Influence of Repeated Shear Stresses on Critical Current and AC Losses in Multi-Filamentary Bi2223/Ag-Sheathed Wires

This paper investigates the influence of shear stresses on critical currents and characteristics of ac transport current losses in Bi2223/Ag-sheathed tape wires. Shear stresses are stresses applied to the flat face of the tape wire in the tangential direction. When an HTS potted and impregnated coil is cooled down, there are possibilities that wires peel off locally from the coil frame and other wires due to thermal contraction. This peeling-off occurs also due to electromagnetic force and external mechanical forces. The wires are released from the shear stresses where the wires peel off and the shear stresses to wires concentrate on areas where the wires are tightly bonded to the coil frame and other wires. This concentration of shear stresses may cause damages to the wire, degrades critical current and influence ac losses. In this paper, a method is presented to investigate the influence of the shear stresses on HTS tape, and data are given on the influence of shear stress to multifilamentary Bi2223/Ag-sheathed wires reinforced by copper alloy tapes. Also, aspects of defects caused by the shear stresses are studied by investigating the transport current loss characteristics.