STP1343

    Fatigue Crack Growth and Crack Closure Behavior of Ti-6Al-4V Alloy Under Variable-Amplitude Loadings

    Published: Jan 1999


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    Abstract

    Fatigue crack growth tests under constant-amplitude and repeated two-step loadings were carried out on a (α + β) Ti-6Al-4V alloy which has duplex structure made up of equiaxed primary α-phase grains with a discontinuous fine β-phase dispersed in the boundaries. It was found that fatigue crack grew along α-phase grain boundaries and that the fracture surface was very rough in the low stress intensity region under constant-amplitude loading. On the other hand, in the high region, transgranular crack growth was observed and the fracture surface was relatively smooth. The crack opening point, Kop, was affected by the amplitude of low-level load, ΔKL, under repeated two-step loadings where the high-level load amplitude was kept constant. Kop was found to be higher than that predicted by KopKmax relationship under constant-amplitude loading and the fracture surface was rougher in comparison with that under constant-amplitude loading which has the identical stress intensity range. It was concluded that the crack opening point was controlled by both plasticity-induced crack closure in terms ofKmax and roughness-induced crack closure resulted from rougher surface in ΔKL.

    Keywords:

    fatigue crack growth, crack closure, titanium alloy, variable amplitude loadings, fracture surface roughness


    Author Information:

    Jono, M
    Professor, associate professor, and research assistant, Osaka University, Osaka,

    Sugeta, A
    Professor, associate professor, and research assistant, Osaka University, Osaka,

    Uematsu, Y
    Professor, associate professor, and research assistant, Osaka University, Osaka,


    Paper ID: STP15762S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP15762S


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