[SY-G1] Symposium G-1

[SY-G1] A numerical study of channel deformation and fracture in irradiated stainless steel single crystals

^○Jean-Michel Scherer^1,2, Samuel Forest², Jacques Besson², Benoit Tanguy¹, Jérémy Hure¹ (1.DEN-Service d'Etudes des Matériaux Irradiés, CEA, Université Paris-Saclay, F-91191 Gif-sur-Yvette cedex, France, France, 2.MINES ParisTech, PSL-Research University, Centre des matériaux, CNRS UMR 7633, 63-65 rue Henri Auguste DesbruèresBP 87 91003 Evry Cedex, France, France)

Stainless steels are widely used as structural materials for nuclear core internals. Due to their proximity with the nuclear fuel, these materials are subjected to high level of irradiation doses. In the last decades, irradiation effects on structural materials’ mechanical properties have been heavily investigated in order to ensure structures’ reliability over nuclear plant lifetime. Irradiation induced defects - such as Frank dislocation loops and nanocavities - can lead to significant mechanical properties changes, as for example a significant hardening due to pinning of dislocations on defects. Under mechanical loading, gliding dislocations may incorporate sessile defects lying in their gliding plane, leaving behind a reduced defect density path. These zones, typically bands or channels of 10-100 nm width, beeing therefore softened by the "defects cleaning”, may localize strain and lead to highly heterogeneous deformation at the grain scale. This process is called dislocation channelling. A peculiar fracture mode called channel fracture is oberved in austenitic stainless steels irradiated at high temperature to high doses, leading to transgranular facets on fracture surfaces. It has been hypothesized [1] that channel fracture is due to nanovoids coalescence in dislocation channnels. Channel fracture is therefore assessed numerically in this study using a strain gradient crystal plasticity model that has been developped in order to take into account irradiation defect densities in the hardening/softening behaviour of the material and that has been implemented in a Finite Element solver [2]. Such model allows to regularize strain localization, and is used to model dislocation channelling. Single crystal porous unit-cells are subjected to simple shear, and the effect of void sizes and dislocation channels widths are systematically investigated. Numerical results are finally used to assess the hypothesis proposed in [1] regarding channel fracture in irradiated stainless steels.

[1] Margolin B. et al. (2016) The radiation swelling effect on fracture properties and fracture mechanisms of irradiated austenitic steels. Journal of Nuclear Materials
[2] Ling C. et al. (2017) Void growth and coalescence in triaxial stress fields in irradiated fcc single crystals. Journal of Nuclear Materials