Load-independent creep constraint parameter and its application

• A load-independent creep constraint parameter R* was proposed.
• The R* at steady-state creep can be used to evaluate constraint for whole creep time.
• The R* can be used for ranking constraint levels for various specimens or components.
• The R* can be used for predicting constraint-dependent creep crack growth rates.

A load-independent creep constraint parameter R* was proposed, and its load-independence was validated using finite element results in previous studies. A fixed distance r = 0.2 mm from a crack tip is chosen to define the R*, and the R* at steady-state creep can be used to evaluate constraint level with little conservatism for whole creep time. The R* can be used for ranking constraint levels for different specimens or components, and for predicting constraint-dependent creep crack growth rates. The constraint-dependent creep crack growth rate equations of a Cr–Mo–V steel have been obtained, and it may be used in creep life assessments.