13th International Conference on Fracture June 16–21, 2013, Beijing, China Application of the Local Approach for Prediction of Ductile Fracture of Highly Irradiated Austenitic Steels Boris Margolin1,*, Alexander Sorokin1, Victor Kostylev1 1 Central Research Institute of Structural Materials “Prometey”, Saint-Petersburg, Russia * Corresponding author: margolin@prometey2.spb.su Abstract The physical-and-mechanical model of ductile fracture has been developed to predict fracture toughness and fracture strain of irradiated austenitic steels taking into account stress-state triaxiality and irradiation swelling. Comparison of experimental data on fracture strain of irradiated austenitic weld metal with predicted results by the model has been performed. The model also allows to describe sharp decrease of ultimate strength on the basis of the proposed mechanism called as “the running collapse mechanism”. Keywords Ductile fracture model, Fracture toughness, Swelling, Irradiated austenitic steels, Vacancy voids 1. Introduction Ductile fracture of unirradiated austenitic and ferritic steels may be sufficiently successfully described on the basis of well known model – The Gurson-Tvergaard-Needleman model (GTN-model) [1, 2], and also on the basis less known model – Margolin-Karzov-Shvetsova-Kostylev model (MKSK-model) [3]. Ductile fracture of irradiated austenitic steels has many features. Some of them are the following. (1) Ductile fracture is controlled by not only evolution of voids, nucleating by deformation (deformation voids), but also by vacancy voids (resulting in swelling) arising under irradiation before deformation. (2) Deformation voids nucleation rate is higher for irradiated steel than for unirradiated steel. (3) Neutron irradiation reduces fracture toughness stronger than fracture strain of tensile smooth specimens. It means that stress state triaxiality (SST) enhances the effect of neutron irradiation on fracture strain. (4) For some value of radiation swelling a fracture of smooth specimens occurs when stress less than yield strength, but fracture surface contains dimples. It means that fracture mechanism is ductile due to evolution of voids. The aim of this paper is development of MKSK-model for prediction the fracture strain on neutron dose for different stress states, prediction the influence of neutron irradiation and radiation swelling on material fracture toughness and also prediction fracture at high level of swelling when stress less than yield strength. 2. The main considerations of the physical-mechanical ductile fracture model The main considerations of the proposed model are following: (а) Fracture proceeds by the mechanism of nucleation, growth and coalescence of voids. Two void populations are considered: vacancy voids and deformation voids, i.e. voids nucleating during the process of material deformation. (b) Polycrystalline material is presented as an aggregate of unit cells in the form of cubes with homogeneous properties of a material. -1-
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