AC Transport Current Loss Characteristics of Copper-Stabilized YBCO Subjected to Repeated Mechanical Stresses/Strains

HTS coated conductors (CCs) in various apparatuses are subjected to mechanical stresses caused by thermal contraction and electromagnetic forces. The repeated mechanical stresses cause fatigue effects on superconductors which degrade the critical currents and influence AC loss characteristics. Therefore, it is important to have knowledge of the influence of the repeated stresses. In order for the CCs to work reliably and stably in apparatuses, they are usually copper stabilized. This work investigates influence of repeated mechanical stresses on the AC transport current losses in YBCO CCs with copper stabilization layers. Repeated uni-axial tensile stresses were applied to the CCs in the longitudinal direction and transport current losses were measured electrically at 77 K. It was found that the influence of the repeated mechanical stresses on the losses can be characterized by the critical currents of the CCs which are affected by repeated mechanical stresses. The experimental results are explained by a model that local cracks in the superconductor layer are developed by the mechanical repeated stresses.