【作者】 李丹；

【导师】 杨庆生；

【作者基本信息】 北京工业大学 ， 力学， 2017， 硕士

【摘要】 碳纳米管(CNT)具有优异的电学、力学特性以及稳定的热、化学性能,将CNTs进行组装可以得到宏观一维结构CNT纤维,将多根CNT纤维相互缠绕可以得到CNT线。CNT纤维和CNT线作为新型材料,具有独特的组装结构特性,在能源、电子、驱动等领域具有巨大的应用潜力。虽然现在对于CNTs已经有了比较深入的研究,但是对于CNT线力学性能及CNT纤维增强复合材料界面性能的研究仍然比较缺乏。本文基于微纳米拉伸实验方法对CNT线的力学性能进行了细致研究,同时结合实验和有限元模拟方法对CNT纤维增强复合材料的界面性能进行了全面的分析。(1)利用微纳米拉伸仪对CNT线进行循环加载测试,采用逐步逼近的方式探究了CNT线的弹性极限和屈服点;对CNT线施加不同的加载-卸载过程,通过卸载后的残余变形分析了不同加载速率下CNT线的塑性变形特性。(2)对CNT线进行了单次加载和循环加载测试,分析了两种加载方式下CNT线的变形与破坏过程,并结合材料断口的电子显微镜(SEM)图片讨论了CNT线的断裂机理;研究了加载速率对CNT线拉伸性能及断裂行为的影响;对比分析了同一速率下CNT线在单次和循环加载下的异同点,对两种加载方式下材料的变形与破坏特性进行了探讨。(3)利用基于微纳米拉伸仪开发的微滴包埋实验装置对CNT纤维与丙烯酸(PAA)及聚甲基丙烯酸甲酯(PMMA)树脂间的界面性能进行了研究,根据得到的界面脱粘载荷-位移曲线,计算了纤维与聚合物间的界面结合强度,揭示了界面失效机理;利用内聚力单元,建立了相应的微滴包埋脱粘有限元模型,在数值模拟结果与实验结果吻合的基础上,确定了相关参数内聚力参数,获取了不同裂纹扩展长度下界面剪切应力的分布情况,阐述了界面的失效破坏过程。(4)通过有限元软件模拟研究了不同的界面内聚力参数对CNT纤维复合材料脱粘行为的影响;分析了材料固化降温阶段产生的热残余应力对界面粘结强度的影响,给出了不同固化温度下热残余应力的分布情况;讨论了不同的基体和纤维热膨胀系数对复合材料界面性能的影响。本文主要研究了CNT线的拉伸变形与断裂机理,分析了CNT纤维与不同聚合物基体间的界面结合强度,并借助有限元方法讨论了多种因素对界面性能的影响。本文工作对CNT线的应用及CNT纤维增强复合材料的性能改进具有重要的参考价值。更多还原

【Abstract】 Carbon nanotubes(CNTs)have excellent electrical and mechanical properties,which are also stable in thermal and chemical performance.The CNTs can be assembled into CNT fibers,which are one-dimensional macro-structures,and then the fibers can be twisted into CNT wires.The CNT fibers and CNT wires,as a unique assembly structure of advanced materials,can be widely used in many fields such as engineering,electronics and drive.Although carbon nanotubes are now a well-established area of interest,there is a limited knowledge relating to CNT wires and the interface bonding performance of CNT fiber-reinforced composites.This thesis carries out detailed research on the mechanical properties of CNT wires based on nano-tensile test system,and performs the comprehensive analysis on the interface properties of CNT fiber-reinforced composite materials based on the experiment and finite element simulation method.(1)In order to indicate the exact elastic deformation of the CNT wires,a group of cyclic loading experiments was performed by using nano-tensile tester with the method of approaching step by step.Different loading forces were imposed on the CNT wires and then were unloaded,and the plastic deformation properties of CNT wires were investigated through the analysis of the residual deformation after unloading.At the same time,the effect of strain rates on the mechanical properties of the CNT wire under monotonic loading was also discussed.(2)Monotonic and cyclic loading experiments were performed at several strain rates to analyze detailed deformation and failure process of the CNT wires and the effect of strain rates.And the failure mechanism of the CNT wires was interpreted by means of scanning electron microscope photos.The comparison of tensile strengths for monotonic and cyclic loading at a same strain rate was listed,and the difference between the deformation and damage characteristics of CNT wires was discussed under the two load modes.(3)The interfacial properties between CNT fibers and polymers of acrylic acid(PAA)and polymethyl methacrylate(PMMA)were studied using the microdroplet experimental equipment.According to force-displacement curves,the interface bonding strengths between the CNT fibers and polymers were calculated,and the interface failure mechanism was revealed.The damage process and shear strength were investigated through obtaining the relations of pullout force and slipping displacement of the CNT fiber/polymer interface.Besides,finite element model of the micro-droplet test was built based on the cohesive finite elements.On the basis of the numerical simulation results consistent with the experimental results,the related cohesive parameters were determined,and the distribution of interface shear stress under different crack propagation length was also plotted.Otherwise,this paper expounds the interface failure process.(4)The effect of cohesive parameters on debonding behavior of CNT composites was discussed.In addition,the influence of thermal residual stress caused by matrix curing on interfacial strength of composite distribution was investigated,and the distribution along the interface of thermal residual stress under different curing temperature was shown.The influence of the thermal expansion coefficient difference between matrix and fiber was also discussed.In conclusion,this thesis focuses on damage mechanism of CNT wires and interface properties of CNT fiber-enhanced composites between different types of CNT fiber and polymer matrix.The effect of a variety of factors on the performance of the interface was discussed by means of finite element method.The present experimental and numerical results will provide a valuable reference for the application of CNT wires and the preparation of CNT fiber-reinforced composites.更多还原