Effects of Stress Ratio on Low-Cycle Fatigue Performance of Various REBCO CC Lap Joints at 77 K

Abstract

In high-performance applications, the REBCO-coated conductor (CC) tapes are frequently pushed to their limits, resulting in fatigue-related failures, particularly at the vulnerable CC joint—a critical weak point in the structure of REBCO coils and magnets. This study investigates the influence of stress ratio ( R ) on the electromechanical durability of ultrasonically welded (UW) joints in two commercially available REBCO CC tapes. Employing a systematic approach, the research investigates fatigue behavior and cumulative damage under varied R values (0.1 and 0.5). Low-cycle fatigue (LCF) tests at 0.02 Hz provide in-depth insights into the fatigue behavior of each CC tape joint. Utilizing a flux-free hybrid welding approach, the study analyzes joint enhancement, electromechanical properties at varying R under LCF. Results reveal a clear R dependence of fatigue behavior in REBCO CC joints. Specifically, at a particular R , employing R = 0.1 results in a gradual degradation of critical current ( I _c ), while R = 0.5 induces a considerably faster and less recoverable I _c decline. The results highlight the interaction between R and fatigue cycles in REBCO joints, emphasizing the need for additional investigation across a broader spectrum of materials to comprehensively understand and optimize their performance in CC coils and magnets.