Date

2012-09-07

Author

Yalçınkaya, Tuncay
Nılsson, Karl Fredrık

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Future fast neutron nuclear reactors (i.e. Generation IV), will provide more sustainable nuclear energy through much more efficient use of the uranium and reduction of radioactive waste. The design life will be at least 60 years and safety must be at the same level as today’s Generation III thermal nuclear reactors. The materials and components will be exposed to much harsher environment in terms of higher irradiation levels, higher temperatures and more corrosive coolants. This requires both development of new materials such as oxide-dispersion strengthened steels and composites, as well as qualification of exiting materials such as austenitic (e.g. 316LN) and FM(ferritic/martensitic) steels [e.g. P91 (9Cr-1MoVNb)] where the latter one is distinguished by softening response under cyclic loading at elevated temperatures. Due to the very long design life, the components need to be designed against creep and fatigue crack initiation which can be related to the accumulated plastic slip in individual grains. The effect of the underlying microstructure (subgrains and grains) and resulting macroscopic observations can only be addressed by a modeling approach at a proper scale. Crystal plasticity theories, e.g. [1, 2] fit very well to this purpose; however their capabilities are limited considering the dislocation microstructure evolution driven by the imposed deformation and the grain boundary-dislocation interactions. A recent study [3] proposes a non-convex strain gradient plasticity theory for dislocation slip driven pattering in a 1D setting at single crystal level. The present paper extends the convex version of the study to a plane strain case consisting of polycrystals with multiple slip systems, focusing especially on the grain boundary-dislocation interaction. In the current framework, both the displacement and the plastic slip fields are considered as primary variables. These fields are determined on a global level by solving simultaneously the linear momentum balance and the slip evolution equation. Introduction of an interfacial otential generalizes the effect of grain boundaries which enables to study the occurrence of dislocation pileups across the boundaries and also subsequent emission to the neighbouring grains. The hardening factors associated to back stress due to plastic slip gradients and slip resistance due to SSDs and GNDs are naturally incorporated in the model. The examples study the grain size effect, sensitivity with respect to the assumed interfacial potential and the diffusion capacity of the grain boundaries. The extension of the model to incorporate a more physically based grain boundary model and the cyclic softening phenomena are addressed as well.

Subject Keywords

Energy, Transport and Climate

URI

https://hdl.handle.net/11511/77146

Collections

Department of Aerospace Engineering, Conference / Seminar