Low cycle fatigue behavior of ITER-like divertor target under DEMO-relevant operation conditions

• LCF behavior of the cooling tube and the interlayer of an ITER-like divertor target is studied.
• For the cooling tube, LCF failure will not be an issue under an HHF load of up to 18 MW/m2.
• Plastic strain in the interlayer is concentrated at the free surface edge of the bond interface.
• The predicted LCF lifetime of the interlayer may not meet the design requirement.

In this work the low cycle fatigue (LCF) behavior of the copper alloy cooling tube and the copper interlayer of an ITER-like divertor target is reported for nine different combinations of loading and cooling conditions relevant to DEMO divertor operation. The LCF lifetime is presented as a function of loading and cooling conditions considered here by means of cyclic plasticity simulation and using LCF data of materials relevant for ITER. The numerical predictions indicate, that fatigue failure will not be an issue for the copper alloy tube under a high heat flux (HHF) load of up to 18 MW/m2 as long as it preserves its initial strength. In contrast, the copper interlayer exhibits significant plastic dissipation at the free surface edge of the bond interface adjacent to the cooling tube, where the LCF lifetime is predicted to be below 3000 load cycles for HHF loads higher than 15 MW/m2. Most of the bulk region of the copper interlayer away from the free surface edge does not experience severe plastic fatigue and hence does not pose any critical concern as the LCF lifetime is predicted to be at least 7000 load cycles. LCF lifetime decreases as HHF load is increased or coolant temperature is decreased.