Intrinsic thresholds in polycrystalline Udimet 720

P.A.S. Reed, W.F. Gale, J. E. King

    Research output: Contribution to journalArticlepeer-review


    The long crack threshold behaviour of polycrystalline Udimet 720 has been investigated. Faceted crack growth is seen near threshold when the monotonic crack tip plastic zone is contained within the coarsest grain size. At very high load ratios R (=P min/P max) it is possiblefor the monotonic crack tip plastic zone to exceed the coarsest grain size throughout the entire crack growth regime and non1aceted structure insensitive crack growth is then seen down to threshold. Intrinsic threshold values were obtained for non1aceted and faceted crack growth using a constant K max, increasing K min, computer controlled load shedding technique (K is stress intensity factor). Very high R values are obtained at threshold using this technique (0.75-0.95), eliminating closure effects, so the intrinsic resistance of the material to crack propagation is reflected in these values. The intrinsic non1aceted threshold value ΔK th is lower (2.3 MN m -3/2) than the intrinsicfaceted ΔK th value (4.8 MN m -3/2). This is thought to reflect not only the effect of crack branching and deflection (in the faceted case) on the crack driving force, but also the inherent difference in resistance of the material to the two different crack propagation micromechanisms. © 1993 The Institute of Materials.

    Original languageEnglish
    Pages (from-to)281-287
    Number of pages7
    JournalMaterials Science and Technology
    Issue number4
    Publication statusPublished - Apr 1993


    • closure effects
    • crack branching
    • crack driving force
    • crack tip plastic zone
    • grain size
    • high load
    • intrinsic resistance
    • load-shedding
    • long cracks
    • micromechanisms
    • polycrystalline
    • R value
    • Udimet 720
    • crack propagation
    • crack tips
    • grain growth
    • grain size and shape
    • crack closure


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