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.