Numerical analysis of the mechanical and electrical properties of (RE)BCO tapes with multiple edge cracks

Abstract

One of the leading causes of critical current degradation in (RE)BCO tapes is the micro-cracks produced by mechanical slitting. These cracks are scattered near the edge of the tape and vary in length and angle. In this work, a tape model with multiple edge cracks is established. Under tensile loading, the effects of the Poisson ratio, crack length, crack angle, crack spacing, and geometric mutation between cracks on the stress intensity factor are investigated using the extended finite element method (XFEM). Tensile experiments were conducted at room temperature to investigate the crack propagation behavior of tapes with multiple edge cracks. The results show that the stress intensity factor obtained using XFEM is more informative than the analytical solution, which ignores the Poisson effect. The stress intensity factor is sensitive to crack length and angle variations and exhibits an evident jump characteristic when a geometric mutation occurs. The jump level strongly depends on the geometric difference. The jump location is the initiation site for crack propagation, which is consistent with the experiment results. The strain analysis of the tape implies that high-strain regions exist at the crack tip before the tensile strain reaches the irreversible strain limit. The critical strain of crack propagation is closely related to the form of crack distribution. It dominates the irreversible strain limit of critical current degradation, which facilitates understanding the early degradation of critical current. Finally, some engineering suggestions are given.

Analysis of Critical Current Dependence on Specimen Length and Crack Size Distribution in Cracked Superconductor

“…Critical current I c (estimated by application of the electrical field criterion E c = 1 µV/cm to the voltage V—current I curve) and n -value (estimated as the index n of the approximated I ∝ I n curve in the electrical field range of E = 0.1~10 µV/cm) are reduced under high electromagnetic and mechanic stresses, as have been reported for the superconducting oxide (such as RE(Y, Sm, Dy, Gd,···)Ba 2 Cu 3 O 7-δ : REBCCO) layer-coated tape [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ], and Bi2223 [ 15 , 16 , 17 , 18 , 19 , 20 ]-, MgB 2 [ 21 , 22 , 23 , 24 , 25 ]- and Nb 3 Sn [ 26 , 27 , 28 , 29 , 30 , 31 ]-filamentary types. In this work, we conduct a fundamental study on the influences of cracks in superconducting layer-coated tape on I c .…”