Crack formation in the tungsten armour of divertor targets under high heat flux loads: A computational fracture mechanics study

Abstract

In the framework of EUROfusion, the thermally induced stress and the consequential fracture of the design of DEMO-divertor with copper alloy heat sink have been analyzed, to assess the structural integrity of tungsten armor of the plasma facing component (PFC). With finite element method (FEM), the influence of mesh and plasticity of tungsten has been evaluated. Due to the lack of material data, especially those of irradiated tungsten under operation conditions, conservative assumptions have been made in terms of plasticity, fracture strength and fracture toughness. The crack initiation and propagation with assumed plasticity and fracture toughness for heat fluxes ranging from 10MW/m2 up to 30 MW/m2 have been analyzed. Thermal stress analysis has been performed with various plasticity of tungsten, to locate the peak stress, which leads to the highest possibility of crack initiation. Extended finite element method (XFEM) analysis has been performed afterwards with various fracture strength toughness. The influence of plasticity and fracture toughness from almost zero up to Kic = 20MPa∙m1/2 has been evaluated. The predicted crack propagation has been verified by results of J-integral calculation.