Robust prediction of long term stress relaxation for bolting steel X19. Results from the European Creep Collaborative Committee assessments

The development of creep related materials modelling and recommendations for model selection have been a main objective of the Work Group 1 (WG1) of the European Creep Collaborative Committee ECCC. The second inter-comparison round robin on creep relaxation modelling is currently being carried out for the bolting steel X19. The forward creep response of this material is challenging (sigmoidal behaviour) and the available relaxation data is collated from several sources, including standard data tables. The ECCC assessors are in this work striving to define relaxation models capable of predicting the relaxation response in the full data range, i.e. strain and temperature and hold time. The initial models of the on-going exercise are here presented, tested and compared according to their ECCC post assessment test capabilities. The initial results show that global models, both engineering and numerical solutions, with sensible amount of fitting parameters, can be found to describe the relaxation behaviour. The successes of these models in extended extrapolation are foreseen to give basis to the update of the ECCC recommendations on relaxation modelling.JRC.G.I.4-Nuclear Reactor Safety and Emergency Preparednes