A comparison between two parameter and ductility exhaustion approaches for creep life assessment

Abstract

To improve the accuracy of creep life assessment for cracked components, the two-parameter fracture mechanics approaches with considering the constraint effect have been investigated and developed over the past decade. To examine the accuracy and applicability of different approaches, in this work, the creep life (including both creep crack initiation and growth life) is comparatively assessed using the two-parameter C*-R*, two-parameter C*-Ac and ductility exhaustion based approaches for pressurized pipes with different initial axial crack sizes. The results show that the life assessment results of the C*-R* approach are sensitive to initial crack sizes. For the shallower initial cracks, the C*-R* approach can give reasonable life prediction results, while for the deeper and longer cracks, it produces conservative results due to the sensitivity of the in-plane constraint parameter R* to initial crack sizes. The ductility exhaustion based approach verifies that the two-parameter C*-Ac approach has better life prediction accuracy for a wide range of initial crack sizes due to that the parameter Ac can characterize both in-plane and out-of-plane constraints and it is not very sensitive to initial crack sizes. The C*-Ac approach also can accurately predict the creep crack growth morphology which is mainly dependent on the initial crack aspect ratio.