STP675

    A Mechanism of Intergranular Fracture During High-Temperature Fatigue

    Published: Jan 1979


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    Abstract

    We have studied the mechanism whereby grain boundary sliding in the crack-tip region causes a triple-junction fracture type of grain boundary damage. This results in an increase in the rate of fatigue crack propagation. It is argued that since grain boundary sliding is a strain rate sensitive process, sliding damage is possible only if the strain rate is below a critical value; an expression for the critical strain in terms of the microstructure and the yield strength is obtained. It is shown, by theory and experiment, that the maximum damage condition is achieved when the tensile-going strain rate is below the critical strain rate whereas the compressive-going strain rate is above the critical value. If both strain rates are below the critical value (enough if they are unequal), then damage due to sliding in one direction is removed by sliding in the reverse direction, and the increase in crack growth rate is not observed.

    Keywords:

    high-temperature fatigue, intergranular fracture, triple-junction cracking, grain boundary sliding, critical strain rate


    Author Information:

    Min, BK
    Research associate and assistant professor, Cornell University, Ithaca, N.Y.

    Raf, R
    Research associate and assistant professor, Cornell University, Ithaca, N.Y.


    Paper ID: STP35906S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP35906S


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