Comparison of the predictions relying on coupled/uncoupled damage-viscoplasticity models for creep test analyses

To enhance the assessment of reactor pressure vessel life under severe acci dent, a cooperative research program is conducted between CEA, EDF, and Fra matome, parts of which are supported by the European Commission. Within the framework of this program, a model based on Lemaitre and Chaboche with pre dictive capability in the field of viscoplastic flow, material damage, and failure has been generalized and implemented in CASTEM 2000 finite element code. In order to validate the model in mechanical situations featuring the same basic characteristics as the severe accident scenarios, analytical ex periments are conducted on the RUPTHER facility: a thin shell tube is loade d with an internal pressure and submitted to an axial thermal gradient with elevated temperatures. The specific question of the interest of the couple d damage approach in the failure prediction is addressed. Comparisons of th e predictions relying on coupled and uncoupled damage-viscoplasticity model s show that, at higher temperatures, failure could be predicted through unc oupled damage evaluation provided the main nonlinear effects like large dis placements and updated pressure are taken into account, while at lower temp eratures coupling between damage and deformation is necessary. Examples bas ed on some RUPTHER creep test predictions are given.