Analysis of creep ductility in a ferritic martensitic steel using a hybrid strain energy technique

Creep rupture data for a modified 9% Cr 1% Mo ferritic martensitic steel was statistically analysed to provide a description of a ductility exhaustion approach for the evaluation of creep damage that occurs in creep–fatigue dwells. Energy approaches have been previously used; however, these require the use of the creep–fatigue test data themselves to identify the constants. This paper describes an approach based on a hybrid strain energy density formulation that uses creep rupture data and hence aligned with time fraction or classical ductility approaches. These current methods, however, tend to be overly conservative. Ductility models also tend to be statistically problematic when fitting to some datasets, particularly when stress and temperature are highly correlated. The method developed here was found to give the highest correlation for the tested models and was statistically robust for collinearity and heteroskedastic behaviour.