Fatigue Cyclic Testing of the ITER CS Inlets

ITER Central Solenoid (CS) is cooled by injecting supercritical helium at the inner diameter (ID), an area with the highest stress. The jacket near the helium inlet is the weakest structural element of the ITER CS due to the high stress concentration. To verify adequate mechanical performance of the inlets, we made six full-scale specimens and subjected them to relevant cycling loading in liquid nitrogen to assess the operational margin of the inlets. To increase fatigue life of the inlets, we used a treatment called ultrasonic peening (UP). This treatment allows for the creation of a compressive residual stress at the surface of the jacket with the highest stress, which significantly delays initiation of the fatigue crack. For comparison purposes, one of the samples was intentionally not UP treated. Test results showed significant advantages of the UP treatment and demonstrated sufficient life to support the ITER CS mission.