Name: Aleksandr Zinovev
Date: October 3, 2019
Crystal plasticity modelling of thermomechanical fatigue in ITER relevant tungsten
Operational conditions in ITER fusion reactor will cause thermomechanical fatigue of the divertor components made of tungsten, due to instabilities in hot plasma called “edge localized modes” (ELMs). Cyclic thermal stresses will emerge in the surface region of divertor components, resulting in the formation of intergranular cracks at the surface. They can propagate into the component, presenting an issue for a stable operation of ITER, while high surface temperature can cause material recrystallization.
A crystal plasticity model is proposed in this PhD project to rationalize the conditions of accumulation of damage and eventual crack formation in tungsten under thermal conditions of ITER. Crystal plasticity was selected because it properly considers crystal anisotropy, the main cause of stress heterogeneity, which leads to crack formation. The model parameterization was based on mechanical properties of ITER-specification tungsten and recrystallized tungsten. Kinematic hardening due to backstresses plays a major role in cyclic deformation, and was taken into account in the model.
The ability of tungsten to exhibit kinematic hardening was shown to have a negative effect on its lifetime under conditions of cyclic thermal load. A qualitative agreement was demonstrated between the model predictions and experiments, in terms of the evolution of surface features in tungsten under conditions of thermomechanical fatigue.
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