LONG TERM STRESS RELAXATION MODELLING

Data assessments, materials modelling and development as well as recommendations for model selection have been a main objective of the ECCC Working Group 1. This paper describes the latest inter-comparison round robin on relaxation modelling. Most models found in the public domain are limited in either strain range or temperature. Here the bolting steel 1Cr-0.5Mo-0.25V steel tested by NIMS, Japan is assessed by a number of assessors striving to define models capable of predicting the relaxation in the full data range, i.e. in both strain (0.1-0.25% total strain) and temperature (450-550°C). The assessors use methods of their own preference giving all model parameters to enable interpolation/extrapolation and calculation of prediction errors within the range of data. The methods include forward creep with different creep strain models as base, classical relaxation models, parametric (Time-Temperature-Parameter curve families) solutions and entirely new modelling approaches. The main target is the general overall model for prediction of relaxed stress up to 3 000 h hold time. However, the model robustness is tested by fitting to a drastically culled data set consisting of only the short term data with durations of 0.1 to 10h. The predictive performance of the models optimised for the short term data are compared with the long term data as well as the long term models. Conclusions and recommendations are given on model interpolation performance, extrapolation ability and model complexity.

HOLMSTROM Bjorn;  POHJA Rami;  AUERKARI Pertti;  FRIEDMANN Valerie;  KLENK Andreas;  LEIBING Benjanmin;  BUHL P.;  SPINDLER Mike;  RIVA Andrea; 

2014-12-17

CSM, Italy

JRC89590

978-88-7484-380-0,   

http://eccc.c-s-m.it/,    https://publications.jrc.ec.europa.eu/repository/handle/JRC89590,