Previous investigations have demonstrated that creep crack growth initiation under steady loading can be described using an R6 type approach. For high temperature assessments, the failure assessment diagram (FAD) and 'yield' stress are determined using isochronous stress-strain data corresponding to the assessment time. The conventional fracture toughness used in low temperature assessments is replaced by a time-dependent toughness, and it has been shown that, for steady state creep, this 'creep toughness' can be determined from data presented in terms of C{sup}* or from measurements of total creep displacements on test specimens. In this paper, three recent extensions to the methodology are described. First, it is shown that for the transient conditions prior to steady state creep, the 'creep toughness' can be determined by formulae similar to those conventionally used to estimate J from test specimens. Secondly, for creep-fatigue loading, it is shown that the approach can be modified by allowing for limited fatigue crack growth. Finally, for non-steady loadings of variable stress and/or temperature, without fatigue damage, it is shown that the R6 approach may still be applied by defining suitably time-averaged stresses and temperatures. Limited validation for these developments is provided by analysis of data from stainless steel compact tension specimens.
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