STP770

    Low-Cycle Fatigue Damage Mechanisms in Body-Centered-Cubic Materials

    Published: Jan 1982


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    Abstract

    The mechanisms of low-cycle fatigue damage of two high-purity ferritic alloys, Fe-3Si and Fe-26Cr-1Mo, have been investigated at room temperature using both polycrystal and single crystal specimens. The cyclic stress-strain behavior and the fatigue crack initiation mechanisms are shown to be sensitive to the applied strain rate and the crystal orientation. In the case of single crystals, high strain rates (≳ 10−3 s−1) give rise to large cyclic stress asymmetries and crystal shape changes. In bicrystals and polycrystals the cyclically induced grain distortions lead to intergranular crack initiation. Low cyclic strain rates favor the formation of persistent slip bands and hence transgranular crack initiation and reduced fatigue lives. These results are interpreted as a consequence of the asymmetry of dislocation motion in the body-centered-cubic (bcc) lattice.

    Other unusual features of the cyclic deformation of bcc alloys, such as the softening and hardening behavior at low amplitudes and deformation banding, are described and discussed.

    Keywords:

    fatigue, high strain, ferritic alloys, crack initiation mechanisms, cyclic hardening, polycrystals, bicrystals, single crystals


    Author Information:

    Magnin, T
    Ecole des Mines de Saint-Etienne, Saint-Etienne,

    Driver, JH
    Ecole des Mines de Saint-Etienne, Saint-Etienne,


    Paper ID: STP32430S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP32430S


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