Comparison of creep rupture lifetimes of single and double notched tensile bars

Creep rupture behaviour and lifetimes have been studied for two notched bars-one having a single notch and the other a double notch-by use of the creep finite element solver, Damage XX, based on Continuum Damage Mechanics (C.D.M.). A physically-based constitutive equation which utilises two damage parameters was used to model tertiary creep behaviour. Its versatility allows a wide spectrum of material parameters to be used which simulated a range of material behaviour. All computations showed that lifetimes for the double-notch testpiece within 95% of those for the equivalent single notch, and therefore validated the double notch geometry being studied. A consequence of the calculations has been the verification of a previous suggestion that the lifetimes of materials which exhibit tertiary creep due to dislocation strain softening (suc as nickel-based superalloys) could be less affected by stress-state effects on ductility, than materials which do not exhibit such softening (such as pure metals and simple solid solution alloys).