Fatigue damage mechanisms and critical current degradation in REBCO tapes at cryogenic temperature

Abstract Rare-earth barium copper oxide (REBCO) coated conductor (CC) tapes are extensively utilized in applications subjected to cyclical electromagnetic loads, which can lead to significant degradation of the critical current ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) due to damage within the superconducting layer. Although previous research has investigated the degradation mechanisms and critical current levels in REBCO CC tapes under mechanical deformation, the mechanical failure behavior under cyclic fatigue loading and its impact on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> remain insufficiently explored. This study addresses this gap by developing a comprehensive fatigue damage model for REBCO CC tapes, focusing on the mechanisms governing their transport properties under repeated loading cycles and varying stress amplitudes. We propose an improved nonlinear fatigue damage accumulation model to predict the fatigue lifetime and damage progression. Additionally, a phenomenological model incorporating the Weibull distribution is introduced to evaluate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> degradation. Material parameters for the models were determined from experimental data, and critical current tests were performed at liquid nitrogen temperature following cyclic loading. The results demonstrate that the proposed damage model exhibits pronounced nonlinear behavior, characterized by three distinct stages of damage evolution. Extensive cyclic loading experiments validated the model’s reliability and precision. This non-invasive analytical framework provides a robust methodology for quantifying and predicting <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>I</mml:mi> <mml:mrow> <mml:mtext>c</mml:mtext> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> degradation in REBCO CC tapes under cyclic stress or strain conditions. The findings advance the understanding of fatigue-induced degradation and offer a predictive tool for assessing the performance of REBCO CC tapes in practical applications, contributing to the optimization of their operational lifespan and reliability.