Finite element creep damage study of nickel base single crystal structures under multiaxial stress states

Based on the microstructural assessment, a two state variable crystallographic creep damage constitutive equation has been presented for nickel base single crystal superalloys, which takes into consideration the rafting/derafting and damage of the voids simultaneously. With the uniaxial creep experimental data, the constitutive equation can model the creep damage behaviour of nickel base single crystal superalloys, especially the dependence of the creep anisotropy on the crystallographic orientation. The constitutive equation has been programmed as a user subroutine UMAT into ABAQUS. Double shear specimens and modelling blades have been experimented on to validate the constitutive equation. The results of the validation were satisfactory. The damage and life behaviour of a turbine blade has been presented as an example of the application. The influence of the crystallographic orientations on the blade lives has been analysed specially for the optimisation of blade crystallographic orientations.