Failure Assessment Diagrams for High Temperature Defect Assessment underVariable Loading Conditions

摘要

A two parameter Time Dependent Failure Assessment Diagram (TDFAD) procedure for defect assessment under creeploading builds on the reference stress approach of the R6, Option 2, procedure for defect assessment, with potential failuresdefined by creep crack initiation and creep rupture. The conventional fracture toughness is replaced by a time-dependent'creep toughness', and tensile properties are determined from isochronous data at the corresponding assessment time andtemperature. The TDFAD approach has recently been formalised and incorporated into R5 as an appendix to Volume 4. Inthis paper, the TDFAD procedure of R5 is first summarised. Methods are then described, for extending the application of theprocedure to non-steady loading conditions of variable stress and/or temperature, using a concept of an equivalent referencestress. A worked example of the procedure is also presented.