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Publication - Dr Harry Coules

    Effects of crack introduction history on fracture initiation in residually stressed components

    Citation

    Probert, M, Coules, H & Truman, C, 2018, ‘Effects of crack introduction history on fracture initiation in residually stressed components’. in: Proceedings of the ASME 2018 Pressure Vessels & Piping Conference.

    Abstract

    If a crack is introduced progressively into an elastic-plastic
    material containing a residual stress field, the incremental
    relaxation of the residual stress field causes the formation of a
    plastic wake along the crack boundaries. This leads to the
    reduction in the J parameter for a crack of a given size,
    compared to a crack with the same dimensions which has been
    introduced instantaneously, having the crack faces released
    simultaneously along the whole length, a 40% reduction is
    observed in the current analysis. This reduction in J is due to the
    dissipation of strain energy which is otherwise available for
    further crack extension, as in the instantaneously introduced
    crack. This is important for the current J-based fracture
    assessment common in the nuclear and petrochemical industries
    such as EDF Energy’s R6 and BS7910:2013 as they currently
    assume instantaneous insertion of cracks as this is inherently
    more conservative. Although many studies demonstrating this
    effect in FE are available, there is little experimental evidence
    for this phenomenon. Especially those including rigorous
    comparisons with specimens that have been ‘instantaneously’
    cracked. This may be due to the difficulty inherent in
    manufacturing such a specimen as manufacturing processes rely
    on the incremental removal of material. The aim of this paper is
    to detail analysis of a novel method of crack introduction that
    aims to replicate the deformation behavior of an instantaneously
    introduced crack tip in a model that has had the nodes released
    in a progressive manner. This will allow specimens to be
    machined in a way that replicates ‘instantaneous’ cracking
    allowing for experimental techniques to be developed to display
    the difference between instantaneous and progressively
    introduced cracks.

    Full details in the University publications repository