Prediction of creep rupture life of a V-notched bar in DD6 Ni-based single crystal superalloy

The circumferential V-type notched round bar has been designed to investigate the effect of multi-axial stress state on creep rupture behavior of DD6 Ni-based single crystal superalloys at 1100 °C. Creep test on both smooth and notched specimens were carried out under 160 MPa and 200 MPa on the minimum net-section. Time to creep fracture was found to be higher in notched specimens than in smooth specimens. Finite element (FE) analysis coupled with continuum damage mechanics (CDM) was carried out to understand the stress distribution and the creep damage evolution under uniaxial and multi-axial stress states. The creep rupture life of the smooth specimen was successfully predicted by the classical Kachanov-Rabotnov damage law. The creep rupture life of the notched specimen predicted by finite element calculation incorporating a multi-axial creep CDM model was in good agreement with the experimental results. Both the fracture morphology and FE damage analysis indicate that rupture initiates first at the notch root in the notched specimen and finally towards to the center location.