REBCO delamination characterization by 90 degree peel test

Abstract

REBCO tape has successfully used in ultra-high field magnets. Mechanically, it is very strong in its length direction but is prone to delamination in the thickness direction. In an epoxy impregnated REBCO magnet, thermal strain alone could delaminate the conductor. Even for dry wound REBCO coil, a conductor with very low delamination strength is still a concern. Therefore, it is important to characterize the delamination strength of the conductor. In the past decade, significant progresses have been made in the characterization of REBCO delamination strength. Among several developed characterization methods, the 90 degree peel test is simple to setup and seems to offer reproducible results. Therefore, this test could be used as a reliable method to characterize the relative delamination strength of REBCO tapes for quality control purposes. This paper presents our development of 90 degree peel test method for quality assurance test of the 40 T all-superconducting magnet project at the National High Magnetic Field Laboratory. We investigated the factors that influence the test results, such as thickness and RRR of the copper layer. We found that peel strength increases with decreasing Cu thickness. We also found that peel strength is positively correlated with RRR of the copper. Despite these effects, 90 degree peel test is still a valuable quality assurance tool to evaluate delamination strength for large volume of tapes with the same copper thickness.