STP1359

    The Propagation of a Circumferential Fatigue Crack in Medium-Carbon Steel Bars Under Combined Torsional and Axial Loadings

    Published: Jan 1999


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    Abstract

    The propagation behavior of a circumferential crack in a cylindrical bar of a medium carbon steel was studied extensively under various combinations of cyclic torsion and axial loading. First, the threshold condition of fatigue crack propagation was discussed in terms of the stress intensity factor. The threshold condition of fatigue crack extension was expressed by a quarter-elliptic function of the stress intensity ranges for Mode I and III. The equation can be derived on the basis of the crack-tip displacement criterion. The threshold condition for fracture is also expressed by another quarter-elliptic function. Next, the J-integral was applied to flat-type fatigue crack propagation with excessive plasticity under high cyclic loads. The crack propagation rate was expressed as a power function of the J-integral range for Mode I, and also for Mode III. The propagation rate is lower under Mode III loading than under Mode I loading, when a comparison is made at the same ΔJ value. The crack propagation rates under mixed-mode loading, as a function of ΔJ, lie between the relations for Mode I and Mode III. Striations were observed on the fatigue fracture surface that was created under mixed mode loading, and the striation spacing was equal to the crack propagation rate as it also was for the case of Mode I loading.

    Keywords:

    fatigue, crack propagation, mixed Mode (I and III), combined tension and torsion, medium-carbon steel, fracture mechanics, J, -integral, sliding contact, fractography, striation


    Author Information:

    Tanaka, K
    Professor, associate professor, and graduate student, Nagoya University, Nagoya,

    Akinawa, Y
    Professor, associate professor, and graduate student, Nagoya University, Nagoya,

    Yu, H
    Professor, associate professor, and graduate student, Nagoya University, Nagoya,


    Paper ID: STP14255S

    Committee/Subcommittee: E08.01

    DOI: 10.1520/STP14255S


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