STP982: Analysis of Fatigue Crack Closure Caused by Asperities Using the Modified Dugdale Model

    Nakamura, H
    Research associate and professor, Tokyo Institute of Technology, Tokyo,

    Kobayashi, H
    Research associate and professor, Tokyo Institute of Technology, Tokyo,

    Pages: 16    Published: Jan 1988


    Abstract

    Crack closure characteristics in fatigue crack growth were examined using the modified Dugdale model developed by Newman. The model can leave elastic-plastic asperities in the wake of the growing crack tip. The analysis showed the influence of the rigidity E of the asperities, asperity length, asperity thickness, and the distance from the crack tip.

    The validity of the unloading compliance technique was examined. The analysis showed a guide of how to determine the crack opening point. When the plasticity induced crack closure prevails, the detected crack opening point gives the correct information regarding the actual one. The crack opening point, rather than the closure point, determined in this way is a useful parameter to describe the crack growth rates.

    Under some closure mechanisms, however, it is pointed out that this technique may not be useful. Especially, when asperities are attached near the initial notch tip like under corrosive environment, the crack opening point becomes an overestimate of the actual level. On the other hand, when they are attached near the crack tip like near the threshold region in an air environment, it becomes an underestimate.

    An analytical procedure was developed to determine the crack opening stress intensity Kop from the contact stress at minimum stress intensity. By using this parameter, the crack tip opening displacement or the crack growth rate is described uniquely.

    Keywords:

    fatigue, crack growth, crack closure, opening stress intensity, unloading compliance, Dugdale model


    Paper ID: STP27225S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP27225S


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