Carbon nanotube yarns (CNTYs) are hierarchical fibers with outstanding mechanical and electrical properties, with promising applications in the composite industry and as smart materials. In situ scanning electron microscopy observations are performed herein on individual dry-spun CNTYs during axial tensile testing in order to study their radial contraction response and structural changes. The CNTYs exhibited significant diameter reduction and untwisting due to the rearrangement of their fibrils during axial loading. In situ measurements of CNTY diameter reduction led to an exponential decrease of the radial contraction ratio with axial strain, with average values ranging between 5.43 and 1.08. The major failure mechanism was identified as fibril pull-out triggered by fibril slipping. The simultaneous stress and electrical resistance decay of CNTYs under axial tensile relaxation tests fit to a Wiechert's viscoelastic model using a Prony series. The rate of exponential decrease of the electrical resistance over time, however, is slower than that of the stress relaxation, indicating that additional charge carrier relaxation phenomena are present. Using the measured structural and material data input, a nonlinear analytical model based on classical theory of staple yarns is able to reproduce the mechanical response of the yarn. The model suggests that the most prominent parameters affecting the axial mechanical response of the CNTY are the radial contraction ratio, the slip factor, fibril radius, and fibril length.

中文翻译：

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了解碳纳米管纱线在轴向拉伸载荷下的径向收缩和轴向机械响应


碳纳米管纱线 （CNTY） 是具有出色机械和电气性能的分层纤维，在复合材料行业和作为智能材料具有广阔的应用前景。本文在轴向拉伸试验期间对单个干纺 CNTY 进行了原位扫描电子显微镜观察，以研究它们的径向收缩响应和结构变化。由于在轴向载荷过程中原纤维的重新排列，CNTY 表现出显着的直径减小和解捻。CNTY 直径减小的原位测量导致径向收缩比随轴向应变呈指数下降，平均值在 5.43 到 1.08 之间。主要失败机制被确定为原纤维滑脱触发的原纤维拉出。在轴向拉伸松弛试验下，CNTY 的应力和电阻同时衰减与使用 Prony 级数的 Wiechert 粘弹性模型拟合。然而，电阻随时间呈指数级下降的速率比应力松弛的速率慢，这表明存在额外的载流子弛豫现象。使用测量的结构和材料数据输入，基于经典短纤纱理论的非线性分析模型能够再现纱线的机械响应。该模型表明，影响 CNTY 轴向机械响应的最突出参数是径向收缩比、滑移因子、原纤维半径和原纤维长度。