Bending–Peeling Method to Measure Interface Strength of YBCO Tape

Modern yttrium barium copper oxide (YBCO) superconductor tape can carry a high critical current under a rather high magnetic field with good strain tolerance. However, the interface between the laminas is quite weak, and the interfacial strength has thus attracted considerable research interests. We designed a new method to analyze the interfacial strength of YBCO tape. A piece of tape was first embedded in a rectangular-section beam of epoxy resin, with the tape plane parallel to the middle cross section of the beam and the tape edge at the beam surface. The epoxy beam height was greater than the tape width. Three-point bending was applied to the beam, with one point on the opposite side of the tape across the beam and the other two points at the two ends. The interface was thus tensed during loading. In this way, the interfacial strength could be directly determined, and the interfacial energy could be calculated from the force-displacement curve. The crack interface was examined using scanning electron microscopy and analyzed using energy-dispersive X-ray spectroscopy. The average interface strength was 5.16 MPa. The experimental data were used to further simulate the crack behavior during the cooling process.