Evaluation of Actual Delamination Strength of REBCO-Coated Conductors Based on the Weibull Analysis Considering Size Effect

Fujikura has developed production techniques of REBa 2 Cu 3 O y (REBCO, RE = rare earth) coated conductors (CCs) and provided high-performance REBCO CCs with long-length and high homogeneity of the critical current. REBCO CCs have a low c-axis strength (delamination strength) which originates from the layered structure. When an epoxy-impregnated REBCO coil is cooled, the radial thermal stress is generated. The stress could cause the delamination of REBCO CCs and lead to degradation of the coil. Therefore, it is important to evaluate the exact delamination strength of the CCs. In this paper, we evaluated the failure probability of the epoxy-impregnated coils at 77 K. We introduced Weibull analysis considering the stress distribution and the sample size effect, and estimated the actual delamination strength of the REBCO CCs. By using the evaluation method, we confirmed the strength enhancement by process improvement.