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    Comparison of R-Curves Determined from Different Specimen Types

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    Crack growth resistance curves (R-curves) have been obtained by testing center-cracked tension specimens (CCT) of three aluminum alloys, one titanium alloy, and two steels. Direct comparison is possible for four of these alloys with R-curves determined from crackline loaded (CLL) specimens.

    Some differences between the two specimens are found in the reported values of Kc. These appear to be a direct consequence of the type of stress-crack length relationship noted during testing. In tough material tested using the CCT specimen, the crack grown first under a rising load but finally continues to extend at a constant load. Since this constant load crack growth marks the end of structural integrity, its recognition is crucial to a rational interpretation of fracture resistance. The CCL specimen type does not discriminate between the changes in crack growth behavior observed for these tough materials. Further, it is shown that fatigue precracking may influence the amount of crack growth prior to instability even though the final value of Kc remains unchanged.

    No evidence of variation in the Kc-value with initial crack length has been observed over the range of slit lengths investigated.


    crack propagation, fracture toughness, titanium alloys, aluminum alloys, structural steels, strains, stresses, loads (forces), steels, tests, evaluation

    Author Information:

    Sullivan, AM
    Head, Naval Research Laboratory, Washington, D.C.,

    Freed, CN
    Lawyer, Environmental Protection Agency, Washington, D.C.,

    Stoop, J
    Head, Naval Research Laboratory, Washington, D.C.,

    Committee/Subcommittee: E08.08

    DOI: 10.1520/STP34709S