Investigation On Mechanical Properties Of CNT Wires And Their Composite Interfaces

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.