Unified characterization of in-plane and out-of-plane creep constraint based on crack-tip equivalent creep strain

• A unified parameter of in-plane and out-of-plane creep constraint is proposed.
• The unified constraint parameter is based on crack-tip equivalent creep strain.
• The parameter is load independent and can characterize overall constraint levels.
• Correlation between creep crack growth rate and the unified parameter is obtained.

In this work, the unified characterization parameter of in-plane and out-of-plane creep constraint based on crack-tip equivalent creep strain has been investigated. Based on the area surrounded by the crack-tip equivalent creep strain isoline, a unified creep constraint parameter AcAc has been defined. A monotonic correlation line between creep crack growth rate and the parameter AcAc can be formed regardless of in-plane and out-of-plane constraint and choice of the isolines, which indicates that the AcAc is a good unified creep constraint parameter. The parameter AcAc is load independent, and can characterize overall constraint levels for specimens with different in-plane and out-of-plane constraints.