COMPLAS 2023

Keynote

Discrete Dislocation Plasticity Modelling of - Type Irradiation Loops in Zirconium

  • Kumar, Rakesh (Imperial College London)
  • Hortelano-Roig, Daniel (University of Oxford)
  • Tarleton, Ed (University of Oxford)
  • Balint, Dan (Imperial College London)

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In this work, a planar discrete dislocation plasticity (DDP) model is developed to capture the interaction between -type irradiation loops (in prismatic planes) and dislocations nucleating from Frank-Read sources. The model is used to study the effect of neutron irradiation on the hardening evolution, subsequent strain localisation and softening by channelling in Zirconium and its alloys. Prismatic loops are modelled by plane strain edge dislocation dipoles in a climb configuration with either vacancy or interstitial character. Irradiation loops have a size taken from a distribution calibrated by experiments, and random character such that mass is conserved in the sample. The effect of the out-of-plane loop segments on the in-plane segments (loops are idealised as rectangular) is captured by an analytical, loop-size-dependent force expression validated by three-dimensional discrete dislocation dynamics (DDD) simulations. Loops rotate and equilibrate under applied stress and the restoring action of the lengthening out-of-plane loop segments, in a manner found to be qualitatively and quantitatively consistent with three-dimensional DDD simulations, molecular dynamics and experiments. Interaction between Frank-Read dislocations and loops occurs by successive intersection and loop size reduction events consistent with three-dimensional simulations and experiments; the dislocation-loop interaction is discretised such that the loop reduces size upon interacting with a Frank-Read dislocation, while a remnant dislocation with double super-jog and reduced mobility is emitted. Loops can be effectively removed from simulations by this process, allowing channels to form that are clear of irradiation defects, which in turn allows enhanced strain localisation to occur, interpreted as incipient strain softening. Uniaxial deformation is applied to polycrystalline samples, and a parametric study is performed to understand the effect of loop density, size, type (interstitial or vacancy) and distribution on irradiation hardening and strain localisation.

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