The correlation between mechanical properties and electric current under thermal shock for YBa 2 Cu 3 O x superconductors

Abstract

High temperature YBa₂Cu₃O_x (123, YBCO) superconductors have been shown to possess high current carrying capability which is confined to currents flowing along the strongly super‐conducting a–b planes within a single oriented domain. Usually, in this material, thermal cycling occurs in the temperature region ranging from −196°C (liquid nitrogen) under actual operation to room temperature under out of operation for maintenance. Micro‐cracks are considered to initiate during these thermal cycles which result in the high electric resistance. Therefore, the existence of micro‐cracks is considered to be a dominant factor in decreasing J_c. In this study, an apparatus for thermal cycling has been designed and built to provide thermal cycles ranging from −196°C to room temperature. To clarify the time sequential deterioration on the mechanical properties of YBCO due to thermal cycles, a sharp notched RCT specimen with 20° of notch tip angle and 0.02 mm of notch tip radius was designed. By using this specimen, the time sequential deterioration of stiffness, dP/dδ and fracture toughness of YBCO for a sharp notched RCT specimen due to thermal cycles were investigated. The results show a correlation between these mechanical properties and previously obtained the super‐conducting properties of this material. Thermal cycling causes the deterioration of mechanical properties which results in the deterioration of critical current density.