STP833

    Post-Yield Crack Opening Displacement of Surface Cracks in Steel Weldments

    Published: Jan 1984


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    Abstract

    Crack-mouth-opening displacements (CMOD) of surface cracks are measured as functions of stress and strain in tensile panels of API 5LX-70 steel plates and welded pipe segments. The experimental results are compared with analytical predictions. For CMOD versus stress, a previously developed model provides good agreement between experiment and analysis for the base metal and the welds. At stresses above net-section yielding, it is observed in seven of nine base metal tests that all the remote displacement is transferred to the crack tip through slip bands extending from the crack tip to the plate edges at 45 deg angles; the two exceptions are in specimens with small (less than 5% of the cross-sectional area) cracks where yielding occurred in the gross section. A model based on this observation is used to calculate CMOD versus strain for net-section yielding; analysis and experiment agree in the intended range, that is, net-section yielding. In the welded specimens, the yield strength of the weld was higher than that of the base metal. Consequently, the base metal began yielding before the weld, and the CMOD in the weld was lower than predicted by the analytical model. A strain-partitioning model partially accounts for the observed behavior, provided the crack is large enough to permit net-section yielding in the weld.

    Keywords:

    crack opening displacement, elastic-plastic fracture mechanics, pipeline steel, surface cracks, welds, yielding


    Author Information:

    Cheng, YW
    Fracture and Deformation Division, National Bureau of Standards, Boulder, Colo.

    King, RB
    Fracture and Deformation Division, National Bureau of Standards, Boulder, Colo.

    Read, DT
    Fracture and Deformation Division, National Bureau of Standards, Boulder, Colo.

    McHenry, HI
    Fracture and Deformation Division, National Bureau of Standards, Boulder, Colo.


    Paper ID: STP32579S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP32579S


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