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    STP942

    Growth of Small Cracks and an Evaluation of Low Cycle Fatigue Life

    Published: 01 January 1988


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    Abstract

    Smooth and through-thickness cracked specimens of JIS S35C medium carbon and SNCM 439 alloy steels, heat-treated in several conditions, were low cycle fatigued. The growth rates of small surface and through-thickness large cracks, da/dN, were analyzed in terms of the cyclic J-integral range, ΔJ, and the strain intensity factor range, ΔKϵ.

    The crack growth rates plotted against ΔJ and ΔKϵ are expressed by straight lines on a log-log diagram. The fairly large scatter inherent in a small crack problem hides some difference in the relations of da/dN versus ΔJ and the da/dN versus ΔKϵ plots between different materials. These relations in a small surface crack are slightly different from those in the through-thickness large crack.

    The equations derived from combining these two relations and the cyclic stress-strain curve express well the fatigue life curves, of which slopes decrease in the lower plastic strain range in materials having a high strength and a low ductility, as well as the usual Coffin-Manson plot.

    Keywords:

    metallic materials, low cycle fatigue, crack growth, small surface crack, through-thickness large crack, cyclic , J, -integral, strain intensity factor, cyclic stress-strain curve, Coffin-Manson law, life prediction


    Author Information:

    Hatanaka, K
    Professor and Senior Research Associate, Yamaguchi University, Ube,

    Fujimitsu, T
    Professor and Senior Research Associate, Yamaguchi University, Ube,


    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP24486S