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    STP1417

    Effect of Transient Loads on Fatigue Crack Growth in Mill Annealed Ti-62222 at -54, 25, and 175°C

    Published: 01 January 2003


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    Abstract

    Transient loads consisting of single tensile overloads and single tensile overloads followed by single compressive underloads were applied to Ti-62222 mill annealed titanium alloy at -54, 25, and 175°C. Tensile overload ratios were 2.0 and 2.5 and the compressive underload ratio was -0.5. Four reference steady-state ΔKImp values, using constant ΔK testing at R = 0.1, were investigated at each temperature. Cycles of delay, fatigue crack growth during delay, minimum fatigue crack growth rate, and crack extension during a transient load were obtained for all tests. Cycles of delay ranged from zero to crack arrest and mixed results often occurred making it difficult to draw many specific conclusions. Higher tensile overloads caused greater delay cycles and underloads were often detrimental compared to overloads only. Low temperature was mostly beneficial compared to room and high temperature that yielded similar delay. Crack growth delay distance was always greater than reversed plastic zone size. Macro- and microfractography revealed that surface crack closure, mode II displacements, crack tip blunting, branching, and tunneling, local state of stress, and residual compressive stresses contributed to the transient fatigue crack growth behavior.

    Keywords:

    titanium alloy, fatigue crack growth, tensile overloads, compressive underloads, temperature, fractography


    Author Information:

    Stephens, RI
    Professor, The University of Iowa, Iowa City, IA

    Stephens, RR
    Associate Professor, The University of Idaho, Moscow,

    Schoenefeld, DA


    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP11094S