Abstract
The R5 high temperature assessment procedures have been developed in the UK and address both creep–fatigue crack initiation in initially defect free components and the growth of flaws by creep and creep–fatigue mechanisms. The procedures were developed some time ago and included a number of novel features such as: the shakedown reference stress approach for structural assessment; the ductility exhaustion method for estimating creep damage; the inclusion of size effects in fatigue damage calculations to enable assessments of thin section components; and the treatment of the effects of crack closure on creep–fatigue crack growth rates. Recently, the R5 procedures have undergone a major revision leading to Issue 3 of the document. In the revision, the above novel features have been retained but other parts of the procedure have been modified. These include: a restructuring of the document with associated new step-by-step procedures to enable easier application; modifications to the ductility exhaustion model to address multiaxial stresses including the triaxial stresses which may be present in regions of high welding residual stress; additional advice for assessment of weldments including fatigue strength reduction factors based on experimental data on austenitic weldments; generalised hysteresis loop construction methods for complex non-isothermal cycles, supported by laboratory data collected under non-isothermal conditions; advice on inelastic analysis when simplified shakedown methods are inapplicable; and rules for determination of interactions between creep and fatigue crack growth. The present review first describes in outline the overall structure and content of R5 Issue 3. Then the new R5 creep–fatigue crack initiation assessment procedures are set out in more detail. This includes the recent modifications and some associated background experimental and analytical work on which these modifications are based. Finally, the paper sets out the new creep–fatigue crack growth procedures in R5, again with some background information on the recent developments.
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