Evaluation of the effect of edge cracks on critical current degradation in REBCO tapes under tensile stress

TL;DR

This study assesses how edge cracks from manufacturing affect the critical current degradation of REBCO tapes under tensile stress, using fracture mechanics to predict crack stability and inform manufacturing improvements.

Contribution

It introduces a fracture mechanics-based model to evaluate edge crack effects on REBCO tapes' critical current degradation under tensile stress.

Findings

Cracks remain stable if stress intensity is below K_{Ic}=2.3 MPa√m.

Edge cracks in evaluated tapes do not cause premature degradation.

The model helps determine safe operation ranges for REBCO tapes.

Abstract

The slitting process used for fabrication of REBa2Cu3Ox (REBCO, RE=Rare earth) tapes of required width will greatly improve production efficiency and reduce production costs. However, edge cracks induced by the slitting process of wide REBCO tapes may cause the premature degradation under a extremely high hoop (tensile) stress in high-field magnets. It is necessary to evaluate the edge cracks of REBCO tapes on the critical current (Ic) degradation. This work aims to evaluate the effect of edge cracks on the Ic performance under tensile stress. Ic degradation under artificial cracks was measured to validate the applicability of linear elastic fracture mechanics for the REBCO film. Linear elastic fracture mechanics was used to get the mixed stress intensity factor of multiple edge oblique cracks. A model considering edge crack properties angle \b{eta}, spacing d, and length a is constructed to evaluate the critical load and critical cracks properties. When the stress intensity factor at the crack tip is less than K_{\rm Ic}=2.3$ $\mathrm{MPa\sqrt{m}}, edge cracks remain stable and do not propagate. Two kinds of REBCO tapes fabricated by different companies are evaluated, and cracks of these tapes will not cause premature degradation. This model could be used to evaluate the operation range of REBCO tapes and improve the manufacturing process.