Interpretation of uniaxial creep damage properties and rupture life considering local necking via an inverse approach

Tertiary creep-induced local necking, which occurs during uniaxial creep tests for creep-ductile materials, has been a long-term concern in the interpretation of creep rupture life under both constant load and constant stress conditions. In this study, a set of short-term, high stress regime, creep rupture tests, in a range of stress and temperature, for a newly developed tempered martensitic MarBN steel, were used to understand the necking mechanics and the underlying deformation mechanisms. An FE-based, inverse approach is developed to determine the full stage creep damage properties under large deformation conditions, utilizing the measured deformed shapes of local necking within the inverse optimization scheme. On this basis, a temperature-dependent empirical relationship of the creep rupture lives between constant load and constant stress creep rupture tests is established. As a demonstration, the feasibility and accuracy of the proposed relationship was evaluated through a benchmark case using the data from the G115 martensitic steel creep tests. The implications of this relationship for broader and more general conditions (e.g., stress range, temperature, materials) and practical applications are discussed.