A Mechanism-Based Framework for the Numerical Analysis of Creep in Zircaloy-4

A deformation-mechanism map has been developed for unirradiated zircaloy-4 based on the creep data available from the literature of the last thirty-five years. These data have been analyzed to identify different creep mechanisms, based on the forms of the relationships between stress, temperature and strain rate. This identification allowed the activation energies and other associated creep parameters to be derived for each mechanism. The creep parameters were used to construct a deformation-mechanism map for zircaloy-4 that shows the conditions under which different mechanisms are dominant. This information provides an important tool for assessing the effects of stress and temperature in design, especially when extrapolating to different regimes. As an example of how this information might be used in a numerical analysis for design purposes, a novel mechanism-based creep framework was implemented within a finite-element code. Although the framework was developed specifically for zircaloy-4, it provides a general example of how mechanism-based creep laws can be implemented into finite-element analyses. This approach allows the creep of complex geometries to be analyzed rigorously, with the dominant deformation mechanisms being identified and evolving automatically in response to the local temperatures and stresses. (May 31, 2012) (Revised: August 28, 2012)