Creep crack growth modelling of Grade 91 vessel weldments using a modified ductility based damage model

This paper reports creep crack growth modelling of Grade 91 vessel weldments at high temperature using a modified ductility-based continuum damage mechanics (CDM) model, which is based on the Kachanov-Rabotnov CDM and utilizing the concept of ductility exhaustion. The proposed model holds a key advantage over existing models in that it requires fewer material constants to be identified and calibrated. The new modified model was implemented into a user-defined subroutine in ABAQUS and then used to predict the creep crack growth of Grade 91 vessel weldments. Creep crack initiation and growth in the vessels were predicted to occur in the heat-affected zones of the weldments associated with the end closures, which is in good agreement with the corresponding vessel tests. Further, the predicted creep rupture lives of the notched bars and the vessels using the proposed model correlated reasonably well against the experimental results. This suggests that the modified ductility-based damage model can be used for creep crack growth and life prediction for high temperature structures with confidence