Engineering models for softening and relaxation of Gr.91 steel in creep-fatigue conditions

There are a number of different approaches for calculating creep-fatigue (CF) damage for design, such as the French nuclear code RCC-MRx, the American ASME III NH and the British R5 assessment code. To acquire estimates for the CF damage, that are not overly conservative, both the cyclic material softening/hardening and the potential changes in relaxation behavior have to be considered. The here presented data and models are an initial glimpse of the ongoing European FP7 project MATISSE effort to model the softening and relaxation behavior of Grade 91 steel under creep-fatigue loading. The resulting models are used for calculating the relaxed stress at arbitrary location in the material cyclic softening curve. The initial test results show that softening of the material is not always detrimental. The initial model development and the pre-assessment of the MATISSE data show that the relaxed stress can be robustly predicted with hold time, strain range and the cyclic life fraction as the main input parameters.

HOLMSTROM Bjorn;  DE HAAN Fredericus;  FÜHRER Ulrich;  POHJA Rami;  JANOUŠEK Jaromir; 

2017-12-20

EMERALD GROUP PUBLISHING LTD.

JRC108432

1757-9864,   

https://publications.jrc.ec.europa.eu/repository/handle/JRC108432,   

10.1108/IJSI-02-2017-0010,