REBCO高温超导带材具有高机械强度、高临界电流密度、高临界磁场和高临界温度等优异性能，在强磁场装置中有广阔应用前景。然而在超导磁体中，REBCO带材承受复杂载荷作用，极易引发微观损伤而导致性能退化。因此本文开展了带材及线圈在特征载荷下的性能退化机理及抑制方法研究，可以为高温超导磁体研制技术的发展提供重要参考。首先对于REBCO 带材边缘裂纹对其力学稳定性的影响进行了研究，为了分析其力学稳定性，通过构造人造裂纹的方式，验证了线弹性断裂力学和最大周向应力准则对于REBCO涂层的适用性。进而构建了定量评估REBCO带材边缘裂纹力学稳定性的方法，推导了边缘裂纹的复合型应力强度因子，明确了影响裂纹稳定性的关键特征参数。本文在此基础上对两种商业化REBCO带材的边缘裂纹进行了表征，结合带材性能退化实验，证实了评估方法的有效性。理解REBCO带材轴向载荷下不可逆退化机理对于带材的制备和应用具有重要意义。本文结合微观分析明确了第二相颗粒对裂纹扩展的影响，构建了非连续裂纹扩展模型。考察了REBCO带材的变形行为及裂纹演化特征，提出了REBCO层裂纹分段演化机制，关联了微观裂纹演化和临界性能退化。构建了考虑概率断裂的超导带材性能退化模型，揭示了REBCO带材轴向载荷下不可逆退化机理。对于浸渍线圈而言，明确界面及材料内部的强度竞争关系对于分析浸渍线圈的失效行为具有指导意义，本文基于带材实验揭示了在树脂-带材体系中法向载荷和劈裂载荷下REBCO带材的脱层机理，明确了树脂-带材-树脂体系中的强度竞争关系，指出浸渍线圈内部的REBCO带材层内极易成为最弱点遭受损伤。进而制备了具有不同内外径比的浸渍和干绕REBCO线圈研究了热应力下线圈性能退化和脱层行为，分析了该过程中的脱层机理。本文还发现特定结构REBCO线圈在经历冷热循环后存在多损伤位点，结合线圈实验和多物理场数值模拟，解释了多重脱层机理。考察了线圈脱层所引发的多物理场变化特征，分析了线圈参数等对浸渍线圈应力分布的影响，提出了抑制线圈脱层行为的措施。同时讨论了将内外半径比作为浸渍线圈脱层判据的适用性，并且提出了考虑树脂层和镀铜层厚度的临界半径比判据。为了能够实现对线圈多参数的快速扫描分析，本文还开发了一种考虑热应力和电磁应力的解析求解方法。
REBCO high-temperature superconductor has excellent properties such as high mechanical strength, high critical current density, high critical magnetic field, and high critical temperature. It has broad application prospects in high field magnet devices. However, one of the challenges is that REBCO tapes in high field magnets are subjected to various stresses, which can easily cause microscopic damage, leading to the quench and degradation of magnets. Therefore, we carried out research on the performance degradation mechanism and suppression methods of REBCO tapes and coils under characteristic loads, which can provide an important reference for the development of high-temperature superconducting magnet technology.Firstly, the influence of edge cracks of REBCO tapes on its mechanical stability was studied. By constructing artificial cracks, the applicability of the linear elastic fracture mechanics and the maximum circumferential stress criterion for REBCO layers was verified. A method for quantitatively evaluating the mechanical stability of edge cracks was constructed utilizing fracture mechanics, the mixed stress intensity factor of edge cracks was deduced, and the key characteristics affecting its stability were clarified. Two types of edge cracks of two commercial REBCO tapes were characterized, and the effectiveness of the method was confirmed by the critical current degradation experiments.Understanding the degradation mechanism of the irreversible stage under the tensile stress was of great significance for the fabrication and application of REBCO tapes. The effect of the second phase particles on the crack propagation was clarified by the mircrostructure analysis and a discontinuous crack propagation model was further constructed. The deformation behavior and crack evolution characteristics of REBCO tapes were investigated. A multistage evolution mechanism of cracks in REBCO layers was proposed, which correlated the characteristic parameters between microcrack evolution and critical current degradation. A degradation model of REBCO tapes considering probabilistic fracture was constructed, and the irreversible degradation mechanism under the tensile load was revealed.It is instructive to clarify the strength competition relationship between the interface and materials itself to analyze the failure behavior of impregnated coils. Based on the tapes experiment, the delamination mechanism of REBCO tapes under transverse and peeling stress in the epoxy-tape system was revealed. The strength competition relationship between tapes and epoxy was clarified. It was found that REBCO tapes were easily damaged in impregnation coils. The wet-winding coil and dry-winding coil with different internal and external radius ratios were prepared to investigate the critical current degradation and delamination behavior of REBCO coils.It was also found that REBCO coils with specific structures have multiple damage sites after thermal cycling. Combined with coil experiments and multi-physical field numerical simulation, the mechanism of this multiple delamination was explained. The characteristics parameters caused by the coil delamination were investigated, the effects of coil parameters on the stress distribution in impregnated coils were analyzed, and methods to overcome the coil delamination behavior were proposed. The applicability of the radius ratio as a delamination criterion was discussed. A new critical radius ratio criterion considering the thickness of the epoxy layer and the copper layer was proposed. What‘s more, an analytical solution method considering the thermal stress and the electromagnetic stress was developed, which could achieve the fast sweep analysis of material parameters, coil structures, and boundary conditions.
