Assessment of Creep Deformation and Rupture Behaviour of India-Specific RAFM Steel by Using Sin-Hyperbolic Creep Damage Model

India-Specific Reduced Activation Ferritic-Martensitic (IN-RAFM) steel is being considered as the potential structural material for the test blanket module of Demonstration Fusion Reactor envisaged under Indian fusion reactor program. The material mainly contains (in wt.%): 9Cr-0.1C-1.4W-0.2V-0.06Ta with strict control on radiologically unfavorable elements (e.g., Mo, Nb, Co, etc.). The creep properties evaluated at 823 K was analyzed for the evolution of creep strain and damage of the material by continuum damage mechanics-based Novel Sin-Hyperbolic model. The model has been implemented in ABAQUS finite element analysis software for predicting the creep curves and rupture life. The model formulae have been incorporated in a user defined subroutine named VUMAT in ABAQUS, with an explicit integration algorithm integrated into the subroutine. The elastic-creep FE axisymmetric analysis for 2D specimen was adopted to reduce the computational time. The creep data for modelling was obtained from the tests conducted at a stress range of 200-260 MPa till failure. The creep curves exhibited shorter primary regime followed by marginal secondary regime and extended tertiary creep regime, in particular at high stress levels of 240-260 MPa. The Sin-Hyperbolic model successfully predicted the sigmoidal bend in creep curves at primary to secondary transition and secondary to tertiary transition at most of the stress levels. Further, the isotropic creep damage formulation in the Novel Sinh model was found to mitigate rapid damage accumulation from the early stages of creep deformation, with damage values reaching to unity or finite value at the rupture. This in turn facilitated successful capturing of the prolonged tertiary creep stage in IN-RAFM at all stress levels.