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    Radiation Effects on the Micromechanics of Fatigue Crack Initiation


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    A micromechanical model is employed to investigate parameters that affect the rate of local plastic strain in and around persistent slip bands in cyclically loaded metals. The model utilizes a solution of the stress field in a semi-infinite elastic-plastic medium under generalized plane deformation. By following the evolution of the stress field, a natural gating mechanism is observed to produce regions of localized deformation. The regions of local deformation develop into extrusions and intrusions that are responsible for the formation of fatigue cracks.

    By coupling this micromechanical model with an empirical correlation developed to predict the increase in critical shear stress as a function of fluence and temperature, an investigation of radiation effects on fatigue crack initiation is carried out. It is determined that longer fusion reactor burn times and lower operating temperatures inhibit the crack initiation rate. Because of irradiation induced-hardening, increases in the fatigue limit are predicted for long reactor burn times (>103 s) and low operating temperatures (<300°C). Irradiation is found to increase the number of cycles required to obtain a failure strain at low temperatures and high-cycle fatigue conditions.


    micromechanical model, persistent slip bands, dislocation dipoles, extrusions, intrusions, crack initiation, critical shear stress, radiation hardening

    Author Information:

    Naughton, TD
    Member of technical staff, TRW Inc., Redondo Beach, CA

    Ghoniem, NM
    Professor and professor emeritus, University of California, Los Angeles, CA

    Lin, TH
    Professor and professor emeritus, University of California, Los Angeles, CA

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP25653S