Three-dimensional analyses of unified characterization parameter of in-plane and out-of-plane creep constraint

Based on extensive three-dimensional finite element analyses, the unified characterization parameter A(c) of in-plane and out-of-plane creep constraint based on crack-tip equivalent creep strain for three specimen geometries (C(T), SEN(T) and M(T)) were quantified for 316H steel at 550 degrees C and steady-state creep. The distributions of the parameter Ac along crack fronts (specimen thickness) were calculated, and its capability and applicability for characterizing a wide range of in-plane and out-of-plane creep constraints in different specimen geometries have been comparatively analysed with the constraint parameters based on crack-tip stress fields (namely R*, h and T-Z). The results show that the parameter Ac in the centre region of all specimens appears uniform distribution and lower value (higher constraint), and in the region near free surface it shows protuberant distribution and higher value (lower constraint). The parameter Ac can simultaneously and effectively characterize a wide range of in-plane and out-of-plane creep constraints, while the parameters R*, h and TZ based on crack-tip stress fields cannot achieve this. The different capabilities of these parameters for characterizing in-plane and out-of-plane creep constraints originate from their underlying theories. The parameter Ac may be useful for accurately characterizing the overall constraint level composed of in-plane and out-of-plane constraints in actual high-temperature components, and it may be used in creep life assessments for improving accuracy.