RRR behavior in NbTi superconducting cable due to fatigue damage

In order to investigate the effect of fatigue damage on the residual resistivity ratio (RRR) behavior in the nine strand Cu-Ni/NbTi/Cu composite superconducting cable, in this study, fatigue tests at room temperature and residual resistivity measurement tests at 12 K were carried out. Through fatigue tests of NbTi composite cables, a conventional S-N curve could be obtained even though there existed a possibility of fretting among strands in the cable. From the electrical resistivity measurement for NbTi strands after fatigue test, it was found that the RRR for the virgin strand from the annealed cable was three times larger than that for as-received one. With increased fatigue cycles at a stress amplitude level, the RRR decreased until 10³ cycles, which was resulted from the accumulation of damage such as lattice defects and dislocation density in the Cu stabilizer.