REBCO Delamination Characterization by 90 Degree Peel Test

REBCO tape has been 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, for instance, the conductor could be delaminated by thermal stress. Even for dry wound REBCO coils, conductors with very low delamination strength are still a concern. Therefore, for ultrahigh field magnet applications it is critical to characterize the delamination strength of REBCO conductors. 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 implement and seems to offer reproducible results. Therefore, this test could be used as a reliable method to screen REBCO tapes of weak interlayer bonding 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 stabilizer layer. We found that peel strength increases with decreasing Cu thickness. In addition, peel strength is positively correlated with residual resistance ratio (RRR) of the copper. Despite these effects, 90 degree peel test is still a valuable quality assurance tool to evaluate possible delamination for large volume of tapes with the same copper thickness.