Quantitative evaluation of the delamination length in mechanical lap joints of high-temperature superconducting tapes using Lamb waves

A mechanical lap joint is a critical part connecting rare-earth barium copper oxide (REBCO) tapes. Until now, the delamination in joints, which causes severe heating, has not been efficiently evaluated at room temperature. This paper presents Lamb wave method to measure the delamination length in lap joints. The dispersion curves of Lamb waves in REBCO tapes and joints are calculated, and their characteristics indicate the reflected wave is more suitable for testing because of the consistency through a broadband of frequencies. Finite element simulation results show the change in arrival time of the reflected wave is larger than the transmitted wave. In the experiments, an ultrasonic probe is used to test the joints from both sides. The delamination lengths in three samples are determined by the arrival time of the reflected wave, and they are consistent with the results obtained by X-ray microtomography with a maximum difference of 2.0 mm.