New Approach to Evaluate Joint Delamination Mechanism of Divertor by Finite Element Analysis Applying Cohesive Zone Model (CZM); Parametric Study on the Maximum Traction under Heating

To evaluate the delamination mechanism of the joint interfaces of a plasma-facing component, a new approach using the finite element analysis (FEA) applying the cohesive zone model (CZM) is proposed. The parametric study on the maximum traction τmax, which is one of the principal CZM parameters, was conducted for compensating the lack of material data. Monotonic heat loading was applied to the surface up to 20 MW/m2 in 1 second. The traction-separation law was assumed to be bilinear, which represents the relation between the representative crack stress and its opening displacement used for CZM. In the parametric study, three assumptions of τmax were defined, (1) equal to the weaker bulk strength (Copper), (2) considering temperature dependency, and the average value of the strength ratio of the interface to bulk copper, and (3) considering as well as (2) but the lowest value of the ratio. Results of the parametric study suggest shear stress-governed (mode Ⅱ) delamination without vertical crack propagation in tungsten monoblock. Meanwhile, the joint interface shows compression, which means the interface remains in contact. Therefore, it is suggested that the degradation of cooling capability does not happen during the heating process unless vertical cracks in tungsten do not propagate into the interface.