Edison Welding Institute, Columbus, OH

    Dodds, RH
    Professor, University of Illinois, Urbana, IL

    Anderson, TL
    Associate professor, Texas A&M University, College Station, TX


    Paper ID: STP13700S

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP13700S


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