Carbon nanotube (CNT) fibers are inevitably subject to severe plastic deformation under complex loading conditions while applying in wearable electronics. In this work, we uncover the time-dependent structure evolution mechanism of twisted CNT fibers by a series of continuous and discontinuous loading experiments. The results reveal that the highly twisted CNT fibers are more sensitive to strain rate and have large stress attenuation during the relaxation process. The in-situ tensile test under scanning electron microscope (SEM) indicates that the twisting angles of CNT fiber decreased during the stretching and relaxation due to the slippage and rearrangement of CNTs. An unsteady ternary model is developed to describe the stress relaxation behavior of twisted CNT fibers taking strain rate effect and the time dependence of viscosity into account; then the constitutive equations are mathematically derived and analyzed. We believe that this work would provide beneficial guidance for designing twisted CNT fiber with high reliability and durability properties.

碳纳米管（CNT）纤维在应用于可穿戴电子设备时，在复杂的负载条件下不可避免地会发生严重的塑性变形。在这项工作中，我们通过一系列连续和不连续的加载实验揭示了加捻CNT纤维的时间依赖性结构演化机理。结果表明，高度扭曲的CNT纤维对应变速率更加敏感，并且在松弛过程中具有较大的应力衰减。扫描电子显微镜（SEM）的原位拉伸试验表明，由于碳纳米管的滑动和重排，在拉伸和松弛过程中碳纳米管纤维的扭曲角减小。建立了一个非稳态三元模型来描述加捻的CNT纤维的应力松弛行为，同时考虑了应变率效应和粘度的时间依赖性。然后对本构方程进行数学推导和分析。我们相信这项工作将为设计具有高可靠性和耐久性能的加捻CNT纤维提供有益的指导。