Damage behavior of Nb3Sn/Cu superconducting strand at room temperature under asymmetric strain cycling

In this study, damage evolution of Nb3Sn/Cu superconducting strand was investigated under asymmetric strain cycling. The results of the fatigue tests indicate that higher strain ranges and peaks can accelerate damage evolution, and damage evolution occurs seriously at the early fatigue stage. Based on the stiffness degradation rule of composites, two independent plastic damage evolution equations of the Nb3Sn sub-elements and Cu matrix were derived to obtain stiffness degradation and fatigue life by considering the effect of strain range and strain peak, respectively, and the accumulated plastic strain of Nb3Sn/Cu superconducting strands was obtained by deriving the total damage evolution equation. The proposed model was verified and validated by studying the fatigue behavior of Nb3Sn/Cu superconducting strands under asymmetric strain cycling. A good agreement between the analytical model and experimental data irrespective of the strain range and strain peak shows that the analytical model can not only predict the stiffness degeneration and accumulated plastic strain, but also describe the fatigue life of Nb3Sn/Cu superconducting strands under asymmetric strain cycling.