Thermomechanical low cycle fatigue assessment of the W-armoured ITER First Wall Panel

The recent transition of the ITER actively cooled First Wall Panel (FWP) from beryllium to tungsten (W) armour tiles necessitates the requalification of the component under high heat flux (HHF) testing. A soft copper (Cu) interlayer is utilized to accommodate the significant thermal expansion mismatch between the W tiles and the underlying CuCrZr heat sink. This study investigates the low cycle fatigue (LCF) performance of the Cu compliance layer using a thermomechanical elastoplastic finite element simulation in Ansys APDL. The simulation models a single tile unit cell subjected to 2 MW/m 2 HHF cycling, utilizing Chaboche non-linear kinematic hardening to accurately capture strain hardening within the Cu and CuCrZr layers. Results indicate that the simulated fatigue degradation can produce effective surface-level debonding of the W/Cu joint before the required 30,000 HHF cycles. The LCF life of the Cu interlayer is predominantly limited by the 12 mm W tile thickness and the minimum water coolant temperature of 70 °C. Furthermore, a novel cycle jump simulation demonstrates that fatigue fronts develop near debonded corners after approximately 8000 cycles, significantly accelerating subsequent interfacial failure. Conversely, substituting the Cu interlayer with a W-to-CuCrZr functionally graded material (FGM) eliminated cyclic plastic yielding, presenting a highly effective design alternative for future high heat flux components. Despite not substituting a design-by-experiment approach, these findings provide a quantitative basis for understanding thermomechanical degradation in the ITER flat tile geometry and highlight critical parameters for upcoming experimental validation.