SOME IMPLICATIONS OF THE USE OF THE PD6493 LEVEL 3 FAILURE ASSESSMENT PROCEDURE

Abstract— Under a natural mapping between the standard R-curve analysis diagram and the failure assessment diagrams of R6 and PD6493 Level 3 the R-curve becomes the RCI (R-curve image). It follows that whenever the assessment point moves along the failure assessment line during ductile crack growth, the implication is that the failure assessment line is the RCI. This result is used to test the conservatism of a specific PD6493 Level 3 analysis by two methods. The first calculates the variation during crack growth of the applied elastic-plastic crack tip opening displacement (CTOD) parameter (or‘driving force') which is implied by the PD6493 analysis and then compares this variation with an independent estimate of it. The second uses an assumed driving force to deduce the CTOD resistance curve implied by the failure assessment line. It is shown by both methods and also by a direct R-curve analysis that this particular PD6493 analysis is conservative relative to an R-curve analysis which uses a crack driving force estimated by the EPRI (Electric Power Research Institute) procedures. However there is inconsistency between standard R-curve analysis and PD6493 Level 3 analysis in that the latter implies a material resistance which, for a given material, depends on the geometry of the structure. A similar inconsistency arises in any failure assessment procedures like the Options 1 and 2 with Category 3 of R6, which require the assessment point to move on a geometry independent failure assessment line during crack growth; indeed, even when the failure assessment line is geometry dependent there is full agreement with R-curve analysis only if the correct RCI is used as the failure assessment line. In a brief discussion it is noted that the new failure assessment diagram studies involving multi-parameter fracture mechanics may help to ameliorate these problems.