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

Abstract

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.

Strain dependence of critical current and self-field AC loss in Bi-2223/Ag multi-filamentary HTS tapes: a general predictive model

“…When a Bi-2223/Ag multi-filamentary HTS tape experiences large enough stress/strain, I c decreases and the AC loss increases [14][15][16][17][18][19][20][21]. Since the stress/strain does not affect the intrinsic pinning properties of the Bi-2223/Ag multi-filamentary HTS tape [43], the increased AC loss can be dominantly attributed to the decrease of I c from the damaged superconducting core [19][20][21].…”

“…The effects of deformation on AC loss also present in two stages. There was almost no change in AC loss when the deformation was less than the irreversible critical value, while AC loss increased sharply once the deformation was larger than the irreversible critical value [14][15][16][17][18][19][20][21]. The deformation-induced damage of superconducting filaments in Bi-2223/Ag multifilamentary HTS tapes was observed experimentally through scanning electron microscopy (SEM) [8][9][10][11].…”

“…Therefore, the irreversible degradation of I c in Bi-2223/Ag HTS multi-filamentary tapes is likely to be related to the defects and micro-cracks of superconducting filaments. In addition, the dramatic increase of AC loss in deformed Bi-2223/Ag HTS multi-filamentary tapes was attributed to the damage in superconducting filaments, which causes the current exceeding I c to flow into the Ag matrix [15][16][17].…”