Comparison of the Predictions Relying on Coupled/Uncoupled Damage-Viscoplasticity Models for Creep Test Analyses

Abstract

To enhance the assessment of reactor pressure vessel life under severe accident, a cooperative research program is conducted between CEA, EDF, and Framatome, parts of which are supported by the European Commission. Within the framework of this program, a model based on Lemaitre and Chaboche with predictive 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 experiments are conducted on the RUPTHER facility: a thin shell tube is loaded with an internal pressure and submitted to an axial thermal gradient with elevated temperatures. The specific question of the interest of the coupled damage approach in the failure prediction is addressed. Comparisons of the predictions relying on coupled and uncoupled damage-viscoplasticity models show that, at higher temperatures, failure could be predicted through uncoupled damage evaluation provided the main nonlinear effects like large displacements and updated pressure are taken into account, while at lower temperatures coupling between damage and deformation is necessary. Examples based on some RUPTHER creep test predictions are given.