STP738

    Procedures for Precision Measurement of Fatigue Crack Growth Rate Using Crack-Opening Displacement Techniques

    Published: Jan 1981


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    Abstract

    This paper describes experimental and analytical procedures whereby the conventional commercial fracture mechanics clip-gage can be used for precision measurement of fatigue crack growth rate in compact-type specimens. Potential sources of error in measuring crack length via crack-opening displacement (COD) techniques are delineated. Comparisons are made between crack-length data obtained via specimen surface observations and COD techniques. Comparisons are also made between data analyzed by the secant and 7-point incremental polynomial methods. It is emphasized that COD techniques can enhance the accuracy of the secant method of data reduction. Steploading procedures using COD techniques are described. Proposed amendments to ASTM Tentative Test Method for Constant-Load-Amplitude Fatigue Crack Growth Rates Above 10−8 m/Cycle (E 647-78 T) regarding incrementing of crack-length measurements via COD techniques are discussed.

    Keywords:

    clip gage, crack opening displacement (COD), fatigue crack growth rate, data analysis, secant method, 7 point incremental polynomial


    Author Information:

    Yoder, GR
    Metallurgist, metallurgist, and mechanical engineer, Mechanics of Materials Branch, Material Science and Technology Division, Naval Research Laboratory, Washington, D.C.

    Cooley, LA
    Metallurgist, metallurgist, and mechanical engineer, Mechanics of Materials Branch, Material Science and Technology Division, Naval Research Laboratory, Washington, D.C.

    Crooker, TW
    Metallurgist, metallurgist, and mechanical engineer, Mechanics of Materials Branch, Material Science and Technology Division, Naval Research Laboratory, Washington, D.C.


    Paper ID: STP33454S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP33454S


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