STP942

    Reconsideration of Macroscopic Low Cycle Fatigue Laws Through Observation of Microscopic Fatigue Process on a Medium Carbon Steel

    Published: Jan 1988


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    Abstract

    In order to correlate macroscopic low-cycle fatigue laws such as the Manson-Coffin relation and Miner's rule with the actual microscopic fatigue process, cyclic strain-controlled lowcycle fatigue tests were conducted on a medium carbon steel under constant-, two-step-, and random-strain amplitude conditions. Through continual observation of the microscopic fatigue process of plain specimens and holed specimens with a very small hole (40 μm diameter), it was found that the total fatigue life is mostly occupied by the microcrack propagation life. Both the Manson-Coffin relation and Miner's rule are derived using the microcrack propagation law. Then, background for the applicability of Miner's rule is discussed.

    The results of the random loading fatigue tests showed that microcrack propagation life can be predicted on the basis of the microcrack growth law in conjunction with the rain flow method for counting fatigue damage. Finally, the microcrack growth law-aided approach was applied to interpret anisotropy in fatigue strength of a thick forged steel plate.

    Keywords:

    carbon steel, microcrack initiation and propagation, microcrack propagation law, Manson-Coffin relation, Miner's rule, fatigue damage, two-step loading, block-random and random loading, rain flow method, anistropy in fatigue strength


    Author Information:

    S, Harada
    Associate Professor, Research Assistant, and Professor, Kyushu Institute of Technology, Tobata, Kitakyushu,

    Y, Murakami
    Professor, Kyushu University, Fukuoka,

    Y, Fukushima
    Associate Professor, Research Assistant, and Professor, Kyushu Institute of Technology, Tobata, Kitakyushu,

    T, Endo
    Associate Professor, Research Assistant, and Professor, Kyushu Institute of Technology, Tobata, Kitakyushu,


    Paper ID: STP24546S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP24546S


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