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    STP1372

    Effect of an Overload on the Threshold Level of Ti-6-22-22

    Published: 01 January 2000


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    Abstract

    The effects of overloads on the fatigue crack growth behavior of the high trength α/β titanium alloy Ti-6-22-22 have been investigated. Fatigue cracks were grown at a baseline R level of 0.1, and single overloads, ranging in magnitude from 2–3 times the baseline level, were applied to determine the effect of the overloads on subsequent fatigue crack growth behavior. Because of the high yield strength of the alloy, 1225 MPa, the number of delay cycles following an overload was not as pronounced as in alloys of lesser strength. A principal effect of an overload in this titanium alloy was to increase the threshold for fatigue crack growth. An experimental procedure based upon the increase in threshold level was adopted to determine the maximum level of crack closure resulting from an overload.

    The novel observation was made that following a sufficiently high overload the rocess of further crack growth involved the emergence of a surface crack ahead of the preexisting crack. It was also observed that the crack growth behavior at distances well beyond the overload plastic zone size could be sensitive to prior overload history.

    Keywords:

    Fatigue crack growth, fatigue threshold, overloads, titanium


    Author Information:

    McEvily, AJ
    U. of Connecticut, Storrs, CT

    Ohashi, M
    National Research Institute of Police Science, Tokyo,

    Shover, R
    U. of Connecticut, Storrs, CT

    DeCarmine, A
    U. of Connecticut, Storrs, CT


    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP13430S